Rebuild and calibration of a B&K Precision model 290 Electronic Multimeter.

deja vu abbey cave precision electronic multimeter model 290 no this is not a repeat of the last one I just did that one's actually right there then I'd actually check my inventory I actually had up until now ahead three when I got that one over there I rebuilt that one that's the one that needed a potentiometer replaced in it actually for a position if this one's in for the high-power ohms range got that one fixed up and yeah I change equipment on my bench like most people change socks yeah I I had so much now I cycle some of my especially my older vintage meters on and off of the bench and I took the old Sentinel which is a kind of a military-grade HP 410 Series multimeter I just moved that over here to the side because I still want that one within arm's reach of this bench because that one can do extremely high frequencies but like I say these meters have some really nice features but I had a saved search for these meters and so I've got three of them now so you know that gives me a working one a spare and to spare for my spare I'm one of those people yeah even if you have a spare you have to have a spare for the spare cuz you never know but I figured three bouquets enough I don't need to be actively looking for these things anymore and what did I see more of these for sale so yeah I actually got its several more of them sake yeah I've got I've got a growing collection here so I thought we'd actually tear into at least one of these they both came from the same seller without power cords so the power cords have been whacked off and usually when this person sells stuff I get the feeling actually this thing it has a number on the side of it one yeah and the other meters have numbers have other numbers on the side I get to feeling a lot of the stuff that he sells comes from either technical schools or colleges or you know old vote text type programs but they were used in schools and they just cut the cords off of everything because everything he ever sells never has a cord on it it's always whacked off which as a cover your but from a seller standpoint that's the best way to do it because with the cord being cut off as a buyer anytime you get something that has a cord missing red flags there might be something wrong now very there may very well be nothing wrong with this multimeter but that anytime you see the cord cut off of something that should make you take a really really hard look at it internally you know electronically is there something seriously wrong with it you don't just want to go shoving it brand new cord on there and plug it in the chassis might be hot there could be other problems you may let the magic smoke out it's usually not a good thing so I figured we'd actually take a look at one of these and see what and if it needs anything now I know I'm going to replace the electrolytic capacitors in it they're old it's just like a radio electrolytic capacitors go bad and stuff like this no different this stereo receiver or a transceiver or anything else so you know caps are going to get changed but really need to take a close look at it now the first thing we need to see as with anything electronic now these actually have two fuses there's an external fuse and then there's an internal slow blow fuse but always check being the cords cut off or not the first thing you want to check on anything that plugs into a wall before you plug it in even if it's sold is working still don't plug it in always check to see if the fuse is the proper rating you'd be surprised how many times now maybe not with test equipment but especially radios you'll see something that you know let's say it calls for a one and a quarter amp fuse or a three amp fuse you know if it needs a three amp fuse don't be surprised if you find a 20 amp fuse and a fuse holder because it kept blowing a fuse and some nitwit decided well we'll just stick a big refuse in there then it won't blow yeah well that kind of defeats the purpose of the fuse then that fuse is meant to protect whatever it's it's installed in you stick a bigger fuse in there eventually the parts start burning up inside so see what we got here it should be a 1 1/4 amp 3a g fuse and it does not look like a 3G fuse it is a and that's a what is that three amp yeah definitely it's a three AG but it's a three amp fuse that definitely the wrong size so yeah first indicator that's got to go it's supposed to be one and a quarter amp so let's pop the covers off of this critter and one of the nice things about these other ones that I got here and it's something to be aware of near buying you know older stuff meters like this especially all the BK equipment that was made in this era had plastic end caps so yeah just kind of look at the Oh condition wise when you're buying this kind of stuff to you know make sure that the the plastics not broken or at least try to be aware if it is or not you know if it is broken how bad is it does it look like it can be fixed because it's not like you can run down to the local store it's not like you can pick up the phone and call BK precision and say hey I need an N panel for my your BK 290 multimeter so just something to be aware of yeah well that's been modified what in God's name do we have here that is not supposed to be there I know what these meters are supposed to have insides like I say I just rebuilt that one that fuse looks correct so there's the the slow blow fuse it should be in here this I don't know what in God's name going here so they put that fuse it's a fuse I know that but they put it in series with the one on the fuse holder heck I'm assuming these are maybe not now their caps so jiminy crickets I'm gonna take this screw off here Jesus tight in caps what in the world do we have here this is a hvw for oh my god there's a foreign fuse yeah that's again not right what well it's thicker whew they've got what I say if this was three amp yeah they have a three amp fuse and this fuse holder and you can see the yellow wires right down to the back of this fuse holder in series with a four amp fuse and it's supposed to be one of the quarter amp fuse yeah that's trash cans yeah I have no idea why they did that definitely not right this fuse holder is just gonna go bye-bye this will be getting put back to factory original let's tear this apart a little bit more now cosmetically this meter is in pretty good condition it's got a little bit of a scratch across the meter face if I get to reflection mm just kinda see it there is a scratch across there so I will buff the lens on this I'm gonna take the meter movement out of it anyhow then I can just pop the lens off of it I can take it out and hit that on a baladora buffer and I just buff yo buff that scratch away um both of these meters I think it was both of them yep that one's bent too I told somebody whacked both of these meters right on this control but the front panels actually buckled in you see that control how it's slightly sideways it's kind of bowed in a little bit and it's also kind of bowed up I don't know if maybe these were dropped at a some kind of weird angle but yeah that shouldn't be too bad to get out that should be just a matter of take this control loose pull it out take a pair of flat jaw high leverage apply and just squeeze basically to flatten the sheet metal back down then I can stick the control incas the controls seem to turn fine so as long as they're not damaged no need to replace them but yeah I don't I just I don't understand that the few situation there ye what it's paid enough you put a too big a fuse in it to start with but in to me you put another fuse in series with it yeah I that kind of dumbfounded by that this fuse would never blow I mean this is a three f fuse it's an ant blower in this one ya got me [Music] and one thing if you ever do get one of these meters I usually do it to mine because I'm usually usual not usually always I'm always using this style meter on a bench I don't need this blasted handle sometimes that can be you know that a little bit of extra width there can be the difference between being able to shove it into a crack or a crevasse actually kinda like that one right there it wouldn't fit where it's at right now with the handle on it but I always take handles off and these are easy to get off they just have eclipse on them so that's no biggie I can easily get rid of the UH of the handle but I always pop those off and then I always try to anytime I take handles off like even carrying handles on the top of equipment when I take the handle off you put something a cat plug or a piece of tape over a hole just something maybe to keep dust bunnies from getting inside of your equipment okay not only that it makes assembling these meters a little bit easier because you can see that's actually kind of what oops this thing together yeah it's it can be a little painting a but trying to get these things put back together okay now I don't think I showed the inside hole no mine my tested sticker fell off I'll actually glue that back on keep the you know the history of the meter the inspector number what was it nine Spectre number nine past this meter but I had I had said in the other video I explained the circuit and I showed it on the schematic so I don't need to repeat myself there but I had mentioned about these meters if you look on the schematic and if you watch the video I did on the other one I explained about the schematic calls for a neon bulb right here they don't have I've never ever seen one that had a neon bulb every single meter I've ever seen had a regular incandescent light bulb with this resistor if it's supposed to be in here but this is a different value but this resistor would normally be down on the board and both of the leads for the neon bulb would come down to this board this bulb is in series because it's incandescent it's actually in series with the one of the main power with the power supply rail in this thing right after the bridge rectifier I think it was and it was a CSA you basically a modification for CSA or government contract stuff I think the reason they did that was they're using the light bulb not as a fuse because you have to remember a light bulb can only pass so much current it but it won't blow you have to remember as the filament heats up that's what the when the bulbs when a bulb starts to glow it can only get to a certain point it doesn't matter how much more load is applied let's say on the other other side of that ball it will never glow brighter so it will never allow more current to pass than a dead short you know if we were to take the other lead just straight to ground well that's the light bulb lighting if you put the light bulb in in a series circuit with a power supply it basically acts as a poor-man's current limiting circuit and I think that's why they did that but yeah like I say the schematic shows a neon bulb with this as an as a modification for CSA contracts but I've never seen one that didn't have this so and some people think this is yes something somebody did no no this is just the way they left the factory this this was factory so otherwise inside it's not looking like it's ever been worked on all original electrolytic capacitors and there's actually the tremor that I had to replace any other one yeah oddball size it's a 5 mega ohm you can see like I had said and that when I had that meter closed up I wish I'd assumed it when it was a part but yeah these had the really big quarter watt trimmer potentiometer is in them but yeah nothing nothing looking too out of the ordinary other than that fuse let me just pop the meter movement loose I guess the main reason I need to take that out is because I want to buff the lens I don't want to do that in the meter or Wallace he was still assembled in here here's something there's something loose it's got to be inside the meter movement oh it just fell out was it did some Oh piece of the lens okay I heard a piece of plastic bouncing around in here it's got to be off the B up right there it's actually off this back corner so yeah I can actually get that just glued back on [Music] the last two screws here let's see fully get this out but actually didn't take the other one this far apart I'm asked set screws do they net1 just push on I have to take the nuts off meter up and out of here is our little light bulb you know like I say just see there's a scratch going across there matter of fact you can see a shadow on the meter face there there you go and it's not one play it you can see it pretty good there yeah that should easily buff out and yet a little corner that's broken off I'll just glue I can glue that back on but and these meter lenses they just pop one you can see there's a couple little fingers there usually get your fingernail in there you'll just pry out slightly on the lens and the lenses just pop off just be really careful once you get the lens off try not to touch the meter face or the needle if you touch the meter face yeah it'll look fine today may look fine next year but five or ten years down the road you have to remember most of these meter faces the back near the actual part right here that's white it's aluminum and if you touch it the oils from your finger will eventually soak through the paint the oil will start to oxidize the aluminum and your paint will start to flake off of your meter face so anytime you have one of these apart never ever touch the meter face now if it's you needs to be clean go clean it but like I say just don't touch it with your bare hands there's all kinds of nasty salts and oils your hands that do nasty things to metal so you can see the inside of it take a close-up look here don't see anything burned up don't think anything has ever been replaced like I say looks original the exception of that fuse holder no doesn't look like anything's ever been restored on the main board here so yeah so yeah all I need to do basically is take this off wait a minute oh okay yeah that that's supposed to go down there cuz that's yeah that's for the yeah that's the fuse for the jack for your meter yeah that's man that's just why did they do that put such a large fuse I just don't understand why they cuz this is the fuse here for your power cord okay you know so if you had a dead short in here and the power supply circuit this fuse would blow this fuse is actually the one that protects your meter the inputs is that as you can see it's attached to the fuse holder there yeah I just I don't know why why they put such high values on there it just really doesn't make any sense to me ya got me so yeah that'll have to go oh and just in case you've never seen one don't seem in a lot of stuff this is a spark gap capacitor so you can see that little line well it's not it did some light here it's not actually a line there's actually a gap trying to get the light behind it but that's actually a cut straight through the capacitor there you can just see some of the aluminum behind it if I get the angle just right you can actually see the gap through there they're called spark gap capacitors because that's actually what they do if you get enough voltage on this thing so you know and they're rated the way they rate spark gap capacitors when they're using them in a circuit like this whatever the maximum voltage it's allowed at the input here so you know in the case of this meter it's a thousand five hundred volts DC or four thousand two hundred volts peak-to-peak AC voltage you know and then there's a there's a margin there the meter can actually handle more than that it may not be able to be read on the on the the meter itself but you know this the the circuit inside the the multimeter can handle it a little bit above that but once you get to a certain point that will arc that will arc over and that's what that's meant to do it's meant to basically because and once it arcs that's a short you know because it's now arcing from one terminal to the next so it basically dead shorts your positive and negative leads together protecting the high voltage from blowing up your multimeter yeah now you might smoke your test leads because now you've created a dead short outside of the meter but that's basically what yeah it's mainly I think the main reason I use those is is more for surge if there were a surge in a circuit you know an instantaneous surge for a very short duration that thing can go it can short it it can absorb that voltage spike without damaging me or like I say it's just meant to protect your meter so yeah it looks pretty good so let me get there's only a couple of capacitors in this thing as you can see you got one two three aluminum electrolytic there and I think there's what three I can't remember two or three tantalum there's one there [Music] I'm pretty sure there was more than one what I changed two or three when I did that other one was I'm trying to look around the camera didn't help oh actually there's a another spark-gap capacitor you can see there you can just see the wires behind it in that position right there so there's another one with the line through it yeah I just that fuse just gets me I don't know what what they were doing there strange strange strange oh there it is there's an right there so you have one two there's two tantalum so blue one now honestly these would probably be fine but the problem with tantalum capacitors is when they go bad they base unlike electrolytic like this aluminum electrolytic when they go bad they can go bad you'd in two ways either are open or a short in either case that usually happens over a really really long time usually you'll start to notice degraded performance in whatever you're using before it actually becomes a dead short painful and capacitors aren't like that they'll be fine one second and there are dead short the next and that's pretty much the tantalum capacitors failure mode is a dead short unlike an aluminum electrolytic it can go open yeah these things when they fail they pretty much just go dead short and when I anytime I replace tantalum capacitors I always increase the voltage rating on them so you know if it's a let's say a 16 volt I'll stick in like a 25 or a 35 or even a 50 volt tantalum capacitor to give it a little bit more safety margin err because honestly just like with radios even even meter manufacturers a lot of times you'll see tantalum capacitors and some of the old fluke and HP meters you can see that either they have the tantalum capacitors will short out and cause problems in the meter and they just run them so close to their actual operating voltage that the things are just yeah they're straining from the from day one so yeah they don't quite nowadays tantalum capacitors yes they are expensive but they're not it's not like they're super expensive like they were back in the day so yeah you can afford it besides that there's only two of them in here just get a cup one or two voltage ratings higher save yourself some headache in the future so there you go yeah I'm I'm feeling good about this one doesn't look like the meter another thing to look at when you're looking at multimeters like this the meter contacts make sure you know none of the contact fingers down in there are blown off there's damage or any of these wafers and these wafers switches are actually broken usually if they're broken you'll be able to tell when you turn the controls you'll get to a plate just won't turn anymore if you ever get a rotor of a wafer switch like this in something doesn't matter if it's test equipment anything that has multi positions older stuff is usually going to have wafer switches like this if you turn it and you get to a point where it won't turn anymore and it's supposed to don't force it a very good chance you could really break the switch take it apart and look at it and see what's binding the switch up before you go breaking this switch so in case let me get some caps changed I just need to check this the fuse wiring on the schematic I got I say put that back to factory the way it's supposed to be I just AM confused by that that weird just double yeah I don't know I can understand using a high quality fuse on the input like this but not that I ever rating like I say that's four amps just I don't get that oh and you can see the chassis x' a little bit bent right there so i'll just pop this controller just like a sad mistake and this is aluminum so it's very malleable so that'd be easy to get bent back in shape and then I can stick a paracord on this thing and we'll see how she works now one thing to remember just like I said with the other meter the probes on these planes to reach over pull the probe down or this one attached to the meter over there the probes that are came with these meters were the PR twenty ones now you don't have to have this probe if you get a meter like this or any old old meter a matter of fact there's lots of YouTube videos people showing how to make probes there's nothing special inside of this thing all that's inside of this switch housing is a switch and a 100 K or 100,000 ohm resistor that's it that's all that's in there when you put it in direct it just goes from the tip down to the positive Jack when you put it in the hundred K position like that it adds the hundred K resistor in between the probe tip and deposits that's it that's all there's inner it's not like there's any fancy circuitry it's not an RF type probe so there's no diodes there's no capacitors there's no none you know demodulation circuit in here it's just a resistor worst case scenario you could all you just get to you know if you needed to make up a set of test leads you only need a negative to go in here for your positive you know for your DC with the hundred 100 K ohm resistor all you would need to do is just take a meter probe and just literally just stick 100 K ohm resistor in circuit you can get the of you know the long meter leads you can still get probes like this cheapies you know this is an old one but you can get stuff like this and in this style you can get the body okay this one you actually yeah which is actually kind of this is a unique probe actually I forgot this is this is actually kind of a rare one has has an extendable tip yeah but anyhow what you could do is on when you're building a probe actually pulled that out of there now grant most of them are gonna head this is actually a bad example cuz normally it's not gonna be like this this you piece would only be about that long it would be up in there and the rest of the tubes Hollow you could just stick your resistor you know solder it in here or in this case it has a set screw which I don't like for probes actually screw connections can fail at some point but just put your resistor in there and then solder your actual test lead to the other end of the resistor and then that becomes your DC probe now for the AC probe it's actually a good idea to try and and do what they did at the factory for this meter you'll notice this cable really heavy it's coax cable they do that for yielding because this meter now it's not like that other multimeter I have that can do take accurate measurements up to like what 720 megahertz and it's usable well out past 2 gigahertz it's just not accurate over 720 megahertz you can't do that with you can't measure voltage or that frequency AC frequencies at high with a meter like this it's fairly low I think this one's good to like a megahertz or something I'd actually have to pull the manual and see but it's just something to remember when you do that when you make up a probe it's a good idea to use coax cable for the AC probe if you plan on measuring at at your Innes in a frequency range because especially at low voltages if you get any leakage in through your cable that can affect your meter reading and it's not hard you can just get some of the cables it actually had a plug you can make your own so as I was saying you can take something like this and turn it into not all three of them like this they still make these today you can get these you can get them from Pomona and some other manufacturers it's a double double banana it's already molded so you know the center conductor is your goes to your positive and then the ground side which has the ten e double banana plugs always have a little tab there that indicates the ground side that's the shield if you make an AC Pro batter one of these matter of fact you could use this just like this as an AC probe okay because it's shielded you know right there you go that's that's really all you need you know you could take this off now usually they come just shorter you know you can get and you'll see that see how that one's shorter and this one's shorter they do they do that to keep the lead length really short because once you get out of here you have to remember it's not shielded anymore so that's why they always keep this probe tip short but you could take this cable if you wanted to just whack the end off if you wanted a little bit extra honestly probably what I would do is if I were to take one of these and I wanted to convert it into a positive probe for something like this what I would do is just cut the ground lead off okay take a regular single banana plug you can shove that back in here as your ground lead so just like the ones that came with this meter it's a long separately and then on the end here then you could put your you know your regular probe tip but that way this that then becomes basically your AC probe your ground will be another jack that gets plugged in here you could leave very well leave it like this too but like I say that leaves you shielding that way you don't have to worry about outside you know signals interfering with your measurements so let me get to get some cats change do a little bit of work to this thing we'll get it fired up and uh see if any smoke comes out which hopefully we don't okay so she lives you can see we have a little red light that's always a good sign [Laughter] so I changed the electrolytic capacitors I didn't take this out to the shop and buff this on to baladora buffer the scratches weren't that bad I was actually able to just do that with a headlight polishing buff ball sitting here at the bench so I didn't have to go out in the shop and fire up the big big buffer he's still a little bit visible there but you just want to be careful when you're buffing lenses if you're using you know big power buffers like the palador buffer I have if you push too hard on something like that it's really easy to just buff straight through the lens it'll burn a hole through that thing in no time but anyhow cleaned the controls I straightened up the sheet metal where it was used slightly bent like I say it's aluminum that was very easy to get flattened out changed the three aluminum electrolytic the two tantalum electrolytic capacitors cleaned the controls and the switches while I had it apart took that crazy fuse modification yeah I don't know what the heck they were doing with this thing but yeah that's been removed this fuse was not put back in I put in a proper one of the quarter an fuse like it's supposed to have and obviously put a power cord on it it's turn going so it has a proper power cord and fired it up light came on flip the themes position that's all the needle moves so hey that's good there and I hooked up a probe so I'm gonna do the alignment on this I think I'll go ahead I'll get plenty get this stuff cleaned off the bench here a little bit I'll just go ahead and do the calibration procedure actually show you me doing the calibration procedure on this because it's actually fairly simple it's only like what 1-day pages or something like that there's not much to it yeah I mean half of its description over here a little bit on the bias adjustment in this page and that's there is there's only what one two three four five six six calibration pots so we'll do that now one thing to remember if you have more than one meter likely like me if you're a a hoarder and you add several meters when you do the calibration on a meter like this make sure you're using the probe that is going to live with this meter for the DC portion okay you can use anything for the AC volts the high-low ohms position and the current that's not that's not important it doesn't matter what you know because that's just straight through the meter probe will be in the direct position for that but when you're in the DC volts position that has this hundred thousand over 100 K ohm resistor in series with this probe tip so if you use another probe there like this probe I is calibrate I use to calibrate that mirror up there so when I calibrated the other meter that's what this probe it major I just have it stuck in here to have easy to grab luckily I have about a dozen of these things no they're not for sale I got to get a lot of them one time somebody was selling not meters they just had a big bundle of these probes and I scooped him up it got him for a couple dollars a piece but like I say just make sure you use the probe when you calibrate the decent the DC voltmeter function on this meter that you're calibrating the meter using the probe that is going to stay with that meter because if you use another probe the resisting you even though it's 100 K it's they're never going to be exactly the same even a precision resistor you know if you get like a point 1% or 0.05 or even a point o 1% resistor still there's a tolerance in there it's gonna be slightly different than the resistance value that you'd find in let's say another probe so make sure you're using the probe it's gonna stay with the meter so I need to go dig that's the other thing I need to do dig out another probe but like say it does work so you know if we stick it to the ohms function there I hope I didn't grab a few grab ground slip here stick it in direct but drop it see we go to zero the zero works properly now it's actually part of the calibration come on stay on there little guy it's part of the the calibration when you would just the part of the calibration is you see how fast the needle swings there very very little movement of the knob here and that needle which so cue it's like really hard but watch as I turn I'll get to a point and it slows down and I keep turning and turning and turning and you have very little movement see how small there's a very small amount of movement there and then once I get up to a certain point it just did very little movement and you have a lot of needle swing that's actually part of the calibration is setting that slow zone if you want to call it that you want that slow zone down here because you don't want the tiniest bump of that thing to be moving that needle a lot you want so you can get a really fine adjustment when you're down here it's very sensitive to set it to zero and that was actually one thing with that other meter when I went to do the calibration on that one it looked like somebody had I guess tried to do an alignment on it remember that one had two broken trimmer potentiometer potentiometer in it but someone had screwdriver at that one and the slow zone was like way up here and once you got to a certain point the needle got the needle sling was really fast again with you a tiny bit of movement you had a lot of needle swing which makes it very hard to set it exactly at zero so that's what you want is this so it's just like that we're up just a little bit of movement barely moves the needle because if you get it up here like this yeah it just it moved such a tiny little you can see I'm barely turning that thing how much swing you get so let me get set up for the alignment you don't need a lot I mean you do need some AC signal generator your DC voltage source you like I say you do need a couple things to set it but yeah there's not a lot to doing one of these of course you're gonna want to have something to reference this to when you do your adjustments so you know I'll be using a multimeter that has a laboratory calibration that meter right there that one's been laboratory calibrated and it's still in calibration so I'll be using that as my reference standard now in the real world should you be doing that well yeah it's not exactly the best thing because you're using a meter that's been calibrated and you're using that to calibrate something else and of course there's gonna always be error every time you do something like that then that would be like taking this meter and using this as a reference standard to calibrate another meter but there's one thing to remember here this is an old analog meter that is if like that mirror right there is a five and a half digit meter I've got four and a half digit that's a five and a half also has six and a half digit meters that meter is several orders of magnitude more accurate than this meter you know even and now this one doesn't have a fairly low position it has what is that 50 millivolt it does have a 50 millivolt scale but still that meter has several orders of magnitude better resolution than this meter so I'm perfectly fine not send honestly I doubt you could find a cow lab it would calibrate a meter like this they'd look at you and go what are you nuts why don't you just do it yourself but yeah like I said just make sure that whatever you're using for your reference standard is accurate if you have a calibrated voltage source hey that's great you know if you've got a voltage calibrator you've got calibration standards hey that's even better but yeah just using just make sure whatever you're using is accurate because the last thing you want to do is is calibrate something and you're calibrating it out of calibration because what you're using is your standard isn't correct so let me get set up and I'll be back Oh a few couple other quick things occasionally I'll get people will ask me and emails now you saw the nuts that are behind like behind these knobs those are just hex nuts do you know nothing but a nut driver or a socket or wrench they're easy to get off but this the nuts on these knobs here you can see their neural they're perfectly round if there's no flat sides and people often ask how do you get those things all for those scratching of the faceplate and gouging those nuts because they're usually using something like this a pair of pliers to try and get in there because you can't use a nut driver on it there is actually a tool for that and that's what this is okay and you can see it's a collet it's got four jaws kind of hard to see and everything you see it's got serrated teeth on the inside edge and then as you move this that tightens it up this is actually what you use and you can see it's very deep this is what you use to install and take those nuts off this one's made by who wall school which I'm not even sure if they're in business anymore I've got two or three of these I mean I actually have them in three different sizes but if I'm not mistaken I think GC electronics still sells I don't know if they sell the smaller sizes anymore but I think GC electronics still sells this size here the large size so you have to go to GC electron they have all kinds of nifty little widgets for doing electronics work but yeah this is the proper tool for taking off and installing those nuts the other thing is when you're doing chord strain reliefs hi see this a lot myself I'll be working on something and B strain relief right here this plastic strain relief it looks like an angry groundhog installed it I mean they're just because they used theirs you slip joint pliers like I just had they're usually Houston something like this to take those things in and out and it just Mars the heck out of those things again there is a proper cold for doing that if you're gonna be doing a lot of electronics work where you're gonna replacing a lot of cords get yourself Perce pain relief pliers that's what these things are made for you that have offset handle that's what they're made for doing removing and installing new strain reliefs okay I think these were made by heyco or not hey Co hi hey HECO h e-- god I'd have to look it up of God well volt Rex would have had it wrong it's SPC technologies actually who makes it be add bolt Rex as the company and it's the strain relief that I actually use but like I say there there is a proper tool for doing it there it is you know you use the proper volt meters and you're saying when you you're working on a radio when it comes to mechanical stuff that's no different there's proper mechanical tools for doing mechanical things so any case let me get set up here and we'll get back and do the alignment like I say only takes a couple minutes it's very simple so let me get set up okay so like I said you need to keep the probe that you're gonna use with one of these meters especially if you want to take accurate DC voltage measurements try to keep the probe you know with the meter so if you have more than one you should have two probes so you're like in the case of this one there's that meter and you can see the probes attached to it same with this one like I say now I'm lucky I got a stockpile of these things so but I like to rebuild you know if you're going to restore your meter you might as well restore what's slightly out of you here restore your probe at the same time so you know check it over - does it need any maintenance this one didn't have a boot on the ground clip and yet it looked like the same groundhog you know it might be chewing on something probably did the soldering job on this one now you know this was the original clip because it is a mule or good you know high-quality 60 series clip but yeah it's seen better days so you know put a new good clip on it don't get just take my word for it avoid Chinese alligator clips like the plague the Black Plague stay away from them they won't do anything but piss you off I speak from experience investing good Muller brand clips that's what this is so this is exactly the same clip just a brand new one it's a Muller 60 series plant get the Muller boots - again don't use cheap Chinese when these are good and flexible you know and instead of doing a soldering job that looks like a maybe a 2 year old hacked at it you do a good soldering job you know you can't even see the hole there it's perfectly smooth you know where normally there'd be this little hole back here where the wire goes through it's perfectly filled in nice and smooth you clean off your flux residue but you once that's done slide the boot on there now it's good for another you know 30 plus years the probe itself there's not much really you need to do to this I just kind of do this preventive maintenance I do replace the 100k resistor that's inside of it so you know here's the original one that was in there that the carbon film I put in a higher quality when the higher precision resistor and this is a metal film but yeah this stick I stick a new resistor in there and but there you can see what's inside the probe not much to speak of there's a switch like I said and a resistor that's it nothing else that's all there is so let me get this screw back together this stuff put away get some other equipment turned on here and we can do the calibration procedure on this I think I've got everything set up here that I need for to do the calibration got my power supply set up already actually power supply the voltmeter them going to be using to check than you the power supply and voltages that I'm going to be using to set this are correct got an AC signal generator turned on already so let's jump into it so here very important always have F your Cal have your owner's manual and this case owners and maintenance manual first thing we need to do is connect an external voltmeter which we'll be using that one back there between the positive meter terminals so what they're talking about it they're two terminals on the back of the meter you want to connect from the positive meter terminal and a common ground or the foil ground of the circuit board so not the ground terminal on the meter you can attach the positive to the positive lead on the mirror and the negative to the actual negative the big trace on you basically the back of the circuit board set the zero controls to the meter pointer rest over the zero mark so down here zero mark and adjust the bias adjustment r53 so that the external meter reads 6.5 volts so let's do that [Music] it's alligator clips on here [Music] and I hate working around cameras let's ground got the ground right there positive terminal and yeah that's a tad bit to come back into focus hocus-pocus focus yeah nine point five volts so that's way too high so we need to adjust our 53 I say we I mean me or 53 that is the second pot remember we needed to check make sure actually we're just slightly off a zero there and now when you look at it at a camera it's off a little bit but you have to remember the cameras off and to the right a little bit unless you're with an analog meter movement remember your viewing angle is very important if you want to take really accurate measurements with a with an analog meter because you can see as I tilt the meter down you can see the needle looks like it's way off a zero now if you go in the opposite direction you tilt the meter back it's going to look like it's the other direction so when you're viewing an analog meter you want to make sure basically your eyeball is dead in front of the needle on the scale that you're looking at especially when you're doing a calibration okay we're going to adjust for 6.5 volts wrong way okay so that's good and just remember when you're working on this meter there is a hundred and twenty volts live in the back of this thing so watch where you're putting your fingers we don't want anybody getting electrocuted next step balance balance adjustments must be set to obtain the following results slowest meter movement of meter pointer through zero at left end of meter when zero control is rotated so like I was saying when we rotate this control just turned it off we rotate this control you can see we gets really fast up the top end you want it really slow and it's like it's off a little bit especially now that we've adjusted the the balance or the bias adjustment on there it's not really slowed down here anymore it's slow like right here which is not close to zero an indication of 0.3 or higher on the 0 to 0.5 volts scale with the zero control set fully clockwise like that and it's yeah it's now we which is fine point three or higher so that's actually fine so the actual adjustment just the balance adjustment set the range switch to 1500 volts 1500 volts function switch to dc+ it is balance adjustment - halfway balance adjustment side when there are 51 great about there is half way no no no no no take zero control to half rotation and there is actually a little tiny perfectioning a little rubber boot on this thing I know approximately where zero is or centered is they're centered half rotation and readjust the balance adjustment until the meter reads zero twin here [Music] there's anything with trimmer pots it seemed to jump on yet turn a little too hard and it just jumps a little too far okay zero now rotate the zero control fully clockwise okay and meter pointer must indicate point three or higher on the 0 to 0.5 volt scale so the zero to point 5 volt scale we can see there's our 0.5 so this second scale there's 0.3 and we're definitely higher than that with like point 4 4 2 pages out of there you keep flowing out of a book readjust the 0 control for a 0 and closely observe the meter pointer through 0 at left end of meter scale pointer movement appears to be too rapid adjust a balance adjustment to obtain slowest movement of pointer through zero so like I say we want the slow movement you see it's really fast up here and then it starts to slow down slow down and yeah it's nice and slow down here to zero so that looks good okay next step we're going to be adjusting the minus DC volts first check the settings and mechanical zero so they have there's mechanical and electrical zero mechanical zero is you turn the meter off and you adjust the adjustment here in the center so the needle rests on zero which I've already done turn the meter back on actually I need to zero at the health actually still still read on zero set the range switch to the 500 millivolt range and a function switch to - set the probe switch to the hundred K position because anytime you use this meter in DC volts the probe switch needs to be in the hundred K own position and apply exactly point five volts DC to the input terminals and adjust the DC negative DC Cal pot r45 for exactly 0.5 on the meter on the 0 to 0.5 volt scale so again we want to double-check make sure we're on 0 we are to check the external meter just to check our and you can see we're point four nine nine to seven so we're within a few thousandths of a volt and I'll attach the meter now said I'm hooking up because remember we're in the negative so that means the red lead the negative lead right here is going to go to your positive because this is the positive when you have the meter set to minus DC volts and this is the negative and yes we're definitely off scale so we want to adjust the - DC cow 45 [Music] we're on this second scale or adjusting for that point five and there we go point 5 volts and positive DC volts calibrations active set the function switch to positive DC volts apply again the same point 5 volts DC to the input terminal and just Cal pot or 46 for exactly 0.5 volts outside one disconnect my probes switch to positive DC recheck 0 good so anytime you ever change anything your function switches or your range switch always check your zero that one's fairly close it is off a little bit [Music] okay point five volts okay so actually I can turn off this noisy power supply over here we're done with the DC volts so next we're going to be doing the AC volts calibration first check the setting of the mechanical zero I've already done that AC volts excuse me so we're the legacy the only time you use the hundred K position is when you're in DC voltage range or mode so we're going to be AC volts so we need to go direct you went to a little critter there on those rolls off the bench we want to connect the clip short it out because remember AC voltage especially when you get into low range there you can see you're touching the probe just touching the probe with my finger tip yeah it pigs the needle that it's very sensitive and one check for zero good okay and we want to go to the point five volt range yep and we're going to apply point five volts RMS we're going to apply point five volts RMS sine wave at sixty Hertz to the input terminals and adjust the AC Cal pot for a point five indication on the mirror zero two point five scale hmm so just so we can see that flip this meter over it AC Gator Clips back in here so this is attached to the signal generator up there I've got them attached to that meter back there so you can see there's point 0.5 volts 500 millivolts RMS now I want to take that and attach that to our probe here this camera just gets in the way okay and we want to adjust our 39 so it reads 0.5 volts mar 30 9 is 1 2 3 over and we're going to we're measuring AC volts RMS so that's this top red scale okay right there okay so I can turn the signal generator off now okay and the last thing to set is our ohms function hi ohms calibration you want to set the function switch to the low ohms position range switch two times 100 set the probe switch to direct which it already is short test leads together zero the meter with the zero here okay zeroed and you want to disconnect the clips and adjust the ohms setting for infinity it's a little sign right there the infinity okay zero control four exactly zero on the left-hand scale and then open the test sleeves and adjust to control for exactly infinity at the right-hand side of the meter scale and now we need to switch the function switch to the high ohms position and without touching the ohms control adjust the high ohms cal pot so the meter reads exactly infinity so basically what you're doing is you've got infinity there and then when you switch to the high ohms position it should read exactly the same which it's not and that is the one I don't know if I can get this cameras gonna be in my way that's the adjustment it's way down in there when this thing's trying to look down and around the camera here got it okay right there so we should all be all calibrated up and this meter is ready to go I think we can actually take where is the resistor actually the one that I took out of the probe right there we can actually check that actually I'd need to go to the say about the 10k range zero the meter just connect the probe okay and you have to do that anytime you change ranges you're going to want to make sure you like I say anytime you change anything you want to check your zero and if you're in the ohms function you're going to want to set your zero and then also adjust the ohms control for infinity with probes disconnected and then the way you read the scale on one of these meters is there's two scales or there's the ohm not to scale there are two scales for the voltage scales but for the own scale it's the top scale up here it goes from zero to infinity so what you do is whatever the number the needle was resting on there you multiply that by whatever you had the switch set to we said it so we have it set to the 10k or 10,000 ohms position and this is a hundred a hundred K or a hundred thousand ohm resistor and you can see the needle you can see we're dead nuts on on 10k there so ten times 10k is a hundred K which is what that resistor is so there was nothing wrong with this resistor like I say I just like it that's probably the hardest-working participate earth because that's the one thing that's you know especially if you're doing a lot of DC voltage measurements that thing can be taking some hits so yeah I just like to change that but there you go so like I say the the calibration procedure on these meters is fairly simple you just need a 500 millivolt or you know 0.5 volt DC voltage source and you need a C power source also at 0.5 or 500 millivolts and on the AC it needs to be sine wave at 60 Hertz as long as you have that that's really all you need to calibrate one of these things it's very simple they're very reliable meters you know fairly easy to work on like I say the only thing is when you're working on these when you're not so much taking a part but when you put these back together don't tighten down really hard on any screws any of these screws that go that are attached to these plastic end caps you can see what's actually holding you turn off my AC power supply over there so not see if I can get one of these pulled out these little clips metal screwdriver there's little critters out of the slot but these little clips okay and that's what the screws bite into but if you tighten down on any screw in here too tight you're gonna break these plastic gears and then that's that's what holds the meter together so yeah just just snug it doesn't need to be you don't need to be King Kong when you put this thing together it's gonna be sitting on a workbench it's not like you're gonna be launching this thing into outer space so yeah just be gentle especially like I say it's plastic it's old and of course plastic gets more and more brittle as time goes on so just snug down the screws and you'll have a good working meter that should last you decades to come and you know once a year just check the calibration just like any instrument once a year check your calibration and as long as everything you know you'll be able to do that without even having to take the meter off of your shelf or whatnot you can just check the the resistance like I say low high power function it shouldn't move off of the infinity symbol there it should stay exactly the same for both high and low power ohms check your DC and AC voltage make sure it's reading correctly and as long as everything's fine you don't have to recalibrate it'll be fine and likes a really nice meters have some nice especially the high power power rooms functions really nice for checking the function of semiconductors and I've showed that in the other video that I did of this you know go watch that one and out that that shows me actually how the high ohms can actually turn on a semiconductor but there you go I thought I'd do a little bit more detailed you know video on this meter especially the calibration procedure so there you go I hope you enjoyed maybe maybe you learned something

Channel: MikesRadioRepair

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Id: rcgJt_jymqc

Length: 67min 20sec (4040 seconds)

Published: Sat Feb 10 2018