#51 Fluke 8520A How far does this rabbit hole go Part1

good evening 10 p.m. on a Saturday night I'm home alone and out in the shop and excuse me if I sound a little funny allergies a bother me and got a little sniffles but we got some fluke multimeter and here on the top we have a power of 80 10a 8 0 1 0 a and here on the bottom we have an 85 28 now I have the 280 10 s fired up and we think about these meters it is a lot of times the displays go dim on them as you can see that one it's very bright and looks good and the other one is also very bright and looks good so no problem in the displace I didn't check both of the meters out they seem to work pretty good pretty much bang on no problems at all let's check them on both ohms AC and DC I have not checked milliamps because it's funny of these things both leaders came in missing the 2 amp fuse connectors I thought that was kind of strange but it is what it is I guess a friend of mine bought all this off on eBay I don't think you I know these two were from one person to see what's going over I'm not sure if both of these would from the same person or not but I ended up acquiring these today so more fun stuff to work on this one is missing you can see besides comes loose bezel that sticks out this side has been cut off some of those painted it black around there I don't know why they've done that maybe they'd bought it with a soldering iron and just cut it off smoothly though maybe they're trying to view it from an angle and that was in the way so they cut it off no idea no idea at all but anyway the 8520 a is the one I was really interested him and the reason for that is that you can put on a set of Kelvin clips and connect it up here and go either to wire or 4/1 and when I saw that he told me about him that's why I was interested in acquiring this meter now all this equipment was supposed to be working but like eBay you go on and buy something you're taking a chance so i'ma turn these two off that's one way you saved the displays there's only turn them on when you need them and we'll fire up the 8520 a and you'll see it goes through the self-test fine and everything good - we get here here I'm gonna just play a show with - 116 point 706 and you cannot get out of this mode I mean you can change you know DC to AC alteration program selection program data all that will come up and work but when you go here to to wire or 4 you get error / 1 + / - manual error Oh Warren says high voltage on the bullets so you know on this movie you got your inputs on the front switch it and you've got two inputs on the back so that is a problem with high voltage on the influence so don't thing I know to do is tear this thing apart and see if I can find anything that's wrong I don't know if somebody's overloaded the front end and has took something now or what per se software issues but it kind of you know I tried to read voltage on the front connection in the back in action and you can't can't get no reading on the meter whatsoever for any voltage test or you can't get to resistance test so something is going wrong that I'm thinking yes with the input/output section and I had to look at that look at the DC buffer stage I have personally never been into one of these in fact this is the first time I've even had a multimeter like this in front of me so you know I still got a lot to run on these things myself but you know like any other piece of test equipment you got to tear it down and find out what's going on so let's pull it apart and see if we can see anything I have two top and bottom covers off if you notice the whole mainboard is shielded on the top we're gonna power supply here and off associated power supply circuit and over here we have our control unit this connects to the front panel and displays and all your controlling is done over here the first thing I noticed when I took this off there's three eproms these looks like 2764 series and under DZ farms a little window or both these tabs that's covering the windows had fell off for just laying inside and I can't find this one Memphis may be a part of the power supply wire but uh you know these chips are erased by ultraviolet light so I stuck the labels back on and put just a little piece of great tape on with this one just to keep any right and getting into it because we definitely don't want any like getting there and erasing all chips I don't know if you could even obtain these chips anymore but you know you could get another unit and read it and copy them over to achieve all those of you playing at home one port define high-voltage be very careful discover associated sheet metal and the circuitry within may present up to eight thousand volt shock hazard so be very careful when you mess around inside of a piece of equipment like this everything looks pretty much well shielded but still you know there's always a chance of shock hazard so to get in here to the elbow and you know look at the influence this cover is gonna have to come off and looks like it's only four screws holding it on so we'll take that off right there alright now we should go to lift up take over all whoa okay I just noticed on does that tell you anything it's a bonus part on the inside to cover on the top looking here this right here in this location let's get a look at that and see what Betty is all right so the area will look in the end this is your a logic part of the board here and this is your buffer logic with your DC buffer and I'm looking right here and I'll zoom in on that a little bit as you see the bullet spot right down this chip connector and there's two resistors here and both of these resistors has raised up off the board about three-quarters of an inch and that one is blown into that is our 255 now I would say B's has been replaced by some money because every other resistor on the board is all the way down flush with the board but these two it's been raised up and looking at it the solder looks a little bit different the rest of the board so we need to find out what are to 55 to 57 years now I'm looking at the two resistors below it and both we don't have both spots on it but you don't really have to bid a flame cuz you're talking about what two reaches to the top cover here and it blacked out the top cover as you saw but if you notice the board is not not charred or fried but the top of those two resistors has been a little hot and that's just rolling on them from whatever born up before we just want to take a little isopropyl and see if that'll clean off make sure that those two does not Barton - yeah I think they look okay that was just flashpoint from whatever blown up before which had to be the two original resistors that was there anyway I'm not to go to the schematic and see if I can find or 2:55 and 2:57 and see what's going on there one other thing I want you to notice is that all these are tantalum capacitors in this quite a few of them in this circuit so we need to deal long tantalum capacitors and what can happen to them tantalum capacitors very seldom fail our you know fall out of spec they either good or they go short and if they go short something like this resistor would be the weakest link and would take it out so you know do you have a suspicion of what caused these resistors to go first so what we're going to do is test these two resistors it's our 257 and 255 well these are 15 ohm resistors I'm hoping I can test them in circuit okay I've looked at the service manual or to 2:55 and 2:57 or 15 own resistors so let's get a check on these and see what we come up with I think we can check them in circuit by looking at the schematic okay that's all 257 and it looks okay visibly and it showing 15.1 times then the oven that doesn't look too good or 255 so let's test it it should be 15 ohms and it's showing about seven point four seven K so that one is definitely baited so to get to the bottom side of the board we've got another shield that we got removed and you see there's six screws around it but you look here and you'll see two riveted threaded rivets in here so will you go try to yank this out it's always good to check but you see what here then when we look on the other side there's actually a screw here it has a screw here so it's they'll need to come out I'll get all the screws out of the back and get that cover off so this is the bottom of the circuit board and right here is wattage resistors all and you can see all the leads here on that row of resistors on both sides if you noticed the factory resistors appointing that way to two resistors and questions and leads pointing the opposite way that's a good indication that they have been replaced before so this problem has already been looked at and walked on me was not satisfied so I got my two new resistors prepared to go in and decided to just leave them up off the board but I put V notches in the resistors this way the V will set down on the board and it'll sort of from underneath and by doing it this way if it gets hot and starts to burn the resistor will not sink down into the board you don't have a firm spot to hold on to okay I've got all new resistors were placed on the DC logic board so we say we just fire it up and see what it does let's say we don't that resistor all 255 suffered a major failure now resistors just don't burst into flames and blown up for no reason so there's got to be something going on there's either something on the output side of it it's shorter than causing it or there's a problem in the boat Israel so what we need to do it's good back here to the voltage rails then check our voltages back there so here we can have our look at all schematic diagram and this is all T the power supply and we have to bridge rectifiers here we have four regulators we have 27 volts positive 15 volts positive our ground rail we have minus 15 volts and minus 27 volts that's very convenient that they already have some test points here that we can check at so we can ground on TP 705 and we'll check these voltage rails and see what we see so right here by our system for the place you can see an empty IC socket that is actually from this jumper I wouldn't here and remove this Joker and this way when I turn it on to check voltages we're not responding our resistors out again and causing any further damage this will isolate this section from rest of the board so we only have the power supply running through okay so here we have our Milo's 15 volts negative and we'll turn it on then I got negative fourteen point seven what we have our negative 27 volts and then we have twenty seven point five looks good 14 volts okay that's miles 15 ohms Ian well here's all positive 27 by trails and as you can see our positive 27 volts rail is about 10 volts higher and it needs to be TP 704 our positive 15 volt rail was a bullet of fines and this hidden wound up here behind this connector and we'll check it only unit owns like help and we had about 300 millivolts on our positive 15 volt rail so we have a problem with our positive 27 volt rail it's way high and our positive 15 volt rail is way low so we have to go back to the schematic and look at this okay so by taking off voltage readings we know that all negative voltages checking out five but our positive rails are wrong 27 volts is that 37 volts and our positive 15 volts is in the middle volt range so we know there's something going on here in this section so we need to go in and check these components let's through here there's a couple resistors these capacitors now as a diode here that comes from 10 3 of the 27 volt regulator it goes down to pin 2 of the 15 volt regulator we also need to come over and check the capacitors over here in the supplier let's move out the 2 voltage here but but we need to check these capacitors and there is also these 4.7 50 volt capacitor so I bought that so we can go in here and we can check these components we have a diode here from the positive 15 volt rail down the ground the resistor there a capacitor here and again these are tantalum capacitors and we're getting here see what we can find out okay after doing a lot of testing of these parts I found that you 7:04 it's not a 27 volt regulator it is actually L in 340 T - 12 which is basically a 12 volt regulator and as you see we had a lot going on between you 705 and you 704 and that's derived Steve 27 volts now I want to have failed is that somewhere outside of this circuit we have a dead short on our positive 15 volt rail so I'm had to pull rest of this schematic and trace this on out and simply find out what is dead short said I think it's going to be somewhere around the DC buffer or somewhere in that location so that you can see I have the 15 volt regulator removed I've got this resistor stuck in doubt put in these just these regulators just plug into a socket and then bolt through the chassis and I got a little own scale and when we check it and it's completely zero we go to diode check gonna steal our way across so there's definitely a - wart on that 15 volt rail so now that we looked at our power supply rail we already know that the issue with the voltage regulators is downloading missing so what we need to do now is look at these capacitors right here these tantalum capacitors and pretty sure since this burned up this one resistor that one of these capacitors is probably causing the problem and since we're having a problem with off 27 volt positive and v 15 volt positive rails we probably need to check these two capacitors right here but now don't let the negative 27 volt even though it was good on the supply we also need to check that capacitor so we'll look at these and see what we find so since this is our resistor that was giving us a problem we follow right down we see the trace going right to the source capacitor here this is the capacitor I'm suspecting it's going to be Vance and when I roll out from ground to this thing under the resistance I'm getting a complete 0 it's a dead short there so we want to pull out this capacitor so we've got off Tesla probes across the capacitor and as you can see it's completely rose and just a verification for you analog junkies boom complete short yeah that chance of them has gone short on us so we have our new tantalum capacitor installed and check make sure and we are up in two megaohms no more short and growing bear however when I come back here and check the positive output of the 15 volt positive voltage regulator we have still have a - short there now pull the regulator on I got a lead stuck in there so I can test it right now on the peel of the output and yeah there's a dead short - growing so we still have something on that if the VOC positive output rail that is shorted to ground okay but since we have this - short on all 15 volt rail let me show you how we're gonna go about locating this now have the multimeter set then you see us 0.1 of an own and what we're going to do is go in here and start removing these jumpers that's in here and see if this changes and if it does then we know that'll help pinpoint the area of well short is that it makes it nice that they put these jumpers in here it helps your eyes too late for the problem yes okay remove that one then as you see we're still at a short that was j22 some will come here to j21 then remove it and off short has gone away some put j22 back in yes I say we're up in 2k ohms now so I definitely something going on right here on Jay 21 so as you can see here on off schematic this is Jay 21 and this is several singles coming in and right here is I'll positive 15 volt rail and once we come off of pin 6 of j21 we see a tantalum capacitor here 10 microfarads it's C 450 we also have another voltage regulator you 407 which is an 8 volt regulator and then we have a diode C off for 12 so we might can expect something here in this area would it be to doubt the regulator the tantalum capacitor or something further on down this rail my first guess would be C 450 10th on capacitor because we know what they do sorry about having the voltmeter upside down but I'm going to get all this in one shot this is J 21 and we have 10 legs and 10 6 10 9 is our power supply side and you can see we into killing range but when we go to pin 6 boom - short so we now we know that the problem lies in this board right here so the first thing was good - I was telling you see for 50 it's right here and it's at a swim camp and it's right beside this voltage regulator so I'm gonna remove this tantalum camp and we see if i short goes away like the cap has been moved we'll go back to ten six and we'll check and now we're reading in a killing range so again another tantalum capacitor has failed so looking through my Talon capacitors I have to not to have a 10 at 25 volts so I put in a electrolytic temporary and we'll check now on pin 6 and see if I'm short is still there I'm pretty sure it's not close the capacitor did check short okay and we are eating in kilohms okay so well we're getting somewhere all right down the moment of truth we're going to do is turn the power off and we're going to check our 15 volt positive rail and we're gonna do it on 10 6 of j21 and that'll tell us if that part is now working our zone and we're now at 14 points 6 3 volts so that's taken care of the short there although when we go to him we check off plus 27 volt we're still show with 40 volts on that and the input of our regulator it's 40 volts and the output of our regulator it's 40 volts so it looks like to me that that regulator is shorted or something that's causing it to short across them so I expected this ileum 340 T - 12 to be bad so I went ahead and replaced it and what we want to do now is check our positive 27 volt rail that is a 12 volt regulator in at least conjunction with the 15 volt regulator and the 12 volt regulator to produce 227 volts so we're gonna go here on our 27 volt test point turn the unit on and we now have twenty-seven point 1 2 volts we go back to our 15 volt rail it still reached 14 point 6 3 but that's close enough so that's like we are getting somewhere alright okay we went through quite a bit to get this far and the next thing is you know will we go through boot up and not have any error codes and most of all will we have anything any voltage so in on the screen so let's turn it on and see what we get yeah and unfortunately you see it showing plus 38 point 7 volts so we still have voltage on the input and as you see if we go into select volts AC it's still showing 44 volts if we go to 2r we come up with an l1 and same thing on 4 wire we're gonna come up with l1 that's telling us that it's still voltage on the input so it looks like that some more telling capacitors that it's going bad in this unit and at this point probably the best thing to do is go ahead and order all new tantalum capacitors and replace all of them and couldn't get all them over out of there so now that we got all our power supply rails are working pretty good I started to go back here on the buffer logic area and pulled the jumper back out on j19 but you know this is why our main problem was was in this area to start with and I had forward to jump around so we're gonna turn the unit on and see what kind of errors we'll get in okay let's cross our fingers and see what happens so you're seeing this as I'm seeing it at the moment this is just a thought I had boom look at that point zero zero volts DC 0 votes AC then we're gonna hit d2 wire I'm setting boom there we go and our for our home setting so let's get him down shoot around look at some more them tantalum capacitors and see if there's anything in that it's uh causing the errors but it's good to see those lights come on yeah I feel like we have made uh some good progress now so we're looking at the error code table in the service manual see if we had a 0-0 blank display would be no errors but we are showing error Oh Warren HP and all the seasons high-voltage presence with own functions selected unfortunately it doesn't give us any more information on what to look for it just gives them a explanation of what it is so you know the next thing we got to do is figure out just what error oh one high voltage yes so again with j19 plugged in we turn the unit on that goes through this past I said we're showing voltage and if we reach over here to select anything in the ohms range because of that arrow oh one okay but with j19 out we turn it on and we get zero which means no errors and then when we hit on two and four wire we'll get our own Freddie well the bad thing about this you know the meter will not function you cannot read nothing or use any other functions on it to test voltage or homes or anything so I'm gonna have to look into the schematic and trace out all the pins on j19 and see what kind of singles is going through a woman and just once you know going on in that area so we spent quite a few times on this on day two of it finishing up for today and it'll probably be next week before I get a chance to get back on it or either the week out there so I'm gonna go ahead and conclude this point of the video as part one and I'm have to do some research and man there's a lot of stuff to go through on the manual for self-test so a lot of troubleshooting involved in it so we got to find out what's going on with our logic that's definitely something and that is causing a problem but as you know always finding the issue isn't always as easy so you know I feel like we fixed the results of the issue my guess is somebody's put something into the front end that caused some problems could be those tantalum capacitors don't help at all so you know we still got a lot of tantrums in there that needs to be replaced I'm sure so in the meantime we're go ahead and get our order up together so can I get these tentacles replaced so if you have any comments you know always feel free to leave them in the muck you know if you've had one of these and you're working on it I am open to ideas so anyway we'll conclude this in its part one and we'll see you next time

Channel: The Radio Shop

Views: 10,653

Rating: 4.9876161 out of 5

Keywords: fluke 8520a, erro1 fluke, err01 fluke, fluke repair

Id: ULQroWJUZdw

Length: 39min 40sec (2380 seconds)

Published: Sun May 15 2016

Reddit Comments

[u/Ninboycl]

Good video. The guy is definitely capable at troubleshooting. Hope he figures out the issue, looks like something is broken on the input side.