Professional Dwell - Tachometer Restoration!

hi everyone and welcome to another restoration at mr carlson's lab let's get started let's test and verify the operation of this professional dwell tack now much of the times these things are sitting under the hood of a car and they're vibrating so they're usually out of alignment and much of the time they really didn't come from the factory aligned very well anyways the stuff has just so quickly moved down the line so we can kind of tweak this thing up and maybe make it as close as possible now keep in mind with all of these and this is something that you need to keep in mind whenever you're working on any of these older devices uh an issue is scale linearity now i've seen this so much and i expect this thing to have this as well with the everyday standard professional dwell tack you got to remember that you're taking a signal in here and of course you're converting that to an analog movement on a scale so unless you're really dealing with a a device that's um you know spent the engineers have spent a lot of time in there's usually some form of scale you know linearity issue so we'll see if this one has it and if so we'll we'll talk about it at that point all right so what i'll do is i'll get a function generator set up obviously because i don't have a v8 in a four cylinder and a six cylinder on my bench here it'd be kind of heavy right so i'll show you how to align one of these things with a function generator it's really simple and i'll share all the math with you as well you'll find that if you look for math and a proper description of this kind of stuff online it's kind of tough to find that's just the way it is right so what i'll do is i'll break it all down to a very simple and very easy explanation and you can write this down on a piece of paper or whatever and save it for the future if you ever want to take one of these things and align it yourself and that'll also go for the dwell dwell is a little bit more complex but i'll share all that math with you as well so let's get going i'll get the function generator set up and uh we'll have a function generator at the top of the screen here for us to look at let's verify or test the eight cylinder high rpm range first so that's the upper scale on the meter here and that's just above the yellow line here so 30 is 3000 rpm and just below the line is the number six which is 600 rpm so that would be the 8 cylinder low rpm setting it's always a good idea to test it at center scale first the very first thing that you need to do before you really try to do any sort of alignment or any type of verification on a meter like this is you need to make sure that the mechanical movement is zeroed now there's a bunch of tricks with this i kind of have to get the center screen because it kind of shadows you can actually see the shadow here so in order to adjust this right onto the zero mark you can see it's very well zeroed you just put a screwdriver in this little adjustment here like so and it can see if i twist this and bring it off of zero or below zero so we want that right on the zero right about there after you've done that what you want to do is take the meter and rock the meter back and forth like this and see if it still sits on the zero which it does you'll find that if you do that and then the needle moves up and stays there or moves below the zero and stays there you know that you have sticky movement inside the meter and that has to be fixed before any type of electrical alignment or any type of verification can be done because the needle can move and then jam up or it can add extra resistance to the movement in the meter and that'll cause you know of course accuracy issues right a lot of the times what happens over time with these meters especially with the older dwell and tach meters is the plastic shrinks and it tightens up on the internal movement of the meter so if it tightens up on that movement of course you're going to get a sticky needle now there are ways to rectify that problem you can kind of see through this hazy area there's a little adjustment screw under the front cover sometimes depending on the meter you have there'll be an adjustment screw on the back that you can get to and that has to be loosened off just a touch and there's a bit of a science behind that and i'll share that with you in another video on how to actually repair the movement of these meters so once that's done and this is sitting on the zero mark and everything is good usually you're good to start your verification process at that point so i'll move this back under here so now in order to do this alignment on your bench you need a thing called a function generator now that's not to be confused with a signal generator there are two different devices a function generator will provide you with a square wave output and you can also adjust the duty cycle of that square wave now there may be some devices nowadays that will you know perform both functions you know a signal generator and a function generator but the uh it's most commonly two separate devices okay the math for this is really quite simple all right so in order to adjust or verify the eight cylinder to do the alignment this is the math for that you can copy this down and use this for yourself if you need this in the future so for a v8 it's four times the rpm equals you put a line here and then divided by 60 gives you your frequency in hertz okay now i know i'm gonna get this question what is this number four and what is this number 60 well the number four is the number of pulses per revolution but in order to make this very easy on yourself it's half the amount of cylinders okay so if you have a v6 that's obviously going to be three times the rpm right and if you have a four cylinder right it's gonna be two times the r p m everything else stays the same okay and here we go so in order to know what frequency we need to enter into our function generator we need to figure out you know what's going to happen at 3000 rpm what kind of frequency we need so in order to do that i get my calculator out here you can see that okay so turn this on so four times three thousand divided by sixty equals two hundred hertz so if we wanted to fill this in we could go three thousand and then hertz we can go 200 so for 200 hertz is what we need at our function generator to make this thing happen okay and then for the v6 that'd be times three and all that we'll worry about that here in just a moment okay and also show you how to do the uh the math for the to calculate the dwell angle that's a little bit more complex but we'll take a look at that here in a moment so and of course that's assuming that this meter is even working at this point is you know as much as i do it's just on the shelf here okay so now what i'm going to do is put the function generator on the top here so i'm going to take a look at that and i have my leads over here so turn on the function generator and see where i'm at where am i at see frequency i'm always away from the mic so pardon the low audio so we need to set the frequency to 200 hertz 200 enter okay the amplitude needs to go at six and a half yes 6.5 volts peak to peak this is not terminated the 50 ohm the 50 ohm output of my function generator which is this cable right here is not terminated so it's going to give me roughly about 13 volts and that's when i need to drive this all right i'll explain more about that later on if i terminate this into 50 ohms it's going to drop the output a lot and the function generator won't have enough output to actually drive this device because it's designed for 12 volt vehicle right so that's a little trick there a lot of people say well can you actually run the function generator without a load on the output well in most cases you can in this case yeah absolutely so of course check with the specs of your function generator but you know we'll start fine okay uh symmetry which is a pulse width should be at 50 or close to let's see what it's at yeah it's fine okay and uh everything else should be okay so go back to frequency all right so now i'll connect the leads up and what do you think drum roll please okay let's see if we're going to get anywhere near 3000 so we should be center scale okay so that's connected to there and i will connect this up to here and what do we get uh about 2800 so not bad you know it's it's off right to be expected and uh this makes me question i wonder what the scale linearity is like so it's a little bit low so let's uh test this at 1 000 okay so we'll get the calculator out here that's actually pretty simple four times one thousand four thousand or divide that by sixty all right so here we just go i'll show you the process again so 4 times 1 000 divided by 60 equals 66.66 hertz is what we need to make this point at 1000. so let's see how good this is down here so 66.66 entree and we're not bad that's not too bad looking at it straight on it's just a touch below the line and it looks pretty much the same at your angle as well so it's a little more accurate on the low end of the scale so let's try at 5500 rpm okay right up here and see what that is and this will really give us a good idea of the scale linearity of this device okay so we'll go four times 5500 rpm divided by 60 equals 366.66 hertz okay so here we go 366.66 and went up to bumped it up a little bit that is way out that's way off so that should be up at this line here so there is your perfect example of your scale linearity issues in a device like this now if this was probably made by sun or something like that it would probably be spot on right you know it hadn't been bumped around and trashed on too bad but um you know so we'll see what happens here right so we'll take a look at the insides and see if there's anything to calibrate that i hope there's calibration controls if there isn't we're gonna have to add them to make this thing calibrate okay so let's go uh let's say eight cylinder low okay so let's try 600 so i'll adjust this all up before i go switching the scale because this is gonna probably pin off the scale here okay so we'll go 604 times 600 rpm divided by 60 equals 40 hertz let's do that or zero enter and we'll go low hey that's almost spot on almost spot on okay so let's try a thousand down here all right i believe if i remember correctly i think that was uh 66.66 let's try that again let's go 66.66 enter and as you can see right scale linearity right let's try the six cylinder high which is this one here six cylinder high rpm range okay so click that up there now the math is the same it's just we change this right here so instead of times four strength times three so three times the rpm it gives us our result oh by the way i think i neglected to mention what this 60 is right here so it's very simple one hertz is equal to 60 rpm and there are 60 seconds in a minute all right so that's what that is right there so number of pulses per revolution over here or again half the number of cylinders and then that all right okay so let's do the math so we want to be a center scale here for 3000 rpm so what we're going to do is we're going to go three times 3 000 divided by 60 gives us 150 hertz so we're gonna have to put that into the function generator so take a look at the function generator again here one five oh enter and i will attach the clip back up again so attach the function generator to the meter here and as you can see it's down about the same so you know what that that really almost looks like either factory miscalibration or possibly something has aged uh maybe the meter itself has been damaged in some way shape or form you know these things they usually see a pretty rough life but it's very close the other one is 2800 looks like about 20 50 or something maybe close to 2900 right okay so let's try the six cylinder low for 600 rpm so let's go clear three times 600 divided by 60 equals so 30 hertz or 30 cycles if you like so 30 enter and you can see you know a little bit far off on the upper one there right usually when you're dealing with that type of scale you're on the other scale that's showing about six just about 600 so i'll move this down here and as you can see it's actually pretty close that's not too bad for the uh for the six cylinder low so and i wonder if the linearity is somewhat the same so again we'll do this three times one thousand rpm divided by sixty equals fifty so let's see what it says at one thousand not too bad a little over you know 1000 there and that's actually not too bad for that skill so yeah [Music] interesting we'll have to look inside and see what we come across uh undetermined there so let's try 1100 okay so three times 11 oops three times 1100 divided by 60 equals so it's 55.55 not bad not too bad for that scale at all so it might be decalibration who knows we'll find out okay well that's good enough for that let's take a look at the dwell next let's check that out and then let's open this thing up and see what's inside let's test out the dwell function and see how well that works so i'll move this over to dwell so now we have a v8 setting here and we have a six cylinder setting you can see they're tied there is no separation here between eight cylinder and six cylinder then you know there's no multiple positions right again the scales are tied together and that all has to do with the ignition system in your vehicle so anyways i'll talk more about that here in just a little bit more specifically the distributor okay so you can see on the top we have dwell and it says 45 degrees and that's the maximum for the eight cylinder setting so that's very important for our math so just say we have a 50 duty cycle set up or symmetries at 50 like it would say on my wave tech so what we do is we go 50 because that's where it's sitting right now and i'll show you that times as 45 is the max we go 0.45 equals and that should give us 22.5 degrees since the bottom scale stops at 60 so that's for the six cylinder if we go 50 percent times because it's 60 it's 0.6 you see how that works right equals 30 degrees now if we look at the two scales you can see we have 30 degrees and if you follow that right above it we're at 22.5 yeah so by varying the duty cycle we can also vary the scale here so say i want the the upper scale to be at say 30 degrees okay so i want the eight cylinders to show 30 degrees and get very close by entering say 66.67 percent but it's gonna round me down to 66 so that would get us very close so if i go say 66 times 0.45 right i'm going to come very very close on the v8 scale to 30 degrees okay and that'd be right center very close it's actually to really get that close at 66.67 right but so i'll show you what i mean here so if we take a look at the function generator again i'll just get this out of the way so i can put the function generator at the top and get this off of here so function generator back up and i'll hook up the leads again and i'll go up there and i'll adjust some stuff and show you what's going on so i'm at 55 hertz it doesn't matter 55 60 hertz whatever for this test should be absolutely fine that's still the same setting that we were using in the six cylinder position there now if i go to symmetry you can see i'm at 50 right now so 50 should give me 22.5 or 30 right same thing 30 is a nice little mark there but you can see i'm above 30. so if we go 20 21 22 that would be 22.5 there so i'm actually at about 23.5 right again 30 would be 22.5 so if i go up here and uh let's say test for 30 degrees up there on the 45 degree scale right i need to set it to 66 so i'll move the symmetry or the pulse width to 66 okay that should be close and as you can see it's a little high there as well so 30 would be right in the center right so again out of alignment just a little bit and that looks relatively linear from that point to that point again since i would be using this myself for v8s it would would you know sit somewhere between probably 28 and 32 right is where this meter would be working for me right so dwell or cam angle if you like uh sometimes it gets confusing when you look in the manuals i'll say cam angle as a dwell you can look at it like that as well so what else can i tell you here about this before we open uh this thing up i i think that's uh pretty much all for this so let's see if we can calibrate this thing let's open it up and see what it looks like inside um you know i have no idea what's inside this thing hopefully it's not disappointing okay let's take a look inside see what's inside this thing this is always exciting so it looks like there's only four screws here and they come out relatively easy which usually indicates that it hasn't been part or cross threaded this one looks a bit rusty okay probably been under the hood of a car when it's raining working on a car or something like that at some time who knows so everything tells a story you know open this up antique dust on this thing so that's out of the way so what do you think's inside not a whole lot by the looks of it little circuit board down there uh this looks like it's just probably gonna slide out of the case and it does for building projects these types of cases used to be very popular let's get this out of the way take a look at the back side actually looking pretty good why the wedge-shaped circuit board that's kind of strange isn't it shaped in kind of a wedge why not just square well we have an adjustment here and four adjustments here so that's five adjustments in total how many positions are there in this so that's off one two three four and five haha i think we have an adjustment for each one look at that six h six l so six high six low eight h eight l so eight high eight low and that would leave this as the dwell adjustment well isn't that nice of them to mark that mind you we could have traced that out pretty easy just by following the positions of the switch but it's still nice of them to do that two electrolytic capacitors which could get changed they are so cheap why not change them so before i attempt to even do an alignment on this i'm going to spray contact cleaner in all of these and move them around and i'll probably resolder this switch because the solder on that switch looks pretty bad it's looks like the there wasn't very much solder when they put that together look at that so re-solder all of those so a little bit to do here so we can probably get rid of this grab a screwdriver here like so that looks to be about 7 16 or 12 probably 12. yeah most likely 12 do i have 12 here no i don't but i have these horribly spree painted vice grips no i don't agree with this but there's a washer behind it so i can very carefully grab on to this without scoring anything as you can see there's space there and let's give it a bit of a twist look at that precision precision with a very scary looking vice grip okay that off of there look at that got to be careful with this so i don't want to pull that out of the meter looks like it's ready to do that what's the ic say okay okay electric it's been a while since i've seen one of those msm4049 so that's a 4049 so basically like cd4049 same kind of idea and if i remember correctly i think that's a hex inverter so anyways very simple design very very very simple design get rid of this because it ended up falling off okay so what i'm going to do is get the soldering iron heated up and get this desoldered and now i can put this off to the side so i'm not tugging on these wires i'm very leery about pulling those out of the meter just actually put a little spot of glue on here or something like that just to be careful and uh i'll start cleaning things up and re-soldering things and then we'll start doing an alignment just before i remove the meter i added a bit of super glue right to these leads so these are super glued directly to the back side of the meter and also put just a touch under this tape that was coming off to keep the dust out of the meter so that worked very well so i don't have to worry about pulling these wires out of the meter anymore the meter is in you know very nice condition it does have a little scratch on it that it's received somewhere along the lines but other than that it's pretty good as long as there's no really bright light directly on it it's pretty good so i resoldered the entire switch here and that's how it should look not like it was so whenever you're dealing with something that's going to have any type of movement or could have any type of movement there should always be lots of solder on the contacts so if you ever take any type of switch apart or anything like that it's always the things that you inspect first anything that really gets the mileage i guess you could say i replaced one of the capacitors here already and this is the one here that came out so this is the one that i had 220 at 35 very good quality capacitors and this one here still needs to be done so let's do that so let's grab this here and that comes out of the board there get rid of that take this out of there 10 volts 47 i have a much nicer capacitor here put it down like so hopefully that'll stay no it won't of course because the solder roll is gonna move it okay stay here we go and there it is in order to clean the switches in here basically all i do is just give it a shot of contact cleaner and move it around a whole lot like so and then let's do this [Music] after you've done that you want to make sure that you hit each end right so that you go through each contact and then rinse it off because what this is doing actually right now is this is removing the debris off the contacts so you do this too much then of course you're just smearing the debris around so give it a good blast every now and then and just wipe the debris off [Music] and that should be good and then of course now i need to do the vrs so if it wasn't decalibrated then it will be decalibrated now so let's put this in here and move this around like so a little bit if you don't do this before you do an adjustment a lot of the times you'll get a you know a very jumpy response so i'm roughly back to where they were they're all going to get realigned anyways you know right there kind of just go one at a time very needed step again if you don't do this kind of stuff and you try to align it you know you're setting yourself up for some issues there it is so i'll dry this all up and i'll get this put back into the case back all back together and we'll do the alignment i think you can do that by possibly just slipping this back up just a little bit from the case i'll show you what i mean here in just a moment so i'll get this all cleaned up and dried up and ready to go many of these meters come from the factory aligned at the top end of the scale for the tachometer settings and then for the dwell it's a little bit different i'll talk about that when we get to that point so i have the selector switch for this meter right now on the eight cylinder high rpm and we're going to align the up to 6000 rpm scale so the first thing i want to do again is make sure that the needle is sitting on the zero mechanically and it is so i don't have to worry about that because we adjusted that earlier right so what i'll do now is i'll go 4 times 6000 rpm divided by 60 equals 400 cycles now in order to save some time here i've already entered that into the function generator so if you take a look at the function generator you'll see that there what i'm going to do is attach the tac to the function generator right now and we'll see where those vrs ended off so we can see that vr is out of adjustment remember i cleaned them and moved them just to random spots so what i'll do here is i'll slide that to the back i'm just going to take this off camera for a second because i've got to poke this in the back here and see what i'm doing and i'll get this up here and move that back like so that looks like that's right on top of the 6000 doesn't it perfect okay so i'll put this back down now let's see how well this tracks so what do you think so let's try 3000 rpm so that should be about 200 cycles correct so 4 times 3 000 divided by 60 equals 200 cycles okay so i'll set the function generator up to 200 hertz 200 enter oh look at that how close that is now that that's pretty decent so now what we'll do is we'll test this at a thousand and if it's right on a thousand then we definitely won't be touching anything so that's very close it's right at the edge of that bars how much closer do we really need to get with this analog scale right so let's go four times 1000 divided by 60 66.66 so i'll adjust this up 66.66 enter look at that does it get any closer that is very good i'm definitely happy with that okay so eight cylinder high rpm adjusted and successful very successful so now i'll set everything up for the 8 cylinder low rpm adjustment let's align the 8 cylinder low rpm setting so that is the second scale down here just below the yellow bar so we want to align that right at 1200 rpm as well so let's do the math here again so we're going to go 4 times 1200 divided by 60 equals 80 cycles or 80 hertz so if we take a look at the function generator i have that already set up to save some time and i'll attach this to the meter with the clip here again and we'll see where we're at and we're over the top again so what i'll do is i'll take this off of here and i'm just going to turn this around and fit this in the back very carefully so that i don't damage anything okay and i need to take that back down to 1200 so let's see get this really close up here so we can both see this make sure i go the right way it's very touchy it's looking like it's right on top of it there isn't it okay so we're doing pretty good at this point so far with the upper scale as that's on top well it's a little bit high i think i could do a bit better than that let's see here i'll put this back in and i am just breathing on this okay that's very close okay so i'll put this down here hey the accuracy is only as good as the alignment right okay so now a little clear so we're going to go 4 times 600 divided by 60 equals 40 hertz so that'll be right at 600 rpm there okay so 40 enter look at that does that get any more accurate than that really that's just spot on so now the truth are going to be some some pretty low frequencies here so let's try it at 200 rpm okay so we'll go 4 times 200 divided by 60 equals 13.3 that's some pretty low frequency okay let's try that out thirteen point what is it three three three three enter oh that's right on and the frequency is so low that it's having a hard time filtering that that's that 220 microfarad capacitor in there that's smoothing things up right so at 13 hertz you can see the jiggle of the needle that's kind of neat it's right at 200. get any more accurate than that so so far so good this is turning out to be a very nice meter actually so i have a feeling that probably somebody got in there over time and screwdrivered it okay so on to the six cylinder high setting let's set up the six cylinder high rpm setting so we need to align that again at 6000 rpm so we're going to go 3 times 6 000 divided by 60 equals 300 cycles or 300 hertz so take a look at the function generator you'll see i have that there already i'll attach the lead up again the signal lead and this is actually pretty close in this one let's see how close that is that's just a little bit low so pop this in there and line it up as close as we can here okay that's very close okay so there we have it right on top so clear three times 3 000 divided by 60 equals 150 which would make sense half of 300 1 5 0 enter look at that that's right on top of that no problems there and we'll try it at 1 000 rpm so 3 times 1 000 divided by 60 equals 50 cycles 50 enter look at that right on top of the 1000 okay so that's successful now on to the six cylinder low let's align the six cylinder low rpm scale so that's up to 1200 rpm here right below the yellow line so three times 1200 divided by 60 equals 60 cycles or 60 hertz we take a look at the function generator so what i'll do now is i will attach the signal lead and whoa it's right off the end there so i'll adjust that up see how accurate we can make this okay there we go very touchy oh i think i'm right on top of it right now there it is right on top okay very touchy you just look at that screwdriver and that's changing so i'll move this out of the way so this will sit somewhat normal okay so if we want to go half scale that's going to be half the frequency 30 hertz just to make things simple let's go 30 hertz and look at that that is accurate right on top of that six so at six cylinders and at 200 rpm that's going to be a very low frequency i guess we're going to see some pretty good needle jitter with this one so for the fun of it let's try that out so let's go three times 200 rpm divided by 60 equals 10 hertz and we're going to see some good needle jitter there 10 hertz there we go look at that right on top of 200 perfect it's almost like it's cleaning the little two so that's perfect so all the scales align up very well on this again i'm actually impressed with this little thing all right so let's see if the the dwell will hold up as well we'll do that next let's align the dwell so in order to get to a solid number like 30 which means 22.5 on the v8 scale so 30 is on the six cylinder scale it's 50 times 0.6 okay so if you recall earlier the math that i showed you so it's 50 times 0.6 equals 30 okay so that should give us 30 degrees so if we take a look at the function generator i have the symmetry at 50 up here and i've moved the frequency around as well so it's back up at 60 cycles i believe yep it's back up at 60 cycles so all i need to do now is attach the lead here and let's see how far off we are and it's a little ways off so i'll just move this out of the way and i will adjust this rate to 30. that's a solid number so that's closer to the camera here right there okay right on top of the 30 or 22.5 all right move this out of the way so let's see how accurate this is so if i want to see 50.4 because i with the percentage with the symmetry i can't go point something so it's either 50 51 52 53. so i can't go 51.5 or anything like that it has to be you know this is the reason that i'm aligning it at the 30 mark so if i want to see if it's aligning up here i can get to 50.4 by giving it about 84 percent symmetry here so i'll go clear go 84 times 0.6 equals 50.4 so it should just be over the 50 line there okay so let's enter 84 into here 84 enter look at that it's just over the 50 line right so almost 50 and a half right there you see that very very accurate even in the dwell setting it's just surprisingly accurate for an analog meter and let's try this so if we go clear though say 34 i believe it was 34 times 0.45 equals 15.3 so we'd be just above the 15 line there okay so i'll give it 34 34 and look at that right above the 15. just a touch above so the dwell is spot on as well so all i have to say it's completely aligned and project successful i honestly have to say i was very skeptical of this sears professional dwell attack but after it was aligned and cleaned up in a few components changed this thing is phenomenally accurate it really is so if you have a chance to pick one of these things up and you are working on a car well you've seen the accuracy yourself so after an alignment it's um yeah just very very accurate i wasn't expecting anything like that from this little device so i imagine most of them are probably like this i can't see very much variation in the circuit it's so incredibly simple so if you work on older cars or you know whatever you need a professional dwell tack for yeah this little device works now this won't work for a 6-volt car system this is designed around a 12-volt system i'm going to design a circuit that will adapt 12-volt you know dwell tack meters to a six volt system so and i will share that as well hope you enjoyed if you're enjoying my videos you can let me know by giving me a big thumbs up then hang around there'll be many more videos like this coming in the near future we'll be taking a look at vacuum tube and solid state electronic devices alike so if you haven't subscribed now would be a good time to do that as well if you'd like to be notified as soon as i post a new video don't forget to tap that bell symbol if you're interested in taking your electronics knowledge to the next level and learning electronics in a very different and effective way and gaining access to many of my personal electronic inventions and designs you're definitely going to want to check out my ongoing electronics course on patreon i'll put the link just below the video's description under the show more tab and i'll also pin the link at the top of the comments section so if you click on the link it'll take you right there alright until next time take care bye for now you

Channel: Mr Carlson's Lab

Views: 47,502

Rating: 4.9606814 out of 5

Keywords: Tachometer repair, Dwell meter repair, Dwell meter alignment, tachometer alignment, tachometer math formula, dwell meter math formula, test equipment, function generator, dwell angle, component replacement, test a tachometer, test a dwell meter, automotive wiring, engine speed, setting breaker points, adjusting breaker points, points and condenser, ignition diagnosis, weak spark, cam angle, weak spark diagnosis

Id: axcbozMpqic

Length: 47min 59sec (2879 seconds)

Published: Wed Oct 06 2021