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frnkfrkl
New member
Yeah, totally off topic but that's where these kinds of threads tend to go. Next thing you know I'll be telling you about my dogs....My name is also Dave, incidentally. So, hi Dave from Dave.
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frnkfrkl
New member
Anyway, the 34B is back together and works. I traced out the wires to the power supply PCB, just in case some goes wrong on THAT end of those wires, I know where to look. I don't ever want to open this thing up again but ya never know. It's like an old car you want to "restore". You spend more time under the hood than in the driver's seat.
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ecc83
Well-known member
Hah! Ha! My grandson has just bought his good lady a sausage dog pup for her birthday...900 quid!!
Dave.
sweetbeats
Reel deep thoughts...
6V where? Between pins 9&11 or pins 10&11, or both? Is it still 6V? The audio chain will function at 6V, but that doesn’t mean it’s functioning right.
What kind of meter do you have?
If it’s still 6V I would also measure for AC volts between pins 9&11 and 10&11. It should be 0.
Also, I would never ever apply abrasives like 600 grit sandpaper to connection pins. The connectors used in machines like the 30 series are standard-grade…thin tin plating. If you apply abrasives it may temporarily help, but when you compromise the plating you accelerate the return of oxidation. I would only, if absolutely necessary (like if there is a lot of oxidation on them), use fine steel wool or fine and broken-in scotch brite pad, and typically not do any of that and simply apply DeoxIT D5 and exercise the connections. If needed I would use DeoxIT Gold or D100. In nearly all circumstances the D5 and exercising does the trick, and does the best job of maintaining the plating integrity. The threshold for what is considered “taking a hammer” to the problem is low on a machine like the 30 series, relative to a more professional machine with higher quality glass fiber PCBs, gold-plated contacts and connections, etc. Approach and handle with care.
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frnkfrkl
New member
Yeah, 6v. It's a digital muti-meter, Tougs M103, set to vDC. That seemed odd to me seeing the rail at +/- 15v. Didn't think to check for AC. Not a single capacitor has been changed in this machine, ever. I was pretty delicate with the sandpaper, just here and there where I saw discolouration. Iso and then,well, not DeOxit, KF something. I do notice the meters dimming when going into play which made me raise an eyebrow. The machine now functions, plays back at the correct speed and exhibits no other real problems. I did, with the help of the schematic and board configuration, trace the wires back to where they go on the power supply PCB. Seems to be quite a few electrolytic caps on that board. Would that be a potential cause of only seeing 6v? I also spotted a bridge rectifier. Tired diodes? I'm not a tech but here in rural Corsica, I'm as close to one as anybody's going to get. Oh, it's a 110v machine. I'm using a Bronson++ 1000 watt power transformer to power the machine. I know it doesn't change the AC (50/60 Hz) frequency, but the machine DOES run at the correct speed. That's what I known that's where I'm at.
sweetbeats
Reel deep thoughts...
“Yeah, 6V.”
6V where? I keep repeating the question…between pins 9&11 or 10&11 of J171? Or both?
Caps and diodes don’t regulate the voltage here. The regulators regulate the voltage. But a failed bridge or main filter cap or regulator can cause faults like this. Also, thanks for sharing the very important detail you are operating a machine designed for 60Hz on 50Hz. Yes if it runs it’s going f to run at the correct speed because the capstan is a DC servo type with its own clocking. An AC capstan motor would lock to the line frequency and run slow at 50Hz if it was expecting 60Hz. But your bigger problem can be, depending on what the voltage is coming out of your conversion transformer, at the lower line frequency, that rectifies lower than 60Hz at the given input voltage, and may be too low for the required level at the input of the regulators. So help me understand where you are measuring 6V. Please be specific. 20 questions can be a fun game but not here. If your +/-15V rails are outputting +/-6V, you have a problem. And the next step is measuring for AC across pins 9&11 and 10&11 of J171, and if you have AC there you need to find why.
6V where? I keep repeating the question…between pins 9&11 or 10&11 of J171? Or both?
Caps and diodes don’t regulate the voltage here. The regulators regulate the voltage. But a failed bridge or main filter cap or regulator can cause faults like this. Also, thanks for sharing the very important detail you are operating a machine designed for 60Hz on 50Hz. Yes if it runs it’s going f to run at the correct speed because the capstan is a DC servo type with its own clocking. An AC capstan motor would lock to the line frequency and run slow at 50Hz if it was expecting 60Hz. But your bigger problem can be, depending on what the voltage is coming out of your conversion transformer, at the lower line frequency, that rectifies lower than 60Hz at the given input voltage, and may be too low for the required level at the input of the regulators. So help me understand where you are measuring 6V. Please be specific. 20 questions can be a fun game but not here. If your +/-15V rails are outputting +/-6V, you have a problem. And the next step is measuring for AC across pins 9&11 and 10&11 of J171, and if you have AC there you need to find why.
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frnkfrkl
New member
Sorry, both. J171, I confirm. Equal on both sides, well, 6.3 and 6.0v. 9-11 = 6.0v, 10-11 = 6.3v. DC. Or the other way around. Ok, I'll take the back off again tomorrow and check for AC. Those main filter caps would be on the power supply board, right? Along with the bridge rectifier? I know where that is and, boy, it's gonna be a bitch to get to it. Forgive my ignorance but what does a regulator look like? Is it one of the transistor type things that usually bolt to something or require a heat sink? I repeat, I am not a tech. And yeah, my 80-8 ran slow but was fitted with a dual pulley capstan. Moved the belt over and that was fixed.
sweetbeats
Reel deep thoughts...
Okay. Yeah something is not right for sure if both sides are running around 6V. That’s with J171 unplugged from the motherboard?
Yes the main filter caps are on the Power Supply PCB, C806 & C807, and C812 & C813…pairs of 470uF caps running in parallel. Honestly that seems undervalued to me. I’d probably replace the pairs with a single 2,200uF cap each side. That’s probably a little overkill, but it’s not too much, and it’s hard to find caps in standard values between 1,000uF and 2,200uF.
The rectification on the +/-15V supply is actually discrete…4 diodes mounted to the PCB.
The regulation is also discrete. Often times they use standard 78xx and 79xx regulators that come in a TO-220 package, so they look like larger 3-pin transistors. But the regulation for the +/-15V supply on the 34B is discrete meaning they used an array of transistors for regulation, Q806, 807 & 808 for one side, and Q809, 810 & 811 for the other…Q808 & Q811 are output power transistors that are mounted to the PCB and fastened to a heatsink. The rest are smaller packaged parts like TO-92 mounted to the PCB.
What you really should be using at this point is an oscilloscope so you can actually see what the waveform of the power is as you move up the supply circuit. You can still try to use the DMM but it’s less effective and can be ineffective at identifying the fault depending on what it is. I forget…has this always been a problem, or were things fine and then recently they suddenly weren’t?
Because the supply uses discrete regulation I have no way of knowing what the minimum voltage threshold is at the input of the regulator circuit. It would be interesting to know what the DC voltage is at the input of one side though, like measuring from a node between the base of Q806 and R814 to ground. But that’s for later maybe. But if it’s always been a problem it may just be the input power and line frequency are to little power. Step 1 is measure for AC volts at the power supply outputs.
Yes your 80-8 would run slow unless it had the optional DC servo capstan. Most had the AC capstan.
Yes the main filter caps are on the Power Supply PCB, C806 & C807, and C812 & C813…pairs of 470uF caps running in parallel. Honestly that seems undervalued to me. I’d probably replace the pairs with a single 2,200uF cap each side. That’s probably a little overkill, but it’s not too much, and it’s hard to find caps in standard values between 1,000uF and 2,200uF.
The rectification on the +/-15V supply is actually discrete…4 diodes mounted to the PCB.
The regulation is also discrete. Often times they use standard 78xx and 79xx regulators that come in a TO-220 package, so they look like larger 3-pin transistors. But the regulation for the +/-15V supply on the 34B is discrete meaning they used an array of transistors for regulation, Q806, 807 & 808 for one side, and Q809, 810 & 811 for the other…Q808 & Q811 are output power transistors that are mounted to the PCB and fastened to a heatsink. The rest are smaller packaged parts like TO-92 mounted to the PCB.
What you really should be using at this point is an oscilloscope so you can actually see what the waveform of the power is as you move up the supply circuit. You can still try to use the DMM but it’s less effective and can be ineffective at identifying the fault depending on what it is. I forget…has this always been a problem, or were things fine and then recently they suddenly weren’t?
Because the supply uses discrete regulation I have no way of knowing what the minimum voltage threshold is at the input of the regulator circuit. It would be interesting to know what the DC voltage is at the input of one side though, like measuring from a node between the base of Q806 and R814 to ground. But that’s for later maybe. But if it’s always been a problem it may just be the input power and line frequency are to little power. Step 1 is measure for AC volts at the power supply outputs.
Yes your 80-8 would run slow unless it had the optional DC servo capstan. Most had the AC capstan.
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frnkfrkl
New member
Holy shit, that’s a lot for a non- tech like me to digest but I get the general picture. I’m going to have to read this 12 more times and google a bunch of things. I don’t have an oscilloscope (and to tell the truth, don’t know how to use one). Your information is invaluable however and I’m pretty good with my hands and learn quickly. Thanks again.
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frnkfrkl
New member
Oh and yes J 171 disconnected from the motherboard.
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frnkfrkl
New member
One further question: all of the components you spoke of are on the power supply PCB, right? That would make sense to me but just wanted to confirm that. 40 year old caps are not ideal, huh?
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frnkfrkl
New member
Sorry, one last thing. The machine had been in storage since about 1999. I had loaned it to a friend and have no idea where it was stored. The belt and pinch roller had turned to tar so I replaced both and reconnected those fiddly little springs for the return arm dampening. Transport is fine. Then intermittent playback - no playback. Reflowed the motherboard and all was well until it wasn’t, bringing the current problem to light. That’s where I am now. It’s functional but, apparently, far from ideal. I’ll get there with your help and, really, thanks again.
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ecc83
Well-known member
Discrete voltage regulator circuits vary a bit but most of them use a series power device and there must be a voltage reference somewhere. That will be a Zener diode or maybe two Zeners in series. If that voltage is present and correct (it will be marked on the diodes and should be on the schematic) the next check is the input voltage to the series transistor which should be a few volts higher than the wanted 15 volts.
Dave.
Dave.
sweetbeats
Reel deep thoughts...
Yes they are all mounted to the Power Supply PCB.
And it depends on the caps. There are computer grade screw-terminal caps in my Ampex MM-1000 from 1967 that are still in-spec. But most of the caps used in something like a Tascam 38 can typically benefit from replacing at this point. Teac used good quality caps of the day. They still work fine a minority of the time, just not as well as they should. Caps do different kinds of things depending on their application in a given circuit, so whether or not an out-of-spec cap is a noticeable problem depends on its function and the type of circuit, and in a lot of cases it doesn’t impact functionality, but rather performance quality. Wholesale recapping is not typically mandatory, but usually there’s some benefit. I recommend focusing on power supplies first if you’re going to do anything. And of course there are times where replacement is necessary, and those situations are going to continue to increase as these devices age.
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sweetbeats
Reel deep thoughts...
Can you verify your meter make and model is Tougs M103? I can’t find anything like that…was trying to find the manual or at least specifications. Thanks.
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frnkfrkl
New member
Hi. OK, I'm a dumbshit. Hey, idiot! How about testing the CORRECT END of the Molex connector? Yeah, pin 11 is on the LEFT side of the connector, viewed from the back of the machine and, of course, I was testing down at the other end because I read words and numbers left to right. I was getting readings that were jumping all over the place and made no sense. Then I went to the OTHER end of the connector and, yeah, +/- 15v DC on the CORRECT pins, no AC when I do it THAT way. Man, I feel stupid. Relieved, but stupid. And very sorry for wasting YOUR time. Really. You spent a lot of time explaining things to me and I dropped the ball but just kept running anyway. My fault. I will henceforth live in a world of eternal shame with mocking fingers pointing at my sorry soul.
My real job is saxophone repair. It's all mechanical, no need to worry about invisible electrons wreaking havoc with a saxophone. If you ever have a question about saxophones, I'm here to help.
sweetbeats
Reel deep thoughts...
Ahhh okay. So, no shame…sometimes ‘1’ is printed on the PCB, or sometimes you can find a ‘1’ on the connector housing noting pin 1.
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frnkfrkl
New member
Thanks, I feel better. I'm going to check out your YouTube channel. I may learn a few things and not have to go begging for help in desperation every time something electronic breaks down here.
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ecc83
Well-known member
No, don't beat yourself up about getting lost on a PCB! Happens to the best of us. Once Upon a Time, GOOD quality kit had the component references and pin Nos' printed on both sides of the board. That is an extra cost we no longer see. For sure it is impractical for those dinky SMT boards but my old eyes can't cope with that stuff anyway!
Dave.
Dave.
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frnkfrkl
New member
The saga continues. All was cool. I put it back together. It didn't work, no playback, meters, like before. I took the back off and started testing voltages. On pin 8, where I'm supposed to be seeing +24vdc, I'm seeing -15vdc. Still +/- 15 on 9 & 10, so, ok there. It looks like on that connector there are 2 or 3 references to ground. 11, 7, and maybe 2. So tested voltages from each of those reference points and was getting a lot of negative dc values, from -40vdc on certain pins to -15vdc on others. So i took the top off and decided I would see what I could see since I have the numbers of the wires from the connector and some are visible on the power PCB without taking the whole machine apart.. While I was in the vicinity, i decided to check the fuses again for the 20th time and, lo and behold, F501, 2A, 250v was blown. I, of course, do not have the appropriate fuse to replace it with. I could put a saxophone pad in the general vicinity but that's not going to help. I am supposing (and actually asking since my brain is fried from trying to read schematics) is that fuse involved in the problem I am having? I notice also that there is not much of a gap between the metal cover that goes on top and the fuse holder itself. There's a strip of foam installed, I imagine, for the purpose of keeping those pieces from touching but it's about dry-rotted and dead. Did I install the cover with the machine still running? Possible. Or is there another hidden cause lurking like a stalker in the shadows just waiting for the right moment to pounce? So, do I change the fuse and hope for the best or try to track down the cause of the fuse blowing. I think, frankly, I am the cause. And, hey guess what? There is a "1" on the connector!