Hi all,
I'm looking for help with a project I inadvertently screwed up by shorting the outputs of this (short ugly story), causing damage that I am trying to repair. I had it working before the mishap, so I know its problem was directly caused by the short. I am trying to get this board working as I have already built a Wayne's BA line stage preamp around it. I would just buy another kit, but Glassware's site has shown it as out of stock for a while now and I haven't gotten any response to my query about availability.
Here's what I've done so far:
1) Replaced the two 10R power resistors, which overheated during the brief short.
2) Replaced the LD 1084 regulator chips
3) Replaced all the MUR410G fast-recovery (Schottky) diodes in bridge with ones marked SR5100-MIG that are of same type and the same voltage and current specs.
4) Replaced all the 1N4007 diodes with same.
I managed to get the unsoldering done with no noticeable damage, and re-flowed the solder on top to make sure traces on top are connected to the diodes. All diodes in place show similar voltage drops across (~1V for the Schootkys). Reisistors on board show nominal resistance. I have no way of knowing how I can check the regulator chips. Both legs of the transformer show the same resistance
When I hook it to my Variac and crank it to 50VAC, output shows something around 4VDC, but one of the power resistors heats up much more than the other. So, there's clearly still something wrong with the one channel, which seems to confirm that the replacement parts are OK--at least on that side. None of the caps appear swollen or out of the ordinary looking, but I don't have any way of checking them except to verify that none are shorted out.
Obviously looking for help with next steps. Any suggestions? I have been working on this project for a couple of years and would really like to wrap it up, but I'm stuck at this point. If I replace the PS with something else, it absolutely has to fit within the 4.5" x 4.375" (114 mm x 112 mm) footprint. I've inspected the board several times and can't find any visual defect that would cause a problem. I can send a picture of the board if anyone thinks it would be helpful.
Suggestions?
I'm looking for help with a project I inadvertently screwed up by shorting the outputs of this (short ugly story), causing damage that I am trying to repair. I had it working before the mishap, so I know its problem was directly caused by the short. I am trying to get this board working as I have already built a Wayne's BA line stage preamp around it. I would just buy another kit, but Glassware's site has shown it as out of stock for a while now and I haven't gotten any response to my query about availability.
Here's what I've done so far:
1) Replaced the two 10R power resistors, which overheated during the brief short.
2) Replaced the LD 1084 regulator chips
3) Replaced all the MUR410G fast-recovery (Schottky) diodes in bridge with ones marked SR5100-MIG that are of same type and the same voltage and current specs.
4) Replaced all the 1N4007 diodes with same.
I managed to get the unsoldering done with no noticeable damage, and re-flowed the solder on top to make sure traces on top are connected to the diodes. All diodes in place show similar voltage drops across (~1V for the Schootkys). Reisistors on board show nominal resistance. I have no way of knowing how I can check the regulator chips. Both legs of the transformer show the same resistance
When I hook it to my Variac and crank it to 50VAC, output shows something around 4VDC, but one of the power resistors heats up much more than the other. So, there's clearly still something wrong with the one channel, which seems to confirm that the replacement parts are OK--at least on that side. None of the caps appear swollen or out of the ordinary looking, but I don't have any way of checking them except to verify that none are shorted out.
Obviously looking for help with next steps. Any suggestions? I have been working on this project for a couple of years and would really like to wrap it up, but I'm stuck at this point. If I replace the PS with something else, it absolutely has to fit within the 4.5" x 4.375" (114 mm x 112 mm) footprint. I've inspected the board several times and can't find any visual defect that would cause a problem. I can send a picture of the board if anyone thinks it would be helpful.
Suggestions?
I've already checked the resistance of various parts, inputs and outputs, and can find no differences between the two sides of the board. Transformer seems to be fine, with the same resistance on each of the HV loops.
I can check voltages, and certainly have on the outputs and inputs, but there are endless possible combinations of places to put the probes. Are there suggestions as far as where I might get meaningful information?
I can check voltages, and certainly have on the outputs and inputs, but there are endless possible combinations of places to put the probes. Are there suggestions as far as where I might get meaningful information?
disconnect R3 (you need only lift 1 leg).
Measure voltage before R3.
If ok - right voltage & no overheating, then diodes & first smoothing cap are ok.
Regulator is likely faulty.
Refit R3. Remove the regulator.
With the regulator out, link regulator in & out pads on PCB.
Measure output voltage.
You should have the same unregulated voltage & no overheating.
This would prove the regulator to be faulty.
You have heeded the warning about dual secondaries, not centre tapped?
Measure voltage before R3.
If ok - right voltage & no overheating, then diodes & first smoothing cap are ok.
Regulator is likely faulty.
Refit R3. Remove the regulator.
With the regulator out, link regulator in & out pads on PCB.
Measure output voltage.
You should have the same unregulated voltage & no overheating.
This would prove the regulator to be faulty.
You have heeded the warning about dual secondaries, not centre tapped?
Thanks, russc, that's just the guidance I need. I'll see what happens when I try that out when I have the chance.
OK, I went through the steps above; here's what I found:
– Disconnected R3 that was overheating on the "bad" half of the board, and measured 25 VDC between it and output ground. Not sure what that means.
– I went ahead and took out the regulator on the same side, and measured 11.5 Vdc just before it. The "good" side (with R still in place), measured similarly, as 11.7 VDC. Also not sure what that means.
– With transformer still attached to the board (w/o R3 and reg), the "bad" side measured 28.1 VAC at transformer input; "good" side measured 12.6 VAC, both not right.
– Out of circuit, the Antek 0218 transformer measured 19 VAC no-load on both output legs—about right. This was with a measured line voltage of right at 120 VAC.
Can anybody make sense of this and suggest next steps?
– Disconnected R3 that was overheating on the "bad" half of the board, and measured 25 VDC between it and output ground. Not sure what that means.
– I went ahead and took out the regulator on the same side, and measured 11.5 Vdc just before it. The "good" side (with R still in place), measured similarly, as 11.7 VDC. Also not sure what that means.
– With transformer still attached to the board (w/o R3 and reg), the "bad" side measured 28.1 VAC at transformer input; "good" side measured 12.6 VAC, both not right.
– Out of circuit, the Antek 0218 transformer measured 19 VAC no-load on both output legs—about right. This was with a measured line voltage of right at 120 VAC.
Can anybody make sense of this and suggest next steps?
Please post some picture of the board with transformer connected.
Also check all parts are in correct polarity/orientation.
Also check all parts are in correct polarity/orientation.
OK:
your 19V AC from the transformer is 26V peak (V x 1.4)
No load, that is what you will measure with smoothing caps.
As you have been removing and replacing components, check you haven't damaged any pads or traces.
Always clean component leads before soldering - fine wet & dry paper is good.
Even new components can tarnish in storage. Dry joints can be very hard to spot.
For testing purposes, keep the 2 supplies separate don't link J1 & J2.
your 19V AC from the transformer is 26V peak (V x 1.4)
No load, that is what you will measure with smoothing caps.
As you have been removing and replacing components, check you haven't damaged any pads or traces.
Always clean component leads before soldering - fine wet & dry paper is good.
Even new components can tarnish in storage. Dry joints can be very hard to spot.
For testing purposes, keep the 2 supplies separate don't link J1 & J2.
OK, I'll separate the joined outputs that form the common. Would I get different measurements if I measure again after doing that?
chrisrng, here's a photo before I disconnected the transformer. It's hard to get a photo that shows every component. I did check again, and all the diodes are correctly installed. Although I have split loom stuff over the wires, there is one green and one blue wire going to each half, just as it was when it was working fine.
I've soldered a fair amount, and I am aware of the damage that you can do when de-soldering. The only pads that I've damaged here are the top ones for the R3 resistors. These are not connected by traces to anything else on the top, and the pads on the bottom are in good shape. I've taken to pulling clipped leads out after a brief heating, then drilling a just big enough hole through the remaining solder in the hole, which avoids a lot of heat and stress on the pads and is working quite well.
All solder joints look well-flowed to me. IMO, a dry joint is unlikely to be the cause of the present trouble, since the board was working fine before I inadvertently shorted it out.
chrisrng, here's a photo before I disconnected the transformer. It's hard to get a photo that shows every component. I did check again, and all the diodes are correctly installed. Although I have split loom stuff over the wires, there is one green and one blue wire going to each half, just as it was when it was working fine.
I've soldered a fair amount, and I am aware of the damage that you can do when de-soldering. The only pads that I've damaged here are the top ones for the R3 resistors. These are not connected by traces to anything else on the top, and the pads on the bottom are in good shape. I've taken to pulling clipped leads out after a brief heating, then drilling a just big enough hole through the remaining solder in the hole, which avoids a lot of heat and stress on the pads and is working quite well.
All solder joints look well-flowed to me. IMO, a dry joint is unlikely to be the cause of the present trouble, since the board was working fine before I inadvertently shorted it out.
Thanks for the photo.
I second the idea of disconnect J1/J2, that will isolated both channel for better diagnosis.
Where exactly you get the measurement? Across C6 or across C7?
BTW, what are the differences of "good" and "bad" channel other than temperature of the R3? Did you check any temperature different between both channel of C6, C7 and C8? A leaky cap will draw excessive current and heated up.
Please take measurement again after you disconnected J1 and J2 and post the result and where the measurement taken on the schematic.
I second the idea of disconnect J1/J2, that will isolated both channel for better diagnosis.
Seems like the components before R3 are ok.
If that's R3, the problem is downstream.
Did you link regulator in & out pads on PCB to measure?
Where exactly you get the measurement? Across C6 or across C7?
Sorry, can't figure out why. Any possibility the transformer windings crossed or some short circuit between channels?
BTW, what are the differences of "good" and "bad" channel other than temperature of the R3? Did you check any temperature different between both channel of C6, C7 and C8? A leaky cap will draw excessive current and heated up.
Please take measurement again after you disconnected J1 and J2 and post the result and where the measurement taken on the schematic.
Since you had replaced all diodes and regulator, and all solder joints are good, perhaps replace C6, C7 and C8 might solve the problem.
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Nothing touching anything.
I did pull out the links connecting the two halves and will repeat measurements tomorrow when I have the time.
I added small "bobbin"-type terminals for the power inputs and outputs so I don't have to keep beating up the circuit board. I did re-flow a few parts connections to the top of the boards where there is a top trace, although I don't believe I've damaged any of the through-hole plating except for the R3, for which the only connection is on the bottom anyway.
New board photo attached. Thanks for bearing with me while I try to work through this. I'll likely order more C6, 7 & 8 in case that's the next step.
I did pull out the links connecting the two halves and will repeat measurements tomorrow when I have the time.
I added small "bobbin"-type terminals for the power inputs and outputs so I don't have to keep beating up the circuit board. I did re-flow a few parts connections to the top of the boards where there is a top trace, although I don't believe I've damaged any of the through-hole plating except for the R3, for which the only connection is on the bottom anyway.
New board photo attached. Thanks for bearing with me while I try to work through this. I'll likely order more C6, 7 & 8 in case that's the next step.
IME with building Glassware kits, I make very sure that the soldered part shows solder on both sides of the board. Maybe only once but I found a disconnection after I pulled a part out, put a new one in and the solder joint (through hole on board) was bad. You couldn't even tell that it was broken. After that discovery, I flow solder all the way through the joint. I saw several of yours that weren't completely flowed in this way. I am just shooting in the dark here, but sometimes the devil is in the details. FWIW, I am not much of a fan of this type of board due to the problem mentioned above.
Good point.
The large caps after the rectifier look to have top traces & you cannot solder from the top.
The large caps after the rectifier look to have top traces & you cannot solder from the top.
I agree that the double-sided board is a little hard to work with, especially after replacing parts. It's also very compact and the small parts are hard to reach without damaging them from contact with the soldering iron.With the exception of there R3s, I have been very careful to avoid overheating and have been drilling holes no bigger than necessary in the solder bridges that remain after pulling part leads out to avoid damaging the pads and the through-hole plating.
A couple of things, though:
– Board was originally working perfectly before I shorted it out, so I can assume that the original connections were OK and still should be.
– Only exceptions are the semiconductors, which have all been replaced. I have not re-flowed solder joints on other components.
I did re-flow the top solder on the prong terminals I installed in holes where the links were. I can clip to one for measurements, then when working, link the two halves together without disturbing the board/traces.
I'm a little unclear about where to take measurements, though. I will leave R3 out of circuit for now and measure voltage across C5, correct? Then, will re-install R3 and measure. Across C6, right? Won't get anything from across C7 since the regulator is still out of circuit.
Since all components are in place on the half that was not overheating, I'll check the output voltage and report back.
A couple of things, though:
– Board was originally working perfectly before I shorted it out, so I can assume that the original connections were OK and still should be.
– Only exceptions are the semiconductors, which have all been replaced. I have not re-flowed solder joints on other components.
I did re-flow the top solder on the prong terminals I installed in holes where the links were. I can clip to one for measurements, then when working, link the two halves together without disturbing the board/traces.
I'm a little unclear about where to take measurements, though. I will leave R3 out of circuit for now and measure voltage across C5, correct? Then, will re-install R3 and measure. Across C6, right? Won't get anything from across C7 since the regulator is still out of circuit.
Since all components are in place on the half that was not overheating, I'll check the output voltage and report back.
Too many times, I have hoped to solve a circuit problem just by staring at it, yet the few times that I was successful, it was worth it. Do you have a photo of the underside? I know, it may serve little purpose, but I am interested in seeing it.
Yes, the reading should be 25V or higher ( 19Vx1.414 - 2 diode voltage drop ).
Yes, the reading should be about 25V and R3 shouldn't overheat, otherwise replace C6. If you got about 25V and R3 not over heated then proceed to next step.
You need to solder a jumper wire across D6, then measure the voltage across C8 and it should be equal to the voltage across C6 (or should be about 25V).
If at this point R3 over heated and voltage reading drop below 25V, pull C8 out of the circuit and measure voltage across C6 again and see if the reading is about 25V.
The voltage reading across C7 should be equal to (VinXR2)/(R1+R2)
Note: Vin is the voltage across C6.
C7 calculator
BTW, what are the value of R1 and R2?
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That's a good photo. IME, it has taken a while to find a solder that flows the way that I want it to. I ended up with Wonder Solder, and still use it. Previous solder jobs of mine look like what I am seeing in some spots here. Specifically, the left AC joint, L/R D1, L/R D2 AND D4. Probably best if I saw it in person with a bright light and magnifier, but those are some of the joints that might need reflowed.
I had an amp once that just shut down for no reason. Turned out that the crimp for the incoming AC wasn't making connection, even though the two parts were clearly touching! Or though it seemed.
You will find it, takes patience though.
I had an amp once that just shut down for no reason. Turned out that the crimp for the incoming AC wasn't making connection, even though the two parts were clearly touching! Or though it seemed.
You will find it, takes patience though.