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Post by audiospecific on Dec 15, 2023 6:10:27 GMT -6
You do not need to solder the top side of the PCB. They are plated through holes. The two I worked on. The plate thru in the corner where the the rotary switch and the regulator was isn't bonded well on the topside. Granted, the ones I worked on I had to fix lands because they used an unregulated soldering iron.
But since the OP didn't form the leads on U1 after soldering, he could have shorted thru, even though I would think the chassis power supply should have shut down in that condition.
This board is a lot better than the Seventh Circle Audio N72. At least the foil thickness is correct on the AML.
There is a lot of variables to building these things up correct. But if you want my professional opinion about your guide, I think you should revise it a little so that they build the power supply section first, then test it, then continue building the rest of the card. Even though an advanced tech would do that, especially if it was the first time building that card.
One thing I question is the heat sink hardware. Because I don't see the typical nylon spacer used on the transistors, and I think I installed them on the ones I repaired :
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Post by audiospecific on Dec 15, 2023 6:33:08 GMT -6
As for the solder flowing through the holes, I'm going to have to improve my technique, sounds like. In the mean time, I'll go through and attack those empty pads from the topside. I can see that R50 now that you mention it. Cooked. What do you think the next move is?
With the card out of the chassis, measure with ohms, collector tab to collector tab on the output transistors heat sink. Avoid touching the screw hardware when doing this. Tell us the resistance.
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Post by audiospecific on Dec 15, 2023 6:45:14 GMT -6
After that, check R58 or measure from pin 13 to pin 1 for 10 ohms and check ground plane connection from analog gnd to psu gnd by measuring pin 5 to 13 for 0 ohm
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Post by lee on Dec 16, 2023 2:04:04 GMT -6
As for the solder flowing through the holes, I'm going to have to improve my technique, sounds like. In the mean time, I'll go through and attack those empty pads from the topside. I can see that R50 now that you mention it. Cooked. What do you think the next move is?
With the card out of the chassis, measure with ohms, collector tab to collector tab on the output transistors heat sink. Avoid touching the screw hardware when doing this. Tell us the resistance.
The collector tab has three conductors each. Please specify which to measure from. |
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Post by lee on Dec 16, 2023 2:09:04 GMT -6
After that, check R58 or measure from pin 13 to pin 1 for 10 ohms and check ground plane connection from analog gnd to psu gnd by measuring pin 5 to 13 for 0 ohm R58 measures 10.1Ω with both legs seated. Is this one of those ones I should lift one leg out? And yes, I get 10Ω pin 13 to pin 1, 0Ω pin 5 to 13 on both units. |
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Post by audiospecific on Dec 16, 2023 9:25:11 GMT -6
After that, check R58 or measure from pin 13 to pin 1 for 10 ohms and check ground plane connection from analog gnd to psu gnd by measuring pin 5 to 13 for 0 ohm R58 measures 10.1Ω with both legs seated. Is this one of those ones I should lift one leg out? And yes, I get 10Ω pin 13 to pin 1, 0Ω pin 5 to 13 on both units.
good. nothing really went bad, or you turned it off before it really had a failure.
which means we have a 70% chance its ok, and your excessive lead lengths were the short.
Next is checking R33 (47 ohms), and R65 (150 ohms if used with relay)
If they are ok, Then lift one lead of R33, R50, R65 (if used) apply power with the chassis+extension card.
In Dc, measure the input and output voltage of U1. when looking straight at it, the left pin should read ~16V and the output should be 8V. You will have to use Analog ground at the input transformer which would be a screw or the ground plane board opposite from the pin side of the input transformer.
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Post by ragan on Dec 16, 2023 11:48:56 GMT -6
What is the resistance measurement across C20 compared to the good unit you have? Ragan, the resistance number on both units start at around 250-400 kΩ and then start dropping. They both settle around 3.200 kΩ. So far, I haven't found a cap with a wildly different measurement, resistance or Farads. What's the deal with the resistance? Will it always go toward infinity (or drop), even if slowly? Multimeters measure resistance by supplying a little bit of current and measuring the resultant voltage drop, then calculating the resistance from Ohm's law (R = V/I). Capacitor resistance measurements don't sit still when you try to measure them this way. Capacitors hold charge, and so as the multimeter leads are trying to supply current, the capacitor is charging, telling the multimeter that voltage is increasing, making the multimeter spit out the calculation that resistance is increasing. When a cap is paralleled with other things in a circuit, there are other paths for the current to take, and current can discharge through those other paths. |
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Post by audiospecific on Dec 16, 2023 12:46:53 GMT -6
With the card out of the chassis, measure with ohms, collector tab to collector tab on the output transistors heat sink. Avoid touching the screw hardware when doing this. Tell us the resistance.
The collector tab has three conductors each. Please specify which to measure from. It would be the center pin to center pin. Even though it does look like an insulated tab instead of a metal tab type in the picture above. I think one of them I repaired they used different transistors than the ones in your picture. |
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Post by lee on Dec 16, 2023 17:20:42 GMT -6
The collector tab has three conductors each. Please specify which to measure from. It would be the center pin to center pin. Even though it does look like an insulated tab instead of a metal tab type in the picture above. I think one of them I repaired they used different transistors than the ones in your picture. Working unit: 5.423KΩ INOP unit: 5.568KΩ These are readings after they started quite high (in the hundreds of KΩ), rapidly descended, then ascended from about 1.X KΩ to the point at which they chilled out. |
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Post by lee on Dec 16, 2023 17:32:46 GMT -6
R58 measures 10.1Ω with both legs seated. Is this one of those ones I should lift one leg out? And yes, I get 10Ω pin 13 to pin 1, 0Ω pin 5 to 13 on both units.
good. nothing really went bad, or you turned it off before it really had a failure.
which means we have a 70% chance its ok, and your excessive lead lengths were the short.
Next is checking R33 (47 ohms), and R65 (150 ohms if used with relay)
If they are ok, Then lift one lead of R33, R50, R65 (if used) apply power with the chassis+extension card.
In Dc, measure the input and output voltage of U1. when looking straight at it, the left pin should read ~16V and the output should be 8V. You will have to use Analog ground at the input transformer which would be a screw or the ground plane board opposite from the pin side of the input transformer.
Thanks again for your patience, guys. This has all been really helpful. R33 is 47.4Ω R65 is 148.7Ω I'm gonna go desolder those one-legs and apply power. R50 is the burnt one, although it still measures 10Ω give or take. I have not yet ordered a replacement. One question: Do I need to have the output transformer connected in order to do this test? |
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Post by audiospecific on Dec 16, 2023 18:17:04 GMT -6
good. nothing really went bad, or you turned it off before it really had a failure.
which means we have a 70% chance its ok, and your excessive lead lengths were the short.
Next is checking R33 (47 ohms), and R65 (150 ohms if used with relay)
If they are ok, Then lift one lead of R33, R50, R65 (if used) apply power with the chassis+extension card.
In Dc, measure the input and output voltage of U1. when looking straight at it, the left pin should read ~16V and the output should be 8V. You will have to use Analog ground at the input transformer which would be a screw or the ground plane board opposite from the pin side of the input transformer.
Thanks again for your patience, guys. This has all been really helpful. R33 is 47.4Ω R65 is 148.7Ω I'm gonna go desolder those one-legs and apply power. R50 is the burnt one, although it still measures 10Ω give or take. I have not yet ordered a replacement. One question: Do I need to have the output transformer connected in order to do this test?
No, this is a para feed output design like an API312 card but runs at 8V as well as +/- 16
The goal of lifting R33, R50, R65 resistors is to test the 3 terminal voltage regulator (u1) to see if it outputs 8V. The rest of it would not be in that circuit.
These 78xx series three terminal regulators are cheap and widely used and its not ordinary to get a bad one out of a batch. I order 2-3 of them at a time in case I get one bad. Even though the positive ones are not bad about this compared to the negative voltage ones (79xx series). That is why someone like me would just build the power section, test it and go forward.
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Post by lee on Dec 16, 2023 18:56:50 GMT -6
So I'm pretty sure I know how I cooked R50, and that is from overbiasing. Maybe the bias test point measurements were wildly off because of the U1 problem? IDK), making me think that if I just keep tweaking it'll get there. The reason I know this? I built a test jig and was trying it out on the working 1081, going through the biasing/gain procedures again. I had my probes reversed and was getting negative numbers (rookie error) and biased a bit too much (it escalated quickly) and R50 started smoking. Now I have to replace TWO of the bastards. But setting the bias trimmer back to fully-clockwise and starting over, I was able to get it to the desired 90mV, only the difference now is that the measurement creeps up slowly from 90 instead of staying put. I would say if I keep my probes on, it goes up a tenth of a mV every 5-10 seconds, which I find concerning.
Calamity Jane over here... fucking hell
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Post by lee on Dec 16, 2023 19:18:53 GMT -6
Thanks again for your patience, guys. This has all been really helpful. R33 is 47.4Ω R65 is 148.7Ω I'm gonna go desolder those one-legs and apply power. R50 is the burnt one, although it still measures 10Ω give or take. I have not yet ordered a replacement. One question: Do I need to have the output transformer connected in order to do this test?
No, this is a para feed output design like an API312 card but runs at 8V as well as +/- 16
The goal of lifting R33, R50, R65 resistors is to test the 3 terminal voltage regulator (u1) to see if it outputs 8V. The rest of it would not be in that circuit.
These 78xx series three terminal regulators are cheap and widely used and its not ordinary to get a bad one out of a batch. I order 2-3 of them at a time in case I get one bad. Even though the positive ones are not bad about this compared to the negative voltage ones (79xx series). That is why someone like me would just build the power section, test it and go forward.
Good news on the U1 front: Left reads 16V, output reads 8V DC. |
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Post by audiospecific on Dec 16, 2023 19:20:22 GMT -6
So I'm pretty sure I know how I cooked R50, and that is from overbiasing. Maybe the bias test point measurements were wildly off because of the U1 problem? IDK), making me think that if I just keep tweaking it'll get there. The reason I know this? I built a test jig and was trying it out on the working 1081, going through the biasing/gain procedures again. I had my probes reversed and was getting negative numbers (rookie error) and biased a bit too much (it escalated quickly) and R50 started smoking. Now I have to replace TWO of the bastards. But setting the bias trimmer back to fully-clockwise and starting over, I was able to get it to the desired 90mV, only the difference now is that the measurement creeps up slowly from 90 instead of staying put. I would say if I keep my probes on, it goes up a tenth of a mV every 5-10 seconds, which I find concerning.
The Qbias transistor in it is not expensive. (~$0.25 ea) unless you get it from a crazy source out there catering to audiophiles chasing rainbows.
I buy like a 100 of them at time at around 0.10 ea but I use them for other electronic experiments besides repairs.
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Post by lee on Dec 16, 2023 20:03:27 GMT -6
I was able to get it to the desired 90mV, only the difference now is that the measurement creeps up slowly from 90 instead of staying put. I would say if I keep my probes on, it goes up a tenth of a mV every 5-10 seconds, which I find concerning. I'd love to get a comment on this. Seems to me like this would eventually find mVoltage creeping up into the "burning R50" zone if left on long enough. |
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Post by audiospecific on Dec 16, 2023 21:05:39 GMT -6
I was able to get it to the desired 90mV, only the difference now is that the measurement creeps up slowly from 90 instead of staying put. I would say if I keep my probes on, it goes up a tenth of a mV every 5-10 seconds, which I find concerning. I'd love to get a comment on this. Seems to me like this would eventually find mVoltage creeping up into the "burning R50" zone if left on long enough.
You probably stressed the Qbias transistor (Q10) and now its slightly leaky. Got get some, and have extras because they are in a lot of stuff. I get mine at Mouser. mou.sr/47YDZs1 |
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Post by lee on Dec 16, 2023 21:41:43 GMT -6
I'd love to get a comment on this. Seems to me like this would eventually find mVoltage creeping up into the "burning R50" zone if left on long enough.
You probably stressed the Qbias transistor (Q10) and now its slightly leaky. Got get some, and have extras because they are in a lot of stuff. I get mine at Mouser. mou.sr/47YDZs1Perfect thanks. Putting together a shopping list now. Great way to learn, but not great for productivity LOL. |
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Post by audiospecific on Dec 16, 2023 22:10:36 GMT -6
You probably stressed the Qbias transistor (Q10) and now its slightly leaky. Got get some, and have extras because they are in a lot of stuff. I get mine at Mouser. mou.sr/47YDZs1Perfect thanks. Putting together a shopping list now. Great way to learn, but not great for productivity LOL.
The transistor parts of them are cheap. If you are building up some its always good to have extras. Because you can get a bad part in a kit regardless of who sells them.
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Post by lee on Dec 23, 2023 19:28:29 GMT -6
Just to revisit this topic, and to solicit hopefully one more bit of helpful advice: I replaced R50 in both my units, as well as Q10. The good news is that the initially INOP unit now measures well and I was able to bias it to 90mV. I was also able to do the same with the operative unit which I may have screwed up slightly by giving it an overbias when testing my test jig. The BAD news is that when I bias up to the required 90mV, continue to creep up a tenth of a milliVolt every 4 seconds on BOTH units equally. audiospecific , you had suggested I might have stressed Q10, but these got replaced on both units. In the time it has taken me to type this out, Unit #2 is now up to 94.7mV and climbing. I do have a few more of these same transistors in case you think that might be it. It sounds like something else needs to get swapped. Is there any chance the trimmers could be the problem? I did buy 3x replacements just in case something had gone wrong with them, it was just an uneducated hunch, and they were cheap enough. Thanks for your help, everyone. |
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Post by audiospecific on Dec 23, 2023 21:05:05 GMT -6
Just to revisit this topic, and to solicit hopefully one more bit of helpful advice: I replaced R50 in both my units, as well as Q10. The good news is that the initially INOP unit now measures well and I was able to bias it to 90mV. I was also able to do the same with the operative unit which I may have screwed up slightly by giving it an overbias when testing my test jig. The BAD news is that when I bias up to the required 90mV, continue to creep up a tenth of a milliVolt every 4 seconds on BOTH units equally. audiospecific , you had suggested I might have stressed Q10, but these got replaced on both units. In the time it has taken me to type this out, Unit #2 is now up to 94.7mV and climbing. I do have a few more of these same transistors in case you think that might be it. It sounds like something else needs to get swapped. Is there any chance the trimmers could be the problem? I did buy 3x replacements just in case something had gone wrong with them, it was just an uneducated hunch, and they were cheap enough. Thanks for your help, everyone.
Lift D6 and C27 since that isn't really correct to begin and c27 shouldn't exist.
EDIT: See if it stills drift. If so, we will have to look at the transistor matching.
If you don't have one, get a DMM with an HFE test because there are transistors that should be in matching gain. plus Emitter base forward bias. w'ell have to go through that
D6 should be a germanium even though a sckottkey should work. Its only there to shut off the transistor when the output is over driven, but why change it?
Btw, I don't understand why all these cloners clone this and not use the same transistors (or even in the group like fashion) , but it should be fine regardless.
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Post by lee on Dec 23, 2023 22:57:30 GMT -6
Just to revisit this topic, and to solicit hopefully one more bit of helpful advice: I replaced R50 in both my units, as well as Q10. The good news is that the initially INOP unit now measures well and I was able to bias it to 90mV. I was also able to do the same with the operative unit which I may have screwed up slightly by giving it an overbias when testing my test jig. The BAD news is that when I bias up to the required 90mV, continue to creep up a tenth of a milliVolt every 4 seconds on BOTH units equally. audiospecific , you had suggested I might have stressed Q10, but these got replaced on both units. In the time it has taken me to type this out, Unit #2 is now up to 94.7mV and climbing. I do have a few more of these same transistors in case you think that might be it. It sounds like something else needs to get swapped. Is there any chance the trimmers could be the problem? I did buy 3x replacements just in case something had gone wrong with them, it was just an uneducated hunch, and they were cheap enough. Thanks for your help, everyone.
Lift D6 and C27 since that isn't really correct to begin and c27 shouldn't exist.
EDIT: See if it stills drift. If so, we will have to look at the transistor matching.
If you don't have one, get a DMM with an HFE test because there are transistors that should be in matching gain. plus Emitter base forward bias. w'ell have to go through that
D6 should be a germanium even though a sckottkey should work. Its only there to shut off the transistor when the output is over driven, but why change it?
Btw, I don't understand why all these cloners clone this and not use the same transistors (or even in the group like fashion) , but it should be fine regardless.
A friend who lives locally might have an HFE on his which I can borrow. One obit of good news is that Unit #1 seems to settle around 91.5mV after being left on for 30 minutes. So I readjusted and will check it in another 30m. EDIT: just checked it, it's now 89.5... I have no idea if a touch of variation is acceptable or what. |
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Post by audiospecific on Dec 24, 2023 1:16:36 GMT -6
Lift D6 and C27 since that isn't really correct to begin and c27 shouldn't exist. EDIT: See if it stills drift. If so, we will have to look at the transistor matching.
If you don't have one, get a DMM with an HFE test because there are transistors that should be in matching gain. plus Emitter base forward bias. w'ell have to go through that
D6 should be a germanium even though a sckottkey should work. Its only there to shut off the transistor when the output is over driven, but why change it?
Btw, I don't understand why all these cloners clone this and not use the same transistors (or even in the group like fashion) , but it should be fine regardless.
A friend who lives locally might have an HFE on his which I can borrow. One obit of good news is that Unit #1 seems to settle around 91.5mV after being left on for 30 minutes. So I readjusted and will check it in another 30m. EDIT: just checked it, it's now 89.5... I have no idea if a touch of variation is acceptable or what. They kind of do that anyways. its when they slowly creep uncontrollably up to 300mv. You need to leave it continuously on for like 2-3 days for everything to burn in. Matching is important for this and the linearity of the signal. I'm wondering how well they do. I still don't get the diode, because there is like 50 different ones that would do the function if you couldn't get an AA144. I can understand going to that kind of transistors, because of to39 heatsinks. There are a few transistors out there besides the originals that could be made in a batch if they are not available. Its just that all 5 in the output have to match and be greater than 112 Hfe (the two outbut, plus the three right behind them). |
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Post by lee on Dec 24, 2023 15:54:00 GMT -6
We may be all right. Unit 1 is giving me a pretty steady 90.2mV and unit 2 usually starts off a couple mV under and settles at 89.3. I'll keep them both powered for a few hours and see where we land then.
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Post by lee on Dec 24, 2023 18:27:56 GMT -6
Update. Both have been powered for two hours. Unit 1 hangs out around 89.X and unit 2 settles at 91.0. This is even though I have trimmed both to 90 after having settled. I just don’t know where on the scale of acceptable this variation is.
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Post by audiospecific on Dec 24, 2023 23:37:58 GMT -6
Update. Both have been powered for two hours. Unit 1 hangs out around 89.X and unit 2 settles at 91.0. This is even though I have trimmed both to 90 after having settled. I just don’t know where on the scale of acceptable this variation is.
That should be ok. That's not really a guide on the real one. Just their build, and Its not going to be exact. At least you didn't get their 1073 people are apparently having issues putting together.
Quite frankly I don't know why they even jacked with leaving it 24V. I would have reworked a few things and gain another 12db of headroom myself instead of dropping 8V with a voltage regulator.
Qbias is a linearity adjustment anyways and you suppose to compare a sine wave and adjust it so that the top portion of the wave is the same as the bottom portion. I would get some AA144 or OA9 to replace that wrong diode so it would saturate the same way.
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