I will check. I’m focusing on Tr500 and Tr501 those are apparently important and they are way off with op amp in and out. I will need to pull them and check they need to match. I’ll be back when I got this part sorted out.
I don't believe the central opamps are in the signal path, or see that the power amp is no longer going to work. I think he just said that nice looking wave was at the speaker terminal. I did say pulling the opamps might actually make it work, and it seems we now do have an output. Where are the speakers?
Will check later on, I know I have trimmer on 0 fully counter clockwise. I should be getting 55mV now but I’m getting 268mV and I the original ones are bad and I got same ones but different package so they are mounted on adapter boards. Now I need to get me some more and I need matching pairs I don’t think I ever put any time matching them when I installed them, I did not think of that. I feel I need to adress first before I continue further on. 🙂 I’ll be back
Emphatically agree with #147. I believe the output stages will bias without IC501, but IC501 is intended to reduce distortion and also servos local offset error at the same time.
I also think compensation at C520 is scary aggressive.
I also think compensation at C520 is scary aggressive.
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Yea, but the signal goes through it, unless I read the schematic wrong.
It auto nulls offset error, but has little to do with bias current adjustment/temperature compensation.
Also note the R536, C520 time constant. Way faster than typical DC servo. It encloses the output stages within IC501 loop to reduce distortion.
Also note the R536, C520 time constant. Way faster than typical DC servo. It encloses the output stages within IC501 loop to reduce distortion.
Ah, the hangover-induced misreading of schematics. I know it very well. 😆
like where this is heading. 😂
So this left side of the amp where the transistor farm is at needs to be working correct for the rest of the amp to work correctly so I really hope I can sort this out with TR500 and 501 I will also recheck all solder and so on. Just need to order from mouser and my partner is pregnant and our first child is will be born any day now so might be a bit slow a couple of days.
So this left side of the amp where the transistor farm is at needs to be working correct for the rest of the amp to work correctly so I really hope I can sort this out with TR500 and 501 I will also recheck all solder and so on. Just need to order from mouser and my partner is pregnant and our first child is will be born any day now so might be a bit slow a couple of days.
Who in their right mind would put childbirth before amplifiers? 😀
I still think you should take a scope shot right after the preamp (by the coil). It will give us useful information.
I still think you should take a scope shot right after the preamp (by the coil). It will give us useful information.
BTW, what’s up with the biasing of the preamp? With those two diodes it’s just barely running in Class AB. What am I missing?
The TR1-2 thing, looks like they are passing a little bit. So IC401 before these can't be ignored. Especially as it's connected to the outside world. Anything could of been shoved it in. Your 81v rails send it 15v+/- with a zener pair that seem fine. Making the Relay401 route less likely.
TR3 looks a bit glazed over. I would be drawn to that as a point of interest.
4:20 and I'm at it again
TR3 looks a bit glazed over. I would be drawn to that as a point of interest.
4:20 and I'm at it again
We actually went to hospital Friday but had to go home, false alarm. Now we wait, and that when the time is right. =)
However, I had some time today. Right now I can only send a signal through the Normal (RCA) and not the balanced input because i need to get me a adapter. It looks like only the balanced output goes through the OP amp, I can't quite interpret the schematis? But if I follow the signal, I have made a measurement on R502 which is the input to the amp board. Here you can see a picture. The signal i'm generating is about the same 94mV. My phone is not able to generat exakt 100mV.
Besides this i have also reworkd entire left side of the board trying to clean up and test traces for continuity. I have checked all transitors and matched them in hFE (exept for output transistors). Just to test i mounted original op-amps and that actrually made things even worse so i Removed the again. Just to test i decided to try to set idle current with trimmer pod VR501 and as soon as i hit 1-10mV it started to oscillate and drawing current and DBT lights up this with no op-amps installed..
I removed the relay to check it but there is no datasheet on it i have no idea how to test it, 8pin realay. Input pins read 700 ohms across and all other pings read OL, so i'm just guessing the relay is fine but i'm not 100% and have no idea how to test it properly. The only part in the entire amplifer that seems to read out of spec is that 18uH inductor.
Something i noticed is when i removed the relay, toched up som soled joints and i replaced timmerpod VR501 just because i questioned my job on installing it. After that voltages at TR500 and TR501 when down to zero UNTIL i start adjusting VR501 and after that i'm back at 312mV.
(i'm not ablte to trace any signal in op-amp, no legs seem to feed signal into it. Maby i need to get me an adapter from RCA to XLR)
However, I had some time today. Right now I can only send a signal through the Normal (RCA) and not the balanced input because i need to get me a adapter. It looks like only the balanced output goes through the OP amp, I can't quite interpret the schematis? But if I follow the signal, I have made a measurement on R502 which is the input to the amp board. Here you can see a picture. The signal i'm generating is about the same 94mV. My phone is not able to generat exakt 100mV.
Besides this i have also reworkd entire left side of the board trying to clean up and test traces for continuity. I have checked all transitors and matched them in hFE (exept for output transistors). Just to test i mounted original op-amps and that actrually made things even worse so i Removed the again. Just to test i decided to try to set idle current with trimmer pod VR501 and as soon as i hit 1-10mV it started to oscillate and drawing current and DBT lights up this with no op-amps installed..
I removed the relay to check it but there is no datasheet on it i have no idea how to test it, 8pin realay. Input pins read 700 ohms across and all other pings read OL, so i'm just guessing the relay is fine but i'm not 100% and have no idea how to test it properly. The only part in the entire amplifer that seems to read out of spec is that 18uH inductor.
Something i noticed is when i removed the relay, toched up som soled joints and i replaced timmerpod VR501 just because i questioned my job on installing it. After that voltages at TR500 and TR501 when down to zero UNTIL i start adjusting VR501 and after that i'm back at 312mV.
(i'm not ablte to trace any signal in op-amp, no legs seem to feed signal into it. Maby i need to get me an adapter from RCA to XLR)
Oh yes, IC401 is just for the balanced input. I hadn't noticed.
You may need to look up the relay, but it sounds like a dpdt and you can't really test the 'on' contacts, if it's not powered. If it's in the circuit you could meter across the switch, expecting to find nothing but a short. I'm finding it less likely now the IC401 has been seen to have it's 15v. How is the 15v for the removed IC's looking? (they are both out, I think you said) I would hope it's a good strong 15v again, but it would be nice to see that at the diodes. Then poke at the bias transistor area, as the previous base voltage of 0.8 is not the -0.6 is should of been. I didn't know vr501 had ever been out before, but it's adjustment and result are hard to ignore.
Even with faults around stage 1 and 2, it's hard to say the 11-12v instead of 15 was due to them. Something in the IC area is dead imo. Pulling them voltages down. The bias area is behind 4.7K resistors, But I would have to look still. That decoupling cap c52? electrolytic is one of the few components that could drag the 15 down, if the chips are out, and it's still not 15
It's a moments work, while your probing the next
You may need to look up the relay, but it sounds like a dpdt and you can't really test the 'on' contacts, if it's not powered. If it's in the circuit you could meter across the switch, expecting to find nothing but a short. I'm finding it less likely now the IC401 has been seen to have it's 15v. How is the 15v for the removed IC's looking? (they are both out, I think you said) I would hope it's a good strong 15v again, but it would be nice to see that at the diodes. Then poke at the bias transistor area, as the previous base voltage of 0.8 is not the -0.6 is should of been. I didn't know vr501 had ever been out before, but it's adjustment and result are hard to ignore.
Even with faults around stage 1 and 2, it's hard to say the 11-12v instead of 15 was due to them. Something in the IC area is dead imo. Pulling them voltages down. The bias area is behind 4.7K resistors, But I would have to look still. That decoupling cap c52? electrolytic is one of the few components that could drag the 15 down, if the chips are out, and it's still not 15
It's a moments work, while your probing the next