Alright Mooly, im finally making some progress 😀 I found a short by measuring resistance between several different components. some of them had barely any resistance between each other and i found that all components between D3 striped side and D1 non striped side were somehow shorted to ground. It feels like i should have found this earlier but i guess i was lacking the basic understanding of amp-layout before 😛
figured it had to be U5 (even though i couldnt actually see any short
) so i re-soldered it and got completely different readings. when i turn on amp with bulb limiter the bulb now shines for a second and then dims out.
new readings:
striped D3: 21.1v
non-striped D4: -21.2v
striped D1: 11.94
non-striped D5: -11.94
I inserted U2 following your guide and turned on the amp (still with bulb limiter), all the empty IC sockets read -11.75v on pin 4 and 11.85v on pin 8.
results so far seem pretty perfect, should i test something else before i insert op-amps and try amp with cheap headphones? 🙂
figured it had to be U5 (even though i couldnt actually see any short
) so i re-soldered it and got completely different readings. when i turn on amp with bulb limiter the bulb now shines for a second and then dims out. new readings:
striped D3: 21.1v
non-striped D4: -21.2v
striped D1: 11.94
non-striped D5: -11.94
I inserted U2 following your guide and turned on the amp (still with bulb limiter), all the empty IC sockets read -11.75v on pin 4 and 11.85v on pin 8.
results so far seem pretty perfect, should i test something else before i insert op-amps and try amp with cheap headphones? 🙂
not that it matters now but i tested this before resoldering and got -6.6 on adapter output. it currently reads 15.9. 😉
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Hey, that sounds much better 🙂 although I think a typo has crept in there somewhere, D1 should always have positive voltages on it, D5 always negative. Just a typo, yes... the values are spot on.
Yes, you can try it with the IC's fitted next. As long as you fit them the correct way around then they shouldn't come to any harm even if there are other issues.
Pin 4 on all the sockets should have minus 12 volts and pin 8 on all the sockets should have plus 12 volts but it needs IC2 fitting for that to happen. So if you just fit IC2 first and then test, you should see those voltages come up on all the other IC sockets. If the supplies are OK then fit the rest of the opamps. Always switch off and wait a few seconds before removing and refitting the opamps so that the rails can discharge.
Before connecting headphones, make sure that the voltage on pins 1 and pins 7 of all the opamps except IC2 is around zero.
If it passes all those checks only then should you connect headphones and try it out.
Good luck, I'll look in tomorrow to see how it goes 🙂
Yes, you can try it with the IC's fitted next. As long as you fit them the correct way around then they shouldn't come to any harm even if there are other issues.
Pin 4 on all the sockets should have minus 12 volts and pin 8 on all the sockets should have plus 12 volts but it needs IC2 fitting for that to happen. So if you just fit IC2 first and then test, you should see those voltages come up on all the other IC sockets. If the supplies are OK then fit the rest of the opamps. Always switch off and wait a few seconds before removing and refitting the opamps so that the rails can discharge.
Before connecting headphones, make sure that the voltage on pins 1 and pins 7 of all the opamps except IC2 is around zero.
If it passes all those checks only then should you connect headphones and try it out.
Good luck, I'll look in tomorrow to see how it goes 🙂
Your ahead of me 🙂 Follow the above by fitting the other IC's and checking pins 1 and 7 of all are around zero.
Ops, a typo indeed. switched the numbers somehow but its fixed now. will continue tomorrow 🙂
To high. You should be seeing a few millivolts at most. Don't despair, lets look at each stage in turn.
Concentrate on just U1, the NJM2068 which is used in the first stage. Pin 8 should have plus 12 volts and pin 4 minus 12 volts. We always always confirm supplies are correct as the first step in troubleshooting. Measure carefully on the actual pins of the IC. Pins 1, 2 and 3 should all have zero volts on them, as should pins 5, 6 and 7. Again, measure on the IC itself.
Begin by checking pins 3 and pins 5. Both must have 0 volts DC present. They are the 'non inverting' inputs to the opamp. What have you got ?
Concentrate on just U1, the NJM2068 which is used in the first stage. Pin 8 should have plus 12 volts and pin 4 minus 12 volts. We always always confirm supplies are correct as the first step in troubleshooting. Measure carefully on the actual pins of the IC. Pins 1, 2 and 3 should all have zero volts on them, as should pins 5, 6 and 7. Again, measure on the IC itself.
Begin by checking pins 3 and pins 5. Both must have 0 volts DC present. They are the 'non inverting' inputs to the opamp. What have you got ?
aw i actually expected something might be wrong cause the bulb limiter is glowing when i turn amp on 🙁
here are pin readings, but some of them are a bit "unstable" going up and down, especially pin 8 going from 3 to 3.5.
1: 0.45
2: 0.17
3: 0
4: ~1.6
5: 0
6: 0.17
7: 0.45
8: ~3.3
at least 3 and 5 have 0v
The supply rails are down. Without knowing the details of the bulb, it could actually all be OK (although I suspect not tbh) and the extra current of all the opamps is pulling it all down. But we need to be sure and its easy to check.
Take the opamps out and get it all back to how it was yesterday when you had both 12 volt rails correct and when you just had U2 fitted. Confirm again that the supplies are as they were and that you have the -/+12 volts (that's how we write it) back on the empty sockets.
If they are still OK then fitting just U2 shouldn't pull things down.
With U2 out of its socket, all the pins apart from the supplies should be at zero volts. So that is something to check as well.
If the bulb is glowing brightly perhaps you have a physical short around the regulators. Make sure the pins aren't touching each other and that there are no solder blobs anywhere.
Take the opamps out and get it all back to how it was yesterday when you had both 12 volt rails correct and when you just had U2 fitted. Confirm again that the supplies are as they were and that you have the -/+12 volts (that's how we write it) back on the empty sockets.
If they are still OK then fitting just U2 shouldn't pull things down.
With U2 out of its socket, all the pins apart from the supplies should be at zero volts. So that is something to check as well.
If the bulb is glowing brightly perhaps you have a physical short around the regulators. Make sure the pins aren't touching each other and that there are no solder blobs anywhere.
With only U2 fitted the -/+12 volt is back to normal, and the bulb is no longer glowing when i turn amp on.
removing U2 turns the +12 rail to +0.33 but the -12 rail stays the same. all other pins are 0 except for on U2 where the pins have the following voltages:
1: 9.35
2: -8.6
3: -10
4: -11.78
5: -10
6: 9.35
7: 7.1
8: 11.86
removing U2 turns the +12 rail to +0.33 but the -12 rail stays the same. all other pins are 0 except for on U2 where the pins have the following voltages:
1: 9.35
2: -8.6
3: -10
4: -11.78
5: -10
6: 9.35
7: 7.1
8: 11.86
That's good.
U2 has to be in place so that the two transistors operate correctly. With U2 in place, the rails are correct as measured at the remaining empty sockets ? Yes ! So U2 appears at a basic level to be working correctly.
You mention having zero volts on all other pins on the empty sockets (except pins 4 and 8 which should have the supply present). That is also correct.
So we now fit just U1 (make sure its the correct way round) and we measure the voltages on just U1.
You should still see zero on all pins except 4 and 8.
If that doesn't happen then remove U1, and in its place fit one of the 4556 opamps (these are all pin for pin compatible with each other) and retest.
Are the voltages now correct ?
If they are then we have to suspect that something has happened to the 2068 opamp.
Take it up to that stage and see what results you get.
When amp is off i see zero on all pins except 4 and 8, when amp is on- several pins are not at zero.
nope 🙁 still the same result as above.
We are only interested in the voltges when the amp is on 🙂
Do the following methodically and post your measured results, then I know exactly what you are seeing. It sounds like you have a construction error (perhaps a short somewhere) because pins 1, 2 and 3 for one half of the opamp and pins 5, 6 and 7 for the other half must all be at zero volts when U1 is removed. So lets see what you have got and then we can try and make sense of it.
So with only U2 fitted, record the voltages on the socket of U1.
Voltages on U1,
Pin 1 =
Pin 2 =
Pin 3 =
Pin 4 =
Pin 5 =
Pin 6 =
Pin 7 =
Pin 8 =
Do the following methodically and post your measured results, then I know exactly what you are seeing. It sounds like you have a construction error (perhaps a short somewhere) because pins 1, 2 and 3 for one half of the opamp and pins 5, 6 and 7 for the other half must all be at zero volts when U1 is removed. So lets see what you have got and then we can try and make sense of it.
So with only U2 fitted, record the voltages on the socket of U1.
Voltages on U1,
Pin 1 =
Pin 2 =
Pin 3 =
Pin 4 =
Pin 5 =
Pin 6 =
Pin 7 =
Pin 8 =
With only U2 fitted,
Voltages on U1:
Pin 1 = 0
Pin 2 = 0
Pin 3 = 0
Pin 4 = -11,74
Pin 5 = 0
Pin 6 = 0
Pin 7 = 0
Pin 8 = 11,82
bulb tester is not glowing unlike when i had a opamp fitted in U1
Voltages on U1:
Pin 1 = 0
Pin 2 = 0
Pin 3 = 0
Pin 4 = -11,74
Pin 5 = 0
Pin 6 = 0
Pin 7 = 0
Pin 8 = 11,82
bulb tester is not glowing unlike when i had a opamp fitted in U1
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Perfect in every way.
Well... you've got to now put an opamp in that socket and repeat the measurements. The current draw from just one opamp shouldn't really be enough to tip a bulb 'over the edge'... but we will prove it and see.
So fit the opamp... lets stick to the 2068... and see what happens.
If the bulb lights and the rails drop then there is no point doing the further measurements. We then have to bite the bullet and link the bulb out and see what happens.
Well... you've got to now put an opamp in that socket and repeat the measurements. The current draw from just one opamp shouldn't really be enough to tip a bulb 'over the edge'... but we will prove it and see.
So fit the opamp... lets stick to the 2068... and see what happens.
If the bulb lights and the rails drop then there is no point doing the further measurements. We then have to bite the bullet and link the bulb out and see what happens.
this time the rails keep the -/+ rails keep the 12v and other pins are at 0, bulb still not glowing 😀
should i insert some more opamp?
should i insert some more opamp?
Yes you can do that. Try just U3 first. You should see similar readings to U1, that is to say zero volts on all but pins 4 and 8. If that's OK then fit U4 and check the same way.
Then you can try with headphones 🙂
Then you can try with headphones 🙂
inserted U3 and its too low again, pin 4 is -6,7 and pin 8 is 7,4.
should i bite the bullet? :|
should i bite the bullet? :|
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Just out of interest, are the other voltages (the other pins) zero ? Even with low supplies like that, the opamps will still function correctly and so you should see zero volts on pins 1 and 7 of U3.
If that is the case then you can try linking the bulb out.
If that is the case then you can try linking the bulb out.