This amp turns on instantly when you apply 12v to b+ and ground with nothing else.
I cannot find any damaged transistors at all.
Pin voltages on the NEC494 appear instantly the main power and ground are applied with no REM.
1: -
2: 5.11v instantly
3: -
4: 0.22v instantly
5: 3.0v triangle wave floating at 0.3v above ground
6: 3.81v instantly
7: -
8: 12.49v instantly
9: switching
10: switching
11: 12 49v
12: 12.49v
13: 5.11v
14: 5.11
15: 5.11
16: -
Pin 4 being dead time control, shouldn't it start out high and drop low instead of instantly going 0.22v?
I cannot find any damaged transistors at all.
Pin voltages on the NEC494 appear instantly the main power and ground are applied with no REM.
1: -
2: 5.11v instantly
3: -
4: 0.22v instantly
5: 3.0v triangle wave floating at 0.3v above ground
6: 3.81v instantly
7: -
8: 12.49v instantly
9: switching
10: switching
11: 12 49v
12: 12.49v
13: 5.11v
14: 5.11
15: 5.11
16: -
Pin 4 being dead time control, shouldn't it start out high and drop low instead of instantly going 0.22v?
Is either Q101 or Q403 shorted?
Pin 4 is simply on a voltage divider. From the values, the voltage you have is correct.
Pin 4 is simply on a voltage divider. From the values, the voltage you have is correct.
Both are operating perfectly.
Q101 removed and tested out of circuit and works correctly. Amp still power on with Q101 removed.
Replaced Q101 and removed Q403. Q403 also works as expected in the transistor tester. When removed from circuit, unit does not power on.
When power and ground are supplied, and Q403 removed I'm getting 2.83v on the base instantly....based on the diagram it looks like the computer controls that?
Q101 removed and tested out of circuit and works correctly. Amp still power on with Q101 removed.
Replaced Q101 and removed Q403. Q403 also works as expected in the transistor tester. When removed from circuit, unit does not power on.
When power and ground are supplied, and Q403 removed I'm getting 2.83v on the base instantly....based on the diagram it looks like the computer controls that?
Replaced Q403, pulled Q101. Now amp does not turn on. voltage at 11 and 12 are zero (.38v)
I'm left wondering if something changed or if I reporwed the amp too quickly with q101 removed and the rails were still high enough to trigger the relays, hence my assumption of the amp being on? I think it is the latter as I co tinie to test...
I'm left wondering if something changed or if I reporwed the amp too quickly with q101 removed and the rails were still high enough to trigger the relays, hence my assumption of the amp being on? I think it is the latter as I co tinie to test...
Measuring from base to emitter on Q403, what is the DC voltage with remote and no remote?
Turns on? Do you mean that the 494 is producing drive pulses?
Turns on? Do you mean that the 494 is producing drive pulses?
2.70v from base to emitter on Q403 regardless of input to the REM. When B+ is applied
Yes. Power supply is being driven, full rail is being generated and the output is briefly oscillating as well
Yes. Power supply is being driven, full rail is being generated and the output is briefly oscillating as well
Is the MCU running warm/hot?
This isn't a class D amp. There shouldn't be any oscillation. Since the power supply is producing drive, connect a signal source and check for audio on the output transistors.
This isn't a class D amp. There shouldn't be any oscillation. Since the power supply is producing drive, connect a signal source and check for audio on the output transistors.
I'm an idiot! Total brain fade on my part. Yes class AB. No signal on the output fets.
What I was mistaking for PWM switching is audible on speakers at initial powerup of the amp when B+ is applied. It vanishes in about 2 or 3 tenths of a second.
MCU isn't hot at all
What I was mistaking for PWM switching is audible on speakers at initial powerup of the amp when B+ is applied. It vanishes in about 2 or 3 tenths of a second.
MCU isn't hot at all
Did you replace Q403 with an exact replacement?
If you lift or remove Q403, what's the DC voltage on the base pad for Q403?
If you lift or remove Q403, what's the DC voltage on the base pad for Q403?
Sorry in retrospect i used nebulous terms...
Q403 is still the original transistor that came with the amp. I removed it, tested it in a transistor tester out of circuit, and when it checked out ok on the tester, I reinstalled it back.
If memory serves me, I think there was 2.8v on the base. I'm not at the shop right now so I'd need to double check when I get back.
Q403 is still the original transistor that came with the amp. I removed it, tested it in a transistor tester out of circuit, and when it checked out ok on the tester, I reinstalled it back.
If memory serves me, I think there was 2.8v on the base. I'm not at the shop right now so I'd need to double check when I get back.