DBA 1600.1D has red and green light

[jfxwave]

Every 5 to 6 amplifiers I get on my bench has something I can't figure out.
I have a dba 1600.1D on my bench.
1. Powers up no shorts, all Power SW50N06, Output 2SC520 and Rectifiers F12020A & F12020C tested good.
2. At idle it consumes .56 amps with no voltage drop.
3. T494 tested good, has +12v on pin 12 and -0v on 7. no pwm on e1 or e2, has .347v on pin 4
4. Op-Amps have nothing. I replaced the PC817 Optocoupler.
5. 12v on both rails.
6. Changed both diodes in5408. changed all transistors down the middle.
7. I get 12v on primary side of the transformer and only 7.4v on secondary side.
8. I tested all resistors and diodes.

 

[Perry Babin]

494, pins 3 and 14?

 

[jfxwave]

This is what i get:
1. 1.57
2. 3.59
3. 4.00
4. 0.31
5. 1.46
6. 3.66
7. 0.00
8. 12.00
9. 0.00
10. 0.00
11. 12.00
12. 11.10
13. 4.99
14. 4.99
15. 4.99
16. 7.39

 

[Perry Babin]

Something is driving pin 16 too high. Since it's in a socket, lift pin 16 and connect it to pin 7. This will disable the protection so be careful when you power it up. This will tell you if the problem is in the audio section or in the protection circuit.

 

[jfxwave]

Power supply came alive, Rectifiers low side -38.4 and high side +50.2 on center pin.
We have pwm and nothing is getting to hot, under 100 except the resistors in front of the transformers 148.
No pwm on output. The Op-Amps has +7.47 on all 8 pins.
Amp at idle is .548 amps no voltage drop.

Forgot to say red light is off green is on.

 

[Perry Babin]

What PWM on the output are you referring to?

If you use the secondary ground as the reference, do you get equal rail voltages?

 

[jfxwave]

Pretty close -45.2 and +46.7

 

[Perry Babin]

What PWM on the output are you referring to?

 

[jfxwave]

Sorry I meant audio waves.
I get rail voltage on the output -45.2 and +46.7 on center pin but no sound,

 

[Perry Babin]

Do you see audio on the two electrolytic caps on either side of Q23?

 

[jfxwave]

No audio, I tested it 2 ways. 1: Oscilloscope 2: Home made audio cable tracer.

 

[Perry Babin]

Do you see audio on the output terminals of any of the op-amps in the preamp section?

 

[jfxwave]

No audio except pin 3 an 5 on the first 4558D only, next to the rca inputs.
I measured pin 4 (-vs) and pin 8 (+vs) and get 0.00v

 

[Perry Babin]

You can't have audio without supply voltage. Follow the supply lines back to the regulators.

 

[jfxwave]

I should have explained myself better, my bad.
I got no audio on any op-amps using a Oscilloscope with input audio playing and amp powered.
I was using the probe in picture to trace audio from RCA with input audio playing and amp powered when i got audio from pin 4 and 8.

Using this cable I can trace audio path.
Please forgive my drawing.

 

[Perry Babin]

My problem was the 0v measured across the two PS pins of the op-amp. Why don't you have that voltage if the power supply is producing rail voltage?

The regulators appear to start with the two large gray resistors on the RCA end of the amp. Read #23 on the Audio Troubleshooting page.