Sony XM-1004gx

[mike49504]

I got this amp in for repair and it appears to be powering up but no output on all 4 channels.

Heres a couple pics of the amp wondering where i start to check.

 

[Perry Babin]

Have you checked all pots and switches?

Drive a strong signal into the front channels. Do you have signal on pins 1 and 7 of IC813 and IC814?

 

[mike49504]

Checked all pots and switches.

No singal on pins 1 and 7 IC813 and no signal on pins 1and 7 IC814

 

[Perry Babin]

Do you have ±regulated supply voltage on the op-amps?

Do you have signal on pins 1 and 7 of IC801?

Do you have signal on pins 1 and 7 of IC805 (on the crossover board)?

 

[mike49504]

I have + - 14.50 volts on IC'S 813,814,815.806.

No regulated voltage on any of the op amps on the crossover boards. Also no signal on 801 and 805

494
1:13.23
2:2.52
3:4.59
4:0.32
5:1.66
6:3.76
7:0
8:13.88
9:0
10:0
11:13.88
12:13.88
13:5.02
14:5.02
15:2.52
16:.03

 

[Perry Babin]

On D812 (under the transformer), what is the DC voltage on legs 1 and 2 (see attached image for pin numbers)?

You may have to check it with a few seconds of powering it up if both are near 0v.

 

[mike49504]

I tryed testing them on leg1 i got -.026 the first time i did it but now i get 0 volts on legs 1 and 2 and tryed it a few different times and get 0 volts on both legs.

I measured whithin a few secs upon powering up.

 

[Perry Babin]

Measure the DC voltage on leg 1 of the 494 again. Is it still ~12v?

 

[mike49504]

yes pin 1 is on the bottom or top of the c494?

 

[Perry Babin]

Bottom left. It appears that you had the numbering correct.

 

[mike49504]

yeah i had the pins right pin 1 is 13.88 volts

 

[Perry Babin]

Confirm that pins 1 and 2 of that diode are at 0v and pin 3 is at ~12v.

 

[mike49504]

All 3 pins are 0 volts

 

[Perry Babin]

Are you sure you're on D812? Pin 3 of that diode is directly connected to pin 1 of the 494 according to the schematic diagram. Check continuity between pin 3 of that diode and pin 1 of the 494.

 

[mike49504]

Ok checked it again

leg1:0
leg2:13.88
leg3:13.23

Pin1 of 494:13.23

 

[Perry Babin]

Lift D812, clamp all transistors and power the amp up through a current limiter.

Does it...

1. Try to draw excessive current?

2. Have DC offset on the speaker outputs of any channel?

3. Power up and produce clean audio?

 

[mike49504]

Pulled d812 off board. Amp doesnt draw excessive current. No dc on outputs.

Amp still has no output on all 4 channels

 

[Perry Babin]

Check for signal on those op-amps again. Also check for regulated voltage on the crossover board op-amps.

 

[mike49504]

I still have no signal on thoose op-amps 813 and 814 and no regulated voltages on any of the opamps on the crossover boards

 

[Perry Babin]

To confirm that you have the scope set correctly, check for signal directly on the terminals of the RCA jacks. Do you have signal there?

See if there's a broken wire/connection between the main and crossover boards. See if you can find regulated voltage on the main board on the pins of the connector that connects the two boards. Then see if it goes through to the crossover board.