Protection

[Hexhclass]

Pin 3 on the 494 is high,I think the protection circuit it self is bad.When I force pin 3 to go low voltages look ok.What usually cause that problem on that board?

 

[Perry Babin]

The attached shows common protection circuits.

I don't know the designations for your board but referring to the attached diagram, what is the DCV on pins 1 and 7 of U2?

 

[Hexhclass]

Pin 1: 7.02
Pin7: 0.127

 

[Perry Babin]

Did the amp play normally when you grounded pin 3?

 

[Hexhclass]

Yes

 

[Perry Babin]

Are the main board designations close to or the same as the diagram?

Either way, find 'Q226' in your amp and check it (shorts, open junctions and leakage).

 

[Hexhclass]

Markings are the same
I replace that transistor,still in protect.

Pin 1:3.828v
Pin 2: 13.45
Pin 3: 4.23

 

[Hexhclass]

Wrong info

 

[Perry Babin]

Does pin 1 stay high if you pull Q225?

 

[Hexhclass]

I made a mistake
Voltages I post earlier was for Q53

Q226
Pin 1: 13.45
Pin 2: 0.001
Pin3: 13.43

 

[Perry Babin]

DCV on terminals 1, 2 and 3 of IC2?

 

[Hexhclass]

393
Pin1: 7.02
Pin2: 2.513
Pin3: 10.02

 

[Perry Babin]

Photo of the audio driver board?

 

[Hexhclass]

I had the audio driver board out at one point and it was still in protect

 

[Perry Babin]

How difficult would it be to remove R29B?

Do you see D11 (that's in series with D12 on the diagram)?

 

[Hexhclass]

Pulling R29b got it out of protect.
I did not sport the diodes in my amp

 

[Perry Babin]

Resistance between pin 8 and pin 8 of the two 8-pin ICs on the audio board?

Do you see an LM2903 on the main board that they could be using for over-current protection?

 

[Hexhclass]

These pins are directly connected 0.1 ohm

Lm2903 no.

 

[Perry Babin]

Do you know what the two components under the top heatsink on the audio driver board are?

 

[Hexhclass]

Sot 223 transistors,I can pull the heatsink when I return to the shop if you need part numbers.