X-PULSE 800.1 amp

[ultra]

Got this amp for repair.
It powers up fine, green led is lit, draws half an amp from the power supply.
After a while, the output relay is activated.
Only problem is there is no sound.
So i opened it up to see what is going on.
Power supply works perfectly, producing 63V to feed the amp.Nothing gets hot or anything.
Audio part, no output fets shorted, uses RFP70N06 (same type as the PWM), driving them with one resistor per pair.
Preamp fine with +/-12V on pins 4 and 8 of the opamps, very clean 100Hz sine.
I replaced the HIP4080 and here is what i got without feeding the amp with input signal

pin 1. 4.89 pin 11. 2.58
pin 2. 5.38 pin 12. 2.57
pin 3. 0 pin 13. 0
pin 4. 0 pin 14. 0
pin 5. 5.38 pin 15. 5.38
pin 6. 5.38 pin 16. 5.38
pin 7. 6.19 pin 17. 0
pin 8. 3.33 pin 18. 0
pin 9. 3.33 pin 19. 2.57
pin 10. 4.89 pin 20. 2.58

What changes a bit with input signal, is the voltage on pins 11, 12 and 19, 20 that drops down to 1.92V on all those pins.

[Perry Babin]

Determine why you don't have something nearer to 12v on pins 15 and 16.

[ultra]

ok, i will come back.
meanwhile, some pics

[ultra]

I found a resistor out of tolerance (it is marked R13) and it measures 3K3.
I do have 11.6V at one side of that resistor but 5.3V on the other.
I powered the amp with an ammeter in series and there consumption was nearly 60mA.
So, i installed a 3R9 in R13 position. I measured 11.6V at pins 15 and 16.
Now, the amp at idle draws almost 1.8 A, it produces sound but the right bank of fets marked as 11, 13 (from the driving pins of 4080) becomes hot. The other side is quite cold.
Do i clamp the amp to its heatsink?

[Perry Babin]

How fast do they become hot?

Do you have a scope?

[ultra]

yes, i have everything

the fets will be too hot to touch within 5-6 seconds.

Of course, the entire board is in the air.

the other side of the fets as well as the power supply fets are cold.

In order to measure anything, i think i have to clamp it to its heatsink.

[Perry Babin]

Confirm that you have the same resistance from the drive pins to all of the FETs. There are 4 sets of outputs from the 4080 (2 FETs driven from each output of the 4080).

Are the diodes in parallel with the gate resistors OK?

If all of that is OK, clamp it and confirm that you have the same high and low side signals for both sides of the amp.

[ultra]

Originally Posted by Perry Babin

Confirm that you have the same resistance from the drive pins to all of the FETs. There are 4 sets of outputs from the 4080 (2 FETs driven from each output of the 4080).

Are the diodes in parallel with the gate resistors OK?

If all of that is OK, clamp it and confirm that you have the same high and low side signals for both sides of the amp.

I confirm the same resistance from pins 11,13 and 18,20 of 4080 to all gate fets.
The output of the above mentioned pins can be seen on the pics below

[ultra]

and this is the high side on the gate, and the low

[ultra]

sorry, its here