Earthquake PA4300 "slave side" (Part 2)

[marko]

OK after having success repairing the main side of my beast project I've now been working on the "slave side" of the amp, this is where i'm up to..

I replaced all 12 irfz44n power supplu fets as they were blown and also changed the 5 3300uf 35v caps for the PS, without a remote wire hooked up the amp is pulling a lot of current and one bank of mosfets are getting very hot whilst the other side was not even warm? I can't take any readings off the PWM as I fear some damage may occur..

Mark.

 

[Perry Babin]

Is the resistance from pin 9 to pin 7 and pin 10 to pin 7 the same?

Pin numbers on 494.

 

[marko]

pin 7 to 9 is 1k ohms and 7 to 10 is 0.700k ohms.

 

[marko]

just checking components around the PWM and Q4 (A1268) has an open circuit on the left to middle leg...

[/URL][/IMG]

 

[Perry Babin]

Did you find the break?

If so, did that solve the problem?

Link to previous thread so I can get to photos easier:
http://www.diyaudio.com/forums/car-audio/291290-earthquake-pa4300-help-needed.html

 

[marko]

Did you find the break?

If so, did that solve the problem?

the remote feeds R7 then ZD3 then Q4, Q4 has a break on this leg, will this cause the power supply to draw a lot of current?

Link to previous thread so I can get to photos easier:
http://www.diyaudio.com/forums/car-audio/291290-earthquake-pa4300-help-needed.html

this side of the amp (master) is fully operationl now, I didn't know if it was best to carry on in the same thread with this side but didn't want to confuse anyone!

Mark

 

[Perry Babin]

The two halves are similar. I wanted easy access to the photos so I didn't have to ask for more to be posted.

I don't know how the circuit is laid out but there will be two identical circuits for the two banks of FETs.

Do the two 56 ohm resistors (R36/37) read the same?

Does either have a bad solder connection?

 

[marko]

R36/R37 both read 56 ohms and the solder looks OK but can re solder to make sure if needed..

under the board there is a previous repair that leads to R36, this is the side that didn't get hot... this leads to R31/R34 on the top side of board.

[/URL][/IMG]

 

[Perry Babin]

The 56 ohm resistors connect between the circuit that feeds all of the gate resistors and ground. Confirm that that's what you have for both sides.

 

[marko]

from ground terminal I have 56ohm on both R36/R37 and then have 220ohms for all gate resistors to R36/R37. seems fine.

 

[Perry Babin]

You'll have to replace the 220 ohm resistors. 100 ohm is the highest that I would use and you may want to go to 68 ohms.

There may be other problems as well but this needs to be resolved before you do any more troubleshooting.

 

[marko]

You'll have to replace the 220 ohm resistors. 100 ohm is the highest that I would use and you may want to go to 68 ohms.

There may be other problems as well but this needs to be resolved before you do any more troubleshooting.

OK, but I'm curious as to why Earthquake used 220 ohm? the master side is working OK with 220 ohm resistors...

 

[marko]

OK, I'll try and source some suitable gate resistors tomorrow as I don't have any in th 68-100 range.

I checked the PWM again and now that has equal resistance on 7/9 and 7/10 (about 1k ohm).

the amp still pulls about 40 amps with NO remote wire hooked up, and just one bank of FETS get hot!

thanks for the help so far, much appreciated

 

[Perry Babin]

Similar amps use an NPN transistor (Q7 and Q8 in this amp?) to drive the voltage high for the FET drive signal. If that's the case for this amp, that NPN transistor could be defective.

You could try powering the amp up without those transistors. The 56 ohm resistors will keep the FETs off.

 

[marko]

Similar amps use an NPN transistor (Q7 and Q8 in this amp?) to drive the voltage high for the FET drive signal. If that's the case for this amp, that NPN transistor could be defective.

You could try powering the amp up without those transistors. The 56 ohm resistors will keep the FETs off.

I'll go and try this now..

I have now 68 and 82 ohm resistors to try for the gates, would there be any prefered out of these 2?

 

[marko]

I have removed Q7/Q8 (they ohm out OK) and now the amp only pulls 0.1amp still without remote lead hooked up.

I also removed R34/R35 as one was reading higher in circuit than the other but out of circuit they are both OK (1k ohm).

 

[Perry Babin]

Are you saying that removing Q7 and Q8 alone (no other changes) eliminated the high current draw?

 

[marko]

Are you saying that removing Q7 and Q8 alone (no other changes) eliminated the high current draw?

yes, all but disapeared. Q15-Q20 got hot instantly but other side cold.

 

[Perry Babin]

Q15-20 got hot at 0.1 amp of current?

Did you check Q7/8 for leakage or simply for shorted junctions?

 

[marko]

Q15-20 got hot at 0.1 amp of current?

Did you check Q7/8 for leakage or simply for shorted junctions?

no, sorry, my confusion! with Q7/Q8 removed and 0.1amp draw all fets cold.

Q7/8 "ohmed" out OK out of circuit.