Please help me get this JL amp off my bench

[rastanearian]

I have been on and off working on this JL audio G-Max amp for a while now.
It blew a few IRFZ44 on one side of the power supply and yet continued to work.
I jumped right in and replaced all the IRFZ44 devices on the one side along with the gate resistors. The driver transistors tested fine so I didn't look any further. This turned out to be a mistake. Actually the bigger mistake was re-installing it without any protection. The same FETs blew again. I had obviously not really repaired anything. OK. Lesson learned.
I was fooled by the fact the amp continued to work even with half the FETs on one side blown. Some were shorted, some were open. I figured the previous owner probably just abused it by using the wrong fuse or driving it into the ground.

I am posting some pics of the board in case someone recognizes this model and can offer some assistance. I have read through the other JL repair threads but none really seem to have the same symptoms

Looking at the pics you will notice that I have removed 8 x 2200uF caps as my ESR meter was reading 0.00 on a few of them. I'll have to put them back before I can take any voltage measurements.

Any comments are welcome.

 

[Perry Babin]

It looks like an E1800.

 

[rastanearian]

I was not aware of that model. the specs are very similar.
the G-Max is 600W where as the E1800 is 640W.

 

[rastanearian]

I wonder how many times they re-labeled this amp.
I found an A-1800 with similar specs and identical chassis.

 

[rastanearian]

Hi Perry,

I'm not sure my power supply can power this amp.
I have a two 15V 9A supplies. These are identical and can be dialed down to the 13 or 14V.
Will one be enough for testing or can I put the two together to increase the available current?
I have been reading through your repair manual and it leads me to believe one supply is not enough for this amp.

 

[Perry Babin]

I think it's something that you'll have to try. Most draw about 15 amps for a short time when powering up. The amp's low voltage protection is very sensitive. If the voltage drops too low for a fraction of a second, the amp will shut down.

 

[rastanearian]

Finally had time to get back to this amp.

Set the power supply to 13.8V on my 10 amp supply.

With no remote power applied there is 0 current draw from the supply.
Once the remote power is applied there is a small current draw and the protection light starts to flash.

I found it interesting that approximately every 1.2 seconds there is an ascending then descending current draw that starts at .4A rises to 8.75A then goes back down by the same increments.

I guess that answers the question of whether or not a 10 amp supply is enough.
Perhaps my two 9A supplies paralleled would work.

 

[rastanearian]

Tried the two 9A supplies together and I get the same result.
The protection light flashes and it periodically pulls up to 19A.
I don't think it is a problem with the supplies. There is still something in there i missed.
As long as the protection is flashing like this I can't get any reliable voltages anywhere.
At least I'm getting good at taking it apart.

 

[Perry Babin]

Is the rectifier shorted?

Does it power up with the rectifier(s) out of the circuit?

 

[rastanearian]

The rectifiers are good. I haven't powered it up without them yet.
A little shy of doing that with no heat sinks.

 

[rastanearian]

With the rectifiers removed the amp did not go into protection.
It seemed stable for a couple of moments before I heard a very high pitched squeal and then a snap just as I removed power.
I haven't found what caused that yet.

 

[rastanearian]

By the way, I never saw it draw more than 1.8A during this very short time.