JL 300/4 - First Amp Repair

[Perry Babin]

When you powered it up, were all of the transistors clamped to the heatsink?

Was the insulator between the transistors and the heatsink in place?


Did you download and read through the files that I sent the link to?

 

[greg_gorrell]

I did download the files, thanks a lot. I read them today and they were pretty helpful. I made sure that they were clamped to the heatsink and that the arctic silver was spread evenly across the backs of them. What do you think about the driver transistors?

 

[Perry Babin]

Was the insulator between the transistors and the heatsink in place?

 

[greg_gorrell]

What do you mean by insulator? I didnt see anything in between besides the thermal compound.

 

[Perry Babin]

The transistors can't make contact with the metallic heatsink. There should have been a clear mica insulator between the transistors and the aluminum heatsink. Was it in place?

 

[greg_gorrell]

I must have wiped that off and not realized it. I didnt see any but if thats the case that would be my problem.

 

[Perry Babin]

Yes. That would be a problem. Can you find them?

If you can't, you'll have to replace them before you can reassemble the amp.

Remove all of the outputs from all 4 channels and replace them with new ones in a single channel. Turn the bias pot fully counter-clockwise for the channel with the outputs installed and power it up for a few seconds. Remove power and check the temperature of the outputs. If they run cool, connect speakers to that channel to see if it will produce audio. Don't leave it on for more than a few seconds at a time without the heatsink.

 

[marchel]

SO you did'nt realized at first that the trans need to be insulated, Ouch!