jbl gto 6000 blown outputs

Hi guys.
I have picked up the above amp from a friend with a stereo install shop. Their tech guy has had a look and passed it on.
It already has a pair of outputs removed, but it flashes in and out of protect.
A quick bit of diagnostics shows that another channel is fried as well. I have now removed all 4 outputs on the rear channel and now it is stable on both the front and sub channels.

This amp has different outputs on the sub channel. It has Tip35/36 on the subs and B688/ D718 on the other 3 channels (4th channel is already gone so unsure of outputs there, but i think we can assume it was also B688/ D718).

Search has found me this, from here:

Got some problems with my JBL GTO 6000; it pulses on and off about 1 sec between. Do you have the diagrams or repair instructions for this amp?



If your amp stays in protect mode and tries to turn on every second there´s most likely a short in one ore more off the output power transistors. Those should be the 2SB688 and 2SD718 power transistors mounted onto the heatsink.

get an Ohmmeter and check each leg of the power transistor . You will probably find a 100% short at one ore more power transistors. If you find it , cut the transsitor out.

Then look for the driving transistors. Those are smaller ones , should be KTA1023 and KTC1027 . Those drive the big power transistors. Again check those smaller transistors for a short but usually those stay ok. If so, get a replacement for the big power transistor. if you cannot find the 2SB688 or 2SD718 you can use the KTB778 and KTD998 as a direct replacement. If you cannot find those use a TIP35C and TIP36C (=BD249C and BD250C in Europe) .

But remember , even if there is just one transistor burned, e.g. the SB688 you have to replace both transistors !!!

My question is, I have some Tip35/36. Can i use them in the rear channel?
If I use the Tip35/36 for the sub and the rear channel, should I use them for the front channel as well?

regards Jack.
Just seen a resistor pulled out as well. have to put that back in too.