lab gruppen 1600 faulty channel B

[discjockeyr]

Hi, channel B of my amplifier was dead and found that 1 of the power transistors on the amplifier was short. Transistor was mj21193. i have remove the short transistor until i found a new one to replace it and amplifier is working most probably giving less power as all transistors are in parallel and the power of each one is added. the strange think that i don't believe is caused by the missing transistors is that on the specific channel the sound is distorted. Not much but if you try to compare the 2 channels there is a distortion on the sound. What you believe may cause this distortion?
Thanks

[Enzo]

Without seeing on a scope or hearing it it is hard to say.

It could be as simple as a slight imbalance due to the missing part. It is also possible there are some smaller parts damaged when the big one failed.

Check the bias for the channel - well check both channels. You might have some crossover distortion that can be adjusted out.

Whenever a power transistor shorts out, always check all the resistors associated with it, and it is a good idea to change the driver too, even if it seems OK. The shorted power transistor can stress the driver even if it doesn't kill it.

And just as an experiment, exchange the speakers between sides. It is possible when the transistor died it could have put some DC on the speaker and damaged it. swapping sides will tell you that.

[discjockeyr]

Dear Enzo, thanks for your reply.
ok, there are 5xMJ21193 in parallel and i found that only 1 was faulty. the transistor was MJ21193 and i did not found in local market the same but an equivalent MJ15025 which seems that have the same specs. Also note that i have replace MJL1302A if this is the driver you mean which actually was not faulty. i have measured all the resistors and seems good. When i try the amplifier with the equivalent transistor the channel every few seconds was going to protection mode but note that the few seconds that was working the small distortion on the sound was there. so to test if the protection mode caused by the equivalent transistor i have removed it completely and now the amplifier is working but again with distortion. I know that i need to replace it with the original type of transistor but the distortion i don't know from where it comes. Speakers are crossed and the problem is not on the speakers