M50 help needed with repair please.

[BrianUK]

Hi all I am new to the forum,but have been using phoenix amp for years

I bought a m50 not working,board was in very good condition,replaced the caps
And replaced all output transistors as one had shorted also found c3423 also
Bad and some resistors around the same place as c3423 were shorted out,
X4 10 ohm resistors under heat sink also changed
This has fixed the amp as it now works and sounds very good
The only problem is c3423 x2 and A1360 x2 all get hot so can't let the amp run for
long,if anyone can help me I would appreciate your time as would love to have this in my car
Thanks

Brian

[Eric D]

If your bias is set wrong they will get very hot.

Other things can make them run hot as well.

[BrianUK]

Thanks how do I set the bias please

Also I have checked all the other resistors and small transistors & diodes best I can and all
Seem fine, I did change all 4 fets IRFZ44N some of the numbers on them are different from the ones I pulled out 210p 5u wk is on the ones I put in is this ok

Thanks for your help

[Eric D]

I don't know what the factory spec bias current on an M50 is. I typically set the bias by turning the amp down (the bias that is), and then slowly turning it up while the amp is connected to a current meter. When I get a spike in current I back off a bit, and the let the amp warm up to make sure it does not spike again.

[BrianUK]

Ok. Are the yellow pots for the bias one left and the other right
Thanks

Brian

[Eric D]

Ok. Are the yellow pots for the bias one left and the other right
Thanks

Brian

Exactly

[BrianUK]

will let you know how I get on
Thanks for your time

Brian

[BrianUK]

Set the bias today, the transistors still got hot ,but did find 2x c2389 in that area bad, so will swap them out when they turn up ,hope this sorts out my problem
Thanks