i bought a peavey musician series 400 amp about a year ago. i played it for about half an hour then i got a lot of distortion. i turned it off. when i put it back on it would not come on. it just gave a putting sound from the amp and blew the fuse, anyone have any ideas where to look.
thanks.
BLows fuses? Start at the start. DISCONNECT any speaker, if it still blows fuses, then check for shorted output transistors.
Sounds like shot power supply capacitors to me and/or rectifying diodes. Regardless, before trying to turn it back on, open it up and look for any burn marks etc. If all looks good, then build a quick light bulb limiter, plug it into that and start taking voltage measurements with a digital multimeter (we can help here).
Light bulb limiter: https://www.ssguitar.com/index.php?topic=2093.0
!!!" DISCONNECT any speaker"!!!
i have not done anything with the amp till today. i checked all the power transistors and hfe is 20 8 20 17 22 21 10 18 i will change 8hfe and the 10hfe ones. are the other ones alright. thanks.
Oh, don't sweat any that are off a bit. We are concerned they are shorted or not. I'd wager your testing is not done at full current, but rather with a meter, and that is like tuning a race car engine at idle. You are blowing fuses, and gain variation will not cause that.
If you are blowing fuses, suspects will be: output transistors shorted. Bias string open somewhere (perhaps at the sensing diode connector). Shorted rectifier.
thanks enzo for the reply. i have read a lot of the resistors caps and transistors in the amp. so far 2 1n 4003 diodes are bad and two of the four lay down transistors. i have 1n4005 diodes i will put in. i cant see any of the transistors for sale. is there substitutes for them. there was also a orange disc capacitor not soldered. i will test the rest tomorrow.
I am not where I can post at the moment, but google "Peavey semiconductor cross reference" or "peavey semiconductor guide". Many places will have it for download.
Here is the Cross Ref sheet.
The last few Peaveys of this vintage that I've seen had either shorted or open main filter capacitors.
i changed the four lay down transistors three has heat sinks. are they the power transistors. i also changed the four large diodes. the amp works now. i cant get reverb now. when i got the amp and it worked for half an hour reverb was working. thanks everyone for your help.
does reverb work using the reverb knob or do you need a foot pedal.