Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Amplifier Discussion => Topic started by: plen on August 06, 2020, 06:55:55 PM

Title: peavey musician series 400
Post by: plen on August 06, 2020, 06:55:55 PM
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.
Title: Re: peavey musician series 400
Post by: Enzo on August 06, 2020, 09:29:19 PM
BLows fuses?  Start at the start.  DISCONNECT any speaker, if it still blows fuses, then check for shorted output transistors.
Title: Re: peavey musician series 400
Post by: joecool85 on August 07, 2020, 08:58:16 PM
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
Title: Re: peavey musician series 400
Post by: Jazz P Bass on August 08, 2020, 01:09:50 AM
!!!"  DISCONNECT any speaker"!!!
Title: Re: peavey musician series 400
Post by: plen on November 18, 2020, 05:58:56 PM
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.
Title: Re: peavey musician series 400
Post by: Enzo on November 18, 2020, 09:02:26 PM
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.

Title: Re: peavey musician series 400
Post by: plen on November 20, 2020, 09:04:19 PM
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.
Title: Re: peavey musician series 400
Post by: Enzo on November 20, 2020, 10:47:38 PM
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.
Title: Re: peavey musician series 400
Post by: Jazz P Bass on November 21, 2020, 11:59:23 AM
Here is the Cross Ref sheet.
Title: Re: peavey musician series 400
Post by: dmeek on November 22, 2020, 03:23:29 PM
The last few Peaveys of this vintage that I've seen had either shorted or open main filter capacitors.