PV Session 400 LTD...again

[Pryde]

OK interesting development maybe

Removed the preamp board and found "evidence" of a short to ground (see pic). This burn/weld mark is right below the 431 transistor (right one in the pic closest to the front of the chassis). Inspecting the solder joints showed some very mild discoloration. OK so I have the 431 out on the bench. Its a voltage regulator I believe. Cant really find a pinout for it so help me diode test it! Maybe this is it...

[Enzo]

Look at the schematic, the 430 and 431 are transistors.

The 430 is like a TIP31C or a TIP29C

The 431 is like a TIP32C or a TIP30C

[Pryde]

Thanks Enzo.
So the TIP32C or TIP30C is a drop-in option for the 431?
Both are avail at mouser for cheap but can't find any 431's

[Enzo]

431 is a Peavey house number. The TIP31C and TIP32C subs are straight from the PV crossreference.

Test them first.

[Pryde]

Wow what a journey with this one. Problem fixed!

After removing and testing the 430/431 transistors they checked fine. I then re-aligned the preamp board to sight the exact burn mark and it was directly in line with the 431's heat sink bolt

I dremeled off both bolts and added foam under the board to isolate them from the chassis. Fired it up and bingo, stable voltage!

Tomorrow I will crank the amp and see if I get that high volume distortion. My theory is the vibration was causing that bolt to just touch the chassis and short out. Seam plausible?

Anyway thanks to EVERYONE for the help and education. I will report the results tomorrow and I hope to close this case

[Enzo]

And next time, run the screw in from the bottom, so the excess length and the nut are up top instead of underneath. Those slot head screws are not originals, I think.

[Jazz P Bass]

They are usually mounted with a pop rivet, are they not?

[Enzo]

Nah, Peavey likes 4-40 machine screws with little phillips heads.

[Pryde]

Apparently I have a new problem. going to start another thread...