Peavey Stereo Chorus 2x12 footswitch killing +15v

[drewl]

After fixing this amp and re-working the footswitch connector, it came back with Q4 blown, the channel switching transistor.

I fixed that, tested it for days and it was fine.
Then it came back with Q4 blown again, and the +15v regulator Q17 bad.

I don't know if the owner is jamming the footswitch connector in wrong or wtf is going on.
The footswitch and cable are good, I tested it and the amp for several hours and days, moving the cable around etc.

Something odd is if you look at Q4, the emitter is grounded.
If this footswitch schematic from Peavey is correct, then footswitch jack ground (pin 4/shield) is tied to pin 3, the common for the footswitch, which would ground the base of Q4
Unless they're using Q4 as a diode?

[g1]

I would not trust that footswitch schematic to match this particular amp schem. version unless you have verified it correct.

[drewl]

I agree, however that's the way it was wired and it won't switch to clean mode unless the shield pin 4 is tied to the ground pin 3.
Everything is functioning properly.

I'll have to see how much current is going though Q4.

I replaced the footswitch plug and wired it all up nice with shrink wrap over the pins so nothing shorts.

[g1]

Then there must be some error in the schematic? No way that Q4 can turn on if pins 3 and 4 of connector are shorted together (with pin4 going to ground).

[g1]

Also, schematic shows 9 pin jack, FS shows 7.

[drewl]

Right?
But that's the way it's wired and the board is the same as the schematic.

Even the older model is the same, I'll post the schematic for that.

It's a 7 pin plug, Jack has 8, pin 8 would be a center pin and 9 the case ground like a standard MIDI jack, but pins 8 and 9 aren't used.

[Helmholtz]

Q4 is on when pin3 is floating and off when pin 3 is connected to ground.
What is the collector voltage of Q4? Does it change with switching?
Does the footswitch work as intended?
Is there a schematic of the switch internals?

[drewl]

Ugh, the damn power pin 3 of the footswitch plug broke, like not the solder connection, like the pin broke , snapped in half.
So I had to make up a whole new plug

I think I'm going to have to replace the pc board mounted footswitch jack, it's a little buggered up and old, wonder if it is failing.

Anyway, Q4 collector voltage floats around .3v until the Clean Bypass is switched on, then it goes up to +15v.
If I can find the voltage feed R62, 22ohm, I think I'll put a mini fuse in line with it, so if there is a short in the footswitch, cable or jack in the future it won't kill Q4 or the +15v supply.

As far as the footswitch and a schematic, it's just like the block diagram I linked except there are four 1K, 2W power resistors for the voltage feeds to the LED's on the resistor board and an extra LED so there is one for Lead and one for Crunch.

Note: The front panel channel switch (Pull Channel VR1B) must be on (In) for the footswitch to operate the channel switching.

Now, where is that DIN jack.....gotta' be around here somewhere....

[g1]

Right?
Even the older model is the same, I'll post the schematic for that.

The similar Studio Chorus 210 has a transistor in position like Q4, but does not show the pins 3&4 bridged in the footswitch.