Coliseum 300 Bass schematic?

[Euthymia]

I've got one of these on the bench right now with a burned up R11 on the preamp board. Can't make out the value.

People have sent me the operators' manual, which has a block diagram but no schematic, and the service manual for the older Coliseum Bass, but I need the service info for the early '80's Coliseum 300 Bass.

Fender has so far not been able to locate anything.

If anyone can point me in the right direction, it might save a good ol' Sunn from the wrecking ball.

[Jazz P Bass]

Sunn 300 R11

What does R11 do?
How is the circuit configured.
Maybe we can reverse engineer the value.

[Enzo]

Look closer to the top of the index page, where it says SUnn Discussion Page. That leads to a separate forum. Try posting over ther as well as here.

[loudthud]

R11 on the preamp is a 4.7K between the minus side of C6 and IC3 pin 2. Just a resistor in the compressor circuit, shouldn't be enough voltage in a +/-15V preamp to burn it up. In the power amp there is an R10 and an R12... R11 might have been from a previous revision.

[Euthymia]

Thanks, loudthud.

This amp had its +15V rail blown out somehow.

The TL072 on the input board was charred and cracked, and a couple of the 10uF/25V lytics on the preamp board were exploded.

The pass transistor and 15V zener for the 15V regulation on the main PCB were shorted as well.

Something bad happened on that 15V line!

[loudthud]

Thanks, loudthud.

This amp had its +15V rail blown out somehow.

The TL072 on the input board was charred and cracked, and a couple of the 10uF/25V lytics on the preamp board were exploded.

The pass transistor and 15V zener for the 15V regulation on the main PCB were shorted as well.

Something bad happened on that 15V line!

That makes sense. The +/- 15V regulators run pretty hot and are prone to failure. They really need heat sinks.

[Euthymia]

I've installed a 4K7 at R11, so we'll see what happens on the bulb.

I just noticed that R114 is missing from the PCB.

Don't know if it was not installed or if it melted its joints and dropped out.

Any idea on the value of R114 or if it's even supposed to be there at all?