Gibson GSS-100 Rogue Tremolo Module

[bobloblaws]

I have a an old solid state Gibson GSS-100 amp here with an unusual issue. It has a module (separate PCB) for tremolo/vibrato effects the output of which is which is engaged by what they called the "rock and roll" switch. In the uploaded files there is a page with the schematic for the module and on another page there is a diagram showing the connections between the modules and the RnR switch. When the switch is open the amp works normally. With a speaker connected to the output when the switch is closed it makes an extremely loud and obnoxious noise. Impossible to troubleshoot under that condition so I connected a dummy load. I discovered that the dummy load gets very hot very quickly when the switch is closed. I compared the power consumption with the meter I have connected to my variac. Under normal conditions the amp is drawing 0.73A but when the RnR switch is engaged it shoots up to 2.1A, 3 times the current draw. I'm uploading a couple of pictures showing a test signal under normal conditions and also under the fail condition. I have no idea what is happening here or what might cause this, please help.



Normal



Rogue

[J M Fahey]

Seems like the Trem module is oscillating big time.
Maybe lost its ground .
WeŽll wait for scope images to answer.

EDIT: that module is not alone floating in vacuum, please upload the full schematic, including the Preamp and Power amp.

[bobloblaws]

Seems like the Trem module is oscillating big time.
Maybe lost its ground .
WeŽll wait for scope images to answer.

EDIT: that module is not alone floating in vacuum, please upload the full schematic, including the Preamp and Power amp.

Right, i forgot to upload the two scope images, they are there now in the original post. I also added the other parts of the schematic.

[Jazz P Bass]

You changed the scope settings for each shot.

Why?

[bobloblaws]

You changed the scope settings for each shot.

Why?

I first had it displaying the regular sine wave, then when I flipped the switch the scale was such that the screen didn't really show anything meaningful, just what looked like a single random line across part of the screen. Pressing the AUTO button changed the scale so that it displayed what you see in the other picture. Here's another pic showing the same sine wave on a smaller scale after then opening the switch again.

[g1]

Ok, that makes more sense if the squared wave is also 10X more amplitude. I was scratching my head a bit why just a difference in waveshape could make such a great difference in heat at the load resistor.

When it is squaring off like that, can you reduce the signal to make it a sinewave again, or does it still stay square?

[bobloblaws]

Ok, that makes more sense if the squared wave is also 10X more amplitude. I was scratching my head a bit why just a difference in waveshape could make such a great difference in heat at the load resistor.

When it is squaring off like that, can you reduce the signal to make it a sinewave again, or does it still stay square?

The square wave is not affected even if the signal is removed. Compare these two pics. One is the the same I posted earlier with the signal applied and which appears to show up as a superimposed "squiggle" as the square wave rises from the negative portion of the cycle to zero. The other photo is with the signal removed.