JCM2000 TSL100...what does this mean?

[acorkos]

Very low output. Swapped tubes, no difference. Cleaned FX loop jacks, jumpered them, too...no difference. Tried all the speaker jacks and impedence settings...no change. Effects send into another amp shows me the preamp is working normally. Guitar plugged into effects return = low/no output

All voltages present and correct on pins 3/4/5 of the power tubes, and on pins 1/6 of the 12AX7s.

Items of interest:
!R21 (100R) on the output jack PCB is a little scorched.
!!R6 and R9 (1R) coming off the power tubes measure 70K ohms in circuit, and R9 is burned/cracked in a small place on the resistor body.
!!!!!!!!!DC voltage measurement on the bias pins are around 18 volts per side...these usually meter around 80-90mV...what's up with this?

Thanks for your help!

Main Schematic

Output Jack PCB Schematic

[Mark Black]

Sounds like one or more power tubes had a problem, leading to overcurrent or overvoltage on the 1R cathode resistors and burning them open (or partially so).

When measuring at the bias test points you are actually measuring across those resistors so a high or open resistance would lead to the high kind of voltage readings you got. High resistance on those would also account for the low/no-output.

[acorkos]

replaced r6, r9 and r21, and with a new set of power tubes, it's rockin' again....thx!

[Mark Black]

Glad to hear it!

I forgot to address the R21 issue - it is in the +24VDC supply to the footswitch jack, so may point to a problem with a footswitch or its cable.