mesa lead/rhythm switch question.

[JimAnsell]

I've had my c+ for like 4 months, and finally went to use the R/L footswitch, and it wasn't working.
i peeked inside, and there was no 680 ohm resistor. not only was it not there, the led and jack were both clean, as if it was never installed :?: :shock:

all i had sitting around here was a 1/4 watt 680ohm resistor, so i put it in and it seems to be working fine.
stock it is a 1/2 watt resistor, so is the 1/4 watt resistor safe to use?
may be a dumb question, but i just want to make sure nothing weird happens.

 

[Allen]

I have a Mk II C that has had the '+' upgrade. Mine has the RP11A pre-amp board. Yours might be different.

That said, on mine, in back corner of my 11A board, underneath the high voltage supply board, is where the footswitch/LED power supply section is located. It consists of the input from the low tension AC tap off the power trans, which is half-wave rectified by a 1n4006, then throttled by the 680 1W resistor which feeds a 470uf/16v cap. The whole supply is regulated by a 1n5352 15v 5W zener. I believe the proper voltage on that supply should be right around 12Vdc.

Note that the 680 1W is a carbon composite resistor. I think they purposely used a carbon comp resistor so that in the case of trouble the resistor would burn rather than something else...

I know because, I recently pulled out my IIC and I think the 470uf cap (date code 1982) failed, which caused an over-current of the resistor...



Hope this helps you.

Best,

Allen