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It had been some time since I got hoodwinked by the JCM900 and the footpedal having LED's inside. I'm going thru all the rental inventory's JCM900's doing preventative maintenance (haven't found ONE amp NOT requiring repairs or tweaks!). The one on the bench has the Front Panel Ch Switch that only works when upside down. Then, the internal latch mechanism in the switch works, but right side up, it's Momentary only. Useful function.
So, went across the street to fetch a JCM 900 Pedal. Years back, I had gone thru those pedals, where the REVERB Switch Button required the LED in series, but the CH Switch Button required the LED to be in series with a resistor, with that resistor/LED network wired ACROSS the switch in Shunt Mode. Huh? With no pedal plugged in, the TIP is Grounded via the jack's NORMAL. Plug in a pedal (or open ckt TRS Plug), you break the normal, and the voltage divider across the TIP turns on the MPS A13, which switches the M5201 Switching IC, switching to CH B, same as pushing the FP switch IN. So, to have the Pedal LED work, the Resistor (2.2k typ) in series with the LED goes across the Switch.
What I brought back were pedals with both LED's in series with the switches. Reverb works fine, Ch Switch doesn't work, but the LED lights up OPPOSITE that of the panel switch. Cute. And, the FP switch only works with the amp upside down.
Now, I only have one circuit diagram on hand for the JCM900, where it's labeled 2500, 2501, 2502, 2100 & 2101
It seemed to me I had come across some other JCM900's whose Channel Switches worked WITH the LED IN SERIES with the switch, just like that for the REVERB. But, I can't find any of those notes in my database, so might just be aging memory problems.
IS the STANDARD wiring for JCM 900 Dual Pedals HAVING LED'S (on the pedal): Reverb: LED in series with the Switch; Channel: LED with Series Resistor wiired ACROSS the Switch????
So, went across the street to fetch a JCM 900 Pedal. Years back, I had gone thru those pedals, where the REVERB Switch Button required the LED in series, but the CH Switch Button required the LED to be in series with a resistor, with that resistor/LED network wired ACROSS the switch in Shunt Mode. Huh? With no pedal plugged in, the TIP is Grounded via the jack's NORMAL. Plug in a pedal (or open ckt TRS Plug), you break the normal, and the voltage divider across the TIP turns on the MPS A13, which switches the M5201 Switching IC, switching to CH B, same as pushing the FP switch IN. So, to have the Pedal LED work, the Resistor (2.2k typ) in series with the LED goes across the Switch.
What I brought back were pedals with both LED's in series with the switches. Reverb works fine, Ch Switch doesn't work, but the LED lights up OPPOSITE that of the panel switch. Cute. And, the FP switch only works with the amp upside down.
Now, I only have one circuit diagram on hand for the JCM900, where it's labeled 2500, 2501, 2502, 2100 & 2101
It seemed to me I had come across some other JCM900's whose Channel Switches worked WITH the LED IN SERIES with the switch, just like that for the REVERB. But, I can't find any of those notes in my database, so might just be aging memory problems.
IS the STANDARD wiring for JCM 900 Dual Pedals HAVING LED'S (on the pedal): Reverb: LED in series with the Switch; Channel: LED with Series Resistor wiired ACROSS the Switch????
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