Fender Roc Pro 1000 Combo Reverb Switching Help

[misterc57]

The reverb works until the footswitch is plugged in.

Here is how the footswitch (P/N 040513 A) is operating

Channel Select - toggles red and off (no light). Amp does channel switch,

Gain Select - toggles red and green. Amp does toggle gain mode.

Reverb - toggles red and off (no light). Reverb is off in both positions.

Schematic attached implies that all three LEDs should toggle red and green. But it has a different P/N 040515.

All of the LEDs have 3 legs. So I am thinking that the green led portion is never turning on and that is why the reverb is not turning on. Both diodes near the reverb switch test good. OL in one direction. .58 in the other.

This amp uses a speaker cable to connect the footswitch to the amp. Is the reverb being toggled to ground to keep it off? Problem at switch or at amp?

Thank you! MC


fender_roc-pro-1000_sch.pdf

[Enzo]

You are misreading the schematic. Yes, they are red/green LEDs, but on THIS model footswitch note that the green side of the reverb and channel select LEDs is wired across. It cannot light green because the wiring shorts the diode.


So the amp reverb works without the FS, but the FS cannot come out of reverb defeat.

The only thing coming to my mind right now is the plain diode in series with the reverb LED on the FS might be shorted. That could upset the voltages inside the amp.

It might be useful to monitor TP29, TP30 to see why we are stuck.

[misterc57]

Good or bad idea?

I replaced the diode in series with the reverb LED, I used a 1N4148. Nothing changed. I then ran a jumper from the switch to the 1N4148, bypassing the LED, and it is working properly now. Reverb switches on and off.

So is it a bad LED? I am okay with making the LED bypass the fix, but I am not sure if it would harm anything back at the amp itself? If it needs the extra voltage drop of the LED for some reason? Or are these voltages so negligible it is not an issue?

Thank you. MC

[Enzo]

It could be. This system works on voltage drops, and if the diode does not fall into the expected range of voltage drops, it won't work.

[misterc57]

It could be. This system works on voltage drops, and if the diode does not fall into the expected range of voltage drops, it won't work.

I see. So worse case is it does not work. I discovered that I can bypass either the LED or bypass the diode, and the reverb switching function will work. I ended up bypassing the diode so the player has a visual LED indicator.

Thank you Enzo!

[Jon Snell]

Good or bad idea?

I replaced the diode in series with the reverb LED, I used a 1N4148. Nothing changed. I then ran a jumper from the switch to the 1N4148, bypassing the LED, and it is working properly now. Reverb switches on and off.

So is it a bad LED? I am okay with making the LED bypass the fix, but I am not sure if it would harm anything back at the amp itself? If it needs the extra voltage drop of the LED for some reason? Or are these voltages so negligible it is not an issue?

Thank you. MC

U10 is like a toggle switch with a spring on or off action.
When the negative input, pin 3, exceeds the voltage of the positive input it toggles the output.
The reference voltage on pin2 is around 0.6volts. if pin 3 goes less than 0.6 the output swings negative and if the reference voltage increases above 0.6volts the output swings positive, this is the control voltage to the Reverb unit.
It could be CR41 has changed value.
No harm will come of changing values or adding diodes in the pedal. At some point it will stop working and then you must return to stock and fix the issue.
3 legged LEDs are multicolour LEDS red one side and green the other in this case.