Marshall Jcm900 reverb switching

[pontiacpete]

The reverb works without the foot switch just fine. When plugging in the foot switch, the reverb does not switch on. The cord to the pedal is making connection to the stomp switches and the switches are turning off and on. The channel switch works with and without the foot switch.
Does anyone know what could cause this issue? Thanks
Marshall_jcm900_dual_reverb_jmp52b_preamp_cd0189_iss7_03 49.pdf

[Randall]

Pretty simple circuit. All the foot switch does is ground the bottom of 330 ohm R51 thru the sleeve of the jack. I would verify by measuring between ground and the bottom of R51 with the switch plugged in. If the switch is indeed working, it should read shorted in one position, and some other high reading in the other, and stay at that reading if you remove the switch plug from the jack.

Another test is to clip lead the bottom of R51 to ground with the switch unplugged. Does it turn the reverb on/off when you connect and disconnect?

[pontiacpete]

Reverb turns off with the FS unplugged when touching R51 to ground as well as grounding the ring. But with the jack plugged in the reverb will not come one when grounding R51 or ring. I’m going to change the 1/4” plug. The weird thing is that the LED goes on/off on the FS reverb.

[pontiacpete]

Well changing the plug did nothing. Hmm.

[Enzo]

Use your mater, don't just change parts. That point you can ground to turn the reverb off, what does it measure to ground with the FS plugged in? And does clicking the stomp switch change that?

Does your FS cable have a TRS plug on its end?

[g1]

The weird thing is that the LED goes on/off on the FS reverb.

That is weird, because JCM900 footswitch doesn't have any LEDs.

[pontiacpete]

With the FS with TRS plug, plugged in it measures 9K to ground. When hitting the switch it goes to 339R.

This is a model PEDL-91003 it’s for the DSL401, VS100R etc. not the JCM900. Wrong pedal

[g1]

With the FS with TRS plug, plugged in it measures 9K to ground. When hitting the switch it goes to 339R.

If you need to make it work, you can just wire it up like a regular footswitch with no LED's.