Mark IIb - Reverb and Footswtich problems

[mtjames2010]

Amp: Mark IIb
Year: 1982
Style: Blonde
EQ: None
Reverb: Not Working
Schematic: http://issuu.com/mtjames2010/docs/mkiib_schemo
Under Chassis Layout: http://issuu.com/mtjames2010/docs/mark_iib_tube_chart

Problem 1: Under Chassis Footswitch Jack seems to control a slight gain boost on both rhythm and lead channels when engaged but cannot get reverb response. I spoke with customer service who said that the jack should only control reverb and EQ, if applicable. I don't have EQ so they said it should only be a reverb control that auto engages the reverb circuit when cable is unplugged. To make things more confusing, the schematic I received from customer services shows a gain boost ft. switch, a channel ft. switch jack, and an EQ ft. switch jack but no reverb footswitch jack.

1 - Can anyone clear up this confusion an explain what controls what?
2 - Does anyone have the schematics for the Mesa Mark IIb switching pedals for me to build the switching capabilities into a custom pedal board? I know the resistances have to be correct but I'm not sure what they are.

Problem 2: Reverb not working. I did the following:
- Checked and confirmed continuity at transducers on both sides of reverb tank.
- Changed preamp tubes
- Checked and changed input/output wires and cleaned terminals and jacks at both tank and amp
- Checked for reverb with switched engaged, disengaged, and unplugged
- Tried a reverb tank from another amp

1 - Is it possible to have a reverb tank offer full continuity and not work?
2 - Any ideas on troubleshooting?

 

[Authorized Boogie]

Amp: Mark IIb
Year: 1982
Style: Blonde
EQ: None
Reverb: Not Working
Schematic: http://issuu.com/mtjames2010/docs/mkiib_schemo
Under Chassis Layout: http://issuu.com/mtjames2010/docs/mark_iib_tube_chart

Problem 1: Under Chassis Footswitch Jack seems to control a slight gain boost on both rhythm and lead channels when engaged but cannot get reverb response. I spoke with customer service who said that the jack should only control reverb and EQ, if applicable. I don't have EQ so they said it should only be a reverb control that auto engages the reverb circuit when cable is unplugged. To make things more confusing, the schematic I received from customer services shows a gain boost ft. switch, a channel ft. switch jack, and an EQ ft. switch jack but no reverb footswitch jack.

1 - Can anyone clear up this confusion an explain what controls what?
2 - Does anyone have the schematics for the Mesa Mark IIb switching pedals for me to build the switching capabilities into a custom pedal board? I know the resistances have to be correct but I'm not sure what they are.

Problem 2: Reverb not working. I did the following:
- Checked and confirmed continuity at transducers on both sides of reverb tank.
- Changed preamp tubes
- Checked and changed input/output wires and cleaned terminals and jacks at both tank and amp
- Checked for reverb with switched engaged, disengaged, and unplugged
- Tried a reverb tank from another amp

1 - Is it possible to have a reverb tank offer full continuity and not work?
2 - Any ideas on troubleshooting?

Not sure that you understood the information we discussed yesterday. In SOME Mark IIB's if there is no EQ, the FS jack under the chassis could have been wired for Reverb only, or for Reverb/Gain Boost...OR however it was requested. There were no hard and fast rules in those days...

Reverb is ON by default if there is no FS connected.

What are you reading on the tank? Should be about 200 ohms on the Output and about 1 ohm on the input.

Thanks!