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This amp has been crazy..it would switch between channels, resoldered the connectors that the ribbon cables connect to and fixed that, it will switch with a foot switch, but not with the push/pull pot. Reverb didn't work, there is a red wire internally that connects to the board and the tab it slides on was broke off the board, fixed it and a new verb tank and reverb works on the clean channel but not the dirty channel (channel 2). The push/pull pot on channel 1 that controls the vintage channel does not work nor does the gain pot. I've been looking at a schematic a little bit and feel like pulling my hair out...any ideas? I know there is 2 op-amps that control some of these functions but I don't wanna start just changing parts.
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Is this one of those "Evil" Twins? Must be or something like it. Proper Twin Reverbs don't have op amps in them.
One of the tricky failure points in the evil ones is the connections to the LED's on the dashboard. The LED's aren't just letting you know what function is on, they are part of the switching circuit for that function. The circuit board lands develop micro cracks, no LED, no switching, or it's into mittens, big headache. Get out your bright light, magnifying glass, and pointy-est tip on the soldering iron, you may be able to get'er working.
I've had one here for years, never have gotten it to work right. After giving it a couple months 'rest' I'll go back in. One of these days. Hope you have better luck with yours.This isn't the future I signed up for. -
Is this the "Evil Twin" with blackface cosmetics or the red knob "the Twin"?Comment
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The '94 (aka "evil twin") is black knob and labelled "Twin Amp". The red knob is labelled "The Twin".
The service manual for the '94 Twin Amp can be downloaded here:
https://allpartsuk.files.wordpress.c...03/94-twin.pdfOriginally posted by Enzo
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I have one of those in my warehouse.
it is a tube amp, the op amps are used to decode the footswitch. None in the signal path.Education is what you're left with after you have forgotten what you have learned.Comment
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Please give a better description of the problems here. If the footswitch works correctly, the op amps are probably fine.Originally posted by pnut5150 View Post
Reverb works on Channel 1 only? Have you cleaned the front panel reverb/channel switch? Does it work when the switch is set for both channels?
The push/pull switches are subordinate to the footswitch. If the footswitch jack N.C. switch doesn't close, the front panel switches will not work. Did you clean the footswitch jack?
Did you check the gain pot with a meter? Check to see if the pot has mechanically come apart so that the wiper is not making good contact with the resistance track.Comment
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G1 is correct on the amp model, Enzo..so the op amps would not control whether the push/pull knobs work? 52 Bill, I do not have the original footswitch, but the one I have which is the same as my JCM900 switch will switch the channels. On the back panel on the reverb switch, I have it set to "both", and reverb is only present on channel 1. I haven't checked the footswitch jack but I will, and the gain or the volume knob for the vintage channel does not work.Comment
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Sorry if I confused. The op amps are in the channel switching circuits, and yes they do handle the pull switching. But they are not in the signal path, which means the audio does not flow through them.
If the thing will not switch from the pull switches, then first suspect is the cutout contact in the FS jack. After that, look right near that on the drawing, see the test points under FOOTSWITCH OPERATION? Go through those test points, using the pull switches and no FS. See which points are not switching voltage right.
A regular stomp switch might switch something here, but it won;t work right. You need the Fender FS. The FS circuit is on the layout page.Education is what you're left with after you have forgotten what you have learned.Comment
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Ok I'll check that out. Thank you EnzoComment
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