71 Fender Deluxe Reverb...Bass GONE from Vibrato Channel...?

[Pastortom]

I just had my 71 Fender Deluxe Reverb serviced to take care of some white noise...... Sounds great now, nice and quiet.....BUT, now there is ZERO bass response on the vibrato channel......LOTS of normal bass on the "normal" channel, but NONE on the other.  The pot seems to be operational; I can hear a microscopic difference when I go up and down with it, but there's just no low end on that channel........ Worked fine when I sent it out, now  nuthin'..............


What's up?

[eleventeen]

Last "unbelievable" fix for this posted on this forum was a parts board where prior servicepeople had sprayed contact cleaner or some other sort of cleaner all over and a large amount of crud had accumulated under the board or between the parts board and the insulation board underneath.


How corroded is the brass strip underneath the controls? Is the parts board warped and wombly perhaps from absorbing moisture?

[Pastortom]

It's a little warped but not too much, and he stated that he "thoroughly cleaned" the board...... Just why, I don't know.....it was nearly spotless when I sent it..........Strip looks nice.........

[eleventeen]

peruse: http://el34world.com/Forum/index.php?topic=19979.0

[Pastortom]

Very interesting.......  I'll pull the board and check it out.  Thanks for the link.

[eleventeen]

I kind of hate to tell you that is the issue, because pulling that parts board out is no simple task. Obviously it's tied into the amp with lots and lots of pretty short wires and the wiring in 70's Fenders is very goofy, for want of a better word.


If it were me, I think I would loosen the screws that hold down the parts board (think there are three) and try to pry the board up 1/2" or so. See if anything falls out. Then I'd douse the board in alcohol (try to get 91% isopropyl vs 70%...it's more expensive...but the $3 or $4  spent is a lot cheaper than dealing with unsoldering all those wires and then resoldering them) try to wet the underside of the board. See if you can get an old toothbrush (the old thin kind, not the new kind that look like fancy sneakers) and scrub the underside of the parts board. Do it outside. Maybe someone will chime in with a superior idea. Yeah, you might blow a $4 bottle of alcohol on it. Use maybe 1/4th bottle at a time and scrub 3-4 times if you can get the board up. 


I myself have never experienced this problem but I've lived in CA which is generally a pretty dry climate most of the time. But I believe these boards can deteriorate and somehow become partially conductive under the right circumstances.