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FDP Forum / Fender Amps: 1985 - Current / DRRI - bass control not working reverb channel

Aftermidnight

Australia

Aftermidnight
Oct 27th, 2016 03:57 PM   Edit   Profile   Print Topic   Search Topic

I purchased a used DRRI and now after sometime the bass control on the reverb channel has stopped working and volume on that channel is way down on what it should be - other channel is fine. Can I get a bit of guidance - what to check - what to eliminate - all the valves seen fine. Thanks.

Brad

willie
Contributing Member
*******

Too Near Atlanta GA

Amp Tech Emeritus
Oct 28th, 2016 04:06 PM   Edit   Profile   Print Topic   Search Topic

Could theoretically be caused by a number of things...first always check V2 or swap it with a known good tube; possible component value or solder connection failures or flaws in C8, C9, C11 or R-21 (midrange resistor to ground off of the bass control). Those are good places to start.

w

reverendrob
FDP Data Goon
Moderator

When I sin

I sin real good
Oct 29th, 2016 01:21 AM   Edit   Profile   Print Topic   Search Topic

Also, check that the fuse is correct.

All too often they're not on used amps!

It won't cause the problems you're describing, but....

Aftermidnight

Australia

Aftermidnight
Oct 29th, 2016 08:33 PM   Edit   Profile   Print Topic   Search Topic

Thanks for those suggestions. I dismantled the amp and found that C8,C9,C11 or R21 had no disconnection visable. I'm not a tech so i didn't measure anything with a multimetter or anything like that, I just had a look to see if I could see any obvious breaks. I can't tell if all the valves are ok - but I pulled them all out and they looked ok. I reassembled the amp. Here's what it's doing. Normal channel - no problem. Vibrato channel - (vibrato and reverb not engaged - foot switch not inserted) loss of volume and bass control not working - when the treble control is turned up the volume increases - its like the volume and the treble control are linked and interactive - if the volume is turned up not much increase - when the treble is increased the volume increases dramatically. Connecting the foot switch and selecting reverb / vibrato works - but the volume is still choked. Can anyone advise if this could be the V2 or is it something else?? Thanks - much appreciated

(This message was last edited by Aftermidnight at 10:34 PM, Oct 29th, 2016)

willie
Contributing Member
*******

Too Near Atlanta GA

Amp Tech Emeritus
Oct 30th, 2016 07:09 AM   Edit   Profile   Print Topic   Search Topic

Sounds very much like you have a tone stack ground issue...

w

Aftermidnight

Australia

Aftermidnight
Oct 30th, 2016 02:13 PM   Edit   Profile   Print Topic   Search Topic

Thanks Willie,

Could you expand on that diagnosis - what exactly is "a tone stack ground issue" and how do i repair it - Thanks

Brad



FDP Forum / Fender Amps: 1985 - Current / DRRI - bass control not working reverb channel




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