6G15 outboard reverb malfunction after a fall

[soapfoot]

Hi, this is my first post. I tried a similar post on another forum and got no real ideas, and it was suggested to me that I should've asked here instead. Hopefully I can contribute something to this community in the future in return.

My cat knocked my 1964 Fender 6G15 reverb from a height of about 5'.

Afterward, the reverb effect was much less pronounced than before... with all controls maxed, you can make out some reverb, but not a normal amount. Anything less than full-up on any one of the controls, and it's hard to make out any reverb effect at all... definitely not normal. I'm usually pretty handy, so "simple fix," I thought. I was wrong.

Here's what I've tried so far-- tell me if I've missed anything.

First, I tried 3 separate original Gibbs/Hammond tanks with the correct impedance ratio, including one known-good from a Super Reverb whose reverb was working well.

Tried at least one additional known-good tube in each position.

Swapped reverb and input/output cables.

Verified that the locking mechanism on the tank was disengaged.

Checked all voltages listed on the schematic/layout; all checked as normal

Visually inspected all connections inside unit (nothing obviously amiss).

Tested for continuity on all connections for wires that run under the eyelet board (all good).

Cleaned and re-tensioned all tube sockets.

Checked footswitch jack and tested both with footswitch engaged and disengaged.

Verified that the guitar and amp were plugged into the correct jacks.

Checked DC resistance on both windings of the OT... both seem within normal range for that transformer.

Manually crashed the pan with my hands (mounted correctly, on the front panel from four springs). When I did this, I got a normal-seeming amount of "KERRRANGGG!!!", suggesting that the fault is probably somewhere on the input side.

...

At this point, I'm not sure what else to check for. Any ideas/thoughts are appreciated, including anything that might help me further narrow down the area of the problem. I'm not really used to something happening with a Fender amp-like product that I can't diagnose and fix myself, but this one really has me stumped.

Thanks everyone,

--brad

[Firestorm]

Check the pots. A fall can knock the wiper out of kilter or allow dirt to wedge between the wiper and track. You just short the wiper terminal to the input terminal to bypass the pot and see if there's an improvement. Also check the bypass caps' leads and solder points. A bad connection there won't affect your DC voltages but will alter the AC gain.

[soapfoot]

Thanks for the helpful suggestions Firestorm.

RE: the pots...

I'll do as you suggest, but I did measure the DC resistance sweep of the pots at several points during their rotation and all seemed normal. For this reason, I'm not entirely confident that this is the problem, but it's worth double-checking anyhow.

As for the bypass caps... I will check that. They have been replaced with Sprague Atoms about 3 years ago, and all connections looked and measured solid, but I'll reflow again just in case.

[Firestorm]

The other thing to do, of course, is reflow all the solder joints, especially the ground connections to the ground buss at the front of the chassis. Some of these were probably tenuous when it left the factory (I've seen some that were cold from Day One, but the purely mechanical connection worked fine for years). I guess the other thing is to confirm the grounds on the back of the pots. Or just take your 1/2" wrench and tighten up the nuts to make sure the washers "bite."

I had an old Epiphone take a nosedive once and it sounded weird for months. Then, all of a sudden, it was fine. Hope your's is not so mysterious.

[soapfoot]

Thanks for the encouragement. I suppose at this point instead of looking for "the problem," it's time to just shore up everything and hope something nails it.