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A near-new Fender 65 RI Twin Reverb came in with Reverb leakage with it's pot fully CCW. This and other production issues I keep bumping into on the newest RI Twin Reverbs and Deluxe Reverbs is slowly making a case for adding the whole lot of them in our rental inventory to visit the shop for a thorough going-over, since at present, most of my income at CenterStaging at the moment is from doing preventative maintenance on gear that hasn't been looked at for 3 or more years.
So, I verified the condition. It was HF leakage, mostly. So, the chassis had to come out of the cabinet. Risky with current builds due to the poor adhesion of the cabinet roof foil, which the front lip of the chassis does such a great job of grabbing and peeling it back, rolling it up to halt extraction. I always slid in a thin metal plate from back to front with light shining thru the small gap so I can see what danger is lurking from the roof foil.
Got the chassis out, set it into the service cradle, and did an initial inspection, before proceeding to remove the control PCB assy. All looked in order. Removed the set-screw knobs, and proceeded to undo the 11mm hex nuts holding all the pots to the chassis. None were tight. Hmmmm........ Still, moved forward and removed the board, then removed the Reverb pot to look closer. I could have just checked the DCR of the end-resistance while it was soldered into the board, but, it's on the clock, so out it came. 0.71ohms end resistance with the pot racked fully CCW. Typical for mass-production pots like this. But still, I removed the cover, so I could make an attempt to lower it (maybe), with a hit on the swage detail of the pot terminals that mate with the wafer contact ends (done with centerpunch in a vise, and a drive pin on the terminal, quick soft blow of a small hammer, not enough to crack the material). Applied a touch of Caig DeOxit before putting the cover back on. End resistance still 0.71 ohms, which didn't surprise me.
Put the pot back onto the PCB, soldered it into place, cleaned up the flux. Then, looked at the foil pattern for the pot. The top of the pot and wiper traces run next to each other all the way down to the 3rd ribbon cable connector. The bottom of the pot ran next to the wiper, but stopped at the back end of the support bracket tab, and joined the Bass pot's support tab with a jumper. OK, it's as I suspected. The pot is getting grounded to the chassis by the mechanical force of the mounting hardware. Leave the mounting hardware loose, you get random results that keep us repairing gear working. Put the PCB back into the chassis, fumbled with the Bright Switches as usual, then after installing all the washers and mtg nuts, firmly tightened them all down.
Put the chassis back into the cabinet, secured it, powered back up to give a listen. Reverb leakage gone. Yes, I could have just tightened up the hardware upon finding it, and shorten the overall task, but what's the fun in that. With 38 relatively new Fender Twins and Deluxe Reverbs in our rental inventory at the moment (not counting the rest that have more age on them), it's things like this, along with the turn-on thumps that now have a viable reduction fix that can keep me working thru the lean times at the end of the year.
So, I verified the condition. It was HF leakage, mostly. So, the chassis had to come out of the cabinet. Risky with current builds due to the poor adhesion of the cabinet roof foil, which the front lip of the chassis does such a great job of grabbing and peeling it back, rolling it up to halt extraction. I always slid in a thin metal plate from back to front with light shining thru the small gap so I can see what danger is lurking from the roof foil.
Got the chassis out, set it into the service cradle, and did an initial inspection, before proceeding to remove the control PCB assy. All looked in order. Removed the set-screw knobs, and proceeded to undo the 11mm hex nuts holding all the pots to the chassis. None were tight. Hmmmm........ Still, moved forward and removed the board, then removed the Reverb pot to look closer. I could have just checked the DCR of the end-resistance while it was soldered into the board, but, it's on the clock, so out it came. 0.71ohms end resistance with the pot racked fully CCW. Typical for mass-production pots like this. But still, I removed the cover, so I could make an attempt to lower it (maybe), with a hit on the swage detail of the pot terminals that mate with the wafer contact ends (done with centerpunch in a vise, and a drive pin on the terminal, quick soft blow of a small hammer, not enough to crack the material). Applied a touch of Caig DeOxit before putting the cover back on. End resistance still 0.71 ohms, which didn't surprise me.
Put the pot back onto the PCB, soldered it into place, cleaned up the flux. Then, looked at the foil pattern for the pot. The top of the pot and wiper traces run next to each other all the way down to the 3rd ribbon cable connector. The bottom of the pot ran next to the wiper, but stopped at the back end of the support bracket tab, and joined the Bass pot's support tab with a jumper. OK, it's as I suspected. The pot is getting grounded to the chassis by the mechanical force of the mounting hardware. Leave the mounting hardware loose, you get random results that keep us repairing gear working. Put the PCB back into the chassis, fumbled with the Bright Switches as usual, then after installing all the washers and mtg nuts, firmly tightened them all down.
Put the chassis back into the cabinet, secured it, powered back up to give a listen. Reverb leakage gone. Yes, I could have just tightened up the hardware upon finding it, and shorten the overall task, but what's the fun in that. With 38 relatively new Fender Twins and Deluxe Reverbs in our rental inventory at the moment (not counting the rest that have more age on them), it's things like this, along with the turn-on thumps that now have a viable reduction fix that can keep me working thru the lean times at the end of the year.
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