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Dealing with vintage gear that uses Omeg or Radiohm pots, which are decent quality pots, I've never been a big fan of cut it off and shove in something that can be made to work. This thread is about the technique I use in restoring older gear. Certainly applies to Vox amps with their Omeg pots.
In the case of this Allen & Heath Mod 3 (next generation from their Mod 2) budget 16 x 8 x 2 recording console, a fully discrete board designed with low budget in mind. While it lacks current drive due to use of single-ended emitter follower stages all over, they did sound good for what they were, can be found and hot-rodded. That's the case for a client of mine. He's willing to roll up his shirt sleeves on this, and do the busy work, while I provide a working sample and detailed steps on how to do the tricky stuff, like removing and pulling apart a Radiohm pot, fully clean it and put it back together and then re-install it into the channel strip.
The biggest difference between the Omeg and Radiohm pot is the use of a metal wiper ring, whereas Omeg uses a deposited contact ring on their resistive wafer. On the Mod 3 channel strips, I've found some of the pots no longer work. It's due to the oxidation of the contact ring, and can be restored.
First trick is desoldering the bent-over PCB leads and carefully prying them away from the solder pads without lifting the pads. A & H's PCB vendor didn't use great material, nor did their board layout person know enough to put large pads down so it can be serviced without self-destruction during surgery.
Here, I used Techspray's Pro Wick # 4 de-solder braid (0.1" width) to carefully remove the solder from the folded-over leads of the pot. Then, using an Erem 71AE 45 deg flush cutting dikes, I set the cutter head flush with the PCB and carefully close the jaws to pry up the solder terminals while not lifting the pad. Then, with a good touch, use the same tool to pry up and partially staighten the leads so the pot comes right out, no damage to either board or pot.
Next is the dis-assembly of the pot. Here, I find that same tool perfect for lifting up the fold-over tabs of the pot cover, allowing access to the innards of the potentiometer. Steps are opening the tabs, straightening them so the bushing plate can be removed, then pull off the plastic shaft, and carefully pry open the pot by separating the resistive wafer from the cover. I use an X-Acto knife. Now, carefully remove the wafer for inspection and cleaning. Here, you can see clearly oxidation on the metal wiper ring. Not sure if it's silver plate, but on this particular pot, I had no continuity between the wiper and either end of the pot. I used a copper cleaning compound, applied with a Q-tip, worked the ring until I got shiny surface. Then, cleaned off the corrosive cleaning compound with alcohol. Before going further, I placed the wafer with it's staked-on solder terminals into a small vise and applied a little bit of force to snug down the connections, without breaking the material.
Next, I applied a light coating of Caig De-Oxit onto the resistive track and wiper ring, along with the rotary wiper/contact assembly. Then re-assembled the pot in reverse. Tricky here, as there's no registration of the shaft with regards to where the D-flat appears. Easy to put the shaft in backwards, no longer aligned with the rest of the pots, so gotta be attentive here. I slip on the metal cover, but don't close the tabs down yet. Here, I want to make sure I have a functional pot again. Having verified that with an ohmmeter, then I fold the tabs of the cover back over the bushing plate. I have found my Optima 505 series IC removal tool (for 8-pin DIP IC's) works really well for closing up pots like this. I couldn't put more than 9 images in on this post, but would be happy to add another for some of these extra details.
Sometimes I encounter pots that have been drenched over the years with contact cleaner and feel just awful when you turn them. During the dis-assembly process, I'll clean out the shaft/bushing assembly, then during re-assembly, apply mechanics Red Grease to restore the nice viscosity feel of a new pot. There's a variety of greases suitable for this, but in this particular case, the original grease was still in good shape, and I didn't have to change it.
Outcome is a restored pot that's nice and quiet, ready for more decades of use.
In the case of this Allen & Heath Mod 3 (next generation from their Mod 2) budget 16 x 8 x 2 recording console, a fully discrete board designed with low budget in mind. While it lacks current drive due to use of single-ended emitter follower stages all over, they did sound good for what they were, can be found and hot-rodded. That's the case for a client of mine. He's willing to roll up his shirt sleeves on this, and do the busy work, while I provide a working sample and detailed steps on how to do the tricky stuff, like removing and pulling apart a Radiohm pot, fully clean it and put it back together and then re-install it into the channel strip.
The biggest difference between the Omeg and Radiohm pot is the use of a metal wiper ring, whereas Omeg uses a deposited contact ring on their resistive wafer. On the Mod 3 channel strips, I've found some of the pots no longer work. It's due to the oxidation of the contact ring, and can be restored.
First trick is desoldering the bent-over PCB leads and carefully prying them away from the solder pads without lifting the pads. A & H's PCB vendor didn't use great material, nor did their board layout person know enough to put large pads down so it can be serviced without self-destruction during surgery.
Here, I used Techspray's Pro Wick # 4 de-solder braid (0.1" width) to carefully remove the solder from the folded-over leads of the pot. Then, using an Erem 71AE 45 deg flush cutting dikes, I set the cutter head flush with the PCB and carefully close the jaws to pry up the solder terminals while not lifting the pad. Then, with a good touch, use the same tool to pry up and partially staighten the leads so the pot comes right out, no damage to either board or pot.
Next is the dis-assembly of the pot. Here, I find that same tool perfect for lifting up the fold-over tabs of the pot cover, allowing access to the innards of the potentiometer. Steps are opening the tabs, straightening them so the bushing plate can be removed, then pull off the plastic shaft, and carefully pry open the pot by separating the resistive wafer from the cover. I use an X-Acto knife. Now, carefully remove the wafer for inspection and cleaning. Here, you can see clearly oxidation on the metal wiper ring. Not sure if it's silver plate, but on this particular pot, I had no continuity between the wiper and either end of the pot. I used a copper cleaning compound, applied with a Q-tip, worked the ring until I got shiny surface. Then, cleaned off the corrosive cleaning compound with alcohol. Before going further, I placed the wafer with it's staked-on solder terminals into a small vise and applied a little bit of force to snug down the connections, without breaking the material.
Next, I applied a light coating of Caig De-Oxit onto the resistive track and wiper ring, along with the rotary wiper/contact assembly. Then re-assembled the pot in reverse. Tricky here, as there's no registration of the shaft with regards to where the D-flat appears. Easy to put the shaft in backwards, no longer aligned with the rest of the pots, so gotta be attentive here. I slip on the metal cover, but don't close the tabs down yet. Here, I want to make sure I have a functional pot again. Having verified that with an ohmmeter, then I fold the tabs of the cover back over the bushing plate. I have found my Optima 505 series IC removal tool (for 8-pin DIP IC's) works really well for closing up pots like this. I couldn't put more than 9 images in on this post, but would be happy to add another for some of these extra details.
Sometimes I encounter pots that have been drenched over the years with contact cleaner and feel just awful when you turn them. During the dis-assembly process, I'll clean out the shaft/bushing assembly, then during re-assembly, apply mechanics Red Grease to restore the nice viscosity feel of a new pot. There's a variety of greases suitable for this, but in this particular case, the original grease was still in good shape, and I didn't have to change it.
Outcome is a restored pot that's nice and quiet, ready for more decades of use.