# PB6 repaired



## drdonh (Aug 8, 2008)

hi

Thought I would share my experience in fixing my potentiometer.

Earlier I reported how my EV was suffering from erratic acceleration. I opened up the potentiometer, and found that the wipers had spread silver compound (the stuff that shorts out the inactive part resistor) along the surface of the active part of the resistor. My first picture tries to show this, but sorry, it is out of focus. I cleaned it up with methanol (the second picture), so it is black again, and put it back together.

What a difference. The ride is so smooth again. I hadn't realized how bad the situation was. Anyways, perhaps doing this will be part of my regular maintenance schedule now.

Don 
ev-a40.blogspot.com


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## Tesseract (Sep 27, 2008)

drdonh said:


> Earlier I reported how my EV was suffering from erratic acceleration. I opened up the potentiometer, and found that the wipers had spread silver compound (the stuff that shorts out the inactive part resistor) along the surface of the active part of the resistor....


The silver compound used to short out the unused portion of the pot looks like the same stuff for repairing broken tracks on pc boards... a conductive silver-bearing ink. I'd think you'd have to re-apply it to the spots where it wore off, and not just clean up the residue from getting smeared across the active portion of the pot, but you can't argue with results if what you did worked.

That said, how long did it take you to repair your PB-6 (as in, yank the PB-6 out, disassemble, clean and re-assemble its pot, then reinstall the PB-6)? Anyone else contemplating doing this repair will probably want to know! I think it would be better to try to solve the core problem here, which is hack-level engineering, but if you have a controller that requires a PB-6 - like a Curtis 1231C - then you don't have much of a choice as to what to use for the throttle. Some people have reported good results using a higher value pot - e.g., 25k - so that the resistance reaches 5k around the maximum mechanical travel of ~20% (ie - if a linear 25k pot has 300 degrees of travel then 20% of that is 60 degrees and the resistance then should read 5k). 

Anyway, cool job on the repair! Save this thread if you would and report back how long the fix lasts. Every bit of info helps both the people that buy the stuff, and the people that design the stuff, make better decisions.


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## drdonh (Aug 8, 2008)

Hi Tesseract,
THe repair didn't take too long, work on the unit itself was maybe 15 minutes. Would have been easier to do on a bench, but my PB6 is hardwired in the car. Maybe I'll add connectors next time so I can take the whole unit out

There was still sufficient silver coating to have the unit read zero ohms in the rest position. I believe that is important as the controller checks for that condition and doesn't fire up otherwize. However, I can see how the coating will eventually wear away and be a problem. A solution may be to scratch the coating back to create an new edge against an unused coated area, and index up the position of the potentiometer. Probably replacement is the best option, but this is a DIY forum after all.

Don


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## CPLTECH (Sep 14, 2007)

Because of my previous experience as a TV-Radio-Audio tech, I question how long that repair will last. We had people that used lighter fluid (yes!) and WD-40, but in no time at all the volume pot would become erratic again. A spray product that worked best for us but is no longer available contained silicone. Not sure what is recommended today or available, but you need something that not only cleans but also leaves a protective film to slow down oxidation (contamination) for a lasting repair. You can be sure there was originally a protective film that the pot had on it.


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