Brief synopsis of my past history with my AFM:
1) Purchased car in late 2014; measured resistance on board; turned out many dead spots during sweep of arm. Per some videos on youtube, I bent arm to make contact with new parts of reostat board. The resistance measurements seemed to now not have any dead spots.
2) about 1.5 yrs later, started to get some funky starting issue; idle would waver(drop to 400-500) when coming to a stop right after deceleration. I checked everything out; the last thing I checked was resistance on reostat board.. Turns out many dead spots again. Even when I would manually press down on the copper loop contact, it still remained dead.
I took sweep arm off and just checked resistance of the the black surface. Seemed like most of the black surface had very bad conductivity; many dead spots. Not sure why so bad; though one thought was the "deoxy spray" I used a few years back on this surface might have been a bad idea. Also, there seemed to be new worn tracks; so maybe when I bent sweep arm, there was too much pressure which caused accelerated wear. (I did have an extra AFM which seemed to correct most of these problems. But in the spirit of passing on wisdom on te board, I decided to see what I could do to fix problem). My conclusion I needed a new contact resistance surface or new board.
I did a search (even going to web page of company that made board). Nobody selling (or making ) replacement boards. I then decided I would try to recoat the black part of board.
I went on Amazon and found some conductive paint : look up "Bare Conductive Electric Paint Pen 10ml ".
I masked off the sweep area of reostat board; I then applied 3 layers of paint. Each time I would apply, and gently wipe off excess. Let it dry 15-30 minutes; and repeat.
I let whole thing dry another 24 hrs.
I re-applied the sweep arm using the least pressure to assure contact throughout entire sweep. And Eureka!!!!
This time I test voltage. Very "linear" and smooth ad even; no negative fluctuations when going from rest to full sweep.
The only two question:
1) Does it actually work in car (I don't see why not); but can't test because lots of rain over last few days
2) How long will paint last before developing dead spots? One advantage of the three layers is that the paint layer has a "thickness" which might lead to more conductive contact area when the tiny contact projection starts carving into paint. The sides of projection should make contact. Worst case scenario: I re-adjust to have arm sweep over new part of board. If I were to do this again, instead of bending copper arm (which would affect contact pressure), I would remove board and elongate the the three mounting holes on board. This way I could just slide board to have contact arm meet new material (saw that on another AFM blog).
So the following are the photos:
Before painting: notice the wear near beginning of sweep surface....probably explains bad idle when coming to a stop
The paint: ($10 on Amazon)
Masking off of sweep part of reostat board:
Applied bead of paint before wiping (a layer had already been previously applied, wiped , and dried)
Finished with tape mask removed:
