Can the panel lights rheostat be cleaned or replaced?

[AndreiC]

When I got my 1970 M20E half of my panel lights did not work. 1.2AMU later (ouch!) the avionics shop diagnosed a short in the lines going to the compass light which was making one of the two small, expensive fuses in the dimmer box blow up. I now have that fixed (and am well poorer for it).

But the pot/rheostat that controls the dimmer is now very unreliable. At full intensity it works well, and also when shut off, but anything in between it is hit or miss; half the time it flickers brighter or lower. Plus, the first 2/3 of the scale is kind of unusable, it is completely dark. Only the last 1/3 does something.

I suspect the pot is dirty. Is there a way to clean it? If not, is it possible to replace just the pot, and does anyone know what part I need? I don't want to go back to the avionics shop for fear of another AMU-scale charge. I know one can switch to a MaxDim rheostat and get rid of the dimmer box completely, but I was going to try first some easier fixes if there are some.

Any suggestions will be appreciated. Thanks.

 

Edited December 1, 2023 by Andrei Caldararu

[LANCECASPER]

15 minutes ago, Andrei Caldararu said:

But the pot/rheostat that controls the dimmer is now very unreliable. At full intensity it works well, and also when shut off, but anything in between it is hit or miss; half the time it flickers brighter or lower. Plus, the first 2/3 of the scale is kind of unusable, it is completely dark. Only the last 1/3 does something.

Are there any LEDs anywhere in the circuit?

[Rwsavory]

You can clean it with Deoxit contact cleaner.

[cliffy]

Yes try some contact cleaner in it and rotate it a few times  

Let the CC dry for a while before you turn on power

 

[Marc_B]

Not sure if these are fairly consistent among Mooneys...but my IPC has SEVERAL numbers listed for the parts for light control box.  Searching IS1N056P251MA looks like a BAS and eBay may have a used replacement.  However the same PN shows "units/assy 2" so I believe both rheostats are the same and it seems like the other PNs can be used as an alternate.  You should easily (and cheaply) be able to find RV4NAYSD502A (which is a 5K ohm linear potentiometer) from several sources.  I'm not quite sure what the differences are between the PNs listed as alternates...

[N201MKTurbo]

I have one of those light controllers that I don’t use anymore. I could make you a good deal on it.

[jamesm]

My 67C had big clunky rheostat in the overhead position. a bit pricey but I re-wired most of my internal lighting it now has a mixture of both LED and incandescent lights on one dimmer circuit. The 2nd dimmer circuit  controls the Engine Monitor and Avionics background lighting. They use PWM  (pulse width modulation) for dimming much lighter and looks much simpler than later model Mooney's with all that extra dimming circuitry.  In My case I am not dropping all that current across the big fat rheostat.

https://seatoneng.com/wp-content/uploads/2020/07/Seaton-Eng-Brochure-2020.pdf

 Seaton Engineering's max dim unit 9100-001-B ~ $340  - $375 range

 

Hope this helps,

James '67C