how to clean detent switch in inductor selector on old radio? - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: January 27, 2021, 10:50:24 pm
content: So I got this ganged preselector with a few inductors on this bakelite-switch old school bread board type deal,the contacts look in generally good shape but there is a hint of green showing from a flashlight inspection.Since this is radio and not a tea kettle, what is the safest way of cleaning this up? I need to take it apart to replace to be what looks like a 75 ohm BNC connector that is dented to a nice hexagon.I don't think its plating, it looks like shiney brass.I see there is very good procedures on youtube, but they are cost sensitive.I just want to make sure this is the BEST option. I see cleaning is typically done with baking soda, salt, vinegar.I want to make sure the surface finish left behind is as good as it can be from chemical cleaning. Are there products better then the home made concoction? I understand maybe using the pure deoxit might be an option also.I am asking because I did what I thought was a good job on a bad motor spin switch, i.e. it looked polished and nice, but the contacts fused after I used it and it emitted the magic smoke. I can't prove anything but I thought maybe I did a good job cosmetically which was some how bad in an electrical sense, I thought maybe with surface finish parameters unknown to me, that lead to excessive arcing or something. Replacing this stuff would be a total pain in the ass. Granted this is just a RF receive signal level, so it should be much less sensitive.my plan after cleaning was to use deoxit grease on the whole assembly.With the motor I did not use abrasives but I thought maybe the plating was gone in the first place (this looks to be just brass), basically that it was screwed to begin with unless replating was done, but I want to make sure I can get the best/safest chemicals to ensure highest probability of success, so I don't need to become a brass smith.

author: radiolistener
author_rank: Super Contributor
timestamp: January 27, 2021, 11:55:47 pm
content: Quote from: coppercone2 on January 27, 2021, 10:50:24 pmYou can use 96% ethanol and cotton wool to clean it.Also old school rubber eraser also works good for thick oxide layer.

author: coppercone2
author_rank: Super Contributor
timestamp: January 28, 2021, 03:11:37 am
content: People seem to argue about that eraser. I bought an expensive super malleable artists eraser from an art store, then I am pretty sure I read a spit on the monitor rant after ward not to use them on RF connectors. I don't know if this is because someone got beat with an antenna after destroying a 1.1mm? connector or something. I have been scared to use it. There is like 3 grades of erasers I have used, the red pencil one, a much softer white premium one and then the dough-like one.I guess alcohol would be my first general method of cleaning this, but my hopes in this working waned when I saw the spec of green substance, I don't think its usually that good. Plus these contacts have a weird shape, it is like a half C with 2 more indents in it, so a more wavy beat up C with a place for a ball bearing's tip to line up, the geometry is such that I expect a cotton bud to get torn up on the edges. Maybe I can take a microscope picture of it when I take it out of the circuit. I think I would need to twist the cotton bud into a little 'rope' and pull it back and forth the contact in order to get any kind of scrubbing.You can imagine these contacts to almost be like a lighting bolt that is offset from the the bakalite by 1mm with a spinning disk under neath.I don't want to take it apart yet because I need to make or buy heat sink clips to put on some pieces of bare wire because I am scared it will go up into the insulation when I resolder it.I am also not sure how it comes apart, it looks like its held into place with some kind of green retaining compound, making me wary about alcohol. Like the bakalite disks have odd-shaped rivets inserted into them that are stamped with the profile of the shaft and glued into place with what I can best guess is loctite green retaining compound, if it was around in the 40's. Retaining compound for people that don't know is something you put between a shaft or loose interference fit to make it a good mechanical fit, i.e. cheaper way to do things that would normally be shrink-fit with heat or pure pressure.Also kinda worried alcohol might take that apart, with its fumes, so I was hoping for an aqueous cleaner, so I can basically put the switch in a pool sideways and rotate it after chemical cleaning is complete on each small section that could be dipped without getting the shaft wet, but I think this might also rust it.I think I can turn one of those copper alligator flat clips into a heat sink clips by hammering it around a drill blank to make a conformal copper jaw so I can desolder it to 'factory' levels of solder reliability, with out solder wicking under teflon cable insulation. I kind of think that the way I think they did this might some how be wrong because my explanation sounds really crazy.I am not beyond buying a bottle of retaining compound to re-glue it though, but I never wanted this kind of complexity. Its a ship in a bottle with working mechanisms soldered to thick RF connectors. I think it might be more complicated then doing a watch repair because of the possibly fragility.great, these aligator clips are made from some weird form of magnetic copper

author: coppercone2
author_rank: Super Contributor
timestamp: January 28, 2021, 05:48:40 am
content: Ok, I noticed you can take the bottom off (unexpected), so I was able to remove this thing easily. It turns out the part with the ball bearing is just the mechanical part, the shaft goes down to the wafers and those have nothing bad there. The green is infact retaining compound. The wafers are free on the shaft, they are supported by alot of solder suspensions from components. The contacts themselves are pretty good looking,so the plan is just to use contact cleaner and deoxit on the contacts and to ultrasonically clean the mechaincal part then grease it (I ultrasonic it, alcohol spray, I spray it down with wd40, shake it off as much as possible then add grease). Even if it breaks it could be replaced, the detents just ensure alignment. The ghetto fix would be to just put a friction fit there so it stays on the setting if that mechanism breaks, but it looks to be in good order. I do have retaining compound so if it gives out I should be able to fix it, the mechanism is pretty simple.Green retaining compound, no rust.. much better then I can see from the little opening I made at first. I was sure some of the green was tarnish but I guess they were just a tiny bit sloppy making it.Had a shoping cart ready with 100$ of swabs, oils, compounds, etc.

author: coppercone2
author_rank: Super Contributor
timestamp: January 28, 2021, 09:23:06 am
content: runs extremely smooth, no damage sustained from ultrasonic cleaning other then a few dots of glue becoming undone (wires from inductor going to posts). I will clean it up in the morning and put small dabs of Q-dope in a few places so it maintains vibration resistance.