EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: DAVEISGREAT on March 01, 2022, 01:27:48 am
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Attached are pictures of front and back of my AM/FM switch from my 1980s Sony Radio. Currently, I only get FM regardless of what position the switch is in. Also, noticed that switch requires more effort to move than it should.
I ohm'd out the switch: the 3 pins on left vertical row show continuity regardless of switch position. the right row is switch dependent(if in top FM position then only pins 1&2 connect, and if in lower AM position then pins 2&3 connect with no continuity to pin 1).
IS THIS SWITCH DEFECTIVE & CAN I REPAIR IT? Don't want to ruin it if not fixable, but am thinking the reason the switch requires extra effort to move is due maybe to carbon build-up or battery acid (the battery exploded and I had to clean it up). But, as title indicates, I'm an EE knob :-DD, but still enjoy repairing electronics :). No clue why it stays on FM all the time, and truthfully no clue if switch is even defective.
note: of course, the four outer pins are just posts holding the switch in place.
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before doing anything try to find a service manual, you will see if this switch is a dpdt (dual pole dual throw) sometimes i use some slight oil to lube a switch, some light grease would be better
Over time the grease can or could dry, getting harder to move the switch
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I have a simple one page schematic and it does not mention switch types. Service manual cost more than old beat up radio is worth. My uneducated guess is DPDT. I tried clean with electronics cleaner to no avail.
One video of a rocker type switch repair illustrated that repair is usually two stages. Cleaning contacts and lubing other moving parts, and of course "taking it apart"!
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Or maybe it does? I can't read a schematic(please see attached picture - can you tell from schematic if switch is good based on my ohm readings)?
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Yes it's DPDT. I had a similar problem and had to lube the switch. Eventually it failed and I replaced it.
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Answering my own question. Yes, the switch's ohm readings I took do match the detail the schematic gives on the switch. Thank you for suggesting to read schematic, for confirmation on the DPDT, & for the lubrication recommendation. Turns out switch was not the problem but, a user error - radio has two separate tuning dials for AM/FM bands that I was not aware of.
The slide-type switch of course still moves with some difficulty, and still not sure if these older slide-type switches can be "taken apart" without ruining them. Suspecting problem is battery acid got in there but don't want to "fix" if these switches are not serviceable. Has anyone had any luck repairing slider switches or "taking it apart"?
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CAUTION: If this is the first time you're attempting to take a switch apart to service it I'd give better than even odds on you making it worse!
If that's the type with two open ends, it should be possible to desolder it and bend the sides out slightly to free the Paxolin base plate. You'll find two contacts in recesses in the bottom of the slide actuator, which will probably drop out of their slots, and may even stay on the fixed contacts staked through the baseplate. Beware of the spring detent mechanism jumping out - there may be a tiny ball bearing with a spring behind it in a hole in the side of the actuator.
Nothing can be done to service the contacts other than carefully cleaning them and possibly squeezing the moving contacts slightly if wear has made them too loose on the fixed contacts. The inside of the shell can be cleaned with a mild abrasive to remove corrosion.
Use PTFE dry lube on the inside of the shell and a trace of plastic compatible non-silicone dielectric grease on the contacts and detent mechanism. Reassemble carefully, checking the baseplate is fully seated and the slider slides, before nipping up the sides to retain the baseplate.
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WOW, AMAZING! Exactly the information I was seeking and could not find anywhere else online, probably only known by a select few, one of who unsurprisingly is a genuine EE Master, and most highly decorated, honorable distinguished member of Dave's forum -- THANK YOU! :D
Yes, this one is open ended on both sides and while I have never taken one apart I feel with your excellent detailed directions I will be able to do so. Just in case though, I will not attempt it until I can locate, and purchase if necessary an exact or at least a working replacement switch. After repairing I will let you know how it went and maybe (with your blessing?) even do my first YouTube video of the process.
Beauty.