Author Topic: Selector switch on Magnavox 7909-10. How to clean?  (Read 73 times)

AlanInSitges

  • Newbie
  • *
  • Posts: 17
    • View Profile
Selector switch on Magnavox 7909-10. How to clean?
« on: August 15, 2019, 05:34:38 PM »
AKA "Series 100" tuner/preamp.

The function selector switch looks like it's completely sealed. Aside from taking the whole switch assembly apart, is there any way I'm not seeing to get some contact cleaner in there? It's a little scratchy.

Thanks.


TC Chris

  • Hero Member
  • *****
  • Posts: 2118
    • View Profile
Re: Selector switch on Magnavox 7909-10. How to clean?
« Reply #1 on: August 15, 2019, 08:27:19 PM »
There's always the option of drilling holes and squirting in some aerosol cleaner.  My '69 4-4-2 developed a noisy heater fan bearing. First I installed an inline switch so I could turn it off (it was always-on for ventilation purposes).  Then it got worse.  No way to oil the bearings.  So I drilled a little hole in the bearing retainer and squirted oil in.  Solved the problem.

If you try this, just drill carefully so the bit doesn't poke in and damage something, and maybe hold a magnet nearby while drilling to catch metal fragments.

Chris Campbell

electra225

  • Hero Member
  • *****
  • Posts: 3333
    • View Profile
Re: Selector switch on Magnavox 7909-10. How to clean?
« Reply #2 on: August 15, 2019, 10:47:18 PM »
I have never seen one that was sealed.  Could you post a picture?  Wires have to come in and out of that function switch somewhere.  Maybe you could squirt some cleaner in where the wires enter the switch. 
I don't need Google.  My wife says she knows everything.

AlanInSitges

  • Newbie
  • *
  • Posts: 17
    • View Profile
Re: Selector switch on Magnavox 7909-10. How to clean?
« Reply #3 on: August 16, 2019, 08:00:40 AM »
I have never seen one that was sealed.  Could you post a picture?  Wires have to come in and out of that function switch somewhere.  Maybe you could squirt some cleaner in where the wires enter the switch.

Yeah I have never seen anything like this one. It's similar to a wafer switch, except the wafers are made of some kind of non-phenolic plastic, and there appear to be spacer rings between each wafer that form a completely sealed unit. The wires connect to lugs that exit between the wafer and the spacer ring. Here's a photo. The piece you see on the back wafer is a plastic bearing race that rides inside the ring and provides detents. There don't seem to be any electrical contacts exposed (there is another race like the one you can see in that space between the two wafers.

I really hope I don't have to take this thing apart because it looks exactly like the kind of thing that I'll never get back together again.

electra225

  • Hero Member
  • *****
  • Posts: 3333
    • View Profile
Re: Selector switch on Magnavox 7909-10. How to clean?
« Reply #4 on: August 16, 2019, 08:28:39 AM »
That is a new one on me.  Never saw one like it.  I would not recommend taking it apart.  I don't see anywhere you can get cleaner in.  Good luck.
I don't need Google.  My wife says she knows everything.

TC Chris

  • Hero Member
  • *****
  • Posts: 2118
    • View Profile
Re: Selector switch on Magnavox 7909-10. How to clean?
« Reply #5 on: August 16, 2019, 05:03:50 PM »
I can't open the photo from the link.  Anybody have suggestions?

Chris Campbell

AlanInSitges

  • Newbie
  • *
  • Posts: 17
    • View Profile
Re: Selector switch on Magnavox 7909-10. How to clean?
« Reply #6 on: August 17, 2019, 03:41:51 AM »
Here's the photo as an attachment.


chazglenn3

  • Full Member
  • ***
  • Posts: 194
    • View Profile
Re: Selector switch on Magnavox 7909-10. How to clean?
« Reply #7 on: August 17, 2019, 08:06:06 AM »
Since it is just "a little scratchy", maybe tuning it back and forth 50-100 times will wear off whatever surface stuff is in there.
Charles
USAF Veteran

SeniorSteve

  • Full Member
  • ***
  • Posts: 163
    • View Profile
Re: Selector switch on Magnavox 7909-10. How to clean?
« Reply #8 on: August 17, 2019, 09:59:54 AM »
If you look at the switch, there is a clear plastic "shield" from the shaft to the plastic ring where the wires are connected.  The actual contacts are generally in this area, next to the white plastic ring.  If the clear plastic has any holes in it, you can spray into them and get to the contacts - capillary action is your friend here.  They aren't as sealed as you think.  Good luck with your project.

Steve

ed from Baltimore

  • Sr. Member
  • ****
  • Posts: 408
    • View Profile
Re: Selector switch on Magnavox 7909-10. How to clean?
« Reply #9 on: August 17, 2019, 08:53:25 PM »
      THAT--is one super sharp, super detailed photo !!      It looks like whoever soldered the connections at the Magnavox factory was paid by the pound--of lead solder used. and it looks like the solder had plenty of rosin in it's core.  It could be that the solder, or at least the resin, has wicked all the way to the wafer rubbing portions of the switch where the real connecting is done and where you can't see.
  If the white switch material is some kind of nylon or plastic, or non-ceramic material, the soldering iron heat may have softened the plastic to the point where the contacts have shifted out of the original position and aren't making proper contaCT any more.
     Finally, if the wire is stiff and thick and goes straight from one wafer to another, the contacts may have been bent out of alignment. The short stiff lead on the ceramic capacitor has actually cracked off some of the ceramic in the photo.  Ideally, wiring to a selector switch like this should be thin, stranded, flexible leads in a semicircular loop with only enough solder to join the wire to the far edge of the switch terminal, not so much solder as to wick up to the rivets or, in this type of switch, to the innards of the wafer.
     Same for a tube socket. A stiff thick 2-watt resistor lead going straight (no curve) to a socket pin, along with a capacitor lead straight from the same  socket pin to another tube socket pin  puts stress on the capacitor lead (with straight wiring, no loops or curves) pours tube and resistor heat into the capacitor, and keeps the socket pin from centering itself over the tube pin. Supposedly, with "little" tubes like 6EU7 and 12AX7, (not octals like 6SN7 with big bakelite bases) the stresses on the tube pin seals shortens the life of the tube, according to the Thomas Sams book available in the downloads section.

I don't know what kind of spray that will dissolve resin that has spread onto a wafer contact area at least one that isn't illegal now, like Freon. Whatever you use, blow out as much excess as you can with an air blast from a lens cleaner spray. Otherwise the dissolved resin just recoats the contact.