How to Overhaul 500-C Pot

Discussion in 'Fisher' started by Vinylcafe, May 21, 2012.

  1. cc43fan

    cc43fan I'll sleep when I'm dead Subscriber

    Messages:
    1,968
    Location:
    Eastern Upstate, New York
    Thank you very much for this helpful tutorial, my volume/on/off control is working quite nicely now. :thmbsp:

    Your instructions are spot on!
     
  2. stltrains

    stltrains Active Member

    Messages:
    128
    I'm guessing that stacked tone control pots would be similar to volume pots. Have any of you rebuilt one. I have a bass stacked pot from a 400c preamp dropping volume on the right channel. Going to look into rebuilding mine tomorrow.
     
  3. yong1234

    yong1234 New Member

    Messages:
    1
    My Fisher 400 on/off switch went broken yesterday, the internal spring part does not engage, re-install the NOS is too much after reading this thread, I found the easiest fix is just to connect the black power transformer wire to the 120v input terminal strip, it works now, but do not know if there is risk with this short cut. thanks for any advice!!
     
    Last edited: Mar 29, 2013
  4. dmac

    dmac Member

    Messages:
    50
    This is a very interesting post. I have a 400 receiver and am experiencing a situation where the volume increase from 1 o'clock to 3 o'clock normally but does not increase at all when I turn it from 3 to 6 oclock. at 6 Oclock it increases again. Both channels increase or do not increase equally. I have tried Deoxit and there is no change. I have limited knowledge and expertise in such matters.

    Do any of the knowledgable folks here think that I need to rebuild (like the photo's show) or replace the POT or could this be some other issue? Any thoughts would be appreciated
     
  5. eduarsan1

    eduarsan1 Luis Eduardo Sanchez Subscriber

    Messages:
    586
    Location:
    Bogotá, Colombia
    When the volume pot is not balanced!!

    For those that have issues when detects that the volume level is not quite the same in both channels in the centralab pot used in our fisher amps this TIP will be helpfull.

    When you are overhaulling the pot you need to remove the soldering shown in the red oval in both sides of the pot, at this point I detected that when you are holding the pot#1 with one hand and the pot#2 with the other hand you can twist the pot #2 a little bit (2-3 grades aprox)
    So see the image:

    [​IMG]

    Hope this tip can helps!!

    Regards

    Luis
     
    Last edited: Apr 27, 2014
    totsuka likes this.
  6. Fisherdude

    Fisherdude Regular Dude - Super Mod Super Mod Subscriber

    Messages:
    27,601
    Location:
    Out West.
    Interesting! That would make sense...if the orientation of the two different sections where changed, meaning if they were rotated with respect to each other, it certainly could change the balance between the two.

    Thanks for the tip!
     
  7. keithpgdrb

    keithpgdrb AK Subscriber Subscriber

    Messages:
    2,294
    Location:
    Bolingbrook, IL
    interesting indeed. I had my volume pot rebuilt, and the problem is still there. I wasn't real thrilled about spending that bread. may try this trick.
     
  8. Danimal1969

    Danimal1969 AK Subscriber Subscriber

    Messages:
    1,110
    After removing the 2 solder blobs and breaking the seal, does the switch portion pop off? Or do I have to remove the entire section of wiring attached to it when I pull the pot?

    Also, has anybody considered using a dremel tool cut-off wheel to slice the solder joint in half?
     
  9. eduarsan1

    eduarsan1 Luis Eduardo Sanchez Subscriber

    Messages:
    586
    Location:
    Bogotá, Colombia
    Danimal

    Use solder wick NOT a dremel, you must take patience, it takes a time to adjust them, and for fo this job remove the pot from the unit as show in the picture.

    The most critical area is between 7:00 and 9:00 so try to equalize in this area to start to have a same level in this sector .

    Regards

    Regards
     
  10. fred soop

    fred soop Super Member

    Messages:
    1,616
    I'd say YMMV. The critical area is where you typically listen. This could vary between people, speaker efficiencies, desired volume, etc.

    My 600-T on the bench with speakers borrowed from a cheap all in one is presently being run at 9:00 but if I used the inefficient, warm, Fisher XP-9 speakers, and turned it up to a slightly higher volume, I'd be at 11:00.
     
  11. Danimal1969

    Danimal1969 AK Subscriber Subscriber

    Messages:
    1,110
    Well I spent several hours tonight taking my 400 pot out and rebuilding it. These instructions were spot on, especially the part about desoldering the switch. I soldered it back on when I was done.

    The pot rotates nice and smooth now (the front support/bushing was all gummed up. I have a couple more things to check before I fire this one up, but this was something I'm glad I did.

    Thank you for this tutorial!!!
     
  12. gkargreen

    gkargreen Active Member

    Messages:
    285
    Location:
    Fairfax, VA
    Excellent work, I have rebuilt numerous pots that had gunk in them, as well as replacing bad power switches on these Fishers. Not sure about all the noise regarding the solder blobs, they are easily removed with a desoldering iron, followed with a little solder wick, if needed. They just pop right off and after the rebuild, which includes cleaning each track with IPA and then treating each track with deoxit on a qtip so as not to get that damn crap all over everything, and then I use a wipe of silicon grease to give the pots a nice smooth action, I use deoxit fader grease but they are all pretty much the same, this is used in Tek pots, and it don't get better than that! I also resolder the switch cover back on, that's called "doing it right". And glad to see that the indiscriminate use of deoxit is being called out, that shit can cause as many problems as it fixes, proper use is required not to screw things up with that evil stuff. Regards the reluctance to buy rebuilt or new pots at $60, if your time has no value, then do this procedure a couple of times and perhaps you will rethink your position, time consuming yes, but I do get paid to do this, although not enough...
     
    totsuka likes this.
  13. ZLodei

    ZLodei Member

    Messages:
    62
    Hello guys!
    I'm in the club of dead Fisher switches.
    Have anybody got NOS or used switch for Fisher X100b pot?
     
  14. gkargreen

    gkargreen Active Member

    Messages:
    285
    Location:
    Fairfax, VA
    yep
     
  15. totsuka

    totsuka New Member

    Messages:
    17
    As much as I love taking things about could I just dunk this part into an ultrasonic cleaner and see if I accomplish the same thing? What you think?
     
  16. TM1

    TM1 New Member

    Messages:
    1
    So, new guy here, but decades long Fisher owner. I have a 101X that works perfect, a 400 with a trouble-some volume pot.. and an 800 C with a constant 60Hz hum. Hum's no matter where the volume pot is.
    Anyway, will this mod to the pot work for my 400? I sprayed it out last week with some Deoxit and it is now worse than ever.. Any suggestions on the 800 C? Some electrolytics have been replaced as have the coupling caps from the Phase Inverter to the output valves. I used Sozo NexGen's! I replaced the main rectifier diodes with FRED diodes.
    Thanks!
     
  17. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    18,153
    Location:
    Glen Burnie Md.
    The Volume pot for the 400 is of similar construction, and the cleaning procedure is the same.

    Sounds like the 800c is in need of a complete rebuild of the power supply and replacement of ALL Electrolytics at minimum. Start a new thread on each of the 400 and 800c. Take pictures of the UNDERNEATH components. Closeup's of the POWER SUPPLY and OUTPUT/P.I. Sections will help with diagnostics. If you have'nt already, build a DBT (Dim bulb Tester) with a 100W bulb. Don't plug the 800c into the wall until advised to near the end of the work.
     
  18. Zepman69

    Zepman69 New Member

    Messages:
    13
    Location:
    Boston, MA
    Buying a soldering iron and such to attempt this this weekend! Hopefully this is the only issue my Fisher has.
     

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