1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Earlly (ca 1971-74) Fisher Quad Receivers--share what you love/know about 'em!

Discussion in 'Fisher' started by illinoisteve, Oct 7, 2014.

  1. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,895
    Location:
    Glen Burnie Md.
    1st thing I'd do is make sure the Switches and pots on the front panel and on the back panel (if it has them on back) are cleaned with DeOxit D-5 then lubed with DeOxit F5 Faderlube. 2nd, make sure the POWER SUPPLY is putting out the correct voltages per the schematic. Then after determining that the voltages are ok (either the board is ok, or it needs work) check voltages on the Tuner board(s). Repair all problems. Then do a recap of the whole thing, as the casp are way past their life cycle time (about 20 years ). Repairs could be as simple as a transistor or 3, or some caps. In any event repair the problems and then update/upgrade all electrolytic caps and some of the film caps.

    Manual is at HIFIENGINE.COM . Registration is required but free. Link to manual https://www.hifiengine.com/manual_library/fisher/495.shtml
     

     

    Please register to disable this ad.

  2. MJ1951

    MJ1951 New Member

    Messages:
    7
    Thanks for the reply. I printed the manual from hifiengine and will do the DeOxit cleaning again.
     
  3. MJ1951

    MJ1951 New Member

    Messages:
    7
    OK - Checked the power supply voltages and other test points and they are in the ball park. Replaced all of the electrolytics as recommended (maybe just for the adventure of it as it turns out).
    It looks like the real the problem may be an op amp on the tuner board. The chip acts as the FM stereo channel splitter and "stereo beacon" indicator. The "stereo beacon" pin is not pulling to ground to turn on the light. There is 12 volts on the other side of the lamp so this side would have to be pulled to ground. And the FM audio is low as though the chip should be providing some amplification.
    I cannot find a spec sheet for the IC. The IC is identified on the schematic as "Integrated Circuit, MPX, HA1115W". Does it sound likely that the IC has gone bad? Anyone know what could be used as a substitution?
     
  4. fred soop

    fred soop Super Member

    Messages:
    2,033
    That IC part number is most likely a "house number". There were several chips in common use, so you might look at several and try to determine if the connections to the various pins make sense. For example, maybe pins 4-5 are audio out on one chip while pins 12-13 are audio out on another.
     
    MJ1951 likes this.
  5. MJ1951

    MJ1951 New Member

    Messages:
    7
    In searching for that part number I ran across a pdf of the 'IC Master Reference 1977'. It does list the part under Hitachi an does have a substitute TI part of SN76105N. I can't find a spec sheet for the TI part on the web either.
    There are some old Hitachi Semiconductor web pages that come up and list the HA1115W part but links under the page are broken. Sure would like to have confirmation that the chip is supposed to work the way that I think it is supposed to work.
    There is a guy on ebay that has a couple of SN76105N - may have to spend the bucks just to test my theory that this HA1115W is bad.
    Still hoping to hear that someone else has seen this problem.
     
  6. fred soop

    fred soop Super Member

    Messages:
    2,033
    Found it here. It is a typical multiplex decoder that could be replaced with LM1800, LM1870, or MC1307. Any of those might also be hard to find today but they do show up once in a while. You would need to modify the circuit board to accommodate a different pin layout. That would be most easily accomplished by making a small board, just large enough for the chip (and possibly some related parts) with short leads to connect to the original position. Of course, you would want to breadboard and test before doing a lot of detailed work.

    https://www.radiomuseum.org/tubes/tube_sn76105.html
     

     

    Please register to disable this ad.

  7. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,895
    Location:
    Glen Burnie Md.
    NTE is still showing NTE722 as a sub for the MC1307. And there is a pinout on the sheet for the 722.
     

    Attached Files:

  8. MJ1951

    MJ1951 New Member

    Messages:
    7
    Very helpful. Glad to see something about the sn76105. I may go ahead with that part. Is there much more that is available from that radiomuseum web site if i sign up on it? Gives me the feeling that it is for "click bait".

    The NTE722 is available from Amazon but it looks like the B+ is on a different pin, and it looks like it does not support the "tuning mute".
     
  9. fred soop

    fred soop Super Member

    Messages:
    2,033
    I've never signed up for RadioMuseum but have found a lot of good information without having an account.
     

Share This Page