Yamaha T-80 sudden failure

Discussion in 'Tuners' started by Drum, Nov 8, 2017.

  1. Drum

    Drum AK Subscriber Subscriber

    Messages:
    195
    I was listening to my Yamaha T-80 and suddenly there was no sound. At first I thought the station had gone out but realized I had nothing on any station. I turned it off and back on and it worked for a day. Then it went out again. This time I only revived it for a few hours and then I could no longer revive it. In hind sight it had been dropping out for a second or so every few days but I kept thinking it was the station.

    The symptoms are no sound and nothing on the signal strength meter. Everything else works perfectly. The station displays normally, the buttons all light, I can change frequency. Even the test tone works. Just no sound and no signal. AM or FM.

    Any ideas?
     
    Last edited: Nov 8, 2017
  2. Aspen

    Aspen Active Member

    Messages:
    300
    Location:
    London, Ontario
    It could be the FM IC, I don't recall the number. My R-9 has done this a few times and it has always come back by itself so far, touch wood. I googled around and found that one of the chips can be faulty.
     
  3. Aspen

    Aspen Active Member

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    300
    Location:
    London, Ontario
  4. Drum

    Drum AK Subscriber Subscriber

    Messages:
    195
    Interesting, thanks. I hope it isn't a chip - assuming they are not readily available. I also have the problem on AM. Nothing displays on the signal strength meter and I have no sound. Not even hiss. Otherwise everything is working perfectly. I can manually tune, fine tune, change modes etc.

    Just took the top off and started poking around.
     
  5. Aspen

    Aspen Active Member

    Messages:
    300
    Location:
    London, Ontario
    Mine does exactly the same thing. 3 chips for sale on the bay for $17. Of course used working tuners can be found for less than $50 easily.
     
  6. Drum

    Drum AK Subscriber Subscriber

    Messages:
    195
    Good to know the chips are available and not too expensive. It does seem like the main issue with the link you provided (had a chance to read it all) was heat from the amp in class A operation. Since I have a stand alone tuner it really doesn't produce any heat to speak of. Would the chip still go bad under those circumstances?

    Right now it won't work properly at all - even when I let it rest uplugged for an hour or so. I am going to leave it unplugged overnight just to see what happens. More data is always good, and I don't relish soldering that chip.
     
  7. Punker X

    Punker X AK Subscriber Subscriber

    Messages:
    3,971
    Location:
    Panic in Detroit
    You need the service manual and check the power supply voltages. Look for poor solder joints, especially around the regulating transistors.
     
  8. Drum

    Drum AK Subscriber Subscriber

    Messages:
    195
    Been poking around under the hood. I found a large capacitor near the power supply that was held in place with that nasty brown glue from the period. It seems like this brown gunk was causing some corrosion on a nearby jumper and diode. I cleaned it off and sure enough the diode was corroded all the way through and no longer making a connection. I clearly need to fix this and hopefully it turns out to be the problem.

    I have the service manual and have found the area I am concerned with (D224 on the wiring diagram), but nowhere does it give the value for this diode. It is kind of corroded so hard to see.

    Two pictures are attached. One showing the brown stuff and corrosion and the other after I removed it - you can see how it corroded through the leg of the diode and I have it raised in the picture.
     

    Attached Files:

  9. Drum

    Drum AK Subscriber Subscriber

    Messages:
    195
    Found a different service manual with a little more info and tracked it down to a 1S1555 Diode. Now I have to order one.
     
  10. Drum

    Drum AK Subscriber Subscriber

    Messages:
    195
    A little research turned up the 1N4148 as a substitute for the not available 1S1555. The diode arrived yesterday while I was out of town. Installed it this morning along with the adjacent capacitor (just to cover all bases).

    Works like new again. $.08 for the diode that fixed the problem - I installed it first and tested to verify that it was the problem. The capacitor is a little insurance in case it had leaked a little - however when removed, it showed no signs of leaking.

    Thanks to AK for the help.

    Pic of new diode and capacitor installed.
     

    Attached Files:

    Last edited: Nov 17, 2017 at 8:59 AM
  11. Aspen

    Aspen Active Member

    Messages:
    300
    Location:
    London, Ontario
    Cool, well done.

    My R-9 definitely has some dread glue and corroded parts. I should get those addressed.
     

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