Nikko Gamma V issue

Discussion in 'Tuners' started by lissenup, Jan 5, 2019.

  1. lissenup

    lissenup Active Member

    Messages:
    296
    Location:
    Vancouver, B.C. Canada
    I picked up a non working Gamma V a few days ago. Opened it and noticed signs of heat and bad caps in the power supply section. Replaced all EC’s on this board as well as all caps on the IF and MPX sections.
    Now the tuner makes music and sounds wonderful - most of the time. Periodically the right channel disappears. I notice that the slightest touch by hand to the pcb brings back the channel. I thought the variable control was the culprit but after I removed that from the circuit still the same issue. I can make it happen by wiggling wires on the main board or putting slight pressure by hand on the board. I have thoroughly checked for solder, cracks, etc. All looks fine.

    Almost feels like grounding issue? Alignment issue?

    The tuner sounds really nice and I would like to make it a more dependable listen. Any comments would be appreciated. Thanks.
     

     

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  2. sregor

    sregor AK Subscriber Subscriber

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    My guess would be the relay on the output. This is a known problem on some of the preamps, so tuner my be the same. Two tests would be 1) tapping on the relay to see if the channels goes in and out, and bypassing the relay contacts. The relay (signal wise) is just before the level controls.
    Also, keep your eye out from broken connections or bad solders. Some can be very hard to detect.
     
  3. lissenup

    lissenup Active Member

    Messages:
    296
    Location:
    Vancouver, B.C. Canada
    Thanks for the suggestion but there are no relays.
    Thanks, however there are no relays in the circuit. After turn on it works fine then after 3 or 4 minutes the right channel cuts out. As soon as touch the pcb it comes back. Even the slightest touch.
     
  4. sregor

    sregor AK Subscriber Subscriber

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    Just going by the service manual https://www.hifiengine.com/manual_library/nikko/gamma-v.shtml . Schematic, parts list and layout show relay (its a reed relay, not one of the large clear cube relays seen in amps). Perhaps it was by-passed already.
     
  5. sregor

    sregor AK Subscriber Subscriber

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    The fact that it is only the right channel greatly restricts the problem. Not alignment, RF problem or power supply problem. Can only be from the MPX chip to the output.
    Scope would make it simple - need to follow the signal from the output of the MPX chip, through the LPF (low pass filters) IC 303 then relay (if present) to output level controls or fixed outputs.
     
  6. lissenup

    lissenup Active Member

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    Location:
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    Thanks. I was looking for one of the larger cube relays. I have the schematic from hifiengine but am not a real electronics guy but can quite often figure things out. Thanks for this lead.
     

     

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  7. dr*audio

    dr*audio Fish fingers and custard! Subscriber

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    Look closely at the traces on the pcb. The Panasonic caps they used leak and eat the traces. Look for discoloration on the traces and scrape off the soldermask. You'll find the copper is eaten away.
     
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  8. lissenup

    lissenup Active Member

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    296
    Location:
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    Will look into this as well if the relay is not the culprit. Really appreciate all of your comments.
     
  9. lissenup

    lissenup Active Member

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    There are a couple of suspect areas on the board that I will double and triple check. Thanks.
     
  10. lissenup

    lissenup Active Member

    Messages:
    296
    Location:
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    Well, the gremlins seemed to have worked themselves out as the Gamma V has been working just fine since I ran it for 36 hours straight. Very nice sounding tuner, a little more laid back and less fatiguing than the Luxman T-03 I have been using.
     
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  11. BeerLegs

    BeerLegs Super Member

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    I have one of these. It was part of a Nikko trio that I picked up this summer. A Alpha III amp, Beta II pre amp and the Gamma V tuner. I'll have to agree with you, it's a very nice sounding tuner. It sounds and the sensitivity is better than a Gamma II that I have. It's a keeper. Right now, I'm having Stereorehab recap it.


    PSX_20190112_120618.jpg
     
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  12. lissenup

    lissenup Active Member

    Messages:
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    Location:
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    The gremlins are back on this tuner. Last night the right channel dropped, I tapped the top of the unit, it came back, but now left channel gone. Turned off for 2 minutes, turned back on and both channels again, but after 3 or 4 minutes left channel dropped.

    This seems to point me to the relay? Is it prudent to bypass, or should I attempt to find a replacement? It is the NEC URT-103 reed relay.
     
  13. dr*audio

    dr*audio Fish fingers and custard! Subscriber

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  14. gklainer

    gklainer AK Subscriber Subscriber

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    Once you get the dropout issue fixed, if you swap out the two opamps it will sound even better.
     
  15. lissenup

    lissenup Active Member

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    Location:
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    Which opamps did you use and did you have to modify any circuits to use them?
     
  16. gklainer

    gklainer AK Subscriber Subscriber

    Messages:
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    Location:
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    I would put sockets in place of the op amps first so you can plug different opamps in and out like tube rolling. That way you can try a few different to see which you may prefer.

    Socket link on digikey: https://www.digikey.com/product-detail/en/assmann-wsw-components/A-08-LC-TT/AE9986-ND/821740

    Opamps I would recommend you try - OPA2134, OPA627, AD8610, AD8620. The OPA627 is very popular among audio enthusiasts.
     

     

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  17. lissenup

    lissenup Active Member

    Messages:
    296
    Location:
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    I bypassed the coil switches by simply soldering a couple of jumpers on the back of the board with the relay still in place. Is this method OK? As expected I get a slight thump on power on/off, but all works.
     

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