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Need help troubleshooting JVC KD-VR320 cassette tape deck

Discussion in 'Troubleshooting and Repair' started by mmiller176, Apr 18, 2020.

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  1. mmiller176

    mmiller176

    3
    0
    Apr 14, 2020
    Need help troubleshooting a used JVC KD-VR320 cassette tape deck that I recently purchased at an estate sale. Not sure how old it is, but I think mid 80s. When initially tested it seemed ok, but started failing soon after I stared using it on a regular basis. The right channel snaps and crackles and has very low volume, although it intermittently sounds normal. The fault is completely random, not physical or thermal, sometimes works ok on power up and fails later or the reverse. Never works normal more than a few minutes.

    On inspection I found no visual signs of board or component failures, all solder joints look ok, and no change when flexing or stressing connections or the board and there are no switches or manual controls in the play back circuit. I verified the source tape on another player and the amp and speakers with other audio sources.

    Probing and prodding around the circuit board near the termination of the wires coming from the heads I noticed that I could stimulate normal sound briefly after touching any of several component pads with my finger. Note that touching or pushing the same pads with a wooden probe had no effect so I don’t think the issue is physical. Using a metal probe I was able to isolate the effect to specific pads connecting to the C1228HA pre-amp. Touching the top of the only electrolytic cap included in the fore mentioned components also effected the sound, so I replaced the cap, but no improvement. Also, re-soldered all the fore mentioned circuit board pads.

    What does touching the pads tell me about the problem? I assume it adds some capacitance to the circuit and allows the pre-amp to return to normal operation, but does that mean I have a bad capacitor or is the amp bad? Also, I haven't been able to find a service manual or schematic for the deck if anyone has one.
     
  2. Bluejets

    Bluejets

    4,153
    879
    Oct 5, 2014
    Find the volume control and get some CRC or WD40, the can with a long applicator tube and squirt some into the volume control potentiometers.
    There is sometimes a slot where the 3 terminals come out from the inside and this is where you need to apply the liquid.
    Being a stereo unit the potentiometer would be a dual unit so both would need a drink.
    A few turns back and forth should cure it if you're lucky.

    At times, these are also installed with the terminals coming out the bottom to keep dust and grime out.

    If the potentiometer is sealed, then no option other than replacement parts.
     
  3. mmiller176

    mmiller176

    3
    0
    Apr 14, 2020
    There are no pots or mechanical switches in the cassette play back circuit. Gain is controlled on the separate JVC amp unit which has been confirmed good. The only pot is in the record circuit. But good to know that WD40 can be used on pots.
     
  4. Bluejets

    Bluejets

    4,153
    879
    Oct 5, 2014
    Short of any links or photos I downloaded this....... looks like a slider volume pot to me.

    Failing that, whatever you are using as an external amp if that is the case.
    Crystal ball all fuzzey ....o_Oo_O
     

    Attached Files:

  5. mmiller176

    mmiller176

    3
    0
    Apr 14, 2020
    That is the system in the picture. The slider and pot next to it is the volume and balance control for the record circuit.
     
  6. bertus

    bertus Moderator

    903
    324
    Nov 8, 2019
    Hello,

    @Bluejets , I would be carefull with chemicals like WD 40 and CRC.
    There might be substances in it that will dissolve plastics.
    I have had some bad experiences with the chemicals.
    At worst I have seen is that the potmeter could not be moved again.
    Also the carbon layer in the potmeter might get attacked by the solvents.
    The contact cleaner is ment to be used on relays and switch contacts, wich do not contain plastics.
    I would rather try dust-off 67 to get rid of dust.

    Bertus
     
  7. Bluejets

    Bluejets

    4,153
    879
    Oct 5, 2014
    Thanks, I'll keep that in mind.
    Hasn't been a problem in the last 40 years or so BUT as they say, never say never.:):)
     
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