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Akai GX-747 Capstan motor does not spin

Discussion in 'Tape' started by anti-doom, Aug 31, 2018.

  1. anti-doom

    anti-doom Active Member

    Messages:
    410
    Capstan motor does not spin. 87 VAC is present. Driver transistor NE-2230 which is placed on metal frame is tested good. What else I need to look for to fix this issue? Thanks.
     

     

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  2. anti-doom

    anti-doom Active Member

    Messages:
    410
    Here are the voltage I got :
    At capstan motor driver :
    + B: 0 VDC;
    + E: 0 VDC
    + C (center leg) : 75.6 VDC

    At D3 diode:
    + neg (-) : 0VDC
    + pos (+): 75VDC
    + 32 V at one (~) leg and 23V at the other (~)
    See attached image for detail.
    Please help me.
    Thanks.
     

    Attached Files:

  3. SweetVintage

    SweetVintage Member

    Messages:
    78
    Replace that transistor anyways. I always replace them whether they test good or not since they have or going to fail. I had several machines with dead motors and that X-istor tested good, replaced and Boom, worked again. just had to set the speed.
     
  4. rojoknox

    rojoknox Member

    Messages:
    94
    Location:
    Gresham OR
    Greetings from RojoLand!

    Please be advised that the transistor in question is a 2SC2336B, not "NE-2230" (that appears to be the part number for the Terminal PCB [printed circuit board]). You would likely have a very different and wrong part using the latter number, if one actually exists. 2SC2336B NPN power transistors can be found on the Dock-o'-the-'Bay but be cautious and look for reputable sellers (good luck!).

    It would be good to check voltages at terminals 64 and 66 of the capstan motor servo board, to see if they agree with your readings at the transistor or terminal board. You're getting Vcc to TR1, but it would appear there's no base voltage present (thus nothing at the emitter too). Also check the components that connect to terminal 66 — I see a 3.3k resistor (R26 or R28 — can't tell well on that schematic) and the resistor marked with a safety symbol and circled (we see only part of it in the partial schemo you posted).

    Take care,

    J. E. Knox "The Victor Freak"
     
  5. rojoknox

    rojoknox Member

    Messages:
    94
    Location:
    Gresham OR
    Greetings from RojoLand!

    OKeh, I got hold of the Akai GX-747 schemo. TR1's base signal comes from TR10 on what Akai calls the Power & Syscon PCB (!), through FR1 — a fusible resistor, which I make out to be 1000 ohms 1/4 watt (Akai P/N ER328520). Measure the DC volts from either side of FR1 to ground. Seems to me FR1 might have blown. If so, it will need replacement, obviously, and I would concur with SweetVintage on replacing TR1 as well.

    Take care,

    J. E. Knox "The Victor Freak"
     
  6. anti-doom

    anti-doom Active Member

    Messages:
    410
    Thanks a lot for the inputs. I am looking for 2SC2336B or something equivalent. I will post the results when done. Thanks.
     

     

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  7. anti-doom

    anti-doom Active Member

    Messages:
    410
    The FR1 fuse resistor is measured as 100 ohms (not 1000) and there is no voltage from either side to ground. Actually one side is 0.006 VDC and another side is 0.007 VDC. Both measured to ground. At TR10, I got 11.8v at B; 12V at E and 0.002 VDC at C (suppose to be 0.8 VDC per schematic). Any thoughts? Thanks.
     
    rojoknox likes this.
  8. SweetVintage

    SweetVintage Member

    Messages:
    78
    The MJE15032G should be a good sub, someone please correct there is something better out there.
    Mouser has them.
    I personally, wouldn't do ANY more troubleshooting on that dead capstan motor until you get that trans replaced. For me it would be an opportunity to introduce more problems that would need to be replaced. I'm 98 percent sure that will fix your capstan problem. Good Luck and be careful.
     
  9. anti-doom

    anti-doom Active Member

    Messages:
    410
    Hi Sweet,

    Thanks a lot. I will replace that transistor first and hope the capstan motor will work again.
    Thanks
     
  10. rojoknox

    rojoknox Member

    Messages:
    94
    Location:
    Gresham OR
    Greetings from RojoLand!

    That's curious about FR1. The schematic does appear to say 100 ohms rather than 1000. But the parts list shows "R FUSE ERD2FC 1/4W 1000G." I guess that's 'G' for "go figger." TR10 is a PNP transistor, 2SA733A P,Q. You might want to check, and probably replace, C17; it could well be shorted.

    Take care,

    J. E. Knox "The Victor Freak"
     
  11. SweetVintage

    SweetVintage Member

    Messages:
    78
    Only other thing I would look for is any inline rectifiers on the Sys Con board. The GX's will either use 4 diodes or a SIP type of rectifier. The SIPs I will replace as a general rule but I believe one DOES run that servo circuit. Check the schema and verify. Been a while since I was in one and again,. some versions use dif types. SIP=Replace, seen too many bad ones so new ones go in.
     

     

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  12. anti-doom

    anti-doom Active Member

    Messages:
    410
    I already ordered the driver transistor 2SC2336B. I will update the result when part arrives. Thanks.
     
    rojoknox likes this.
  13. anti-doom

    anti-doom Active Member

    Messages:
    410
    Replaced the driver transistor 2SC2336B and the capstan motor still not running. Any idea?
     
  14. anti-doom

    anti-doom Active Member

    Messages:
    410
    Capstan motor is running now. Problem was one trace that feeds 85 VAC from transformer to Syscon board was corroded. Solder a bridge there fix the issue. But another issue comes up, capstan motor runs too fast. Any idea why? Thanks. BTW, driver transistor 2SC2336B was replaced with new one.
     

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