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Yamaha CA-1000 repair. My first Yammy!

Discussion in 'Yamaha' started by smurfer77, Jan 29, 2017.

  1. smurfer77

    smurfer77 AK Subscriber Subscriber

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    Hi folks,

    This is my first post in the Yammy forum; I'm using found lurking over in the Exclusively Sansui forum.... but here we are :).

    Here is a pic of the unit that I recently obtained being desecrated by a Sansui brochure (my Sansui AU-777A in background).
    [​IMG]

    Okay, so the situation is that I have good sound on one channel but on the other I have nothing (well, almost nothing). I slid the unit out of the wood case (not that easy!) and then I can see someone has worked in here before. A 68ohm resistor has been replaced by two resistors adding up to 60ohm, for example. One of the TO3 socket pins was touching, but not soldered to the board. Fixed that up. Also replaced output transistors on the good channel (some old toshiba in there but previous tech put on-semi on the other side, so I tested those and matched up on both sides).

    Got no bias across that bad channel outputs and can see B+/B- are okay. Base of the output transistors is sitting at 0V. Voltages rediculous at driver transistors (some huge value sitting on the Base). The voltages coming from "S" and "C" which are meant to be 3.9V and 1.15V are something more like -30V each (just on the bad channel amp board, other board is okay).

    And now I'm off to bed and will tackle it tomorrow. I know nothing about these Yamaha units so would be very grateful to pick the brains of the resident experts and says my time and wits. I guess my plan if I don't get advice is to check out that Operation (A/AB) relay in the morning first and think about what on the front half of the main boards can pull that +ve rail down. Maybe someone has seen this before?

    Thanks in advance and it's great to say hello to the yammy fans at last!
     
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  2. avionic

    avionic " Black Knights " Subscriber

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    No you won't. The only relay is the protect relay.
     
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  3. avionic

    avionic " Black Knights " Subscriber

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    The CA-1000 uses micro-switches for class A/AB rail switching. Its actually switching power transformer taps for the DC rails.
     
    Last edited: Jan 29, 2017
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  4. avionic

    avionic " Black Knights " Subscriber

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    I wouldn't even bother with the "class A" until you get that other channel under control. A,B,C and S are the class A/AB bias switch* connections.

    * not the micro switches, but the center slide switch.
     
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  5. avionic

    avionic " Black Knights " Subscriber

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    That needs to be rectified. That 68Ω is a fusible 1/2watt I believe. . Need to check all the transistors and diodes on that assembly.
     
    Last edited: Jan 29, 2017
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  6. avionic

    avionic " Black Knights " Subscriber

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    TR604,605 and 606 are suspect.
     
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  7. smurfer77

    smurfer77 AK Subscriber Subscriber

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    Thanks for the posts Avionic. That 68 Ohm resistor that has been replaced by two resistors adding up to 60Ohm is R619 which on my schematic has 85mA written underneath it, so I will replace by a 0.5W resistor unless corrected. Also, thanks for telling me about the switch (not relay) - it sure looks like a switch on the schematic (but I had read in other threads people mistakenly talking about a relay in the CA-1000 model.)

    Following the unwanted negative DC voltages, they increase as I move from "B" (-25.5V (should be +1V !)) to other side of R616 (-26.4V), ther side of R617 (-27V) to other side of R620 (-27.5V). At that point I checked C608 (which has -50V on the other side of it) but it isn't leaking - I replaced it to double check. So then followed the increasing negative DC voltage further, hoping to find the source, to the other side of C612 and R622 (-34V) which is at the base of TR610. Checked that D602 is not leaking (and voltage drops done to -33V) going towards TR608. On the other side at TR609 I also have a negative DC votlage on the base about -15V. TR610 and TR609 do not seem to be shorted. So I'm not sure how that could be coming through from -B onthe other side of TR609/610. Okay... time to just start pulling transistors and testing. I will start from TR604 and work my way up - votlage at TR601-603 were reasonable.
     
  8. avionic

    avionic " Black Knights " Subscriber

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    Last edited: Jan 29, 2017
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  9. mbz

    mbz Super Member

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    Have you replaced TR606?
     
  10. smurfer77

    smurfer77 AK Subscriber Subscriber

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    I pulled it this morning and it tests good.
     
  11. avionic

    avionic " Black Knights " Subscriber

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    What are you using to test the transistors with ?
     
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  12. smurfer77

    smurfer77 AK Subscriber Subscriber

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    So far I only used my cheapie parts tester (the type that identifies part type, and hFE and junction voltage). I could test using the lab power supply, but according to my observations noted above (with the negative voltage creeping up in value towards TR610) I think I likely have troubles elsewhere. I have about -25 to -26 V on all pins of TR606... so I have bigger/other problems right? Let me know if you still think it's worth testing TR606 properly with lab supply (or swapping out with other channel). Off for some mountain biking but will check around TR610 tonight hopefully. Thanks for all the input.
     
  13. mbz

    mbz Super Member

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    Not sure I'd be chasing negative voltages. My question is where is the positive voltage?
    That top rail should be at +50V fed by TR704 etc.. Maybe measure voltage at B+, B- on
    power/relay board. Also check F701,4
     
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  14. mbz

    mbz Super Member

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    What about 50+, 50- on the power amp boards.
    Some confusion since power board has B+, B- which become 50+, 50- on power amp, different to B+, B-
    on power amp.

    Complete the job, also measure F702,3. In circuit will be OK.
     
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  15. avionic

    avionic " Black Knights " Subscriber

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    Would just need to check for the front end regulated +/- 50v on the inop channel. If FR701/704 were the problem neither channel would work.
     
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  16. smurfer77

    smurfer77 AK Subscriber Subscriber

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    Sorry, should have mentioned, all voltages coming into the main amp board have been checked including B+/B- and 50+/50- (which are fine). The voltages measured at the points on the rail where the bias class switch lines come in are bad, but that guess is coming from the issue on the board itself (?)

    Okay, I will start thinking the other way around, looking where the +ve voltage went instead of trying to find where the -ve voltage got in (although I guess the answer is probably the same). I'm starting to fear for PCB traces... a bit of oxidation here and there...
     
    Last edited: Jan 29, 2017

     

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  17. mbz

    mbz Super Member

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    My mistake on the B+/- 50+/-, but I'm thinking you will end up on the B- or 50- rail if you keep chasing the negative voltages.

    How can C & S be -30V or so?
    I like TR605, especially TR606, also R619.

    Have fun, back youself and learn.
     
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  18. mbz

    mbz Super Member

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    Sorry to bombard you. Can you check TR606 by measuring the voltages at E, C, B.
    This can be done by measuring at point C and at R617, each side, wrt chassie.
     
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  19. avionic

    avionic " Black Knights " Subscriber

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    TOL -- Had a CA-800 one time that was giving me weird voltages.Like this. Ended up being a real dirty normal/class A slide switch.Needed to disassemble and clean the switch.
     
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  20. avionic

    avionic " Black Knights " Subscriber

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    Another thought.If this board has a missing or lifted ground connection " E " black wires. You will get some odd readings. This board has 3 ground connections.
     

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