Yamaha CA-1010 amp power up/voltage issues

Discussion in 'Yamaha' started by rschweitzer, Jul 4, 2018.

  1. rschweitzer

    rschweitzer New Member

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    I have a Yamaha CA-1010 amp that was operational when I got it, powered up, produced audio although very distorted and scratchy sounding. Initially found some bad caps on the power supply. Replaced all the electrolytic’s on that board and checked all voltages and they were stable.

    The amp distortion issues appeared to be out of tolerance fuse resistors. I replaced those and the few electrolytics on those boards. I cleaned the output transistors, replaced the MICAs and added fresh heat sink compound. And this is where I made a huge mistake that I hate to admit. I inadvertently installed the outputs transistors backwards. PNP where and NPN should have been and I did this to both amps. Naturally the main B+ and B- fuses blew. Once I saw that , I retraced my steps and proceeded to check every component on the amps starting with the outputs TR318/320 and TR 319/321. Then I went backwards to TR316/306 and TR 317/308. I removed these components, then removed the pre-drivers, checked the diodes, zener, etc. Everything checked out. No opens, no shorts. Fuse resistors had already been replaced with metal films and those where checked again and are good.

    Upon power up with one amp installed, no protection relay click. Voltage checks are not good. At TP 1, I have 23 V with the output transistors installed. Removing those, I am back to 0v and the protection relay will click on. But that is expected since there is no output signal. B+ is 64 volts. It starts at 51v and climbs to 64v and this is still without the output transistors installed. B- sits at 51v.

    Without any amp connected, B+ and B- are fine at +-/55V.

    Further back, the collector of TR306 should be 2.4 V and is 55V.

    This is quite puzzling especially with components that all appear good. Problems like this are normally right up my alley. I could use a fresh set of “eyes” on this one.

    Thanks,

    Rick
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

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    Did you have a load hooked up when you first powered it up ?
     
  3. avionic

    avionic " Black Knights " Subscriber

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    First thing I'd look at. Outputs of course then emitter resistors .What are you using to test your transistors with ?
     
  4. avionic

    avionic " Black Knights " Subscriber

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    I have a hunch , one or more outputs are failing under load.Were these the OEM transistors ?
     
  5. rschweitzer

    rschweitzer New Member

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    Thank you for the reply's.

    No load when I first powered it up.

    The emitter resistors appear ok, .6 ohms in the circuit.

    I have a Fluke 115 multimeter.

    The transistors,TR 318, 320 and 319, 321, I believe are the originals that came with the unit from the mfg. They are 2SC1403B, NPN and 2SA745B, PNP. Using the diode function on the meter, the ECB junctions all test normally. No shorts between the emitter and collector junctions.

    I don't have replacements for these yet. But I think I found some NOS on Ebay.

    I do have the NTE equivalents for TR 308, 316 and 306, 317. The originals here all test good.
     
  6. rschweitzer

    rschweitzer New Member

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    Also, found some 2SC1403B and 2SA745B equivalents from another thread, ON-Semi, MJ211934 and MJ21193G.
     

     

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  7. avionic

    avionic " Black Knights " Subscriber

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    Yes they are about the only game in town nowadays.
     
  8. avionic

    avionic " Black Knights " Subscriber

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    Go with the originals for now.. I'm not much of a NTE fan.
     
    Last edited: Jul 5, 2018
  9. avionic

    avionic " Black Knights " Subscriber

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    What does the "class A" voltages look like at the same test points.Should be a steady +/- 22 vdc. ballpark.
     
  10. rschweitzer

    rschweitzer New Member

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    Class A mode, -24 and + 64. Tp2 or terminal O, is 50mv. Again, the output transistors are not installed.
     
  11. avionic

    avionic " Black Knights " Subscriber

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    + 64 volts..WTF...Need to get that +B power supply rectified first.Almost like the class A relay has a welded contact.
     
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  12. avionic

    avionic " Black Knights " Subscriber

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    Have you replaced the two largest filter caps yet ?
     
  13. rschweitzer

    rschweitzer New Member

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    Yeah. I had also checked the rectifiers D602 and 603 and they checked fine. I thought the relay was also good. But it must be bad considering the voltage being whacked.

    Will get back to you. Thanks.
     
  14. avionic

    avionic " Black Knights " Subscriber

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    Either that or a solder bridge..
     
  15. avionic

    avionic " Black Knights " Subscriber

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    Double check your installation polarity /wiring.
     
  16. rschweitzer

    rschweitzer New Member

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    Have new caps installed. 18,000, 71V. Originals appear good. Dont have my ESR meter, so cannot check.

    Wiring is good to the Amps, red B+, wht B-.
     

     

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  17. rschweitzer

    rschweitzer New Member

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    Rest of wiring, black E, purple O, orange E

    I took pictures before I touched anything. Helps when reassembling!
     
  18. avionic

    avionic " Black Knights " Subscriber

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    Are you sure that the two caps are oriented on the circuit board correctly?
     
  19. rschweitzer

    rschweitzer New Member

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    The caps, yes. I was careful to note the position of each. But I will recheck these again.
     
  20. rschweitzer

    rschweitzer New Member

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    Turns out the new 18,000 uf caps that I installed got smoked. Hence, the ridiculous voltage readings.

    Re-installed for now the originals and now back to normal. Without the output transistors, "A" is 24.1V, B+ and B-. The relay for its age looked brand new. I cleaned the contracts and tested it in and out of circuit and all is well with that.

    Thank you for leading me back even further to something I did not suspect. With no load, the voltages were fine. I could have easily applied a dummy load to the capacitors and uncovered the issue, eliminating the power amp altogether. Lesson learned!
     
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