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Yamaha CR-450 help

Discussion in 'Yamaha' started by dneu201, Jun 23, 2018.

  1. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
    604
    I have a Yamaha CR-450 that was fully recapped and worked perfectly for about 4 months while I owned it. I sold it to my aunt to use in her shop and it only lasted 3 months until it started blowing power fuses. When I picked it up to take home and look over, I noticed my cousin had wired some extra outside speakers into it in series. The night it stopped working he had it turned up 3/4 for 3 straight hours.

    The issue it has is consistent blown power fuses upon turn on. I checked all solder joints and tested each diode directly after the transformer. Can someone recommend where I should look next?

    Thanks!
     

     

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  2. wajobu

    wajobu Boing Boom Tschak Subscriber

    I think your cousin is the problem, other than that I suspect one or all of the output transistors are fried. The best thing is to take it to a local (reliable, reputable) technician to diagnose and have fixed. Most of what's in a CR-450 can be fixed...I don't think there are any "unobtainium" components within. It's a nice little receiver, often sold with a companion Yamaha manual turntable.
     
  3. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
    604
    Lol. I agree my cousin is the problem. I called him an idiot and told him he doesn’t deserve this receiver and gave him an junky insignia to use for the time being. I have experience replacing output transistors so I will unsolder then today and check them to see if any are bad.

    Anything else I should check while looking? In the past, when I’ve seen output transistors go it blows the speaker channel fuses and not the power fuse.
     
  4. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
    604
    I just went through and performed a diode test on each output transistor; all 8 of them tested fine. Any idea what I should try next?
     
  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,696
    Location:
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    TR511,512,513 and 514 are the 4 driver transistors. These need to be checked as well.
     
  6. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,696
    Location:
    Fort Dodge, Iowa
    Which fuse(s) blow upon power on ?
     

     

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  7. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
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    Just the main power fuse next to the transformer.
     
  8. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,696
    Location:
    Fort Dodge, Iowa
    I suggest building a dimbulb tester. -- Will save you some money on fuses.
    Then remove fuses F501-504 and then check to see if the bulb dims down. Or..... see if it still blows the mains fuse.
     
  9. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
    604
    Could I do this with a variac? I have one I use with my tube amp.
     
  10. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,696
    Location:
    Fort Dodge, Iowa
    Do you have some way to visually monitor actual current flow through the variac ?
     
  11. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
    604
    Yes. It has a meter that I can see while turning up the voltage.
     

     

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  12. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,696
    Location:
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    Don't let it exceed 3 amps .
     
  13. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
    604
    Ok. Quick update on this. I’m building a dim bulb tester this weekend, but tried powering on the amp with all the speaker channel fuses pulled out. The amp still blew the power fuse.

    Would that help me narrow down that the issue is not in the amp section and probably a power section issue?
     
  14. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
    604
    I just finished building a DBT. What wattage bulb should I use? I have a ton of 60 watts but it seems most people use 100 watt.

    Thanks.
     
  15. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,696
    Location:
    Fort Dodge, Iowa
    Try the 60. After first checking D808 bridged rectifier and C808 and 807 main filter capacitors for shorted circuit.
     
  16. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
    604
    Ok. I'm running a test of the bridge rectifier now. Here are my readings:

    1. Across the two "AC/Wave" inputs: OL (switched the probes and read .456V)
    2. Across the postive output and wave input: 0v (0v after switching the probes)
    3. Across the negative output and wave input: OL (.458 after switching the probes)

    It looks like the "-" side is good but the "+" side has an open diode. Is there another part I should check? The two filter capacitors right next to the bridge rectifier are brand new. Should I suspect them to be bad that quick?
     

     

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  17. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,696
    Location:
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    Double check there polar orientation ( +....... -/+..........-)
     
  18. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,696
    Location:
    Fort Dodge, Iowa
    Check it like 4 individual diodes 1.AC1---- pos , 2. pos ---- AC2 , 3. AC1---- neg, 4. neg ---- AC2..
    of course measure the forward and reverse of each diode.
    Due to being connected directly to the power transformer you need to check it out of circuit.
     
    Last edited: Jul 8, 2018
  19. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
    604
    About to remove the 2 filter caps for testing. Should I use a resistance check on these?

    Ok. Here is what I got:
    AC1----pos - .461V
    pos----AC2 - 0V
    AC1 ----neg - .459V
    neg ---- AC2 - .461V
     
  20. dneu201

    dneu201 AK Subscriber Subscriber

    Messages:
    604
    I just ran a resistance check on both filter capacitors. They both continued steadily rising on the DMM. No OL errors or high readings in the Mega-ohms.
     

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