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CR-1000 humming from both channels

Discussion in 'Yamaha' started by sssboa, Mar 17, 2017.

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  1. mbz

    mbz Well-Known Member

    Messages:
    511
    Location:
    Melbourne, Victoria
    Also, could you measure the dc voltage at the collector of TR802. A safe measuring spot
    is probably at FR803. Also measure the dc voltage drop across TR802 collector-emitter by
    red probe on FR803 and black probe on +50 pin. This is going over old ground, but I like
    to confirm that TR is ok.
     
  2. sssboa

    sssboa Active Member

    Messages:
    328
    I think I get it. The 2 red cables I mentioned enter power supp. board at points RE then diodes D813 and D814 work as rectifier and send DC charges to filter caps through -B and +B. How do I check AC current on those 2 red cables, are they both live (they look the same)?
     
    Last edited: Mar 19, 2017
  3. sssboa

    sssboa Active Member

    Messages:
    328
    OK, I will do it when I can. U mean to measure at the leg of FR803 that is closer to TR802?
    TR802 is TIP31C now (was 2SC1061).
     
  4. zaibatsu

    zaibatsu Active Member

    Messages:
    283
    I wouldn't discount this bit of important advice from mbz, I've found this to be a common occurence after handling of boards that haven't had all solder joints re-flowed (ideally with fresh solder). It's time consuming but often the culprit, particularly if you're sure you didn't do anything wrong yourself. You only need to touch a component or board (occasionally even just move it slightly) to potentially disturb a questionable solder joint.

    I'd personally be carefully reflowing all joints in the amp first, before further troubleshooting.

     
  5. mbz

    mbz Well-Known Member

    Messages:
    511
    Location:
    Melbourne, Victoria
    Yes, that's basically correct. I would say that -B and +B are the outputs of the AC/Rectification/Filter caps process.

    These two wires are live, strickly no touch. One will act as the ACTIVE, the outher as NEUTRAL, the AC return wire. Important NEUTRAL is NOT EARTH, it is live.
    I don't see a nice way to measure the AC current (no series resistor to measure AC voltage). So you would insert an AC meter in series.

    The power supply naming is a little confusing (same as CA-1000).
    The red wires eventually supply +B and -B as in the first quote. These supply the output transistors/stage on the power amp boards. See F601, 2.

    The other 50V supply that powers the tone/filter/... boards comes from the power supply unit on the "relay board", see +50 and -50.
    Now when this supply connects to the filter board it undergoes a rename to +/-B which creates some confusion. (+/-B was a generic term
    in the valve days for the main supply). The point being, the filter board 50V?/52V?/62V? is supplied from the relay board. The AC provided
    by the 2 yellow wires, that's why the interest in measuring the AC voltage.

    Happy for others to correct me.
     
  6. sssboa

    sssboa Active Member

    Messages:
    328
    Ok.
    Ok. I have schematics in front of me. There are 3 cables coming from transformer. 1 White and 2 yellows. So how do i measure the AC voltage on them and what value should I expect?
     
  7. mbz

    mbz Well-Known Member

    Messages:
    511
    Location:
    Melbourne, Victoria
    On the POWER/relay board measure between the two yellow wires,
    orientation is not important with AC. Expect about 100Vac so use extreme care not
    to short on chassis etc... This "must" be ok but need to confirm. I am
    more interested in the dc voltage drop across the collector/emitter of the
    transistor, hopefully it's blown again. It would explain things.

    Yes, leg of FR803 that's closest to TR802. I will followup on suitability of TIP31C.
    Hopefully there is 0-5Vdc indicating the TR is toast.
     
  8. sssboa

    sssboa Active Member

    Messages:
    328
    power1.jpg
    Thx for advice. I will have to wait to middle of the week to test everything and report here.

    Meanwhile I also have one unit dead (another CR-1000), it doesn't start up, no lights on etc. I wonder if I could have killed it somehow measuring the voltages. What If I tried to measure DC voltage with multimeter set to DC but there was AC really in the point? I guess I would rather blow the multimeter than the amp? Otherwise I don't think I made a short with the pin of the probe itself. So far I measured AC in the 2 red cables going to the pcb of the dead unit, it read 74v or so, all fuses seem ok too. To measure AC in yellow cables I will have to unscrew the pcbs as access is difficult, btw what is the role of the white cable also coming from transformer next to 2 yellows?
    Will report later.

    powerboard.jpg

    .
     
  9. mbz

    mbz Well-Known Member

    Messages:
    511
    Location:
    Melbourne, Victoria
    Apologies again, I have not worked on the CR-1000.
    If it makes it easier, you can also measure the AC by placing one probe on FR801 (either side) and the other probe on FR802.
    Maybe measure the transistor first. The AC "must" be ok as it's straight from the transformer.

    The white wire is used for grounding. Hopefully you are looking at the schematic.

    I will check if you have another thread on the CR, so I can read what has been tried, however, if the amp looks dead the power supply is a good place to start.
    On Power/relay board measure dc voltage at +50, +33, -50, +12, -12
    If all +50, +33, -50 are dead then it could be an AC supply issue(yellow wires), however low probability or the rectifier D801,2 (also low prob) or failed components or bad connections
    to components. Candidates for failure are FR801,2,3,4 and the transistors. Resistors can go open, also many bad solder connections.

    You measured the AC voltage between the 2 red wires as 74V. Measure the dc voltage at the +B (orange wire) and -B(white) also on the power board.
    Expect about 50Vdc.

    If power is OK, you could try running the CR as a seperate using the PRE-OUT/MAIN-IN into another amp.
     
  10. sssboa

    sssboa Active Member

    Messages:
    328
    At FR802 it's 63V, at +50 it's 61V, drop 2.5V
    At point E3 it's approx. 0V
    AC on 2 yellow cables for relay board is 106V
    On -/+B it's -/+50V DC
     
    Last edited: Mar 23, 2017
  11. sssboa

    sssboa Active Member

    Messages:
    328
    Meanwhile in my dead CR-1000 I localized a dead fusible resistor FR803. Is it the reason for my problems or result of them?
    How do I find replacement? It's 22ohms 150mA. In Digikey I see in specs Watts not mA.
    Also so many options and some sound the same: safety, fusible, flame proof, flame retardant coating.
    Go for metal not carbon?
    I would use this occasion to buy replacements for all fusistors in my CR-1000.
    In schematics FR803 is described with symbols 1/2P 47. What does it mean?
     
    Last edited: Mar 23, 2017
  12. mbz

    mbz Well-Known Member

    Messages:
    511
    Location:
    Melbourne, Victoria
    No good, will come back to this

    E3 is an earth so expect 0V +/-

    My CA-1000 was 103Vac, 106V is fine

    The red wires from the transformer provide this, it's fine.

    The problem is clearly TR802c-e voltage drop=2.5V. This has been replaced by TIP31C, appears to be a good choice.
    This might be caused by TR801 which "drives" TR802.

    I have to assume that the orientation of TR802 is correct, interchange b-e, it wouldn't work otherwise.

    Maybe you should wait for someone more knowledgable to chime in. My next step would be to test the
    components around TR801, ie, measure resistance of R801,2,3,4 in circuit is fine. Has TR801 been replaced?
    Test TR801 with diode function of your multimeter.
     
  13. mbz

    mbz Well-Known Member

    Messages:
    511
    Location:
    Melbourne, Victoria
    Yeah, the FR's act like a fuse, so replacing the fuse does not fix the problem downstream. The FR's do age/drift so maybe it was tired. I think you have to replace it
    and closely monitor for other issues. I'm not sure what the best practice is for replacings FR's. There are Vishay CMF series and Tyco Electronics FRN series and
    Yageo FRM series. The spec's aren't great (Vishay ok?). The problem is to find a supplier in the size you want. Maybe wait for others to chime in (I'm still waiting
    for my copy of Electronics for Dummies...)
     
  14. sssboa

    sssboa Active Member

    Messages:
    328
    I replaced TR 801, 2 and 3 in one go when I had a popping/crackling problem. The problem was cured, but now don't know which one was causing it.
    TR801 (2SC1213) was replaced with KSC2383. The amp worked ok for 2 months or so.
     
  15. mbz

    mbz Well-Known Member

    Messages:
    511
    Location:
    Melbourne, Victoria
    My money would be on the 2SC1213. I'm having issues with a CA-1010 and the 2SC1213's are candidates, however they've tested OK when removed...

    Back to the problem of 62Vdc.
    TR801 looks very suspect, a near short between collector and emitter could give you the 62V you are seeing.
    Suggest testing this TR, in circuit is ok. Replace TR801 if you have a spare.
    Otherwise you need to work through R801,2,3,4 and D803,4, C804,6, the caps would be low probability.
    Some things to try,
    - resistance check R801,2,3,4, in circuit ok
    - test TR801, replace if possible
    - measure dc voltage at TR801 ecb
    - measure dc voltage at D803/R801/R803 node
     
  16. sssboa

    sssboa Active Member

    Messages:
    328
    TR801 replaced - no change
    dc at D803/R801/R803 is 52v
    resistances ok
     
  17. mbz

    mbz Well-Known Member

    Messages:
    511
    Location:
    Melbourne, Victoria
    OK, I'm stumped.
    The zeners are doing their job, the resistors are within spec.
    It "must" be either TR801 or TR802.
    Best to wait for someone else to chime in.
    Fresh eyes needed.
     
  18. mbz

    mbz Well-Known Member

    Messages:
    511
    Location:
    Melbourne, Victoria
    If I understand correctly, the CR was working OK for 2 months after replacing TR's for distortion/popping issue.
    Then the CR developed a hum. Has TR802 been replaced after the hum began. If not please do so. The
    circuit appears very simple, your measurements have ruled out the zeners and the resistors.

    Replace TR802.
     
  19. sssboa

    sssboa Active Member

    Messages:
    328
    OK, I think I will.
    TR802 was replaced 2 months ago to tackle the popping/crackling and it was a success.
    To me the strangest thing is that my both CR-1000s worked great until I started to mess with Filter Amp board and Tone Amp. The problems appeared the moment I switched on the amps after resoldering some wires there and replacing the small caps. Coincidence?
     
  20. sssboa

    sssboa Active Member

    Messages:
    328
    I found an equation Power (Watts) = Resistance (Ohms) x Current (A)^2
    Using this formula I found that most fusible resistors on power board of CR-1000 are 0.5W, e.g. 22ohms 150mA will be 22x0.15^2=0.495W so roughly 0.5W. Does it make sense?
    All resistors but 1 gave results just shy of 0.5W. One gave around 1.6W so 1.5W would be alright.
    Can this formula be used? The results were sensible that gives me hope :)
     
    Last edited: Mar 24, 2017

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