Yamaha A-1000 Repair and Info Thread

Discussion in 'Yamaha' started by tmsears, Apr 13, 2017.

  1. Assuming that no wires have been cut/disconnected and with the power off/removed, measure the resistance (use the lowest resistance setting on your multi-meter) between 0V on the transformer secondary and the designated ZERO VOLT REFERENCE point. It should measure 0R (ZERO Ohms).
    If it measures zero Ohms, power on and measure the AC & DC voltages between both points. Again, you're looking for a ZERO - 0V (ZERO Volts).
    Anything other than ZERO (allowing for meter inaccuracies) indicates an unknown fault.

    View attachment 1002331

    View attachment 1032069

    Good Luck!
     
    Last edited: Oct 25, 2017
  2. tmsears

    tmsears Active Member

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    I got zero on the meter after accounting for inaccuracy, and the reference is zero, So I will move forward to the next step. I plan on keeping my DBT connected throughout all of this unless there is reason I shouldn't.

    EDIT: I powered the unit up in a DBT with a 100watt bulb and 0v on both AC and DC on the reference.
     
    Last edited: Oct 28, 2017
  3. tmsears

    tmsears Active Member

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    I tested all of the components inside of the triangle, and they all read identical to the corresponding components on the opposite (working) channel. This was done with the power disconnected.

    I am now moving on to the voltages. It may take me a bit to do, but when I finish i will post the results.
     
  4. tmsears

    tmsears Active Member

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    Well, here are hte measurement for all the voltages. I have them paired up as they are in the schmatic, but I tested each line anyway since I was at it:

    AC coming out of the secondaries:

    RE= 47.6V
    BL= 0v (reference)
    BE= 28.2

    DC Rail Voltages (with ac present as noted):

    HB+ 57.9Vdc and 128.2Vac
    HB- 57.9Vdc
    LB+ 34.3Vdc and 75Vac
    LB- 34.5Vdc

    DSC -30.2Vdc

    LX/LP+ 33.8Vdc and 74.3Vac
    LX/LP- 33.8Vdc
    RX/RP+ 49.7Vdc and 109.6Vac
    RX/RP- 33.9Vdc

    Now, I am not an expert by any means, but I don't think that is normal. I found it odd that D162 was spewing 128Vac straight out of the positive dc terminal..
     
    Last edited: Oct 28, 2017
  5. tmsears

    tmsears Active Member

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    Maybe @avionic or @Hamish119 can weigh in. I assume that both of the bridge rectifiers are shot? if so, can anyone suggest suitable replacements? Would I need to go ahead and replace those big diodes as well?
    Are the big caps fried now?

    I am on a limited budget as usual but shipping kills me more than anything else so a single mouser order would be the best option if possible.
     
  6. Thanks for the 'interesting' (and confusing) voltage measurements. :confused:
    Here's why they're confusing;

    The maximum AC voltage from the secondary winding on the transformer is <100V (RE - RE). That suggests the 128V AC must be coming from an external source (nothing but the bulb limiter should be connected to the amplifier).
    Or it's a 'ghost' reading. :eek:


    Furthermore, if it is from an internal source, it should be seen equally on both channels as there is only 1 x transformer, 1 x lower voltage/higher current bridge rectifier (D168 - for Class A operation), 1 x higher voltage/lower current bridge rectifier (D162 - for Class AB operation) & 1 x set of smoothing/reservoir capacitors shared between both channels. :idea:

    Can you measure the AC voltage at the smoothing/reservoir capacitors?

    However, there is a further anomaly with the plus & minus ?X/?P DC voltages. I'm assuming (dangerous) that the 'Auto Class A' switch was OFF: i.e. the amplifier was in Class AB mode. Therefore, I would expect these voltage measurements to be closer to the plus & minus HB voltages. :idea:

    Whilst on the bulb limiter/tester, measure the plus & minus ?X/?P DC voltages with the 'Auto Class A' switch ON. The measured DC voltages should be within 1 volt of the voltages measured on the 33000µF capacitors.

    Also, don't forget to measure the plus & minus 22 volt rails - they're critical to the correct operation of the amplifier.

    Good Luck!
     
  7. tmsears

    tmsears Active Member

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    Oh, trust me, if there is incompetence to be had, I will fully accept responsibility. I agree the reading is odd, which is why I tested it three times in a row...I had the amp plugged into the DBT, with a 100watt bulb. The bulb stayed dimly lit, and never wavered from that brightness the entire time. The only exception to note is that I am using a cheapy $30 multimeter from Home Depot (home improvement chain). I actually have two of them. Also, the electricity here runs a little high, at around 122V.

    I did measurements again, This time with the other multimeter and the results are the same. Tried the DBT on a different power outlet - again, the same. Checked the DBT, and it is working fine. I checked the voltages on the power outlets that are built into the amplifier and they read at about 102 volts or so, I am assuming, due to the DBT.

    Didn't know a ghost reading was a thing, but that wouldn't surprise me.

    Using the reference point, on the smaller of the smoothing caps that is closest to the main amp board one leg measure the 128Vac and the other leg measures the 75Vac. On the larger cap closest to the main amp board one leg measures the 75Vac and the other leg, which has all the ground wires connected to it, measures nothing.The others measure nothing on AC.

    Yes, the Auto class A switch was off.

    I just finished testing them. All the ?X/?P voltages drop about 1 volt when Auto A is turned on, and they are all still within 1 volt of the 33000 caps.

    Sorry about that, I took the measurements with the others before and wrote them down, but I forgot to post them. 22+ is 21.5Vdc, 47.1Vac. 22- is 14.5Vdc, with no AC present.
     
  8. Excellent work!

    Ignoring the other issues, the low -22V issue needs to be resolved first. Any voltage anomaly at the power amp input stage will be propagated to the output stage with GAIN!

    As the plus & minus HB supplies are good, check the voltage (with reference to 0V) at both ends of D604.
    You should measure -9V at the junction of D606 & D604.
    You should measure -15V at the junction of D602 & D604.

    Yamaha_A-1000_-22V.jpg

    Good Luck!
     
    Last edited: Oct 29, 2017
  9. tmsears

    tmsears Active Member

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    At the junction of D606 & D604 = -4.6Vdc
    At the junction of D604 & D602 = -9.2Vdc
     
  10. That's NOT good! :no:

    Check that the Zener diodes are the correct values: i.e. 1 x 9V1 + 2 x 6V2. The measured voltages suggest the the installed Zener diodes are 4V7. :eek: :no:
    Or it may be that resistors R759 (on Equaliser 1) & R760 (on Equaliser 14) have substantially increased in value!

    Measure the 'in circuit' resistance of R759. If it's >675R, disconnect Equaliser 14 and measure it again. It should be less than or equal to1k8.

    With Equaliser 14 disconnected, measure the 'in circuit' resistance of R760. If it's >1080R (10 x 27k in parallel = 2k7... 2k7+1k8 in parallel = 1080R). Good hunting! :whip:

    Good Luck!
     
  11. zaibatsu

    zaibatsu Active Member

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    Did you do the diode swap (re: D605, D606) I suggested in post #206?
     
  12. tmsears

    tmsears Active Member

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    Will when I get some free time, hopefully today or tomorrow.
     
  13. tmsears

    tmsears Active Member

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    Yes, yes I did. I just finished pulling up the mouser order to make sure I had ordered the ones you referenced in the post. Replaced all 6 of them
     
  14. tmsears

    tmsears Active Member

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    Here is what I removed from the equalizer 1 board, per previously mentioned post:

    IMG_20171031_020303104.jpg
    The one on the right is different from the others. I do not recall the order of where it originated from.
     
  15. tmsears

    tmsears Active Member

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    OK, I have not had the chance to take any more measurements, but I looked and I can confirm that I did install the (4) 6V NZX6V2B zener diodes in D601-D604, and the (2) 9V NZX9V1E zener diodes in D605-D606. Made sure I had not put any of them in backwards, etc. Mouser hasn't messed an order up yet so I will assume they are the correct type? Hamish's Whipping List is next up on the to-do list :biggrin:.
     
  16. tmsears

    tmsears Active Member

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    I measured R759 with the equalizer 14 at 518 Ohms. So, I disconnected it and re-measured.The resistance "climbs", slowly but surely, until it reaches 1380-14000 Ohms.
     
  17. zaibatsu

    zaibatsu Active Member

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    Yes those diodes sound correct to me, and it sounds like R759 is toast. Should be a stable value.
    Replace it and proceed with the Hamish list.
     
  18. tmsears

    tmsears Active Member

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    Probably will replace all of the power resistors, the three on the equalizer 1 board and the one on the #14 board. That was the end of @Hamish119 's list so far - I had only skimmed through it before I started, and I thought it would be more work than it was, when it really wasn't.
     
    Last edited: Nov 2, 2017
  19. tmsears

    tmsears Active Member

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    So, pardon my ignorance, but doesn't the issue of the bridge rectifiers spewing out AC on the DC outputs still need to be addressed? Or is that normal?

    I hate to try to count my eggs before they hatch, but I have limited funds so I need to make my shipping from mouser count. Any troubleshooting help to identify parts needing definite replacement would be most appreciated. I will be charged the same in shipping wither I buy 1 component or 50.
     
  20. zaibatsu

    zaibatsu Active Member

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    What's the current build state of the main cap / PSU board assembly?

    I've never seen an output failure on this amp family go back that far (especially since you caught the fault and turned it off quickly), so I actually wonder if this AC issue was pre-existing and perhaps the cause of the hum you were struggling to track down earlier.

    If the issue was created by the melt-down, your main caps should still be fine. If it was pre-existing then the caps may have seen a beating, but maybe the amp wouldn't have clicked / worked at all if the rectifiers weren't working properly.

    - Rectifiers aren't expensive and it won't be hard to find a match for both of those if needed.
    - I doubt you'll need to replace the caps to get the amp going in any case (you can measure them with your basic tester if you like just to see if the numbers seem normal, even though it's not a proper working-voltage test), and wouldn't bother doing that until / unless you get it working.

    Maybe avionic and hamish can confirm / deny / elaborate.
     

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