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CR-2020 Repair Advice

Discussion in 'Yamaha' started by sajjad amer, Mar 29, 2018.

  1. sajjad amer

    sajjad amer Active Member

    Messages:
    255
    Location:
    Lincolnshire, United Kingdom
    When switched on it lighted up and there was no relay click. Signal meter needle was in the middle. So I did the service bulletins and changed voltage regulators to TIP41.

    After service bulletins the lights are no longer working. However unit still powers on and meters are where they should be but no relay click. I have literally rebuild the whole board as it was burnt, re-flowed the solder and where needed applied jumper wires. I have recapped it and double checked to make sure black earth wire is soldered where it should be still no relay click and no lights which were working before I messed with it.

    I have one confession though, during service upgrades I have gone for same value but higher wattage i.e 5 watts instead of 3 1/4. I have changed the 33 ohm and 2 fuse resistors, 22 and 10 ohm each to 5 watt.
    could this be the reason for relay not clicking. ? Could some one please guide me what am I missing here ?
    Many Thanks and Happy Easter.
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Not a wise decision. Please list the FRxxx #´s for the fusible resistors you replaced.
     
    Last edited: Mar 29, 2018
    Goldie99 and sajjad amer like this.
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    22Ω @ 150ma ------> no larger than 1/2 watt with flame resist coating
    10Ω @ 220ma ------> no larger than 1/2 watt with flame resist coating
    These are suppose to be fuses.

    Would you replace a 2 amp fuse with a 20 amp fuse ?

    Well thats close to what you did using a 5 watt resistor ...
     
    Last edited: Mar 29, 2018
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  4. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Need to check for DC voltage at the output of each power amp. Check at a testing point before the protect relay contacts. You may have a shorted output transistor or and issue in one of the power amplifier assemblies. And the protect circuit/relay is working like it should.;)
     
    Last edited: Mar 29, 2018
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  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Page 12 of the service manual shows a illustration of one amplifier assembly. Note the solder lugs marked O and E along the top of the circuit board. Put your meters black test lead on the lug marked E (ground) and your red test lead on the lug marked O (output). Check for DC volts with power applied. This is also your test point for DC offset. It should only be an few millivolts. Ideally zero volts.
     
    Last edited: Mar 29, 2018
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  6. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Be extremely careful. Don't short Test point O to test point E with power applied. Or you will definitely destroy and output transistor or two. If there not already shorted.
     
    Last edited: Mar 29, 2018
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  7. sajjad amer

    sajjad amer Active Member

    Messages:
    255
    Location:
    Lincolnshire, United Kingdom
    http://cpc.farnell.com/webapp/wcs/s...estType=Base&partNumber=RE07469&storeId=10180
    http://cpc.farnell.com/webapp/wcs/s...estType=Base&partNumber=RE07467&storeId=10180
    http://cpc.farnell.com/webapp/wcs/s...estType=Base&partNumber=RE07462&storeId=10180
    Apologies for late reply, had to work over holidays as replacement. Above are the links to the resisters I used, there was no Fusible option, so I used ordinary resistors I will search for correct parts and rectify this issue.Thank you for advice.
     
  8. sajjad amer

    sajjad amer Active Member

    Messages:
    255
    Location:
    Lincolnshire, United Kingdom
    Right Side is -4mv
    Left Side is -3mv
    Kindly guide me about next step, many thanks in advance.
     
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Nothing wrong with the amplifiers..That leaves us with either the protect circuit itself or the power supply for the protect circuit.
     
  10. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Last edited: Apr 2, 2018
  11. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Need to measure the DC voltages around TR702 on the power supply board in the protect circuit.
    B. -- ?
    C -- ?
    E -- ?
     
    Last edited: Apr 2, 2018

     

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  12. sajjad amer

    sajjad amer Active Member

    Messages:
    255
    Location:
    Lincolnshire, United Kingdom
    voltages across TR 702 (2SB544)
    B--18.88
    C--0
    E--18.88
     
  13. sajjad amer

    sajjad amer Active Member

    Messages:
    255
    Location:
    Lincolnshire, United Kingdom
  14. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Need to remove and check for and B-E short.
     
  15. sajjad amer

    sajjad amer Active Member

    Messages:
    255
    Location:
    Lincolnshire, United Kingdom
    checked out of circuit , it tests fine. :confused:
    BJT-PNP
    ECB
    hFE122
    Vf 643mv
     
  16. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
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    Have you replaced any capacitors in the power supply yet ?
     

     

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  17. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
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    Guess you can reinstall it.
     
  18. sajjad amer

    sajjad amer Active Member

    Messages:
    255
    Location:
    Lincolnshire, United Kingdom
    Reinstalled the transistor. I have only recapped the vertical board not the horizontal board as yet. Would you suggest I do that? I wanted to fix it first before starting complete recap, but happy to do as per your expert advice.
     
  19. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    At least take a look at the caps in the protect circuit..
     
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  20. Goldie99

    Goldie99 Well-Known Member

    Messages:
    771
    Location:
    The original Boston, UK
    @avionic - did you see the service bulletins re. fusible changes ?

    My first thought was to completely agree with your fusibles comments - but, there are a couple of service bulletins on the hifiengine site specifically making the changes (more or less) as Sajjad's made.
     
    sajjad amer likes this.

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