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A-700 Restore

Discussion in 'Yamaha' started by Scottfer55, Mar 6, 2018.

  1. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Ahhh I see that. Wow that’s clean, I’ll take your advise and remount as I do have replacements on hand. I did use the film caps as you can see in the pic on the small bi-polar caps. The big caps that I installed were mostly lower in esr and voltage loss. The capacitance values were closer to spec on the new caps. Nothing stood out as being way out of tolerance or specs. Thank you for guiding me through this, I’m nearly complete and hopefully back in business after so many years and I’m glad it didn’t get trashed. It’s actually something I enjoy doing I’m already eyeing what’s next on my shelf to open up lol.
     

     

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  2. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Bad news, after soldering all the caps and reorienting the bias transistor I powered up the amp. With the DBT in line the relay clicked, I cycled power about 3 times and the relay energized each time. I felt like I should adjust the idling voltage so I unplugged the amp set it on it’s side to attach the leads to both sides of R307, I mistakenly set the meter to dc volts instead of dc mv. Plugged it in to straight power without DBT and no relay click. The amp was standing on its side so I could attach the mini grabbers to the bottom of the board on R307 they were not touching anything else I made sure of that. So I unplugged it and tried it without the meter hooked up on the DBT, still no relay. At this point I’m stuck. The lights still light up. Could the meter setting being on dcv instead of dcmv caused a problem? Kinda bummed out right now. What should I do? Thanks
     
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    No..
     
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  4. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Check all of your fuses with your ohm meter.
     
  5. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    I checked F501 and F502 both checked good
     
  6. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Start checking your power supply voltages.
     

     

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  7. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    Did you get check the bias reading while it was on DBT (in mV), and was there some small value present on both channels? The reason I mentioned that was to make sure you didn't mess up something with the bias transistor orientation. Did the bulb dim and stay dim as normal?

    You don't need to flip the amp, you can just attach your grabbers to the tops of the two emitter resistors next to each other - that gives the measurement across one of them. They're mounted like that to give you easy test points.

    Sounds to me like something blew when you took it off the DBT though... question is what and why.

    With the amp still on the DBT I'd be checking DC volts at the relay (on the hot side). There must be DC present if the relay isn't clicking. You can gently squeeze the front and back faces to pop the cover off and measure directly at the terminals, avionic might have a suggestion on a better place to read from.
     
    Last edited: May 14, 2018
  8. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    No I didn’t get that reading, After the 3 or 4 good power ups and relay clicks (while on DBT) I didn’t do anything besides turn it onto it’s side, clipped on the meter, plugged into house power, turned it on and once the relay didn’t click I unplugged it.
    I won’t have a chance to get back to it until Wednesday evening if that but I’ll check the voltages while on the DBT at the relay and as @avionic said at the power supply. Will the voltages be normal while on DBT? As the block diagram indicates? I may be in over my Head here. I’m hoping you guys can be patient and help me
     
  9. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    You really can't skip steps like that.
    3 or 4 "good power ups" don't really mean that everything was good, those bias numbers may have been running away without you knowing and it was important to check for low/sane/stable values before giving it full power. Relay click just means no DC present at outputs, but it doesn't mean that everything is stable.

    I've got my fingers crossed for you, but relay click before and no relay click now may point to an output stage failure.
    Would be nice if it was something else / minor. I'd be double checking your work, esp the orientation of that bias transistor (face writing should have faced same direction as original part, best to always confirm actual ECB with tester though). See question in prev post re: bulb dimming too.

    Voltages will all be lower on DBT, just check DC (V, not mV) at relay L and R to see which channel is causing it to stay in protection.
    I'd leave it on the tester until you figure it out.
     
    Last edited: May 15, 2018
  10. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    I did confirm the ecb with my tester, I’ll go back and recheck again though. I measured 36v dc on both hot sides of the relay contacts.
     
  11. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    The bulb dimmed and stayed dim
     

     

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  12. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    Unlikely.
     
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  13. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Rechecked orientation of ecb on bias transistor and it is correct. Confirmed all polar caps were installed correctly, the Panasonic’s were different as they don’t have the same paint scheme indicating the negative but the top of the cap has the - stamped on it so I’m almost certain all that is correct.
    Thinking back on when I cleaned the idle adjustment pots I know that I probably didn’t leave them in the same position they were in, could the idle adjustment have been so way off that it caused this? I should have checked the idle voltage while on the DBT but then again I thought since I had a relay click all was good. Painful lesson there. I’m basically venting because my wife doesn’t seem to care lol.
     
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  14. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,768
    Location:
    Fort Dodge, Iowa
    My wife is the same...Join the club.:biggrin:
     
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  15. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    You were so careful and patient with everything, I'm kinda bummed too.

    Certainly could have done it, but from what you've said it's unlikely - because if the idle was high enough to be damaging, the bulb wouldn't dim and the relay wouldn't have clicked.

    So at least so far - it sounds like you haven't made any mistakes (avionic has a better eye for this though!), but 36V DC at relay terminals both sides means something's wrong - so just keep it on the tester for now.

    I'd inspect all the standing turquoise flameproof resistors, see if any are burnt in the middle.
     
  16. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    For future reference, just clip your grabbers onto these two to check idle:
    idle.jpg

    I presume by Panasonic you mean the Chemi-Con silver caps, you've got those oriented correctly.
    Everything I can see looks correct, there's no chance you slipped with the leads and shorted anything while it was off the DBT?
    Have you checked the board for any solder bridges / shorts / solder spills?
    Also check that no wires have lost connection or broken where they join the board.

    36V on both channels says either the same mistake was made on both channels or something common to them is the culprit, that's why avionic wanted you to check the PSU voltages.
     

     

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  17. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Yeah the chemi-con, don’t know why I said Panasonic. Off to the job site, thank you mr. @zaibatsu for your insight and time
     
  18. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    No I was very careful and the mini grabbers are insulated up to the tips when it’s attached to the test point. You made it clear in a prior post how critical it was to not short anything out. I also now see where you said grab the tops of those two resistors for the test points!!
     
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  19. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    All look good
     
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  20. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Inspected board thoroughly with magnifying glass, no problems
    All wires are intact
     

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