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SA-7500 no protection relay flyback diode?

Discussion in 'Pioneer Audio' started by Eastham, Oct 1, 2018.

  1. Eastham

    Eastham More Class-A than ever!

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    So its currently 10PM here in sunny Cyprus, enjoying some relax time and well, I got bored and decided to have a little muse at the schematics of my SA-7500 because I remember noticing no relay diode.

    [​IMG]

    Is there any reason they wouldn't add one and if not, should I add one? I know that the early SX-737's never had these diodes either and it's common practice to add one. I got a bunch of 1N4001's that should do nicely (I think).
     
    Last edited: Oct 1, 2018

     

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  2. Watthour

    Watthour Electron Rancher - JS3600

    It would not be a problem to add a diode. However, a percentage of DC relays now contain a diode staked right across the coil terminals. Perhaps Pioneer originally selected a relay with that feature.
     
  3. Eastham

    Eastham More Class-A than ever!

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    The original was a ASR-010-0 which I replaced with a Omron MY4-02-DC24, not sure if the original had a diode but I didn't notice one when I opened it up to temporarily replace the reed assembly since the plastic holding the original reed contacts cracked and the left channel was making intermittent contact.
     
  4. Watthour

    Watthour Electron Rancher - JS3600

  5. Eastham

    Eastham More Class-A than ever!

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    I don't think the Omron I used has a diode but I'll have to check and have a little experiment when I get back to good 'ol blighty.
     
  6. Dolf

    Dolf New Member

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    It didn't, I just checked the broken Omron MY4-02-US-24DC I pulled from my SA-7500. That's probably what killed it. I added one after replacing the relay.
    Interestingly, both the SA-8500 and the SA-8500II do have a flyback diode in the schematic, whereas the SA-7500 and SA-7500II do not.
     

     

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  7. Eastham

    Eastham More Class-A than ever!

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    The plot thickens. I wonder why the engineers at Pioneer didn't add one, maybe they thought the 2SC1384 could handle the surge current.
     
  8. kevzep

    kevzep Its all about the Music

    I wouldn't overthink it, just slip one in there, I have found Pioneer were not that vigilant in fitting flyback diodes on their relays.
    Some models have them some don't....
     
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  9. Eastham

    Eastham More Class-A than ever!

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    Good point, I'll be plopping one in there once I get home. With any luck it will fix the poping issue on start up I've had since installing this new relay. Everything else is new since I did a full restoration a while ago, new caps, transistors offset and idle current adjusted to spec.
     
  10. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

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    it won't.
    there is a delay of SEVERAL seconds after power up BEFORE the relay engages.

    There can be a lot not working in the protection circuit and everything will seem ok. Just because the relay pulls in is NOT proof. Protect is as much if not more about when the relay lets go.

    first test is difficult to do on this model. short across R18 the 4.7k ohm resistor, and the protect should open the relay - as if the power was turned off.
     
  11. kevzep

    kevzep Its all about the Music

    As Mark says, it wont cure the popping issue, there is something else going on.

    Follow Marks instructions.

    I am finding a lot these days that the capacitor which charges up and then turns on the relay driver transistor is often faulty, lowZ or even short circuit..
     
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  12. petehall347

    petehall347 the brandy coffee man Subscriber

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    tell us the delay time in seconds . 4 seconds is pretty quick . i prefer 7 . manuals often state several seconds which i found to be about 7 seconds .
    if it has a new relay driver transistor it might switch on at a lower voltage so an increase in capacitance of the capacitor that works with a resistor to cause the delay may be needed .
    switch off time also important like mark said .
     
  13. Eastham

    Eastham More Class-A than ever!

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    I had a theory that would be the case, I know the protect circuit works after having issues with the notorious 2SC1384's causing it to go into protection. I should be back home this Thursday so I'll get back with how long it takes for the relay to pull in on start up.

    Would I be correct in thinking that C22 is the delay cap?
     
  14. petehall347

    petehall347 the brandy coffee man Subscriber

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    c20 100uf 16v .. when it is charged up the voltage is high enough on q11 base to turn it on and then q11 grounds the relay and then click .
     
  15. Eastham

    Eastham More Class-A than ever!

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    Oops, yep that's the cap I meant (My brain likes to sabotage me...). If everythings okay with that cap I'll try bumping it upto a 220 and see what that does. Wonder if it might be worth replacing the big filter caps aswell, they're the only caps I left alone since they still hold a good amount of juice well after being turned off.
     
  16. Eastham

    Eastham More Class-A than ever!

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    Okay guys I was a little too tired to mess with my amp yesterday after all that flying and lack of sleep. The symptoms are similar to that of my Yamaha CR-620 when it had the wrong cap installed, it takes about 2.5 seconds for the relay to pull in from cold causing a thump but if I power cycle it quickly it takes about a second or so longer with no thump.
     

     

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  17. Eastham

    Eastham More Class-A than ever!

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    Yep guys, upping the cap to 220µF did the trick! They relay now pulls in a much more appropriate 3.5 to 4 seconds. Added my flyback diode and buttoned it up for hopefully the last time now. Thanks everyone! :D

    DSC_0590.JPG
     
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