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Another Yamaha P7000S modified by me. |
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kedwardsleisure 
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Joined: 20 January 2009 Location: Staffordshire Status: Offline Points: 4947 |
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 Posted: 06 February 2017 at 1:48pm |
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hopefully be ok, smpsu windings are usually fairly low resistance, it's the inductance that matters. Difficult to say until the proper IGBTs are in there
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Kevin
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Earplug
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Joined: 03 January 2012 Location: Europe Status: Online Points: 7216 |
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Posted: 06 February 2017 at 4:48pm |
+1 Have you checked the output devices? There may be a fault on one of the boards causing an overload on the SMPS. |
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Earplugs Are For Wimps!
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ceharden
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Posted: 06 February 2017 at 7:09pm |
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Hi Kevin,
Just curious why you think having the co-packaged diode on the UD version would cause the premature failure. It's not unusual to use them in half-bridge configurations. Having an additional diode in parallel on the board shouldn't cause any issues. You may have experience to the contrary.
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kedwardsleisure
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Posted: 06 February 2017 at 8:51pm |
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quite possible having 2 parallel diodes could affect the switching characteristics, I certainly wouldnt sub one for the other. First thing you do with a bounced repair is make sure the correct parts are fitted then look for alternate reasons for repeat failure after that.
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Kevin
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christth
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Posted: 07 February 2017 at 9:48am |
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@ Earplug: At first i started/tested the PS as per the service manual, with resistors (22k 3w) on +B to G to -B on the high voltage rail and (10K 1/4W) on -15V to G to +15V. Everything was fine at that point. I then installed the PS in the amp and had the amp running for some hours playing music, couldn't hear any distortion or other artifacts. It stopped working at the next power up a couple of days later. Have done some quick measurements on the output modules and couldn't find any shorts, will do a more thorough test before i hook them up. Wouldn't the protection circuit sense a short in one or more of the output devices? Q101 and Q102 would draw power form the driver (q103-104) in case of a short in OP devices? Parts is on their way from Mouser, I'll start over and take it step by step :)
Edited by christth@hotmail.com - 07 February 2017 at 9:55am |
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Earplug
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Joined: 03 January 2012 Location: Europe Status: Online Points: 7216 |
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Posted: 07 February 2017 at 6:51pm |
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Hi,
Ok. I don't have too much experience with the P7000, but did battle recently with a P5000. IIRC, there are a couple of 5W dropper resistors on the AC input. These would randomly burn out and I couldn't find anything wrong on the board, so just upped their value slightly and that seemed to cure the problem. A bit odd, but maybe does show that the SMPS has been designed to work on the edge of falling over and crashing.  Edited by Earplug - 07 February 2017 at 6:52pm |
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DjLeco
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Joined: 21 April 2009 Location: Bucharest Status: Offline Points: 817 |
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Posted: 07 February 2017 at 8:27pm |
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I used without problems 2 types of IGBT (I don't like originals, even they never had ben failed at mine amps).
I put with no problems and no modifications IRG4PC50WPBF (warp ones, even if Lower IC than originals). At the one that I have presented here, I have used FGA60N65SMD, IGBT,s greater current capability Those 6,8R/5W resistors (R410-R411), are put there especially (fusible ones inside at 145 celcius degrees) to protect other parts of SMPS if IGBT-s are shorted. When turn on, mains runs through it and if there-s something wrong, those fails, open circuit (one or both) and must be both replaced even one of it shows OK at multimeter. If everything is ok, then the relais "short em", applying "clean unlimited" mains to SMPS input part.
Edited by DjLeco - 07 February 2017 at 8:39pm |
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kedwardsleisure
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Joined: 20 January 2009 Location: Staffordshire Status: Offline Points: 4947 |
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Posted: 07 February 2017 at 11:29pm |
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the p/pc series power supplies would've had the full weight of yamaha's design department behind it, and, like all japanese designs, are engineered for reliability. My philosophy is not to replace, upgrade or modify anything unless it's a known or proven stock fault, for example the various little mods that the old C-Audio pulses (C-audio in general really) have had over their lifetime.
Certainly in the west, a failure, fire, injury or material damage caused by an incorrect repair might be construed in the courts as criminal negligence and is best avoided in the trade. |
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Kevin
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Earplug
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Posted: 08 February 2017 at 10:53am |
Ok, understood. I know that they had been replaced a couple of times by someone else before the amp landed on my desk. As I said, it seemed to be a random fault, ie the amp would work fine for a week or so, then fail. I replaced with a slightly higher value (10R, iirc) in order to reduce the inrush current a bit. And I obviously thoroughly tested the thing before returning. Afaik, it´s been working without any issues for several months now. I imagine that the probem could have been something as simple as a bad 'tolerance spread' on the amp, along with drift due to it's age. |
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christth
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Posted: 09 February 2017 at 3:06pm |
So a standard 5w ceramic 6.8r resistor will not "Fuse" early enough? The original part has following printed on it's casing, and says: 135 degree C, 5EG 6.8ΩK MICRON 4NK Can not find these in any search. Mouser and Farnell has not (that i could find) a resistor with these specs. What do you use? Do you have a link or part number? Would this work: http://no.farnell.com/te-connectivity-cgs/sqmw56r8j/resistor-5w-5-6r8/dp/987578 Edited by christth@hotmail.com - 09 February 2017 at 6:54pm |
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kedwardsleisure
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Posted: 09 February 2017 at 3:53pm |
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the inrush resistors on the yamaha have a built-in thermal fuse that opens if the resistor element gets too hot. It stops them burning the board or cracking open. It's an extra layer of safety especially if the relay fails to close for whatever reason.
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Kevin
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DjLeco
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Posted: 13 February 2017 at 4:22pm |
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Exactly!
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DjLeco wrote: