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Old 11th September 2006, 03:46 AM   #11
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Only a single secondary winding? I'd want to know, if there were more than one, what the others are doing.
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Old 11th September 2006, 04:37 AM   #12
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Thanks Echo another question arises; Is it wired like 20-0 , 20-0 on the secondary or is it 20-0-20?

Shawn.
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Old 11th September 2006, 09:24 AM   #13
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Likely someone previously just "repaired" it with the wrong caps.
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Old 11th September 2006, 12:27 PM   #14
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Well, he says 'The original caps were 35VDC rated'. But were they really the originals?

The reason I asked about other windings is that usually regulated supplies are run off of these, rather than tapping off of the main filter caps and regulating it down. I've no idea how Onkyo might have done it, but if the other windings look OK, and the regulators are not trying to fry themselves, then pinkmouse ought to be close to the truth, and I'd put some 50V caps in there and call it a day.
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Old 11th September 2006, 12:39 PM   #15
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Thanks for the replies. This unit appears to have never been serviced. I'm wondering if the caps managed to keep it together in over-voltage conditions for a long time. That's frightening. It looks like the STK power IC's have managed to hang in there too. The transformer has (what looks to be) a single primary winding, then loads of secondaries. I haven't checked thoroughly yet, but I think that all of the secondaries are too high. The only yardstick that I have currently is the working voltage on the caps themselves. It seems the center tap fro ground is okay. I have symmetrical voltages off of the rectifiers. The transformer has never been opened. There's still un-cracked varnish sealing the bands etc.

I will order the roadmap for this one. I want to check if the transformer part number is correct. I assume it is, because even with a Japanese transformer installed, the secondary voltages are too high. Then Ill figure out what the normal turns ratio should be. If it turns out to be a transformer with short in the primary (tapping another voltage) and somehow not causing severe current draw, I'll be blown away. It's kind of what I'm leaning towards at the moment.

With regards to shorted turns causing current draw. I told someone once that they shouldn't mount a torroid in a metal enclosure with bolt going through. I told them that if there was an electrical conduction path, the mouting would look like a shorted turn. They tried it and proved me wrong!? There was no increase in VariAc current, no sparks, no nothing. Was I wrong in not recommending the metal box? Is there no problem. Is it possible the primary of my transformer wouldn't pull excess current if the original connections remained but there is a short existing somewhere along the windings?

This is one of the more curious failures I've seen. I'll start first with the service manual.

I saw the question whether these 35WVDC caps were factory. I believe so. All of the filters had some sort of white paint/adhesive holding them to the boards. The paint was not cracked yet. You're right, I had to ask myself the same question.
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Old 12th September 2006, 05:09 PM   #16
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Okay, so as to not leave anybody interested hanging. We have some professional relations with Onkyo. I did tell them my findings. They were going to send me the schematic, but now they're going to swap out the whole unit. No questions asked. So the bad news: they probably won't tell me what the failure really is. I've asked that they tell me the failure, but you know how that's going to pan out.
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