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Old 14th January 2011, 06:58 PM   #21
johnm is offline johnm  United Kingdom
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Quote:
Originally Posted by Mooly View Post
That's it for tonight

Check all those passives john... hopefully this can be a success story.

Do we assume the amp proper is Ok... have you checked the audio outputs just for interest to make sure they are not short.
Well I was assured it was all working fine until that PSU gave up and it was turned off very fast. It's very complex in there but everything LOOKS ok at any rate. Not sure how to test the outputs I'm afraid (eeek!).

Anyways enjoy your evening - I'm just about to have a pint of Crabbers - um ummm!

Cheers!
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Old 14th January 2011, 07:04 PM   #22
Mooly is offline Mooly  United Kingdom
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I'm going lol

Yes but bulb across the DC output rather than the windings themselves.

Low value resistors usually check OK in circuit... yes they do interact so if you are unsure over any then lift one end and confirm. Many will read OK in circuit though.

If R622 has failed open or gone high that may have caused a bit of other damage... so we need to sure exactly what parts have failed.

It's a case of pieceing all the evidence together first and rebuilding carefully rather than just replacing any thing obvious.

Goodnight
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Old 14th January 2011, 08:57 PM   #23
johnm is offline johnm  United Kingdom
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That 0.22-ohm resistor reads 1.6 on the 200-ohms setting on my multimeter. Doesn't sound right so I'll lift a leg on it and measure again tomorrow.

It's labelled 0.22 then the ohm (omega) sign, then a K afterwards. Hope it hasn't been "repaired" with a 0.22k instead!

Incidentally here's the two halves of the PSU in better quality than that manual scan (hope the original poster of these on Audio Karma doesn't mind my using them here to fault find):

Click the image to open in full size.

Click the image to open in full size.

Will replace with fresh scanned images from a proper copy of the user manual once mine arrives from Canada.

- John

Last edited by johnm; 14th January 2011 at 09:12 PM.
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Old 15th January 2011, 07:11 AM   #24
Mooly is offline Mooly  United Kingdom
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That's a bit clearer...
The 0.22 ohm is critical as it's used to sense current in the switching transistors to provide overload protection. You need to be sure on this one... and measuring low values isn't always easy. Does your meter read 0.00 with the leads shorted ? 0.22 ohms is getting near the resistance of the actual meter leads and contact resistance so I would expect a reading of around 0.3 or even a little higher on a normal meter and leads.

I suspect better to replace it tbh as it will have been stressed by the transistors failing.
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Old 15th January 2011, 08:39 AM   #25
johnm is offline johnm  United Kingdom
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Morning Mooly!

Yeah definitely better to be safe than sorry - a 5W 0R22 has been added to my online Farnell list. Later today I'm going to remove the 6 dodgy transistors too (Q601, Q613, Q609-Q612 and - possibly - Q602 as that's right next to the two red ones that blew) as well as all electrolytics, to be replaced with 109C low ESR types. I'll also test the remaining resistors.

Shall I go ahead and order 6 BUT11A transistors or the TIP150s?

Cheers,

- John

Last edited by johnm; 15th January 2011 at 08:52 AM.
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Old 15th January 2011, 08:53 AM   #26
Mooly is offline Mooly  United Kingdom
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Hi John,
The 0.22 ohm needs to be a non inductive (or low) type really...
C604, 606 and 608 need replacing along with C613. Are you planning replacing all the electroylitic caps in the PSU ?

BUT11 are pretty universal. I mentioned the BUT11AF but I see that the tabs may be by design in contact with the board below... I can't tell from your picture. If they are then get the BUT11. The BUT 11AF is a 100% isolated package and needs no isolating washer.
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Old 15th January 2011, 09:04 AM   #27
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Would something like this fit, at 22mm by 8 mm
WELWYN|W22 0R22 JI|RESISTOR, WW 7W 5% 0R22 | CPC
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Old 15th January 2011, 09:11 AM   #28
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Amazed that CPC don't list the BUT11 as it was such a common device.

Looking at,

ON SEMICONDUCTOR|MJE13007|SI-N 400V 8A 80W | CPC

which on first examination looks a reasonable choice.
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Old 15th January 2011, 09:25 AM   #29
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This was the one I was looking at as it's the same type as the original:

WELWYN|SQM5-0R22JI|RESISTOR, 5W, 5%, 0R22 | Farnell United Kingdom

Doesn't say anything about low inductance though, though as it's a ceramic wirewound I would have thought it's low enough already?

Anything I order has to be from either Farnell or Ebay at present also. Farnell have both the BUT11A and the TIP150s in stock.

In answer to your other question all the following transistors are metal backed:

Q601, Q613, Q610-612, Q602. Q604 has a metal tab but is free standing. Q603 is a circular metal can'd Sony A911.

I was looking at this article about testing transistors about halfway down: http://www.kpsec.freeuk.com/components/tran.htm

I'd rather only replace those that need replacing if poss.



- J

Last edited by johnm; 15th January 2011 at 09:42 AM.
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Old 15th January 2011, 09:46 AM   #30
johnm is offline johnm  United Kingdom
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Quote:
Originally Posted by Mooly View Post
Amazed that CPC don't list the BUT11 as it was such a common device.

Looking at,

ON SEMICONDUCTOR|MJE13007|SI-N 400V 8A 80W | CPC

which on first examination looks a reasonable choice.
Ah good find! Do I need to worry about the hFE with these modern transistors or are they all pretty well matched these days compared with those old Sankens? The Sanken datasheet for the 2SC2023 says vce=4V, Ic=0.5A (which means nothing to me I'm afraid!).
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