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Old 15th January 2011, 06:30 PM   #41
johnm is offline johnm  United Kingdom
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Hi Mooly.

Managed to find a site which has photos of the same SMPS which some other guy was working on (you can see the state of the blue caps in some shots!). From the underside of the board I can see C2023s, so I know this is a UK model (the US/Canadian version uses 2SC1986). Thankfully on the topside I can see Q602/Q604 look absolutely identical (dark grey body, very thin metal tab, angled at the edges) to the ones on my board, not to mention that circular Sony branded Q603. So this means Sony definitely used C1810's for those two positions and that these parts do not appear to have been replaced on my SMPS board. So we know that part number was an error in the service manual.

Here's the site: Picasa Web Albums - 895720 - SONY TA-F6B PLPS

You can JUST about see Q602 in the upper-right corner in this picture from the above album, and if you squint can just about make out the C18... so I'm pretty much happy that's sorted that one out:

http://picasaweb.google.com/895720/S...50347770120706

Is it perhaps best to desolder these C1810's, then run a multimeter check on them, and reuse if OK, or would you go ahead and use new MJE340s anyway?

Can also see R622 in those pictures and it's exactly the same markings as mine, so that's also a relief - I'll measure it again tomorrow once I've desoldered a leg and if OK I'll retain that.

Last edited by johnm; 15th January 2011 at 06:38 PM.
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Old 15th January 2011, 06:57 PM   #42
Mooly is offline Mooly  United Kingdom
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They don't make 'em like that anymore

It's always good to test the devices because it pieces all the evidence together. Even if in the end we fit new, we know just what got zapped and that helps determining how far back into the circuit problems may have occured.

R622 is very important and when the transistors fail it puts a short on the main rail with all the current flowing directly through that resistor. The volt drop across that resistor in normal operation determines the overload and current limiting of the switching transistors. It is a critical part value wise.

C606 the 0.47uf could be an odd one to get... you don't see that value nowadays in elecrolytics... not common anyway.
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Old 15th January 2011, 06:59 PM   #43
Mooly is offline Mooly  United Kingdom
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I'll look in again tomorrow... it's a case of one step at a time and build it up carefully checking along the way.
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Old 15th January 2011, 07:22 PM   #44
johnm is offline johnm  United Kingdom
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Tomorrow I'm going to remove all the transistors we've mentioned thus far, and clean up the PCB in the process so it's as clean as possible. I'll probably have to extend a few wires when I solder in new components as there are a few lifted traces there by the looks of things.

I'll test that resistor, as well as Q603, 603 & 604. Keeping them crossed I'll be able to reuse all those, thereby keeping some of the circuit working to its original design.

I'll order 6 BUT11s for the remaining transistors (I won't bother with the MJs as the BUTs seem better spec'd).

Yes that 0.47uF is a pain as Farnell have no 105C versions. There are some chinese 105C ones on Ebay, but not brands I recognise. I may go for a Cerafine or perhaps a Sanyo Oscon - something that uses less than the usual amount of electrolite or none at all for safe long-term high-temp running. Hope they are low enough ESR for that particular position. Thinking about it perhaps I could use a film cap there instead like a 470nF polyester? The other caps are taken care of, but still awaiting one from Farnell for C613 which won't arrive until Feb (pain in the ***!). That's probably for the best as it ensures I won't be rushing to get it all up and running as soon as possible

Thanks ever so for all your help again today Mooly - I owe you a beer or three!!!

- John

Last edited by johnm; 15th January 2011 at 07:32 PM.
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Old 15th January 2011, 07:59 PM   #45
johnm is offline johnm  United Kingdom
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P.S. What wattage should RT601 be on the SMPS board? Mine's been replaced with a modern Bourns blue type - which is great - as long as it's the right wattage.
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Old 15th January 2011, 11:52 PM   #46
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Wow, John, I'm definitely following this now!
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Old 16th January 2011, 06:54 AM   #47
Mooly is offline Mooly  United Kingdom
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Wattage of the pot... you can calculate it.

250vdc across the resistor chain of 100k + 1k + 2k2 gives a current of 250/ (100000+1000+2200) which is 0.00242amps. Just ohms law of I=V/R

That gives a volt drop across the pot of 0.00242*1000 which is 2.42 volts.

And watts is I*V which is 0.00242*2.42 giving 0.0058watts or around 6 milliwatts. So no problem.

I would think a film small poly cap would be OK for the 0.47uf. Sometimes the "poor" (by todays standards) charactersistics of original specced components can be an advantage in certain circuits where those characteristics are part of the design. That won't apply to this cap though but it certainly can to semiconductors.

C613, I nearly mentioned the value of that as 33uf is a value not perhaps so common these days. A 47uf would be fine here.

If a part doesn't fit such as lead spacing on that 0.47 cap for instance, then it's best if possible to drill a new hole for one of the legs so it connects to the original print.

C801 and C805 (the 1000uf 200 volt caps) are in series on 240vac mains. The 220k resistors across each should be checked. These serve only to keep the voltage across each cap the same as any difference in capacitance and leakage current would cause a huge imbalance and cause one cap to see an overvoltage. It's an old trick.
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Old 16th January 2011, 12:57 PM   #48
johnm is offline johnm  United Kingdom
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Thanks for all that Mooly - much appreciated.

Unfortunately not having a great day with the old health today, so I'll have to make a start on things tomorrow instead .

On the plus side all bits I need (thus far) ordered from Farnell

- J
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Old 16th January 2011, 12:59 PM   #49
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Quote:
Originally Posted by thefragger View Post
Wow, John, I'm definitely following this now!
Haha thanks - get the popcorn ready!

It was your superb thread over at AK that got me interested in buying a TA-F6B in the first place
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Old 16th January 2011, 01:01 PM   #50
johnm is offline johnm  United Kingdom
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"A 47uf would be fine here."

Ahaa that's good news - Farnell told me my 33uF 400V cap won't ship until April due to not being in stock - ridiculous time to wait so I've cancelled that part. It's good news in that I have a Panasonic 47uF 450V in the parts box which is less than 6 months old. Only thing is there's a very slight dent in the casing which is why I never used it before - assume that dent (not severe) won't effect the way it works? I may just order a new one to be on the safe side though.

- John

Last edited by johnm; 16th January 2011 at 01:03 PM.
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