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  #1  
Old 01-13-2011, 08:20 AM
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Sony TA-F6B help

Hi folks!

I have just received a very nice condition Sony TA-F6B, for the price of postage & a donation to a charity, from a very generous guy. It's sold as unworking. The seller said it made a loud popping noise (from within the amp) one day and was dead from that moment on. He gave it to a local tech who declared he couldn't fix it...

Having read a couple of the superb & very helpful TA-F6B threads here I thought I'd give it a go. I'm not a pro by any means, but possess good soldering skills and am adept at basic level measuring and adjustment of amps. Have rebuilt Quad IIs from scratch, as well as a ST70 'kit' and a GB150D amp so hopefully I'm good to go with this project.

I've checked the part which usually goes first according to some threads here - the thermal fuse on the input of the mains. I get a continuity reading on my multimeter so I guess in this instance it hasn't blown.

I need to take out the PLPS next and replace all the caps - got some Panasonic & Rubycon 105Cs on order. At a cursory glance with the top of the PLPS off, it looks like the two small value (C606 & C608) caps have been replaced, and the voltage adjustment pot replaced by a quality bourns item.

I've noticed that the original Hitachi output transistors (2SB655 & 2SD675) have been replaced by modern OnSemi parts (MJ21193 & MJ21194) which is a little disappointing. I'll order the original items if/when I manage to get it working so it's all functioning to original spec.

I've also noticed that the relay (RY801) on the mains inlet board (marked PSU Board 'B' in the service manual) has been replaced by an item lacking a cover, unless the tech just lost the original cover. Could someone let me know a suitable replacement for this part please as it appears Sony part number 151527800 is no longer stocked anywhere. Not sure how competant the original tech was as many of the screws are burred, or even of a different type to the originals, so I think he was quite heavy handed. Hopefully he overlooked something simple.

Will post some pics one the camera has charged up

Cheers,

- John

Last edited by ST70fan; 01-13-2011 at 04:50 PM. Reason: typos
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Old 01-13-2011, 08:55 AM
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Just spoken to the seller again and he sent me a few pics of the amp BEFORE he sent it to his tech. It looks the same as I have it now so I'm guessing the previous owner must have had a problem too and got it 'serviced', and it worked for a while before it then went 'pop' on my seller.

Last edited by ST70fan; 01-13-2011 at 09:05 AM.
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Old 01-13-2011, 10:48 AM
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Well I have found the problem. I've just had the PLPS board out of its housing and it looks like some amateur has done a real botch job on the underside. There's lifted solder pads visible by the lower two power transistors (Q610/612). Worse still these transistors are NEC 2335s so have evidently been replaced. A wire has mysteriously been placed linking the two middle legs of the upper power transistors, which are the correct Sanken 2SC2023s (Q609/611). There is NO insulation on the legs of the transistors so they could short to the circuit board quite easily.

The biggest problem is that the heatsink/clamp (Sony 'F-shaped plate') for these four transistors is entirely missing!!! The second is that according to the service manual Q609-612 all need to possess the same hFE ranks/codes, and it's obvious they don't from the replacements fitted! In short - no wonder this beauty doesn't work now!

In terms of damaged components, Q613 & Q601 appear damaged, and possibly J603 (which is a jumper? It's between the two collectors of Q613/Q601).

I am not sure how to proceed and could really do with some advice please. If I repair, I need to get hold of that F-shaped clamp (or fashion one from aluminium sheet?) for the power transistors. I also need to get hold of an hFE matched quad of new power transistors. I'd also need the two (special grade? They appear red as opposed to the black ones used on the underside of the board) SHK 2023s ('R' variant?). I also have to hope that nothing else has been taken out on that board from those blown transistors!

The other option is if somebody on here happens to have a spare PLPS board (for the UK model) or knows of someone that might I could fit that instead.

Here's a picture of the hatchet job:





Any advice on how to proceed would be much appreciated

Cheers,

- John

Last edited by ST70fan; 01-13-2011 at 06:00 PM.
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Old 01-14-2011, 07:27 AM
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Anyone?
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Old 01-14-2011, 07:32 AM
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free service manual:
http://www.eserviceinfo.com/download...ony_TAF6B.html
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Old 01-14-2011, 07:39 AM
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When you replace the caps in the power supply, you must use 105║C caps.
The Onsemi outputs are excellent devices, no need to replace.
The heatsink clamp is a must, that's why it failed. That is going to be your most difficult task.
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Old 01-14-2011, 07:58 AM
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Thanks for the service manual link, I downloaded the full paid version from them last week I also have an original on the way as some of the scans aren't 100% clear on the circuit board layout pages.

Hey Warren - As for PLPS yes I have ordered only 105C devices, and I've paid attention to their life-span too.

The problem I have is:

1) sourcing that F-shaped clamp. I guess it's pretty much unobtainium, so I think I'd have to fashion this from aluminium if someone out there can give me the exact dimensions of the original. Failing that I think I can eye-ball it from other pictures I've downloaded from here of it installed. The original looks like it's made from steel? I assume if I used a slightly thicker bit of aluminium plate to make up for the lack of strength compared to steel, it would be strong enough and would still fit (looking at it a minute ago it would definitely fit).

2) I also need to source 6 2SC2023s - two of which are the 'R' variety (according to the service manual), and the other four can be either all 'O' or all 'R' variety which I believe refers to the hFE batch according to page 4 of the service manual:



Failing that I'd need advice on choosing a suitable modern substitute which would still keep the thing working to original spec. (or better).

I am perplexed by the two red C2023s which are marked SHK rather than SK (Sanken) as per the other four. Would SHK denote a Radio Shack part? If so this was probably two other parts which were replaced originally.

Thanks,

- John

Last edited by ST70fan; 01-14-2011 at 11:09 AM.
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Old 01-14-2011, 09:22 AM
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p.s. still trying to work out why it was those two red power transistors on the side of the PLPS that blew, and not one of the four underneath which are the ones without the clamp/heatsink.... ???

Then again two of the transistors underneath have been replaced at some point - perhaps as they're not all matched now that caused some sort of imbalance which blew those two red ones? And I don't know if those two red ones are original either...
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Old 01-14-2011, 11:21 AM
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There is a very good chance you can find a donor unit. There are few techs who understand switching supplies.
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Judge Maxwell: Of what?
Hugh: Music.
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Judge Maxwell: Then shut up!"

Last edited by dr*audio; 01-14-2011 at 11:25 AM.
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Old 01-14-2011, 12:22 PM
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Whoever worked on this certainly didn't understand them, or had a copy of the service manual either!

I may have a lead on those power transistors however (though I'm sure there must be modern equivalents out there that would work?) - fingers crossed!
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