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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc. |
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30th Jun 2022, 12:05 am | #21 |
Octode
Join Date: Jul 2006
Location: Perth, Western Australia
Posts: 1,969
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Re: TC-377 recording woes
It has normally referred to certain Hitachi 2SC 458 transistors whose leads go black and they become unreliable. Usually associated with various Akai reel to reels where around 20 small signal semis need to be replaced. I've not heard of it in Sony gear.
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30th Jun 2022, 11:02 am | #22 | |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: TC-377 recording woes
Quote:
So what was the problem? It was the transistors, the problem with the transistors was that as you look at the base of the transistor you have the three lead out wires, the center one would have a very very thin chemical/metallic film spreading out from it and reaching one or both of the other lead out wires either side of the center one, under a certain light and a certain angle it would show up as a slightly iridescent film and it was conductive. By either tapping the printed circuit board, bending the board, wiggling the transistor or applying heat (soldering iron) to it's connections the fault would disappear.....for a while. The mechanical shock or heat would break the connection between the lead out wires and the conductive film. Two cures: 1) Scrape the film deposit off the base of the transistor or replace the transistor(s) which is what I always did. When I got back to the UK Radio & TV trade I came across engineers that were baffled by certain faults in Japanese stuff (mainly TV's) they passed them over to me, it was the same problems as has been described so far, I fixed the fault and showed them what to look out for, the problem wasn't limited to Sony stuff either, some Hitachi stuff I came across also had the same transistor problems. The range of products that it affected was wide, from TV's (mono and colour) radios, Hifi, cassette players, reel to reel tape recorders, language lab equipment etc. During my servicing years I never had the above problems with larger signal transistors, just the small signal types, the ones with a slightly recessed rectangular base and had a chamfered corner and those with a D or semi-circular type base. I always wondered what the thin conductive film was, something leaking out between the transistors center wire and encapsulation, a film deposited by an external component such as an electrolytic capacitor, or maybe some chemical used in the PCB manufacture. The first visual clue was that the transistor leads had developed a Black oxidized coating on them, hence the term "Black Death" which I coined with respect to those types of transistors. Lawrence. |
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30th Jun 2022, 12:56 pm | #23 |
Octode
Join Date: Jul 2006
Location: Perth, Western Australia
Posts: 1,969
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Re: TC-377 recording woes
Here's a link to a service company's experience with the particular Hitachi 2SC 458 faulty transistors.
https://reeltoreeltech.com/defective...d-transistors/ Other forums including Tapeheads discuss the problem in relation to Akai tape machines. A Google search brought these up. I think it's helpful if possible to identify both the transistor type and the equipment in which it is found. Pertinent to this thread, as far as I'm aware the Sony TC 377 does not have such problems with its transistors. |
30th Jun 2022, 1:27 pm | #24 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: TC-377 recording woes
The Sony TC-377 was relatively new when I was at Sony in the 1970's but it used some of the same types of transistors that the earlier tape recorders used, some of the transistors in them had the black death syndrome, replaced lots of faulty ones back in the day.
The rectangular encapsulated ones usually had flat leads, the colour of the transistors being Black, Brown or Green, the ones with the D shaped encapsulation were Black in colour and had round leads. Here's one type: https://www.radiomuseum.org/tubes/tube_2sc634~2.html Lawrence. Last edited by ms660; 30th Jun 2022 at 1:37 pm. Reason: link added |
30th Jun 2022, 3:34 pm | #25 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,600
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Re: TC-377 recording woes
I have replaced a lot of 2SC 458 transistors (with alternative transistor) on several different Akai machines particularly the DS 4000 series, main fault symptom being noise often continuous background, other times intermittent.
I also have not heard the term "Black Death Syndrome" and in the case of the 2SC 458 I do not think bad ones had blackened leads or the metallic film issue, although not being aware of that possibility may have missed it, if it was present. David |
30th Jun 2022, 3:56 pm | #26 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: TC-377 recording woes
Here's another thread, Black Death Syndrome was almost certainly the problem with the transistors:
https://www.vintage-radio.net/forum/...d.php?t=149409 Lawrence. |
30th Jun 2022, 10:51 pm | #27 |
Octode
Join Date: Mar 2006
Location: Lund, Sweden
Posts: 1,632
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Re: TC-377 recording woes
Thanks for the detailed explanation Lawrence. Sortof like a tin whiskers type of thing then, albeit occurring on the outside of the component and with a different chemistry.
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1st Jul 2022, 10:10 am | #28 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: TC-377 recording woes
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