TC-377 recording woes

[TIMTAPE]

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.

[ms660]

Originally Posted by ricard

That's interesting. I wonder if that was actually the problem I had, and replacing the output capacitors in the recording amp just temporarily cured the problem as the output transistors would have been heated by the soldering work, assuming that heating the transistors indeed is a temporary remedy for the 'black death syndrome', which I've never heard of before. Could you elaborate?

Back in the 70's I was chief service tech. at Sony of Canada, when I started the job the other engineers at the service depot were having problems cracking certain faults, the faulty items ended up on my bench, most of the faults came across as intermittent in nature, often showing the symptoms of a dry joint or an intermittent crack in the printed circuit board or a noisy resistor, after investigating the various faults I was satisfied that neither of the above was the cause even though tapping the board could either bring on the fault or cure it, sometimes curing it for months but then the fault would re-occur, it could also be brought about by flexing the circuit board or by wiggling a transistor, it being a specific component it's connections to the circuit board would be suspected, the connections would be re-soldered and that would cure the fault....or so it would seem, the item would bounce back with the same fault, sometimes in days, weeks or months.

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.

[TIMTAPE]

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.

[ms660]

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.

[DMcMahon]

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

[ms660]

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.

[ricard]

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.

[ms660]

Originally Posted by ricard

Thanks for the detailed explanation Lawrence.

No problem, it's worth remembering if there's an intermittent noise fault that's not the usual switches etc.

Lawrence.