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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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30th Mar 2015, 12:21 am | #1 |
Pentode
Join Date: May 2011
Location: Bath, Somerset, UK.
Posts: 149
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Transistor question
knowing very little about transistors I need to study and learn pretty quickly so that I can repair a circuit so could someone please help me out with an explaination as to the following;
The circuit I am attempting a repair uses the following transistors marked; 2SC945 (Q) (R) 2SC1211. (C) (D) Are there modern day direct replacement equivalents to the two above transistors if the originals cannot be found What is the significance of the letters Q, R C D etc etc which follow the number. Does it matter if the correct transistor number is found but the end letters differ? How can I tell what are the correct pins? A stupid question maybe, but as I said, I know very little about them. Thanks in anticipation John |
30th Mar 2015, 12:43 am | #2 |
Moderator
Join Date: Jun 2003
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Re: Transistor question
A quick google suggests that these are pretty standard general purpose small signal NPN silicon transistors. A large number of substitutes will probably work, but it's difficult to be certain without knowing the application and seeing the circuit.
The leadout seems to be e-c-b but you can sub different transistors with different leadouts if you wire them correctly. The suffix letters normally indicate the gain grouping, or in some cases a nonstandard leadout. |
30th Mar 2015, 10:46 am | #3 |
Pentode
Join Date: May 2011
Location: Bath, Somerset, UK.
Posts: 149
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Re: Transistor question
Thank you for that information. I did wonder about these. They are used in a Taoe recorder speed stability circuit known for leaky transistors so I was thinking of changing them over.
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30th Mar 2015, 12:05 pm | #4 |
Heptode
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
Posts: 782
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Re: Transistor question
I should leave them well alone! Silicon transistors shouldn't leak and it's highly unlikely that there's anything wrong with them.
Jim |
30th Mar 2015, 8:49 pm | #5 |
Pentode
Join Date: May 2011
Location: Bath, Somerset, UK.
Posts: 149
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Re: Transistor question
How do you know if this is a silicon transistor?
From what I have read a lot of Early Akai reel to reel control board transistors become leaky over the years? It is true that the capacitors in the unit quite possibly could be causing the problem, in which case these can be changed first to see if that cures the problem on one certain speed, but isn't it a case that if a component is suspect, or known to give problems on a particular model/make it is best to change it? Forgive my ignorance but I am trying to learn a little here. Last edited by Nightcruiser; 30th Mar 2015 at 8:54 pm. |
30th Mar 2015, 8:58 pm | #6 |
Octode
Join Date: Jan 2013
Location: Barnsley, South Yorkshire, UK.
Posts: 1,517
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Re: Transistor question
It would be easier if you divulge the model of the Akai recorder and the precise problem with it; then, those knowlegeable on the model may be able to point you in the right direction.
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30th Mar 2015, 9:11 pm | #7 | |
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Re: Transistor question
Quote:
http://www.alldatasheet.com/datashee...EC/2SC945.html http://english.electronica-pt.com/co...ce?ref=2SC1211 I agree with Jim, transistors like these rarely fail. |
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30th Mar 2015, 10:42 pm | #8 | |
Heptode
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
Posts: 782
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Re: Transistor question
Quote:
The 2SC code is what makes these transistors silicon types. The first Japanese types were made of Germanium and were coded 2SA and 2SB. Silicon types are coded 2SC and 2SD and FETs are 2SK and 3SK , the latter being dual-gate MOSFETs. It's certainly true that if a component is faulty it should be changed but you first need to ascertain that it is faulty before doing this and transistors, particularly silicon transistors, are the least likely components to fail. Jim |
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30th Mar 2015, 10:53 pm | #9 | |
Rest in Peace
Join Date: Apr 2008
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Re: Transistor question
Quote:
I would second that there are likely to be other causes of faults in this circuit but if other users have experienced frequent leakage issues I would not dismiss it as a possibility. |
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31st Mar 2015, 12:10 pm | #10 |
Heptode
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
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Re: Transistor question
What was the nature of the leakage Lucien? Do you mean Icbo?
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31st Mar 2015, 1:17 pm | #11 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
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Re: Transistor question
Sorry Jim, you will find silicon devices coded 2SA and 2SB, the overall type number indicates development.
Most of us will think of OC transistors as germanium, but some e.g. OC200 are silicon. A book like Tower's Transistor Selector will give much help with earlier transistors from many countries. |
31st Mar 2015, 1:38 pm | #12 |
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Re: Transistor question
'OC' just means cold cathode triode, just as 'EC' means 6.3V triode.
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31st Mar 2015, 2:58 pm | #13 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
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Re: Transistor question
On Japanese transistors, the legs being black, tarnished or even hairy could sometimes be an indication of present or future faillure. It seems this type of corrosion breached the hermetically sealed package.
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31st Mar 2015, 3:31 pm | #14 |
Heptode
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
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Re: Transistor question
I had a suspicion someone would say that! Head descending below parapet!
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31st Mar 2015, 4:48 pm | #15 |
Pentode
Join Date: Feb 2009
Location: Wirral, Merseyside, UK.
Posts: 118
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Re: Transistor question
I agree with nicklyons2,the more information you give,the easier it is to solve your problem.Forum members are very helpful and understanding with a vast knowledge of electronics and willing to help
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31st Mar 2015, 6:17 pm | #16 | |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
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Re: Transistor question
Quote:
I worked as chief service tech for Sony of Canad back in the 70's, when I started the job all the bench engineers that I was responsible for were having problems with 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 a crack in the printed circuit board, after investigating the various faults I was satisfied the neither of the above was the cause even though: 1) Tapping the board could either bring on the fault or cure the fault, sometimes cure it for months then the fault would it re occur. 2) Bending the board, ditto as above. 3) Wiggling the transistor, as above but because we are down to a specific component dry joints at it's connections would be suspected, the connections would be re soldered and voila! fault cured 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's the transistors sure enough, I never did a chemical analysis 'cos I know zilch about chemistry, what the problem with the transistors was is that as you look at the base of the transistor you have the three lead out wires, the centre one would have some type of 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 centre one, under a certain light and angle it was slightly iridescent and was conductive for sure, 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. All this work was done by myself in Canada. When I got back to the UK R & TV trade I came across loads of engineers that were baffled by certain faults in Jap TV's (mainly TV's) they passed them over to me, it was the same problems as described so far, I fixed them no problem and showed them what to look for, this particular problem put a lot of UK engineers from fixing Jap stuff, the problem wasn't limited to Sony stuff either, Hitachi's had the same problems. The range of products that it affected was wide, from TV's (mono and colour) radios, Hifi, cassette players, reel to reel, language lab products etc etc. Never had the above problems with the power transistors, just the small signal types, the ones with a slightly recessed rectangular base and those with a D or semicircular type base. I always wondered what that thin conductive film was, something leaking out between the transistors centre wire and encapsulation, a film deposited by an external component such as an electrolytic capacitor, or maybe some chemical used in the PCB manufacture. Suggestions anyone ? So there yer go, certain silicons do leak! The above condition described has led many an engineer a merry dance... Lawrence. |
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31st Mar 2015, 6:58 pm | #17 | |
Rest in Peace
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
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Re: Transistor question
The metallic tracking seen on some semi packages may be silver electromigration due to surface moisture and contaminants forming an electrolytic bridge. It can certainly happen internally where silver-loaded bonding agents are used as these provide a ready source of silver ions. I have also heard of the oxide / sulphide coating on silver plated leads (which turn black where exposed) causing failure of the packages hermetic seal as mentioned above.
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31st Mar 2015, 7:07 pm | #18 |
Moderator
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Location: Oxford, UK
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Re: Transistor question
I don't think there's any doubt that silicon transistors can fail for a number of reasons, it's just that the OP has been very unlucky if this is the explanation for his symptoms.
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31st Mar 2015, 8:11 pm | #19 |
Octode
Join Date: Nov 2011
Location: Manchester, UK.
Posts: 1,872
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Re: Transistor question
Folks - I've just been tangled up with a fault where the bias conditions on a ss transistor (working as am amplifier - 2sc***) seemed to be all wrong - Ice was too large, meaning that Vc was too low and the thing half-wave rectified my music. This fault appeared on a 40 yr old Japanese amplifier quite spontaneously.
As I soldered and de-soldered components around the transistor, the fault would go away for a day or two, and I'd think I had fixed it - but then it recurred. All the passives around the transistor measured OK. I cut Rc about in half in the end, bringing Vc up and it now works - but it sounds like the problem being perhaps tangentially discussed here, and perhaps I ought to follow Paul's advice in my Akai AA6300 thread and change the transistors! cheers Mark |
31st Mar 2015, 8:12 pm | #20 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Transistor question
Without a picture i couldn't say if the types the OP has were the ones that developed the fault I previously described.
But I would say that at the time I spent at Sony in the '70's, that particular problem was responsible for about 70% of electronic faults, excluding tape path wear and other mechanical problems such as dry joints etc, the type of transistors that were prone to that problem at that time were the green ones, the brown ones and the black ones, all with a rectangular base, of the types that had a D shaped/semicircular base only the black ones seemed to suffer from that problem at that time. Lawrence. |