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Need info/cross ref

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Silverht

New Member
I am trying to repair and RCA Stereo/amp.
I have these little transistors that I am trying to figure out what they are.

A107
M 128 (or M 120)

They are paired with

C107
M 128 (or M120)

Any ideas?

The front face is 1/8" or 3.1750mm.
 

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Silverht

New Member
Wrong type of casing. 2SA107 and 2SC107 are very old... This set of transistors are from this century.

After doing some serious research I did find a 2SA107 and 2SC107 in this type of casing. I am sorry for doubting you. Thank you for pointing me down the right road.
 
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Silverht

New Member
Even more confused on what I have

The A107 as pictured above I have figured as a TO92A case.
hFE reading = 2 PNP or 28 NPN

BUT running an Ohm test I get these results (1=E 2=C 3=B)
2P, 3N = 1M Ω
1P, 3N = 1M Ω
1P, 2N = Infinite
1N, 2P = Infinite
1N, 3P = 1M Ω
2N, 3P = Infinite

Then the C107 same casing and pins
hFE reading = 4 NPN or 67 PNP

Ohm test results
2P, 3N = 41M Ω
1P, 3N = 1M Ω
1P, 2N = 1M Ω
1N, 2P = 59M Ω
1N, 3P = 1M Ω
2N, 3P = 1M Ω

Plus the datasheets you supplied to me above list the 2SC107 has both a NPN and PNP. And does not state what the 2SA107 is. I am guessing I have a 2SA107 NPN that has a short between base and emitter. And the 2SC107 is PNP with some weird defect. But I REALLY could be wrong. Please help, I am really confused.
 

Silverht

New Member
I have read in many places on the internet that the test for open/closed using a resistance test can tell if a transistor is PNP/NPN and is good/bad. Are all these places wrong?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I have read in many places on the internet that the test for open/closed using a resistance test can tell if a transistor is PNP/NPN and is good/bad. Are all these places wrong?

Basically yes, they are wrong, but not for an old analogue meter - digital meters don't work, you MUST use the diode test range to check transistors in this way.

It requires 0.7V or so to forward bias a silicon junction, the way digital meter resistance ranges work don't provide enough voltage to do this.
 

tvtech

Well-Known Member
Most Helpful Member
Basically yes, they are wrong, but not for an old analogue meter - digital meters don't work, you MUST use the diode test range to check transistors in this way.

It requires 0.7V or so to forward bias a silicon junction, the way digital meter resistance ranges work don't provide enough voltage to do this.

That's why I still use my old YEW Analogue meter. It never lies :p

Cheers
 
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Silverht

New Member
:mad: Well... I am back to square one on what I can use in place of these. Using the diode setting I had ALL open readings. :confused: How can you have all open readings and still get a hFE value that is within spec for the transistor??? Yes, I check the multimeter with a known working diode and tested right. Anyone know what I can use in place of these A107's and C107's? Can I get away with making some out of small diodes? :rolleyes:
 

tvdykes

New Member
a107 may be a digital transistor

I've got a similar problem. A 2sa107 crosses to an NTE 160 which is a RF germanium transistor. There's no way this is correct. Digital transistors have internal resistors which mess up readings when checking them, usually including a fairly large value in series with the base.

There are numerous prefixes for digital transistors, for example: HTA, DTA, etc. I haven't found the correct one yet.




If it is a digital transistor (I think it is), the transistors may be good, even if they check almost open. I would say checking the gain (hfe) if your meter has that feature would offer a reasonable test.
Also, I seem to recall digital transistors to have the more squared-off case shape this has.
 
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