Well, I'm sure this post hasn't been sitting here unanswered since Jan 1, 1970.
I'm also pretty sure that the replies to it went into that big digital s**t-can in the sky, too.
Didn't save any of them when they were still up, but I seem to remember wondering what people would pay for a simple go/no-go transistor tester. No meters or such, just five or six LEDS. Red ones to show a shorted terminal, green ones that stay dark if a terminal has an open circuit.
Hey, I still haven't even perf-boarded it to try out. So I'll skip griping about the s**t-canned posts. The idea was to have sockets on one end, to take the tiny TO-92 and larger TO-220 parts. Figure that four posts arranged to touch the flat legs of flange-mounted RF power transistors would be the simplest way to test those.
Trouble is, there's no way to do it in-circuit. None. The higher-power the circuit, the harder this is to do. Even the small TO-92 transistors are usually installed in parallel with resistors that place too many "extra" current paths across the leads on the transistor.
Testing a bipolar transistor is all about the current flow. With those "extra" current paths in the circuit, a tester can't tell the difference between a transistor that has a short in it, and one that doesn't. Never mind a transistor with internal leakage from the collector to the base. Those resistors in the radio will "leak" current, so long as it's soldered in place. No way for a tester to tell the difference between that current path and the one inside the part.
What the tester wants to know, is are there any "extra" current paths through the part? If there are, it's probably damaged. It also wants to know if any of the desired current paths (INSIDE the transistor) are broken and act like an open circuit instead. With the "in-circuit" parts still connected in the radio, the tester can't tell that, either. Those parallel "extra" current paths will fool most transistor testers.
Still gotta wonder what people would pay for a self-contained (Out-of circuit) go/no-go tester that runs from a 9-Volt battery, and would check all the bipolar transistors in a typical (non surface-mount) radio, NPN and PNP both?
Hmmm. If somebody answered that question the last time I asked it, that post is long gone now, along with the question.
Gotta wonder how much less trouble it would be to use than a mulitimeter on the ohms scale. I haven't done it that way in 27 or 28 years, so I'm not a good one to ask.
A lot of folks just get lost in the woods trying to remember which polarity the leads have to be on the ohmmeter. I sure did. That's why I quit trying to use the ohmmeter method in the first place.
73
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