HP9100B: transistor specs needed

[isanchez]

(04-18-2016 09:37 AM)jebem Wrote:  Having zero information on that particular machine, this is what I would do:

- power on the machine.
- take readings of the voltages presented to all those transistors in the 3 legs.
- identify the transistor layout, meaning to find the emitter, base and collector pins. There are several methods to do this, the basic one is to remove one of the good ones and using a digital ohmmeter in diode checking find out the two junctions and note the forward voltage readings; a regular junction well show about 0.5V, a Darlington will have a much higher value at the Base-Emitter junction. Also check the reverse volage readings for leaks. But of course a transistor checker would be highly recommended, as it will give you the transistor type and its static gain (at least).
- draw a partial schematic of the transistor connections in the PCB.
- at this point there is enough information to identify the transistor basic characteristics, like it is a PNP or NPN, and what is the collector to base working voltage.
- from here it is a matter of selecting one from thousands of possible matches and this is the good news! As those transistors are working as simple low frequency switches (all on saturation state or all off cut off) the only real concern that I can think of is the working voltage that in this application can be relatively high.

EDIT to add this:

I got this LCR-T6 Transistor Tester recently and it is a good option as it will identify the component by itself.

Hi Jose,,
thanks with your instructions. I am going ahead with it. One additional question: Is it necessary to remove the transistor to determine the type PNP or NPN, with a multimeter? Even to determine if it is blown?
Thanks again for your valuable help

Kind regards

Ignacio