hp-91 transistor substitution

[joseaem]

(09-20-2014 07:17 PM)jebem Wrote:  

(09-20-2014 05:10 PM)joseaem Wrote:  Hi all.
I'm owner of an old HP-91 calculator (year '79 more less). It makes all functions so well, but it have a 'little' problem at display. All results and all digits have the minus sign activated or bright.
Open the chassis, I discover a transistor phisically break (see picture attached).
I need a valid commercial reference of this transistor, and perhaps the oher 2 additional transistors near, because for me it's impossible find them in tables and internet.

The numbers are 'M712 3-393', 'M712 3-374', '4-071 M741'

Thanks in advance

The 3 transistors are from Motorola (the "M" indicates the manufacturer, and the 3 digits are the manufacturing date).

So the references are:
"3-393" --> this probably is a PNP transistor
"3-374" --> this probably is a PNP transistor
"4-071" --> this probably is a NPN transistor

Edited to add this:
My cross reference comes from this information here.
(just for reference, Motorola identification code is "185")

You are lucky because the transistors cases have the Emiter (E), Collector (C) and Base (B) pins well indicated, so that is a good starting point: it means they are bipolar silicon NPN and/or PNP semiconductors.

Take a digital multimeter set to measure Volts, put the negative probe to the Emiter pin and the positive probe to the Collector of each transistor.
If you are lucky, a voltage will be there during the normal operation of the calculator.
If the reading is positive, the transistor should be a NPN type.
If the reading is negative, the transistor should be a PNP type.

I would use fast switching high gain transistor for both NPN and PNP positions, capable of about 0,5 to 1 Amp of current, working with at least 50 Volt Vcb, and a minimum of 0,5 Watt of dissipation power.
There are thousands of possible replacements that will work on that position.

For example:
NPN: PN2222A
NPN: PN2907

One final note:
You may like to acquire the Manuals on CD/DVD from this MoHPC.
They have lots of manuals including Service Manuals as well (the HP-97 is included and it is close enough for this task).

Olá, como vai você ?, How are you?
Thank you for your early response. I'll try to test the items you comments. If you see the response of our collaborator in this thread (thanks a lot Paul Berger!!) affortunately this transistor not affect the seven segment display (SSD), it seems something related to powering, that is, in this case the transistor/s perhaps are additional problems ...

Along the next days I'll perform some probes and I'll tell you the results

Best regards