|Re: HP-55 transistor info needed|
Message #4 Posted by Steve on 6 Sept 1999, 6:23 a.m.,
in response to message #3 by Viktor Toth
Since it's part of the DC-DC converter, I can't see it being particularly critical. If, as you say, the voltages from the DC-DC converter are correct, then I'd suspect that the problem is elsewhere.
I can't see that undervoltage is likely to damage the calculator, and I also can't see that crushing the transistor could have damaged anything other than the battery.
The segments that display... Are they the same segment in each digit? I would probably try manually turning on the segments by using a probe with a 1K resistor in series with it to try to get other segments to light.
I'm assuming (from your description) that the 55 has cpu + drivers + display.
Depending on the way that the display is strobed, you should be able to light up all of the like segments in the display. This would be a good check of the display. Obviously you've got to know (or be able to figure out) where the appropriate conections are, but it _shouldn't_ damage anything. That way you can check the display.
If the display is OK and the drivers are OK, then it only leaves one thing...
I've noticed with older devices that soldered joints can fail in a way that is almost invisible.
You may be well advised to go over the entire board, gently levering all connections to the board with (say) the lead of a resistor. I do this while watching the connection carefully with a loupe. Alternatively you could resolder every connection...
But you've probably tried all this...