HP-97 free transistor

Hi, well, i'm a little bit embarassed of the situation... I opened my HP-97 to repair the gummy wheel problem but when i finish the job, the calculator didn't work at all!!!

I open it again and i fond a completely free loose transistor in in back case!!!

The problem is that i don't know where is that transistor is fiting nor where to solder it!

- on the keyboard board i have 3 transistors

- on the card reader reader, i have one transistor

- on the back of the printer board i found one transistor

- on the main board i found 4 transistors.

The number on the transistors is : M624 3-393

I found that number on other transistor on the calculator so it don't help me...

I look at some pictures but i seems that there is some PCB revision because i have some transistors on the main board that are not on th pictures i saw... ;-(


Edited: 26 Aug 2004, 11:02 p.m.


You will find the service manual for the HP-97 in the internals directory of the MoHPC CDROM collection



I've seen similar problems on old hardware with discrete transistors. One solution is to carefully examine the solder side of the printed circuit boards with a magnifying glass and a strong light source. You can usually see where the transistor fell out. There will be three blobs of solder with tiny holes in the center where the transistor leads used to be. After replacing the transistor, check the other components on the board for deteriorating solder connections. You will probably find more loose connections. It wouldn't hurt to lightly touch up all suspect connections with a soldering iron.


It could be the transistor was knocked loose. Also there is a fairly common problem where one of the transistors in the power supply (on the display board) blows up... usually resulting in several pieces of shrapnel. Three or four other neraby transistors witness the carnage and also commit suicide.


I found the place where the transistor goes but the holes ar full so there was heat when it quit the motherboard. i replace it but nothing works back on the calculator. only the red dot signaling a low battery even with a fresh battery. I also notica a wire that i accidentally desolder from the printer advance switch before having all these problem. Eben with the wire solder back in place, nothing is working except the red LED dot...

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