HP33 Display, contact corosion?

[TorstenHamburg]

Hello from Hamburg

here my next question around the HP33: Some segments of the display do not work, maybe contact problems. The connectors seem to be ok, [see picture Display_HP33_1]. But the connection between the contact strip and the PCB doesn't look so good. Could this be a cause for a malfunction of the contacts?
The contact strips seem to be pressed into the hollow contact body without soldering. (Same issue as in the 80's with wire wrap connections?).

With kind regards
Torsten

[teenix]

The connections look pretty good, so maybe it is just poor connections between the display pins and the flexible circuit board. There is a spongy film that is partly there to support the display pins and hold them against the printed circuit contacts when everything is assembled. Maybe this has degraded a bit over time and has flattened out.

I guess you would need something thin inserted against the original padding to increase the pressure on the connections.

cheers

Tony

[TorstenHamburg]

Thanks a lot, Toni

Is it right, that the spongy film is glued on both sides - the metal plate and the side with the printed circuit contacts for the display. It seems so when i try to insert somethig above or undernece the spong. I wont like open the chip-sandwitch if it is not neccesary.

Regards
Torsten

[Mike T.]

If you do get the urge to open the sandwich, mark the positions of the chips before you do, and make a note of the orientation etc. Then just for good measure take a couple of photographs and make sure you use an anti static mat. They will almost certainly try escaping when let loose and being NMOS that will end badly..

I know I killed my first HP33C that way, 'teenix' now has the shell which I expect he is putting to good use but it took me 20+ years to get a replacement!

[teenix]

Yes, the padding is glued and difficult to work with.

Is this actually, the problem though? If you can turn the calculator and and put pressure on the display module, do the segments light properly? If so, then this is most likely the cause. Maybe some spongy padding against the display that puts a little pressure on the display board when the case is assembled.

Still plugging away at the Spice. Temporary living in a caravan is making life difficult. New keyboard shown in image.

cheers

Tony

[TorstenHamburg]

Hello all

Still having problems with the display on my 33E.

Now I noticed that the display segment B is not fully visible on several characters. See photo.
When I look at the display from different angles, it seems like something is covering the segment.

Also, the "minus sign" is missing.
Is the calculator recoverable?

Best regards from Hamburg/Germany

[teenix]

The minus sign could be a contact to the LED, or it could be the LED segment failed. The sign digit only has the "G" segment. The 2nd pin from the left side of the display is the connector.

Does the "B" segment light fully when looking from different angles, or still just partially. If partially, then it's possible that those segments are beginning to fail. If fully visible, then it could be the little wire connectors inside the device that connect the LEDs to the circuit board, although this would be odd as they are quite small.

Problems can arise from poor connections from the CPU as well. It the back case is removed and the calculator can be powered up, putting minor pressure around the frame that supports the ICs might confirm this.

cheers

Tony