HP-27S needs helps !


This is a non working HP-27S (s/n 2820A02945).

- The case has been opened by someone before and the display does not properly get in contact with the PCB anymore.
I have to firmly press the PCB against the LCD display (and with force) to make it shows something like "MEMORY LOST" on power up (which is normal with new batteries inserted)...
Even with a small block of foam installed between the PCB and the back case can't give a satisfied result.

- About the serial number :
The first (left-most) four digits date code are 2820(HP-22S) ... not the 2749 for HP-27S ?

Any ideas ? Thanks



I can't help regarding the hardware,
but a note about the date code:
> 2820(HP-22S) ... not the 2749 for HP-27S ?
The first four digits have the format YYWW,
where Year of production = 1960+YY,
and calendar week of production = WW .

See also http://www.hpmuseum.org/collect.htm#numbers




If it has been disassembled before, it is possible that the circuit board was not fully compressed onto the rubber zebra lcd strips before the twist tabs where turned, resulting in loose connections and missing lcd pixels. Or, one other possibility is that the zebra strips had been removed, then reinstalled upside down.

I would disassemble and carefully clean the zebra strips and lcd contacts with isopropyl alcohol, then reassemble. The zebra strips should be blue/black on older machines, white/black on newer ones. The black sides face the center of the lcd.

Straighten the tabs so the pc board drops on, center the board on the tabs and press in the center between the top and bottom row of tabs, then re-twist to seat. I always use this order for the tab re-twist:

Bottom left - Bottom right -Top center
Top left - Top right - Bottom center

The order is important since the bottom left and right side tabs have small nubs that center the circuit board on the frame. Always press on the pc board below the tab you are seating.

Just be careful with the six twist-tabs. You'll only get about 5 or 6 tries before they fracture.

Good Luck


Following instructions, I've carefully cleaned the zebra strips and the LCD contacts with isopropyl, put them back together & re-twisted the tabs with force.

Since the contacts of the three top twist tabs (used for ground connections) were not adequate made in touch with the PCB pads ... I have to add a wire directly from the battery (-) and the PCB pads where appropriate.

Powered it up & amazing, it works !

Even not a programmable, this is a wonderful algebraic calculator I've ever seen. A real keeper.

Why they did not make this calc again ? :-(

Many thanks for all of helps,


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