recent HP 35 "Red Dot" on Ebay


I purchased Ebay item 260941694606.

Cleaned it up and it works and has the bug:

2.02 bug - quicktime

Below are some pictures.

Seems to me it is 1143a-00026 but the top case was probably replaced at some point.


Interesting picture of the back side.

"Following any trig function Z is duplicated into register T". Now that's a useless and unhandy feature! Maybe this was some kind of memory limitation?


Edited: 26 Feb 2012, 2:17 p.m. after one or more responses were posted


"Maybe this was some kind of memory limitation?"

Absolutely correct. HP added one more scratchpad register in the CPU on the next generation (the 20 series) to eliminate this limitation.

Comparing the circuit board in this 1143A with Kees van der Sanden's 1143A33130 seems to support that this unit is indeed a Red Dot, and a very early one at that.

Note the revision number and date on the board in 1143A00026 vs. the revision number in 1143A33130.


What is the date?
1211 and 1219?

I have an early, non red-dot SN 1143A 34416 with the same board layout and other PCA markings except instead of 1211 I have 05-72

This has the bug, but I also have what seems like a keyboard problem.

1/X acts like +, X<>Y seems to drop the last digit and makes the number negative (weird), R(down arrow) acts like CHS, STO acts like EEX, RCL acts like CLX.

Bad ROM or keyboard traces? I've been over it a couple of times and haven't seen anything..


I think the 03-72 and 05-72 are either month and year or week and year, probably month.

Note, however, the numbers on the board below, which seem like week numbers, not month. I think that the chips are also dated with year week numbers.


As I recall some of the keyboard traces go under the separation in the battery compartment where corrosion may have occurred if it ever happened - though your battery compartment looks pretty clean. Weird also that mine and the other 1143A have that red capacitor or whatever it is and yours has the black diode or whatever that is...

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