HP-65 Program "persists" and steps "disappear"

[n1msr]

Just had an HP-65 revived with one of the teenix CPU boards plus a card reader and LED repair.

The calculator seems to work fine if I read in a program from a magnetic card, or transfer a program via Bluetooth that the teenix CPU board offers (the original CPU board failed).

But manual entry seems to be an issue. The symptom observed is described below, but it might be the W/PRGM <--> RUN switch that is the cause.

Today I was typing in programs from the Standard Pac because some of the cards I have for the HP-65 it can no longer be read. This is when I came across some strange behaviour:

1. I type in the first 4 steps of program STD 01A (personal investment):

STO 1
STO 2
STO 3
R/S

I then go to RUN mode, hit RTN to go back to the start of program memory. Press a numeric key then R/S to run the program. I check the R1, R2 and R3 registers. Only R3 has the number stored. (R1 and R2 are zero). Next...
I hit RTN to go to start of program memory
Switch to W/PRGM mode and SST
The first instruction is STO 3. The first two steps (STO 1 and STO 2) have gone.

Also, when I clear the Program, turn off the calculator and turn it on again, there is a different (previous) set of program steps in the program memory starting LBL A. Weird.

The only other symptom I have observed is when switching between W/PRGM and RUN mode, there is a flash in the LED display. I am not sure if this is affecting the memory.

I have contacted teenix.org and will be checking the switch contacts. But wanted to post this here in case another has seen this kind of thing?

Regards,

Mark.