HP67 - can be programmed but then does not work

[ovalsa]

Hello all,
I have an interesting problem - I have purchased a bit corroded HP67. Opened it, cleaned, put together again. Switched on in RUN mode it displays 0.00 but the calculator does not make any calculations. When you hit any key the display shortly blinks (normal behaviour) but it shows zero all the time. When switched to W/PRGM mode it is possible to enter a program and calculator responds fully correctly to all keys (the codes are generated and written to the memory correctly). The program cannot be executed (switched to RUN mode it does nothing except of short blink of the display).
Does anybody have any idea where to try to find the problem ??
Regards
Ondrej