HP-25 - what could be wrong, simple question

[PANAMATIK]

Hi Alberto

The HP-25 DATA line ACT pin 11 is connected to RAM pin 4.

I encountered partially defective ACTs in the past where calculations could be done but for example one keyboard row was not working and I tracked down the fault to the pin at the ACT chip. The same could be in your case with the DATA line. If you are sure that the RAM is working in another HP-25, then the DATA line must be under suspicion. But check also Phi1 Phi2 and SYNC and ISA pins if they are connected to the ACT. Any interruption can cause the error.

See HP-25 schematic

You can completely remove the RAM chip and do all calculations with an HP-25. Not so with HP-29C, if the RAM is missing no calculation can be done, because the X-register is stored in RAM and the result is always 0.00.

HP-25A or HP-25E repair kit can repair your calculator.

Bernhard