HP-25 - what could be wrong, simple question

[teenix]

(06-07-2019 09:45 PM)albertofenini Wrote:  Hi Everyone,
these are the waves captured from the unit under repair and a working one,
blue waves are from the working one, red waves from the broken one,
both were powered with an external pack of batteries, in RUN mode and displaying a 0.00
both have a good electrical connection between pin 11 of the ACT and pin 4 of the RAM
we don't know if the ram transplanted was working or not since it came from a broken unit
Any idea ??
Thanks for help !!

Assuming the same vertical scale was used, it looks like the faulty data line is about half the amplitude and suggests it is being loaded by something.

If replacing the RAM chip didn't change anything, the PCB tracks are clean, and no solder shorts are on the data pins, it may point to the ACT data pin as being the culprit.

cheers

Tony