Restoring HP25 S/N 1702S13138 - Very strange take a look

[teenix]

(05-29-2019 09:00 PM)albertofenini Wrote:  Both units have an identical PCB version, and all of the components are identical
except for the ROM, the working one (the unit pictured on the left) has a ROM 1818-0153,
the faulty one (pictured on the right) has a ROM 1818-0168

However if you look at the yellow circled areas you will certainly note some differences
The working one has three diodes and a capacitor more where the faulty one has
two less diodes in the PSU area and just below the ROM has a resistor instead of an expected diode.

The 0168 is a replacement for the 0153. Maybe it was a code change.

Maybe the power supply had some modifications also. The PCB holes look filled with solder from the original assembly process.


cheers

Tony