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

[teenix]

(05-31-2019 12:16 PM)albertofenini Wrote:  What's your guess for a wrong Vdisp, where and what could we investigate ?
Take care !!

Hi Alberto,

It looks like here were 2 power supplies for the HP25.

One is shown at Jacques Larporte's site and another at the HPCC site.

https://archived.hpcalc.org/laporte/Wood...W_main.htm

http://www.hpcc.org/cdroms/schematics5.0/index.html

One design has less components but a more complex coil arrangement.

If the other 2 voltages are ok, and the display works ok, then the Vdisp voltage only has a few components to check, coli, 2K2, 10uF and a diode coming off the coil as shown at the HPCC site.

Other usual problems as generally discussed, such as high resistance (or shorts) due to corroded pcb tracks, "gunk" under chips, old components, something wrong with the power path to the display.

Only guessing as usual, but hope it helps.

cheers

Tony