HP-65 logic board repair - help required

[Alberto Fenini]

ciao a tutti,

last summer I have tried to repair an HP65 board,

the project is still open, I have got stuck in searching for replacements parts for the PSU, but I'll work on it again in the near future.

Now, I'm dealing with another one :


The board looks clean, even if I think that the circled diode has been replaced in the past.

This is how the display looks like :


The first thing I have done has been to measure the three values

Vss = 6.38 V

Vgg = -12.40 V

Vcc : 7.91

which look good to me, very close to those of a working HP65 I have.

So the question is, what could be wrong ? The Hybrid ?

What can I measure any further to troubleshoot the board ?

Thanks again for help, Alberto

[John Robinson]

Alberto, check your clock signals next, PHI1, PHI2 and SYNC. Refer the document I sent you, if you can't find it, email me and I'll send it again.

Cheers,
John Robinson