Re: Restoring an HP65 : 29th june update Message #29 Posted by Alberto Fenini on 28 June 2012, 6:33 p.m., in response to message #28 by Alberto Fenini
ciao a tutti,one more update on this project.
Since all the discrete components had been changed, I had decided to start removing the ICs as well and measure the PSU values.
The hybrid is very sensitive, easy to break, so I started with the three ROMS : 1818-0074 (lower left), 1818-075 (lower right) and 1818-0073 (upper right).
Well, these are the values :
without all the three roms:
Vss : 5,06 V
Vgg : -11 V
Vcc : 6,26 V
with the 1818-0074 soldered back:
Vss : 4,95 V
Vgg : -10,87 V
Vcc : 6,24 V
with the 1818-0074 AND 1818-0075 soldered back:
Vss : 4,80 V
Vgg : -10,71 V
Vcc : 6,25 V
with all the three ROMS soldered back:
back to the old values ....
Then I desoldered a 1818-0118 from a HP55 , it should be a ROM 1024*10 with the same pin out of the 1818-0073 that looks to be the guilty on my HP65 board.
The values are :
Vss : 4,80 V
Vgg : -10,71 V
Vcc : 6,25 V
but still the display doens't work.
It's getting better, but still I'm missing something ....
What else should I try ?
Thanks for help, Alberto
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