Rebuilding an HP65 logic board from scratch - any advice welcome

[teenix]

(03-30-2019 10:01 PM)albertofenini Wrote:  UPDATE :
We have been able to get good Vcc and Vss, but not a good Vgg..
Investigating we have discovered that the anode of CR1 was not connected to the negative of C4 as it should be.
We have noted that this connection is done with a layer inside the PCB.
We also think that this PCB has more than one hidden layer as also the Ground signal goes thru a hidden layer.
We tried to short connected the anode of CR1 (with an thin wire) to the negative of C4 but
after that we lost all the Voltages to a mere 1,7V,
They didn't get back to good values even after removing the wire.
More in general we have discovered that this PCB (which is not very flat), has a bad ground trace.
Points that on the diagram should be connected to ground and then interconnected, like the negative of C4 and the positive of C5
or the Transitors's Emitters in reality are not, unless the PCB gets gently bended.
It looks like an internal middle layer trace is damaged or may be a cold joint is the problem,
even if we have checked all the thru-layers joint and they are good.
Basically, it has two problems : non continous ground trace, and missing/broken trace between
CR1 and C4, which is just about Vss
What can we possibly do to fix this ?
Thanks in advance !!

If the via connections to the inner PCB layers have been broken, possibly by PCB age and/or removing some components, then it will be very difficult to repair the PCB. The only practical repair method I can think of would be external wire connections to restore the connection(s).

cheers

Tony