Unusual HP-21 ?

[jch]

(11-26-2017 07:44 AM)PANAMATIK Wrote:  This is exactly the HP-21 board version which I used for one of my low power prototypes. You will need some extra work to install the LP module, because the display driver chip distance is different to normal boards. (see LP manual "Replacement").

Yes, I was thinking about that, but how is the LP module dependant on the power supply?
And I will get into that dilemma too.
I'm eagerly waiting for this little gem and I hope I'll be able to perform a successful transplant.

(11-26-2017 07:44 AM)PANAMATIK Wrote:  You can try to apply 6V and -12 V directly from a (ripple free) lab power supply to pin 1 and 2 of the ACT and check if it works. This would proof that the switching power supply is causing the problem.

However, the power module supports also the inductance and capacitor for the oscillator and the POR signal generation (derived from Vss through another capacitor).
Before removing the power supply module, the clocks were present, but I would bet this is not enough to report that the ACT is healthy?