Early (earliest?) HP-41C find.

[Diego Diaz]

Hi Didier, Patrik, all...

Thanks for the preliminary M-code research Didier. Hopefully we'll soon have more feedback on this, as several users are checking the NUT2-D.ROM file.

This is the bottom side of the CPU board Patrik.

   

Apart from the obvious tracing errors:

- Q2 is connected to PWO thru a piece of wire.

- C10 is connected to Vbat with a thick wire jumper soldered to a scratched part of the trace.

You can also see that there is no Q3. The one that makes DATA go LOW qith every Phi2 pulse.

It would be interesting to find out (sould it be possible) the reasons why HP included this on its first production batch.

The Service Manual estates that Q3 (and associated resistors R4 & R5) should be removed when ROM IC's are replaced with 120K ROM 1LG9-0001. I can't see why Q3 is depending on ROM IC's since Q3 only deals with DATA line and ROM IC's are not connected to DATA whatsoever. (?)

The PCB seems to be from 1978 52nd week.

CPU IC is (obviously) of the first generation 1LA5-0001.

Power supply is 1826-0566 in ceramic package. (MIL specs?)

I'm using the early 41C board schematics as refference to draw this one's. Will post it once it's finished.

Best wishes.

Diego.