Thanks to everybody that took the time to answer, sorry that my sickness and the efforts to do my dayjob has been holding me to answer early.
To summarize:
- The manuals for the non-plus variants have been found OK, God bless the kind soul KO4BB that hosts the manuals for these and many others, donated and I'll try to contribute the EEPROM contents for 7150 that seem to be missing, the 7150+ are there already.
- The software part of the calibration procedure is very clear and logic, the hardware plug is described in one manual as 2mm and in the other as 2.5mm, and I still have no clue, it's a stereo or mono jack and how are is the strapping done, but I guess I'll look closer into the schematic.
- The LEDs are confirmed 5mm, I've ordered 10 "milky" and 10 clear to be sanded, I'll see which is more pleasant to the eye.
- Replacing the panel sockets is a whole different
story, I was looking at the pictures of the mod and I've seen the the cuttings that have been done in the surrounding PCB and thought, hell no, with my luck I may cut some trace in an inner layer, I still hope to find some sockets that are protruding more in the outside, to not have to cut the PCB.
In regard with the calibration, it seem that on fleabay there are available few precision Russian old new stock resistor decades, with 0.02% precision or better, on a very acceptable price, did some one used such things together with
http://www.ebay.de/itm/AD584-4-Channel-2-5V-5V-7-5V-10V-High-Precision-Voltage-Reference-Module/221991435819 to build some kind of controlled voltage source, the specialized calibrators are out of my budget
.
Or any suggestion on calibration, I know that I will be faaaar away from the 6.5 digits, but still better then the 20% error now, I'll also measure the relays and surrounding components, barring a catastrophic failure of the calibration EEPROM, it's most likely something on the analogue front end.
Or if there's some one around Mannheim that has some calibration gear, please PM me.
The fun starts in Christmas/eoy vacation