I just did a repair of a 1970's Analogic AN2546 and found out the following.
J2 upper connector
1 SIGNAL +
2 SIGNAL -
3 NC
4 DP1
5 NE555out 388Hz block wave?
6 NC
7 NC
8 DIG5B1 (+5V when >1 or <-1)
9 NC
10 NC
11 100Hz block wave?
12 DP3
13 STROBE
14 HOLD/SAMPLE
15 +5V
A NC
B ANALOG GND
C NC
D DP2
E NE555 reset?
F NC
H NC
J SIGN (+5V when >=0)
K NC
L NC
M CD4013 pin 13?
N DP4
P NC
R EXTERNAL TRIGGER
S DIGITAL GND
J1 LOWER CONNECTOR
1 110V~
2 NC
3 110V~
A 230V~
B NC
C 230V~
Rest: NC
The voltage differential between SIGNAL+ and SIGNAL- must be between -2V and +2V.
To get a decimal point in a certain place, connect DPx to GND (pin S).
The following sections of the AN2535 manual also apply to the AN2546:
- Figure 5
- Grounding
- Figure 6
As for the repair: the DS8880 chip on the display board was faulty and I managed to find a replacement SN75480 on Aliexpress. Now it's working fine again!