Hp91 with very dim display

[AndiGer]

Lately I had an HP-97 with a dim display. Maybe not as dim as that one of the TO.
I disassembled the display PCB and found Q1 "exploded" -broken into pieces. After replacing that one and measuring around with a DMM I found that Q3 and Q4 had disintegrated, too. I also replaced those with no better result.

It showed that the resistance was not correct of R5. Instead of 4.0 ohms it showed up with nearly exactly 1000 ohms. After replacing that one (I only had several 10 ohms handy I solder 2 of those in parallel) the display showed up in normal brightness.

If you have the service manual I found out during that repair that in figure 4-23
a) connection from Vb going to R5 does not exist going to R7 that goes to ground
b) bat trim R1* should be R2* - but R2* is replaced by a cap. My guess: 2.2µF