Open a new topic in order to not confuse readers:
I was not able to process
correctly the D/A adjustment after a short on pin 1 and 2 of the IC33
DAC. VR6 and VR7 didn't had any effect.
-After
replacing IC33 DAC and IC27 (4560) , VR6 and VR7 where active. And i
was able to process a sort of D/A adjustment. i say a sort because it is
like the adjustment is half done : The pots course works half, the
MG speed is too slow event all the way up...
The official adjustment procedure says:
"TURNING VR7 CLOCKWISE,ADJUST SO THAT THE LIT LEDS SHIFT TO (1 & 8) IN THE SHIFT FROM ( 2 & 7) to (1 & 8) ...
For
me, it shift from (4 & 8) to (1 & 8), the 8 never moves
whatever i turn VR7 and VR6. It may be a good start point to
investigate?
Then:
- tested with several New DAC, result is the same.
- replaced IC22(MCU) result is the same.
- replaced IC21 (LM13700) result is the same.
- replaced IC17 ( 4011) result is the same.
- replaced IC6 (LM393 comparator) result is the same.
- replaced D9. result is the same.
There are so
many ICs that could have been damaged by the short on IC33 DAC pin 1 and 2
that I do not know anymore where to look?
Where to look if the D/A is done only half ?
What signal levels should i find on IC6 pin 1, 2, 3 when calibrating?
I'm a bit lost but, what is good is that i learn a lot at every step.
Any clue or explanation of how the D/A adjustment works, is welcome.