If either the row or column signal was shorted or open, that would
cause a blank display. You may want to examine the right vertical
edge connector carefully with a bright light. Maybe the A38 or B38
left spring is damaged.
Check the protection diodes on the A38 and B38 signals for the second
vertical bay. One may be shorted. They are CR2245, CR2246, CR2261,
and CR2262 (or check them all since it is easy enough to do).
On a 7904 you could swap P2265 and P2266 at the readout board causing
the vertical and horizontal readouts to be swapped but the 7903 lacks
horizontal B connections so that will not help in your case.
On Thu, 19 Jul 2012 18:02:40 -0000, "keithostertag"
<keitho@...> wrote:
David- Thanks much. I had seen the one sentence in the manual stating that data for channel 2 of a dual channel plugin is routed via A38 and B38, but I hadn't gotten far enough along in my thinking to follow up on it. I'm still not good at reading schematics.
Yes, vertical channel 1 right works fine.
I decided to swap the entire readout board from my 7844 to the R7903, since they are the same board. No change- right vertical chanel 2 still does not display. So this clues me into looking more closely into the connectors from the backplane through A4 to the readout board...
Thanks,
Keith Ostertag
--- In TekScopes@..., David <davidwhess@...> wrote:
The horizontal readout centering does not look that far off to me. I
would check and calibrate the horizontal CRT centering before deciding
it is a problem.
Does the right vertical channel 1 readout work correctly? Did you
really have it set to 1 volt/div and uncalibrated when you took the
picture?
If the right vertical channel 1 readout is working correctly, then we
know the time slot signals are making it to the right vertical. I
suspect we will find that there is a broken connection between either
the right vertical channel 2 column (pin A38 to pin 11 of U2190) or
the right vertical channel 2 row (pin B38 to pin 11 of U2180) and the
readout circuits.
There are a few connectors that should be inspected between the
readout board and the backplane board that carry those signals.
David Hess