So I have now narrowed down the issue with digital channel 7. I have had some weird readings from the CA3030 op amp that channel 7 uses. With nothing connected to the inputs, here were the voltages I got on each pin of a working channel, and then channel 7, the nonworking channel:
The scope's digital function has 28 inputs, only 14 of which can be used at a time, 1a-14a or 1b-14b. The front A/B switch must switch these channels in some way. I have not located where this is done. Anyway, there are 14 digital sections in this thing, all of the odd numbered channels plus channel 14 is done on the bottom board, and the rest of them are done on the top board:
This is the channel that has gone kaput:
Here is the same photo without the paper:
Here is the back of this board, the fourth section from the bottom is the problem channel:
Feeding a 1hz 5v square wave from a 555 timer into the digital channel 7, I was able to see some pulsing activity on some of the pins of this op amp, but the output is pegged high with no change. Doing the same on the other channels, I could see activity on both the inputs and output of the op amp. So I think this section is where the fault lies. It MIGHT be somewhere in the circuit that switches between A and B channels though.
I have done some other playing with the scope's adjustment trimpots on the outside.
The 28 trimpots underneath the display let you adjust the voltage gain for each of the digital channels. I adjusted each of these (excluding channels 7a and 7b) to make it so 5V peaks the bar graph to the top of the screen.
The high/low trimpots on the high/low LED display are the voltage thresholds for what voltage is considered high, and what voltage is considered low.
Anything you guys want me to measure the voltages on to try to track down the issue? Thanks for the help