An EBay find. It was quite clean when it arrived. Some pictures:
Opening it up (there was something moving around in there, turned out to be a loose screw):
Top side:
Bottom side:
Next step is to check the PSU, those caps look scary..
The big caps are 4500mF; way beyond the capability of my LCR meter (ET4401), so I will check them by hand… First reform them for a while by putting them at 25V through a 10K resistor:
Fixing the column blanking
Column blanking on the device did not work. First check is the signal on pin3 of U17, which compares the “position” where to blank. The signal shows:
This is with the pot all turned left. Turning it all right shows:
which seems correct as the comparator compares it with ground to see what to blank. Checking pin 7 shows no signal whatshowever, though. Conclusion: dead comparator or shorted U15E inverter..
U17 is an 1820-0321 IC COMPARATOR 710HC, probably a Fairchild uA710. This is a high accuracy and high speed comparator.
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