I’ve recently acquired a hand full of older DEC terminals. My favorite of these is a DEC VT220 from September 1984. It originally started up fine, but over the last 6 months it’s acted up in a couple of different ways. I thought I’d post about how I resolved these issues in case anyone else runs across them.
The first problem arose a few days after powering it on. The picture would roll sideways, so that static text looked like a bunch of lines moving
horizontally. I consulted the service manual and in section 8-4 it mentions an adjustable horizontal hold circuit which sounded like what I was looking for.
Before we continue, I just wanna reiterate that CRT’s are dangerous, and have the potential to fatally shock you, so make sure you know what you’re doing before disassembly, and be careful!
Disassembly of the 220 was rather straight forward, with only a hand full of screws to remove from the body, and we were in like Flynn. The R203 potentiometer was in an easily accessible area, and after identifying it, I powered on the terminal and began to adjust it. Like magic with only an eighth of a turn the image stabilized and everything was readable again.
The second problem I had was it not powering on. I thought for sure that something on the power supply had given out, or maybe that it blew a fuse, but to my surprise the actual rocker switch on the back went bad. I wasn’t able to source an original part; however, I did find a compatible part at Mouser Electronics part #R5ABLKBLKFF0.
Installation was pretty straight forward. I tie wrapped the wires in pairs, and took photos of the original installation to make sure everything went into the same place. I used a pair of wire snips to cut the “wings” off the original switch, and once these were removed the piece came out without issue. The replacement part snapped in without too much effort. I then wired everything back up, and it powered on ready to see another day.
https://www.instagram.com/p/BZikNgvlLnH/