Defeated by a Commodore 1950 Monitor

[Mark J. Blair]

I pulled the main board out in order to solder some test points onto IC401 pins 15 (vertical drive output) and 12 (horizontal drive output). While I had it out of the monitor, I could see that IC402 is a Sanyo LA7830.

With it back together, here's what I see on the drive outputs of IC401. Trace 1 (yellow) is the vertical drive, and trace 2 (blue) is the horizontal:

https://www.dropbox.com/s/m7a97lypdqknofx/TEK00000.PNG?dl=0
https://www.dropbox.com/s/0c80wuqkbr245n7/TEK00001.PNG?dl=0

The vertical drive looks pretty dead, and the horizontal drive doesn't look anything like what I expected.

Now, I took these measurements with no video input to the monitor, with the expectation that the drive oscillators should free-run on an analog monitor this old. Is that a reasonable expectation?

I think that IC401 is pining for the fjords, so I'll order at least one replacement and a DIP socket to stick it in. Maybe I should order extra chips, and one or two replacements for IC402 as well, and tuck them inside the case to help out the next person to repair this monitor? :)


-- 
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/