> > How many connections does it have? If just 2 then it could well be a fuse. Not > really to protect the machine in the event of flashover in a monitor putting > high > voltages on the lines, but rather to meet the legal requirements in some > countries that any device linked to a modem needs such protection (the UK had > such rules at one point, there were boxes containing 24 fuses and 48 zener > diodes to connect between the DB25 connectors on termnal and modem). > > The other possibility would be some kind of interference filter, but (a) those > would normally have more than 2 connections and (b) filtering a high speed > video signal is not generally a good idea. > > Are any of these fuses (let's suppose they are that for a moment) testing as > open-circuit? If not, I think we can ignore them for the moment. >
Hello Tony, They have 2 connections only as far as I can tell. There is a track passing underneath them, but I can't see any solder around the track, so unless there is a small connection underneath then I think there really are only 2 connections. They all test for closed circuit across the 2 connections I can see. I have since discovered that the comparator being used on the outputs of the G176 to drive the monitor sense input to the VGA chip is faulty (I have just written a new blog post in the last few minutes: https://robs-old-computers.com/2017/08/19/decstation-220-faulty-parts-found/). Regards Rob
