I spotted this little Sony FDM-404 monitor on eBay with a very cheap buy it now a couple of days ago, listed as non working.
Sure enough it was as dead as a doornail. Zero power consumption.
I had a hunch. This uses a 6V centre *negative* power connector (because of course it does) unlike the other 98.4% of the world, so if you use any old 6V adapter something will likely go pop.
In we go.
Nothing obviously blown up, though hidden just behind those capacitors under the power switch is a fuse. A fuse which upon inspection turned out to be blown. Hmmm.
Quick look at the circuitry and hey look, there's protection built in which if you connect the supply backwards will present basically a dead short and pop the fuse. Oh if only more devices had that. I've only had a really quick glance at the schematics, but it looks like over voltage protection is also provided.
One new 1.25A fuse in and sure enough we had life.
Image isn't bad at all for a device like this - obviously it wasn't ever designed to be used as a computer monitor so photos look better. The camera hasn't done it justice either. This is also straight out the box without me adjusting anything. It's sharp enough that dot crawl is an issue even at this size.
I suspect the geometry will be a lot better if I chuck a new set of caps at this. Sony stuff from this era usually has issues with the electrolytics suffering from high ESR. Geometry isn't ever going to be perfect just due to limitations of the design of these CRTs - it's a wonder they managed to make them work at all.
Helpfully the service manuals from this era are decent (assuming you can find them), and have a full component list.
So I can go and make sure I have them all in stock before going through it and changing them. Most look to be pretty standard values so I probably have them on the shelf (well technically in a box under the bed actually) so probably won't need to order much.
There's an obvious parallel between this and the Watchman of the same era - they both use the same bizarre CRT design. You can see a clear difference though when they're next to each other. CRT size being 1.8" and 4" respectively for a start.
The Watchman also contains batteries and a tuner, whereas the one I've just been working on simply uses a composite input and has no battery supply - yet there's still that little spare space in there! I'll post the schematics when I'm at an actual PC later - for a monochrome composite monitor it's absurdly complex. I have to wonder how much of that is to handle the geometry correction - which must be a nightmare on this thing.
A good way to spend time whilst the weather is not quite good for Rovering...
