Troubleshooting a Sony Watchman FD-40A

[MathematicalJ]

I have a Sony Watchman FD-40A that I'm trying to use to display component video. The picture is wonky in either one of two failure modes:

• The picture appears with an oscillating vertical saw-tooth (first bit of the YouTube video below) with otherwise very dirty picture, or
• the picture skews hard right from top to bottom dependent on how much and where brightness is on the screen.

Here's a video demonstrating the issue. You won't want to watch the whole thing, just enough to get the idea.
https://youtu.be/RGuaJqVHJno?t=34


I can switch between these failure modes by turning the tuning dial.

I have ruled a few things out:

• The video input connection is fine, as I get the same result when I tap directly into the video and ground traces.
• The video source works fine on other devices.
• A cleaner 6v power supply *does* clean up the vertical sawtooth slightly, but it's still there, and the picture generally looks like garbage.

Before I start poking around at voltages, I thought I'd ask here to see if this is a common enough problem that someone knows what it is. The dirty video suggests a bad cap. I don't know what to think about the tuner making a difference.

[TERRA Operative]

Component or composite video?

The watchman models ever offered component video input.

[MathematicalJ]

Yes, sorry, I meant composite of course.

[james_s]

They're B&W so there is actually no difference. The green/sync component output is monochrome composite sync and will display just fine on a monochrome composite monitor. It can look slightly better since you won't get the chroma dots crawling around.

That isn't really relevant to this issue though.

[TERRA Operative]

I would start by isolating the tuner section entirely, seeing as it's basically useless these days.

Find the main driver chip, download a data sheet and find the composite video input pin.
Then trace it back to the input jack. Somewhere along the way it'll probably split off to the tuner section, usually through a switch or similar.
I've found that the manufacturers at least loosely follow the reference schematic in the data sheet (they are all pretty similar with the notch filters and stuff anyway) so it should be pretty easy to map the few caps, inductors and resistors between the input jack and driver chip.
Then just desolder the closest component to that split heading towards the tuner.

Once you have that isolated, you can start properly tracking down any other faults (like bad caps etc).

Can you take a few decent photos of both sides of the PCB and internal construction etc?