I thought the customer must have dumped it and got a new one by now but it turns out they had been away for a week.
Previously it wouldn't display anything other than its setup menus despite being unplugged for half an hour.
So we got it as far as the customer's kitchen table (I'm sure glad I didn't have to move it further.)
After removing the back I poked around the UV board where the MM1313AD A/V switch chip lives. Plenty of electrolytics but no obvious leakage or other issues. My next move would have been to take the board off to check for solder joint deterioration followed by an oscilloscope to see if there were signals going in to the chip but none coming out.
But I decided to do a signal test first.
At power on there was the usual delay and up came exactly what you'd expect from a tuner with no signal. So we fixed up a DVD player and up came perfect DVD playback.
No amount of tapping the UV board with a screwdriver handle produced any disturbance in the picture.
So we put the back on and reinstalled it in the living room.
That was about three hours ago. I told the customer to leave it unplugged overnight if it happens again.
So now I'm wondering what to charge for taking the back off and putting it on again. They need an A/V cable for the VCR which I'll deliver tomorrow.
Old Guy