First post, by terrorinstinct
I've been trying to fix blooming on a big-screen CRT TV for almost a year now off-and-on, and I'm at my wit's end. (For the VOGONS connection, I was planning on using this TV for TV-in/TV-out shenanigans on my Win9x machine.)
It's a Sharp XFlat 27F631 (service manual here) I picked up off Craigslist, the mains filter caps were worn and causing the HV protection to kick in almost instantly until I replaced them, but after I fixed that the picture was suffering from massive bloom. By massive I mean a minimum of 15% difference between dark colors and white. I know some picture bloom is expected due to the nature of the technology, but this is pretty ridiculous.
Facts gathered from troubleshooting so far:
- Turning down the screen voltage pot on the flyback doesn't help, at least not without turning it down so much you can't see anything
- The bloom is horizontally-based, i.e. the amount of picture expansion at a line of output is directly related to the brightness of that specific line
- The bloom is totally dependent on the picture brightness with no time or raster-position factor at all
- 5V and 9V linear regulator ICs both test good in-circuit and don't vary significantly with picture brightness
- There's no voltage marked B+ on the schematics, but it's probably +130V
- Replacing the bypass caps on the +130V line coming out of the main power supply (C723 and C725 on the main PCB schematic) didn't improve things
Are there any guidebooks or tips I could use to narrow down the source of the fault further than just replacing every replaceable component between the outlet and the electron guns? Looking at the CRT FAQ, arcade monitor guides, TV repair guides, other retro games forums, etc. hasn't yielded anything useful. It's either "replace filter caps until it's fixed, I guess" or "your tube is dying, sorry kid" with no real success stories. I'm about ready to offload this thing to someone else, which would be a right shame as the picture is absolutely beautiful in every way except for the blooming.