Sony 1270Q shutdown

I recently brought my old Sony VPH-1270Q out of storage to use as a basement system. It turned on without issue, and ran for about 10 minutes before it just shut off on its own. I was playing with the convergence crosshatch when it shut off, and there was no indication of a problem. Now it only turns on for about half a second before it clicks off. I'm very experienced with electronic repair, but this one has me stumped for now, and I don't want to spend a ton of time on it. I do have the full service manual.

I've thoroughly checked it over for obvious problems like bad soldering, physical damage, water damage,... I traced the protection signals to the CPU board, and none of them seemed to be active in the brief time it would stay on. I also confirmed that the power supply voltages were present and not too high. I had to look at them with an oscilloscope because it shut off too quickly to take a reading with a volt meter. The HV is coming up just before shutdown.

Since it didn't seem to have an obvious fatal problem, I tried jumpering the power on signal to force it on. It will stay on and everything looks normal (rules out the power supply shutting itself down). All the protection signals at the CPU board are correct, the fans are running, there is HV and deflection, and nothing has blown up. I haven't left it on long enough for the CRTs to warm up yet because I would hate to ruin a good set of CRTs.

Does anyone have any suggestions before I pull the CRTs and wait for a 1271, or 1272 to show up on Craigslist?

I decided to try powering it up for longer so I could get a better idea of what's happening. As a safety measure, I turned the screen controls to minimum first. After letting the CRTs warm up, I carefully turned up the screen controls, and I was able to get red and blue rasters. I couldn't get any green, but I suspect that's just because the CRTs are biased fully off (200v on the cathodes). The raster is blank with retrace lines, flickering at about 40 Hz, and with heavy keystone distortion, but I suspect that's because the convergence and geometry controls aren't operating. Holding the power on button caused the raster to jump slightly, but there was no sign of OSD.

I'm starting to think the problem is related to the system control circuit since I can't find any reason it should be going into protection shutdown.

Believe me, I don't want to put much time, or money into it since it's not the world's best projector. Since it was already there, and I still have the hush box I made for it 10 years ago I figured I might as well set it up for old time's sake. It really didn't look that bad with an 85" curved screen, although it's been 7 years since I've used it, so my memory might be faulty. Blu-Ray didn't even exist, and there wasn't much HD content available where I lived.

Curt,

I'd take a high hour 1271, or 1272 since I could reuse the low hour CRTs from my 1270, but I'm in Austin Texas. I'll just have to keep an eye out for something on Craigslist. There's a G70 for $300 near me. Even if that's a good buy, I'm not sure I want to invest that much into this project. What's a fair price for one (assuming the CRTs are good)?

I will post back with any results I get on the repair. It's so frustrating that it was working fine, then just died for no apparent reason.

Thanks,

Andy
Edited by andy2000 - 2/12/13 at 5:48pm