CurtPalme.com Home Theater Forum

[vinyldavid]

Hey guys.

I finally got around to bringing up an Ampro 1700. Amigaman was kind enough to help me get it up the stairs and essentially set up the entire thing. Everything was going great until we put up a picture of a zebra. The white turned to green.

At this point the brightness and contrast were both around 50%. Picture source was (and remains) my MacBook Pro outputting 1080i.

Amigaman thought that it might be the AGC bringing down the levels of a Red and Blue before Green.

After a few minutes of playing with things, the image went dim and the blacks were crushed out. To bring back normal picture level contrast needed to be at 80% and brightness at 76%.

He thought that the HV power supply went bad. I have spares at my storage area.

Today I brought home a spare and installed it. Same image issue, so it's not the HV power supply.

Any ideas? Maybe the video amplifiers?

I do have another working projector, but this one is already aligned, atop a 6 foot tall rack, and would have to go down two flights of stairs (and bring the other one up, plus alignment).

[amigaman]

To add to this, the image going dim was equivalent to a severe drop in G2.

Initial tests were done at a brightness of 50 and contrast of 80, and that's when images with bright white elements on dark backgrounds (like a photo of a zebra) would make the black balance shift toward green. Reducing the contrast to around 60 reduced the effect, of course at the expense of overall image brightness.

The drop in G2 (or apparent drop in G2) coincided with a couple quiet arcing sounds and some screen flashes. After stabilizing, the image remained dark. This lead me to believe there was an internal arc which killed the HVPS, but apparently that isn't the case.

I'm not used to Ampro stuff, so any ideas are appreciated.

[Curt Palme]

I would measure the G2 line. Should be at 500-700 volts normally. Ampros liked a high contrast setting, so a setting of 80 would be normal. If you had a good pix at 50/50, brightness and contrast, I'd say THAT would be abnormal, go figure.

For the 2000, what you'd do to set the G2 controls is mute each tube with the remote, and use the G2 trimpot on the neck board so that the raster was barely lit on the tube face. It's been probably 10 years since I've seen a 1700, actually, make that 14 years!, so memory is a bit fuzzy. I know the 1700s didn't have the service control codes like the 2000 did, but I think the G2 setting is the same. I would have suspected the HVPS as well (the X1685s were really unreliable), but since you've swapped that, I'd look at the G2 voltage.

Keep in mind as well that a short or partial short on one G2 line will usually drag down all three tubes. I'd also disconnect each CRT socket completely to see if the other two tubes brighten up. IF so, that's where your problem is. Post some pix of the internals of the set. If they are a rectangular CRT output board, I've got stock. If it's the older round ones, then I have nothing, although a bunch of the parts between the two types are probably the same.

[Curt Palme]

I would measure the G2 line. Should be at 500-700 volts normally. Ampros liked a high contrast setting, so a setting of 80 would be normal. If you had a good pix at 50/50, brightness and contrast, I'd say THAT would be abnormal, go figure.

For the 2000, what you'd do to set the G2 controls is mute each tube with the remote, and use the G2 trimpot on the neck board so that the raster was barely lit on the tube face. It's been probably 10 years since I've seen a 1700, actually, make that 14 years!, so memory is a bit fuzzy. I know the 1700s didn't have the service control codes like the 2000 did, but I think the G2 setting is the same. I would have suspected the HVPS as well (the X1685s were really unreliable), but since you've swapped that, I'd look at the G2 voltage.

Keep in mind as well that a short or partial short on one G2 line will usually drag down all three tubes. I'd also disconnect each CRT socket completely to see if the other two tubes brighten up. IF so, that's where your problem is. Post some pix of the internals of the set. If they are a rectangular CRT output board, I've got stock. If it's the older round ones, then I have nothing, although a bunch of the parts between the two types are probably the same.

[amigaman]

Yep, G2 is that easy of an alignment on this one. We do have the rectangular neck boards.

I'll check out the G2 voltage and disconnect neck boards shortly and let you know. We have spares of just about everything for this one, so swapping things is no problem. We got a pair of these from an old Ampro service tech, so he had lots of extras.

I have no experience with Ampros, but it definitely seems like the 1700 adds some sort of black level correction as the APL changes, on top of the normal white limiting. That's what I attributed the green shift to, but I'm hoping these are all related problems.

We'll see, and I'll keep you posted. Thanks for the advice!

[amigaman]

On second thought, the black level shift could just be slow DC restoration circuitry.

I'll address the big brightness issue and worry about the green shift later though, if it's still a problem.