CurtPalme.com Home Theater Forum

[erothfus]

So my G90 has developed an interesting "tick." The BLUE registration zone-19 area is no longer "stable." That is, it jumps to its vertical limit (255) randomly, averaging once every couple seconds. I can adjust the value to the point where the jumping slows dramatically (around 190) although it quite skews the area. I've worked around the problem by adjusting GREEN and RED to the same skewed value. So everything is converged (i.e. watchable) although the zone-19 area is quite skewed.

I obtained a service manual, and my theory is that one of the transistors on the DB board - Q105 or Q107 - may be failing.

Anyone seen/fixed anything like this?

[cmjohnson]

I'd be more inclined to think it's faulty computer memory. Faults in the memory in the memory locations reserved for zone 19.


CJ

[oliverg]

There are 3 memory areas in the G90, user - service and factory.

Usually (and this is happening a lot lately) the Dallas NVM - IC333 is goes bad after between 6 and 11 years. After that the lithium battery fails.

You can try holding down S202 for 5 seconds (you will lose any USER data) but usually if the machine starts acting up, the data is corrupt anyway. Now I've noticed there is a chip 334 that apparently backs up the user memory but I don't know if that's "frame" type data or actual data.

I've just ordered two from Newark @ $44 each. Don't get the powercap version.

Also, you never know - the problem might actually be elsewhere, like a deflection board. From what you've written you might have a problem similar to mine, which I've traced to either the E, ED or YA boards.

If its any of those you'll have to stand in line behind me cos I'm buying them off Curt as soon as his part's machine is ready!!!

Seriously though, with any luck the S202 will fix the problem. I haven't confirmed this myself but if there is valid data in 334 it may copy it across during the init of 333.

The other things to check are IC 101 and 102 - they relate directly to Zone 19 - input signals H.SIN / V.SIN. There's also a bunch of rectifiers - which I think you've picked up on already


Good luck.

[erothfus]

What a great forum, 2 replies in minutes!

I read some of the memory-related postings, and that's an interesting thought. Though this "tick" is the only problem my G90 is experiencing. The setting for Zone-19 (as well as all other zones and settings) always remains intact. In other words, if I set zone-19 to 192, it stays there. Also, the ticking behavior changes as I change the setting for the zone. That isn't conclusive evidence that memory ISN'T a problem, but tends to make me think otherwise.

I'm going to give the S202 a shot this weekend. I can then go through the re-config process...I get better at it every time I play with it.

I did notice, too, that IC101 and IC102 may be an issue. Though I think I've convinced myself otherwise since Zone-18 works fine. On the schematic, zone-19 and -18 are both fed the same input signal before the transistors.

Any other ideas out there? I'm thinking seriously of putting a scope on the output (X10 for Zone-19) and trying to find the glitch at that point, as well as the input to the 4-zone stage.

[erothfus]

After a little more research into the schematics, my previous opinion about Q105,107 on DB was a bit misguided. The DB board seems to generate the sub-wave basic wave-forms, passing them to the DD board which does the work of shaping the sub-wave-forms based upon individual settings for registration. Had I thought a bit more, I would have realized that since zone-19 works for RED and GREEN, then it couldn't be Q105,107 that was failing.

So, my LATEST opinion is that the culprit is IC303 on DD. This is an analog multiplying 8-bit DtoA. It looks like each one of these ICs takes an analog signal in, and multiplies it by the value of the particular registration data. IC303 is dedicated to zone-19. It takes, as input, the X10 sub-waveform from DB (which is the zone-19 waveform) and multiplies it by the 8-bit values that are serially loaded into it. Each chip on the schematic is marked with 2 sets of RGB, so I'm not confident on what exactly is happening. Though it is becoming clear that the X10 signal is probably OK since zone-19 works for RED and GREEN. Also, since everything else appears to be working well, I'm skeptical that it is a memory problem. Interestingly, the DD ICs all daisy chain together, being loaded serially with their registration settings. Since everything else appears to work, IC303 can't be completely blown...just DtoAs C and G (3 and 6).

Anyone had a DD board out of the G90? How hard would it be to try to replace IC303?

[oliverg]

Eric, I have a copy of the SM if you need it - it has a step by step of how to remove each and every board

PM me your email address.

Kind regards

Oh .. I just saw it in your signature