CurtPalme.com Home Theater Forum

BruceR · Joined: 05 Nov 2018 Posts: 14 Location: Brisbane, Australia

I've solved the problems I spoke of in my last post regarding this projector. At first, all seemed OK, but when I tried to set it up again, I found the Red MG Focus has no effect, any zone. The others seem to do something, but it's a bit hard to tell in a couple of zones due to the bad overall focus. Blue & Green are OK. Interestingly, it doesn't seem to be all that visible on a normal image which is still nice and sharp from a normal viewing distance. It counts up and down from min. to max. OK, but the focus doesn't change on the screen. I've swapped the D, EB & EC Boards with a scrap G70 I have, which are the ones associated with focus as far as I can tell, but it's still the same. There is about 11,150 hours on the tubes, but the picture is still excellent, apart from the red focus. Now that I've swapped the YB Board with the scrap unit which got it going again, it's assumed the identity of that one showing about 850 hours. I swapped that board back again, which again gave no pic. on any input as before, and the red focus is still faulty. I've even compared the coil resistances on the tube necks which are all pretty close to each other and within tolerance I'd say. I really don't know where to go next. I suppose I could just put up with it as it's not that noticeable, but I would like to fix it if I can. Thanks in advance to anyone who has any ideas.

**Curt Palme** · Posted: Tue Sep 03, 2024 8:28 pm Post subject:

It's usually the focus output board, which (if I remember correctly) is located under the internal keypad. There's also the focus driver board located on the left side of the set, next to the convergence board, but failure of those is pretty rare.

BruceR · Joined: 05 Nov 2018 Posts: 14 Location: Brisbane, Australia

Thanks Curt, been there, done that, but to be sure, I did it all again today.

The boards you speak of would be the EB & EC & the one along the side is the D board.

The EB has four sub-boards, three EBA's, one for each color, plus another one (EBB), for what I don't know, the EC has three ECA's, one for each color. I hadn't done this previously, so I re-seated just the ones associated with red on both boards which made no difference, then I swapped red with green (green focus is OK), on both boards, which again made no difference.
Just for fun, I re-seated the EBB board, no difference.
Then I did that all over again using the boards from the spare projector, and guess what? Still no difference.
Possibly I've got two boards from two different projectors with the same fault, but that's a bit of a stretch, and the spare projector isn't running, so I can't compare.
I suppose in desperation, I could swap the red tube with the spare projector, which wouldn't be all that hard, but again, that's a hell of a stretch.
If I ever get to the bottom of this, I'll let everybody know, although it's probably one of those obscure faults that no-one else will ever see.
I'll have to think for a while about where to go next.

Thanks anyway.

**Curt Palme** · Posted: Wed Sep 04, 2024 2:36 pm Post subject:

BAd focus yoke? That's possible. At this point I would put a 'scope on the waveform going to the focus yoke, and compare the red to the green, just to see if the waveform changes are you adjust it. If so, then I'd say the focus yoke is bad. If not, it could go back as far as the processor board, that isn't generating signals?

BruceR · Joined: 05 Nov 2018 Posts: 14 Location: Brisbane, Australia

Thanks for the suggestions Curt. It's ceiling mounted, so I added a couple of temp. test points to the EB board. The waveform is missing at MG.V.R (Out), OK on green where I can see it clearly, and its DC level ramps up and down as I change the setting there. Waveforms are there on both MG.H.R. (Out) and MG.H.G. (Out). I compared the red and green yokes via those test points to ground with my meter, both read 33 ohms, (or was it 330), anyway, both identical, so it looks like the yoke is OK. I suppose you're going to tell me those waveforms are generated on the YA board, because the spare one is the only board that will not work with either of the YB's in this projector. It runs for about ten seconds, then gives a momentary 88 and shuts down with no code in the window, just the standby LED showing after that. I can use either YB with the original YA, but the focus still does not work with any combination that will run. So, at the moment, the only board I cannot swap is the YA. I realise this has become a bit of a brain breaker, but thanks for any help you might be able to give.

**Curt Palme** · Posted: Fri Sep 06, 2024 3:13 pm Post subject:

I no longer have a D50 service manual, but yes, I think you're right then, the YA board is bad.
You may be able to fake it to better than it is for the time being by jumpering the red focus drive to the blue. Then use the blue to adjust the red. SInce blue is less critical in focus than R or G, do the red, and hope that the blue parameters follow close enough so that it's useable.

BruceR · Joined: 05 Nov 2018 Posts: 14 Location: Brisbane, Australia

It's a G70 Curt, I might not have made that clear. Here's what I EVENTUALLY found today. The signal path from the D board to the EB board follows a pretty convoluted route. Following the circuit diagrams showed a direct, but a pretty tortuous path to each board via various connectors/motherboards, so it should read a couple of ohms at the most. So I soldered a wire onto the back of the vertical red mg out terminal on the D board, then did the same to the EB board, but to the in terminal, expecting to read continuity, but I saw 30K instead. This was on the spare unit. So I transferred both boards to the main unit, and it read exactly the same! I refused to believe (big mistake) both projectors could have the exact same fault with exactly the same reading, so I double, triple,quadruple checked my connections, pored over the diagrams to see where I had gone wrong, but found nothing. Back to the spare unit. I transferred everything to green and checked again, 1.5 ohms! Back to the main unit, 1.5 ohms, now I'm getting somewhere. Back to the spare unit, transferred everything to blue, 30K again. Damn! Back to the main unit, 1.5 ohms again, perfect.
The spare unit is a non runner, so I can't compare them working, but it's looking like both have motherboard problems, one with both the red and the blue, and one with just the red. This is a worry, because it's looking like motherboards might be starting to fail on these. That's enough for one day, I'll try jumpering between the D and the EB boards tomorrow and see what happens, hopefully it won't cause some kind of patterning, because getting the motherboards out of there and back again would be a hell of a task.

**Curt Palme** · Posted: Sat Sep 07, 2024 7:42 pm Post subject:

Sorry, I meant the G70. Smile

I've never had a motherboard problem, but I haven't worked on one in 15 or so years. Stuff happens over time for sure. But.. you can always hard wire a jumper in if you want. I'd also check each module for bent pins. I've done that a few times.
I think the G70 motherboard is only double sided and not multilayer. Assuming that's correct, I'd put in a jumper between the two points where you're reading the open, and see if that works.

BruceR · Joined: 05 Nov 2018 Posts: 14 Location: Brisbane, Australia

Well, that was it. Jumpering from MG.V (R) on the D board to MG.V.R (In) on the EB board bypassed the open track on one of the motherboards and got the red focus working again. But considering the issues with the spare unit, will this be an ongoing problem? That one was handy as a test unit, until one day, it came up with a 32 code, but swapping the EC board (or any other board for that matter), made no difference, and later, with a 37 code as well, but all the fans start spinning, and swapping them with one from another projector, one at a time, made no difference either. Now I find there's an open track like on my main unit, but blue as well. So it looks like the spare might have multiple motherboard problems which might be a sign of things to come, and might eventually render these useless like some G90's, one of which I also happen to have. That's inevitable I guess, nothing lasts forever, but it will be a real bummer considering I've got two sets of brand new tubes for these, plus those in the spare unit which are pretty good also. When I started looking for this fault, I thought it might be a rare one that no one else will ever see, now...not so sure, I've got two out of two. At the start of the year, which is summer here, we had horrendous humidity, over 90%, felt like 100% some days, whether that was a factor, I don't know. And thanks to Curt for steering me in the right direction.

BruceR · Joined: 05 Nov 2018 Posts: 14 Location: Brisbane, Australia

Below is a post to a particular member, but it remains unread, not sure if I did it right, so I'll post it here for all to see, maybe he will too.
Might be a sign of things to come with G70's.

Hi Robert. It looks like we've got a similar problem, but a different cause. In my case, changing boards made no difference at all. The jumper only gave a temporary cure, other faults started to progressively show up. I found that a series of fine tracks on the MR mother board, just to the front of where the EB board plugs in, were corroded, and going open, one after another. I've also got a donor unit, from a completely different source, but unbelievably, its got corrosion in exactly the same place, so I'm thinking maybe this will be a problem with all of these as time goes on. After repairing the best of the MR boards, and fitting three new tubes, it looks like my last B board (three now) has failed, and I don't have another. So everything has come to a screeching halt at the moment, and maybe this is the end for these two. I can add a pic. of the corrosion if you like, but it may not be of much use to you. Regards.