CurtPalme.com Home Theater Forum

[waterlily]

Hi,

Long time lurker first time poster

I have spent a few hours searching but could not find any clues for this problem.

The projector:
1252 upgraded with the Y, etc boards from a 1272 for 21 pt convergence.


The problem:

For 6-7 yrs, the RED tube has always had an extremely bright AKB line (gets much worse to the point of blooming and having to turn G2 down when no jumper in the CFB board)
On power on an error code 18 flashes briefly for a sec then disapears.

The best I have been able to do is use it with the jumper shorting the CFB board and adjusting G2 to keep things in check.

So far so good for years until...

yesterday... all 3 tubes are now very dim, enough that I can look directly into the tubes and nothing projects to the screen.

At the CFB board;
With the 2 pin connector CFB shorted I am measuring
2.8 volts pin 1 and 2,3,4
exactly 2.8 v for all 3 tubes, changing G2 has no effect on the voltage here.

If I remove the short on 2 pin conn. on CFB board, RED tube becomes VERY bright, the raster is too bright and I can see the return lines, AKB line is so strong it is blooming like crazy.

So I dial G2's down to min. and slowly bring them up until I can see an image.
For B and G I can see the AKB attempting to compensate *until* I increase G2 enough for an image to appears on the tube.

G2 for R I cannot see any AKB compensation, by the time I have an image on the red AKB line is burning very bright and blooming like crazy.

I bring up the pluge pattern and adjust all 2 G2's so +5 IRE is equally barely visible on all three tubes.

Now on the CFB board I measure;

1,2 --> 11v
1,3 --> 11v
1,4 --> -10v -what the?


Another thing, since the dimness the pluge pattern for RED no longer shows no matter the G2 level.

(BIAS/GAIN are at factory default for all the above)

Increasing G2 enough for a moment for any of the three tubes will result in saturation point where the raster starts becoming visible and I see return lines but it will still remain dim.

Image contrast and brightness controls have no effect (the numbers change but the image doesn't) regardless of CFB short or not.

All I can figure out is that something with the drive for RED is not right, the tube is too bright and I think this is what is hosing AKB and maybe causing the overall dimmness?
Reading the service manual, seems like AKB and tube drive revolves around CA board?
Could this be a bad red tube?

Since, I have torn the PJ completely apart, redone nearly all solder joints on most boards, disconnected, reconnected everything to no avail so far.

Tonight I will try to swap the neck boards to further narrow this down as was suggested over in AVS

Help!
Any ideas or suggestions from the experts?

[waterlily]

Hi,

So I wasn't able to switch the neck boards, but I tried swapping the G1 and G2 leads between Green and Red at the back of the G1/G2 adjustment block. This made no difference in focus or brightness or change the overall behavior
Thinking I could have a bad RED tube messing up the AKB somehow, I even tried the PJ with the neck board from the red tube unplugged from the CRT but no change.

To recap:

With CFB board shorted (AKB disabled?)
1-2 (B) +2.8v
1-3 (G) +2.8v
1-4 (R) +2.8v

Is this why the tubes are so dim? (shouldn't this be 4v?)

AKB lines look fine at equal intensity for each tube, combining into a dim white line projected on the screen.
All 3 tubes look great with sharp focus. Just the image is dim.

Removing short on CFB board (AKB Enabled?) I get wacky voltages:
1-2 (B) +11v
1-3 (G) +11v
1-4 (R) -10v and Red tube raster is visible wiping out the image, and I can see the diagonal return lines.

Then I have to dial the G2s wayyy down until all looks ok again, but the voltages above remain.

Contrast and brightness controls do nothing, the numbers change but the image doesn't.

Adjusting G2 has no effect on the voltages at CFB regardless if jumper is set on CFB board.

Pluge pattern for RED is missing in the BIAS test screen, the on screen BIAS numbers are there but I can raise G2 till I see the raster and no pluge pattern squares. (All the other test screens, inc. Gain show fine)

Any ideas? I have seen some CA boards on ebay, is this worth a shot ? (I see labels such as brightness/contrast, drive gain control and AKB on the connectors for this board)


Is this something anyone has run into before?

HELP!!! ^^;

[Curt Palme]

I'll email you as well. No question that this is a strange problem. I haven't seen this before. You're on the right track though, it could be the CA(G) or CA(B) boards, something could be fluctuating there, or check the G2 lines to see what the voltage is. The screen/focus block might be drifting, causing these issues.

[Curt Palme]

I'll email you as well. No question that this is a strange problem. I haven't seen this before. You're on the right track though, it could be the CA(G) or CA(B) boards, something could be fluctuating there, or check the G2 lines to see what the voltage is. The screen/focus block might be drifting, causing these issues.

[Curt Palme]

Actually re-reading the above post, this has to be a video issue, forget the G2 part..

[Curt Palme]

Actually re-reading the above post, this has to be a video issue, forget the G2 part..

[waterlily]

Hi Curt,

Thanks for the reply!

You mentioned differences in the 1270 vs 1252 boards,
So I can't use both the CA(RG) and CA(B) from a 1270 in the 1252 ?

Bummer... I pulled the trigger and purchased a set of both on ebay
(I noticed that I could plug the connector from the main board directly into CA(B) bypassing the CFB board, I was hoping I could do this when I get the 1270 CA boards...)

Will anything go up in smoke if I try?

I will try switching the CA boards outputs to the neck boards across tubes to see if the red 'overdrive' when AKB disabled behavior goes to another tube.

With AKB enabled all 3 tubes look fine just dim as G2 is 'locked' at 2.8 volts reading at the CFB board.
When I 1st turn on the PJ, things get really bright (rasters and return lines visible for a splitsec during filament warmup) but quickly the PJ dials things down to a dim level for all three tubes.

I noticed also that the heatsinked IC for RED on CA(RG) gets warmer than the one for G or B .

[Curt Palme]

You can try it, you won't blow up anything, but the 1270 boards are missing the AKB connector. That affects the image. I can't remember what happens though, it's been a long time since I've swapped them.

[Curt Palme]

You can try it, you won't blow up anything, but the 1270 boards are missing the AKB connector. That affects the image. I can't remember what happens though, it's been a long time since I've swapped them.