Projection TV convergence problem? What does this picture show?

You can do the convergence surgery through the front panel of this model without removing the back and setting off the booby trap.

Replace both STK convergence IC's, also check low value resistors. ...5, or 1.0 ohms approx. The booby trap is the optical sensor under a hole in the DVI metal box. Unplug power plug and wait a minute, remove panel, unplug all wires to the DVI module and you can work on it safely with power on.

Also you can work from front for convergence job only, if this model uses long retangular convergence board (no screws, held in place with snap hooks with metal box. you can get it out from front and reach deep to release one of cables from holders and unplug from the small stand up PCB.

snipped-for-privacy@signaturefactory.com wrote:

Dont forget there maybe a open Pico fuse as well.

kip

Thanks for the info. I am working from the front.

I have already checked the resistors and replaced the one STK convergence IC that controls the red (Blue is controlled by the other and green is controlled by a combination of the two).

Yes this is that model and the convergence board came out nicely but I found no problems with it and after replacing the STK the same problem is still present. Any other ideas? I really appreciate the help.

Pico fuse where? I don't see any on the convergence board itself. Thanks for the help.

We they are there you have to trace back and locate them if no voltages to Stk,s.

kip

First of all, you cannot just switch red and blue. There were old Sonys that had the red and blue well matched and the convergence affected them somwhat like the middle set of rings on a tri-color CRT.

Now, OP, you have confused the issue switching s*it around, show me the crosshatch with the connections correct.

Put the thing how you found it, post a pic then, then I will look at it. From the pic you have, you have a foldover, but not a real bad one, it is more like a voltage amp clipping.

Then this could also very easily be a fault in the blue channel of the DCM. Do you know how to definitively check if the STKs are good with a scope ?. Also, you can't even do it in that set without extreme measures. jusat hook it back up right and let me see it.

You might find that a resistor, say a 1 ohm, overheated and became LOWER, like 1/4 ohm. I have had it happen.

You might find a leaky Zener diode, All kinds of parts that cost less than a dollar. Which one ?

First thing, is to put it back together, I don't mean the back, but I wanna see all three colors with each hooked up to the proper outputs. This color switching technique doesn't work anymore. I need to see the problem, not the problem as modified by you.

Put the thing back right, don't put it together, I couldn't care less if your cat crawls in there. UNtamper the set and show me the picture, and tell me if it is with new STKs, and where they came from and if there was a change in the symptom after their replacement.

Then we can proceed.

Any of you out there wonders why it costs $300 to fix these things, take a crack at it.

JURB

No Voltage NO output...Simple!!

Thanks, it seemed to me to be a decent test but I unjderstand it may not have.

I will do this but the crosshatch was basically identical to what I showed and that is why I posted it.

I appreciate your help.

I don't but I do have the equipment to do it. If you point me in the right direction I should be able to scope it.

I checked the resistors with a 4 wire ohm meter and all were within 0.1 ohm of value.

I will do this.. Unfortunately I'm no where I can acccess the TV now but I will do this shortly.

I purchased new STKs from someone on ebay. I only replaced the one controlling the red channel. Symptoms didn't change after I replaced it.

I truly appreciate your help. It seems to me that it should cost more than $300 when paying someone to fix. Either you have someone who is really talented and deserves high hourly pay or you have someone who isn't and just replaces everything at the board level to find what's wrong. Either way you pay a lot.

Is one stk cold yes or no ??

If both are warm .... Did you go into service menu sections and try and realign sometimes when they go it will kick back the DCU..

Yes.

I think you are right, it looks like I need to back up and start over. I hooked the outputs from the convergence board back up how they were originally. The picture I get is:

I remember the hatch looking much more like that shown in the previous (where I had output swapped). But now, looking at the previous hatch I see that red was very hard to see. The red lines are very faint when hooked properly and near the top of the picture are quite wavy. When watching TV the center of the picture looks just OK but near the top we see a wave of red. I looked at both circuit boards attached to the red yoke and I see no bad solder joints, no capacitors that look like they've gone, and no other components that are obviously bad.

Any suggestions?

snipped-for-privacy@aol.com wrote:

First of all why is the "black" area red ? Have you cranked the G2 for some reason ?

Regardless, it seems you have eliminated yokes and STKs as suspects. That leaves the DCM. You said the symptom did not change when you changed the STK, but did it stay EXACTLY the same ? There are alot of out of spec STKs out there. The ones that aren't completely dead somettimes have poor high frequency response, and that is critical in alot of sets.

At this point in time I do not know how to get into the alignment mode, and although you never try to adjust out a circuit fault, just how it responds to adjustments may lend a clue. If you happen to know how to get into the convergence alignment mode, let me know. There is no doubt one of these things will darken my bench someday.

I don't know if it has a cursor based system or the old siz/lin/trap etc controls. If the set allows you to see the whole picture while adjusting the crosshairs you can see if it changes when you do so, if not, perhaps somewhere in the service mode there is a DC offset value. If the pattern moves uniformly the problem is in the DCM. Even if it doesn't the problem could be in the smoothing/buffer stage at the output end of the DCM.

You don't even want to know what the DCM costs, so all other suspects must be eliminated first. If the problem is in the DCM, and it turns out that the output is clipping the waveform before it gets to the STK, that might be no more than an OP AMP, but if it is in the waveform generator itself, we are talking some hairy s*it, err scary s*it. Also, because most of it is SMD components it is not practical to swap comonents of red and blue channels to see if the problem follows.

In the last picture, I am not really seeing the red lines, but I do see the abberation. When you had it "cross channeled" I will say that this is not normal though, that is if you took a normally working set and swapped the yoke plugs I would expect the H linearity errors, but the errors in the vertical lines at the top are defiitely not normal. The general trapezoidal shape is to be expected (that's why you can't just switch them), but the 'wave' in it is not right. My remaining brain cells still scream STK, but that has been eliminated. The exceedingly rare shorted convergence yoke is also exonerated.

I know the set is an incredible bitch to work on, but at this point I would compare the waveforms at the + and - inputs to the red V channel. You should have a very similar waveform on each, or practically nothing if it is setup as an inverting amp. Those STKs are nothing but overgrown OP AMPs. You should be able to get the spec sheet at datasheetarchive.com. You may find that a little (pf) capacitor has suddenly decided to be a resistor and is making the STK behave badly, wouldn't be the first time.

In some sets you can switch the yokes, AND the DCM outputs to the STKs as a definitive test, but I wouldn't count on it here. It would probably entail cutting foils and installing jumpers, and then you can't be sure of yoke polarity.

You said one STK is getting hotter, which one ? The one feeding the offending color or the other one ? If the offending channel is cooler I would look for perhiperal components in that stage (which are few). On the other hand if the offending channel is getting hotter I'd look for something across the output. Zener diodes, small caps etc.

You got a fun one there. Good luck.

JURB

Yes I did crank it otherwise the red lines are almost not visible at all.

I'm still wondering if it could be the yoke. If you look at the picture from when I swapped outputs on the convergence board you'll see that no red is visible. Yet blue was. So it seems like the convergence output is fine but it must be something beyond that.

I do believe that it stayed exactly the same.

I do have the service manual and so am able to get into alignment mode. Basically you hit the button on the convergence board and then you hit menu to do green, 100+ for red and input for blue. But red is almost unadustable and very difficult to see.

Why couldn't be a shorted convergence yoke?

I did get the data sheet. I'll take a look at the + and -.

Would it hurt if I just switched the yokes?

The red channel STK heats up almsot immediately.

Again thanks for all your help.