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Discussion Starter · #1 ·
After lurking on this board for some years now finally have a problem

that has me stumped, and I need help. I have a Sony 1271Q that I have just changed the tubes on and I have a problem that I cant figure out.

The electrostatic focus was near the maximum adjustment on the old

tubes, but with the new tubes all three pots are at maximum and the

focus is not quite there. I have checked the potential at the focus block

and it is the correct voltage (14.4KV). The red , green, and blue are

all maxed. The voltages are set properly on the screen drives (4v onCFB-5 board). The dynamic focus appears to be working properly, the HV is correct and regulating. The tubes that I used for replacements are 07MSP and the original ones where 07MP. Could this be the problem? The only other thing that is different is the stigmators are backwards compared to the service manual, but this is how the were when I removed them.

Any help is appreciated. If a mod is required I can do it.

Drew
 

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Hopefully someone who works on allot of these can help you out. I do know this, no matter what you read your focus voltage at it has to adjust near center of range. If not the voltage is wrong, the divider is bad or what is going in is to low or to high. I think it is service manual and troubleshooting time.
 

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I have heard of this problem when using 07MSP tubes in projectors designed to take 07MP tubes. I believe there is a modification that can be made to accomodate them, I suggest you have a search through the forum to see if you can find it.
 

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Discussion Starter · #5 ·
pasey25,


I checked the posts and supposedly this only happens with the barco projectors and not the Sony. It is possible it is the focus block. I don't

think it is a leakage problem because the one tube that was leaking would have different focus than the others.
 

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Maybe Curt could tell you for sure.


Since the tubes changed, I doubt it is the focus block. You could pop one of the old tubes back in and see if the focus is OK- if so you know the block is OK. I would look at the schematic to see if there is a resistor in series between the tube and focus block; if so you may need to change the value, just like with the Barcos...


--Kieth
 

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HI,


My 1271 had 07MSP when I bought it and the focus was pretty much maxed out to get the best result. Because of this, (and some wear on the blue tube) I bought a set of 07MP tubes and re-tubed. Now the focus has enough range. The best focus is more in the middle of the adjustment for all three tubes. Some people say these two types of tubes are directly interchange-able but that's not my (or your) experience.


Also, my CPC (Astigmatism) rings appeared backwords according to the service manual as well but I verified they are correct. When they are backwords they don't work right. In my case they have to be the opposite of what is shown in the manual to be correct and I expect it's the same for you.


It's a bummer because I thnk 07MP tubes are harder to find these days. When Sony sold them they were always at least $100 more than the 07MPS tubes.


My guess is whatever focus mod was done for the barco's would also work in your case. It may be interesting to see if the pots are increasing or decreasing resistance when they get to the max point. If the resistance is going up then adding resistors may fix the problem. However, some carefull analysis of the circuit should be done.


Good Luck,


Brian
 

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Discussion Starter · #8 ·
Brian,

Thanks for the follow up. I had seen your earlier post and wondered what your resolution was. Unfortunately, I don't have the option to replace these tubes. I purchased them over 6 months ago for the ridiculously low price of $700 for the set. They are in mint(read unused or barley touched) condition and even with the imperfect focus they are better than the +11,000 Hr tubes that they replaced. I was hopping someone would come forward with a mod that could be done to boost the focus voltage. I have some ideas, but they would all compromise the HV regulation. If I need to change to a different flyback transformer or different focus block, this is something I can do. I used to work on electron microscopes and Mass spectrometers, so I know my way around HV circuits.
 

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I have not checked the prints on this unit but if it has a wire off the focus block that goes to the chassis and if you want less focus voltage, you could put and resistor in series with the lead to ground this should give you less voltage as most focus blocks are just dividers off the 2nd anode. If you want more you would have to check, (which is sounds like you might have), the 2nd anode voltage. and if there is any adjustment within specs you might try that. Some direct views pull the focus voltage off the HV triperler and sometimes they have a resistor off it that you can play with.


Good Luck
 

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Discussion Starter · #10 ·
RODDMOD,

I need more voltage for the focus, the voltage is derived from one of the two flyback transformers. There is a tap half way up the voltage multiplier.

There is no resistor in series with the 14KV at the tap, or at least that is external to the focus block. Internally there must be a resistor to sum the dynamic focus. Also, when I measured the focus voltage with the Pot all the way up it read 10KV, I was experiencing significant loading from the probe. This also indicates series resistance. If I put resistance in series with the HV lead to the tube anodes, I can increase the voltage at the focus tap, but I will reduce the output of the HV circuit and probably degrade the regulation.

Drew
 

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I guess the next thing to try is the focus block. HV resistors can drift, I have limited experience with the Sony projectors. I would be interested to know what you find. You might want to see if you can contact Sony tech support or maybe one of the dealers here on the site can help.


Good Luck:confused:
 

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What was the effect of placing the CPC magnets on the same way as the service manual said ?? As opposed to the way they came off the neck.


Graham
 
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