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Discussion Starter #1
If someone has the newer XG 135LC service manual could you look at the methods of adjustment section and verify what the voltage is for the cathode adjustment at Test Point 7501 for the Video Out PWB.


The older NEC 1350 service manual in section 7 illustrates CRT cathode amplitude at 4.0v +/-.1 Vp-p


The actual measurement is less than 1.0v Vp-p.


There is screen capture of the wave form in the schematics section of the manual showing this voltage level to be .4 volts not 4.0 v .


I'm thinking that it's a typo in the old manual and was wondering if this could be confirmed in the new manual.


Thanks!

Paul
 

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Could someone take a measurement at one of these test points 7401, 7501 or 7601 with a scope and advise what voltage your seeing with an external cross hatch pattern input ?



Thanks!


Paul
 

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The test point numbers you mention aren't the same but are you refering to the cathode amplitude test points on the individual CRT neck boards? Those should not exceed 3.35 V PP with a 100 IRE input and contrast at 100%. If it is higher than that you risk the tubes. Turn down red and blue drive controls and green cathode amplitude VR7505.


Maybe the waveform capture was done using a 10X probe? I don't see the waveform in my 1352 service manual.
 

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My voltages are around 1.0 Vp-p. And yes, it's the cathode amplitude I'm refering too.


It's possible a 10x probe was being used as I'm using one myself. However with the digital scope I'm using, the scale is automatically adjusted based on the probe type.


My measurements were at 100% contast, cross hatch pattern input via. s-video using AVIA as per the setup instructions.


I'm just going through this procedure just to baseline all the measurements and this one voltage is messing with my mind.


The book actually says "Below" 4.0 Vp-p in the "Simplified" CRT replacement setup section. I'd just like to know if there is a hard set rule for this voltage level as some constant.


Now this is on the Video Out PWB. Not at the CRT neck cards.


Now this is an NEC 852 projector I',m using a 1350 manual. Is the procedure different in the newer service manual ???


Thanks!

Paul
 
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