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Discussion Starter · #1 ·
Just wondering, when measuring the Cathode DC voltage level it says to connect the meter to "K" the cathode.... where exactly is the "K" ...is it on the back of the neck board ...


Thanks in advance
 

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Discussion Starter · #4 ·
This is confusing:


I set r5 for 140vdc...no problem. Then I set R8 ...it says adjust for a grey raster .. I am assuming this means it is just barely on. then it says make sure one of the tubes R8 should be set at maximum .... does that mean this particular crt would be really bright????? How do you know when you get to a maximum..because my R8 keeps turning...so I assume the maximum would be the brightest point? Now the the confusing part...now when I check the vlotages they are all off again..... HELP!!!!!
 

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You set R8 first for maximum brightness, then you set R5 for 140V cathode voltage. Then, with all tubes lit up, displaying some low IRE field (from Avia), set each neck boards R8 so that the raster is gray (color balance for low IRE).


Cary
 

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Discussion Starter · #6 ·
Got it,


so the 140 vdc is set when R8 is at a maximum, then one tube is left at maximum (adjusted later using G2), and the other two are turned down using R8 until the raster turns grey.... for those of us that don't have avia I guess that means when they just turn on. The resulting voltage is not necessarily 140vdc ...in my case is was around 147vdc.
 

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If you adjust the K voltage you will change the overall grey scale tracking. Adjusting the R8 pot is done in the middle of a series of steps to arrive at a correct gain or gamma curve. The procedure is as follows.


Black and White Level Adjustment


The three big pots that run down the middle of the projector between the green and blue CRTs are your reference focus pots, the little pots are G2's. The G2 adjustments are effectively separate brightness controls for each CRT, so that they all extinguish at the same video black level. Setting G2s is a basic step in adjusting color temperature at the dark end, so it is touchy. When set correctly, as you watch a black and white picture, the dark gray areas should not be tinted.

1) Set Brightness to 5

2) Set contrast to 0

3) Adjust pot so that raster is just turned on, viewing into the CRT face

4) R20=Red, R45=Green, R19=Blue


The drive controls are like separate contrast controls for each CRT so that bright areas look white and un-tinted, but since your eye adjusts its own white balance, you need a colorimeter or 6500 degree white reference to get that just right. Having the gear and knowing how to adjust a set properly is why ISF techs must charge a reasonable fee to do that job right. The drive controls are small trim pots accessible through marked holes on the rear panel. Obviously when you touch the G2 you will alter the grayscale and (overall) the gray/white tracking!


rule #1, touch the G2 in very (very!) small movement.

rule #2 you need all the routine to be applied, if you alter the G2 you've to set-up everything again, that means the black levels, the cathode voltage, the peak level, the gain, the cutoff of the image and so on.


1) with a white video signal (all white) set bright=10, contrast=0 act on R8 of all the tubes (the very small pot that you will see on the lower-right of each board were is located the socket of each tube), until you reach the maximum brightness, you will easily find a position in which all the colors "explode";



2) turn on the crosshatch or feed a certain image, like the windows desktop or whatever else. B=10 and C=0 (important!) Act on the three small pots located at the top of the video control board (the last one on the right BEFORE the two input board sockets) in order to make the recognizable image or the crosshatch DISAPPEAR at all (no recognizable shapes), look directly into the tubes, or, if you have a mirror, just use it.


3) Measure the cathode voltage level, right now... you need a good tester (voltage meter) in order to measure 140V. The point is on the same small board located rear each tube, the same in which you found R8. it's on the middle-left portion, close to the socket pins, and it is called "K" (cathode). Connect the meter to ground and to K, and measure the volts. Reach 140V acting on the other small pot (very close) called R5, adjust 140V for all the three tubes, with NO signal, B=5 and C=0;


5) B=5 and C=0 again, adjust the G2 (very small movements!). They're located on the FOCUS/BIAS board, on the right of the green tubes (BE CAREFUL, THERE ARE SOME DEADLY VOLTAGES), the three small pots, on the top of the board, close to the respective on/off tube switches, to be acted with a small screwdriver, the raster has to reach the point where it comes barely visible, it's at the point of disappearing completely.


6) Feed a gray bars screen (with AVIA), go on the board with a lot of pots, the fourth, beginning from left (waveform board), and act on the three upper pots, one for each color, raise the contrast to 6-7 and check it out the gray scale. Turn ALL of the three to MAXIMUM and check for any dominant, lower the respective level(s) until you reach a perfect or a very acceptable gray scale (look at the bright zones), obviously you lower the most powerful colors, one of the three, the lowest, has to maintain the MAXIMUM! (it's the gain level for the three colors);


7) set C = 1-1.5 and check the gray scale at very low bright levels, are they correct? if no, touch the respective G2 (adjusting them to lower the possible dominants), again, very, very small movements, smaller than before!!!!!! Then do step 6 again (you will see that if you touched the G2, you altered the GAIN), repeat until you reach the best position for G2 (at the very low contrast level) and the GAIN at the high contrast level... you have to maintain an acceptable GREY scale at all contrast positions.


8) Set B10 and C=0, check out the R8s (As in the first step), in order to reach a gray raster. Again, one of the three R8s has to be at the MAXIMUM! You lower the two other dominants (most powerful tubes).


That's it!


DON'T touch anything else. There are some thousands volts on the G2, the focus, and the Anode (!), DON'T touch anything on the three small boards where the tube sockets are located (the ones were are located the R8/R5).


Hope this is useful for ya!
 
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