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  #31  
Old 02-05-2015, 09:48 AM
DaveWM DaveWM is offline
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ok what is the voltages on both sides of the 100k?
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  #32  
Old 02-05-2015, 09:51 AM
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my last post i said there was an additional 100k but it was a 180k, also good. there are no other 100k resistors on the chroma board except each one at the g1 wires.
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  #33  
Old 02-05-2015, 09:59 AM
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the 180k has 405 one side and 179 on the other if this matters. if i let it warm it goes to 185 v
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  #34  
Old 02-05-2015, 10:12 AM
DaveWM DaveWM is offline
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I am trying to figure out the G1 voltage, IIRC you had about 160v, but if the 100k resistors have 185 then it should be 185v, which is in the normal range for the G1. Note this is highly dependent on the CRT bias so maybe you adjusted it at some point and got the differing voltage being reported now.
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  #35  
Old 02-05-2015, 10:18 AM
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this voltage is from the 180k that i thought was another 100k, was my mistake but the voltages on the g1 are 100v probably because i have the chassis hanging out of the cabinet. but still they are low and this 100v is at each 100k resistor , g1.
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  #36  
Old 02-05-2015, 10:28 AM
DaveWM DaveWM is offline
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ok lets start over again

CRT
G1 voltages
cathode voltages
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  #37  
Old 02-05-2015, 10:36 AM
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ok im going to do this with no yoke or crt plugged in, is this ok ?
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  #38  
Old 02-05-2015, 10:40 AM
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ok with these things no plugged the cathodes are 340v and the g1 99v i guess lower from befor because the crt and yoke are not plugged and the bias is still ccw.
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  #39  
Old 02-05-2015, 11:32 AM
DaveWM DaveWM is offline
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well you should test them with everthing installed, that being said those voltages are wack.
the 99v does not make since, if the 100k resistors have 180 one the low side, then the G1 should be the same.
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  #40  
Old 02-05-2015, 11:37 AM
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no the 100k resistors dont have 180v the single 180k resistor i mentioned has that on one side.
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  #41  
Old 02-05-2015, 11:58 AM
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Timmy,
Check your email at 1:20 pm. I scanned a Magnavox "series 45" schematic (CTC16 variant) which you have. The only thing is, there are no voltages on the tubes, only sources like 405 volt supply, etc.
I am ALSO sending a series 41 (similar to CTC12) schematic which HAS VOLTAGES on all the tubes.
On a 41, the blanker feeds into demod tubes' cathodes and the CRT bias sets the bias on the CRT via the B&G drive controls.
Also the 41 schematic shows you CRT voltages:
cathodes =322 volts
G1s = 195 volts
G2s = 700-735 volts

The 12GN7 should measure about 250+ volts on plate pin 7 if too low, pix is bright, too high and pix is dark.
Dont forget that 100 mf @ 25 v cap across the contrast control, jump in a new one

Whatcha got for volts on CRT pins?
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  #42  
Old 02-05-2015, 12:00 PM
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ok well 100v on the G1 is clearly the problem, so now you need to check all the pin voltages on the 6GU7's these are the difference amps. I am still a bit lost since I thought you said you had over 200v on one side of the 27K power resistors. If that is the case you should have the same voltage (200v) on the G1's.
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  #43  
Old 02-05-2015, 12:27 PM
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the g1 166v-171 cathodes 305v -310v all plugged in . the contrast i touch a cap at the contrast pot and gets nice bright only for a second. g2 anywhere between 546v and 1046v depending where the drives are. the 27k resistor i was talking about was the gig single 27k high wattage resistor , had 405 on one side and i think it was 244 on the other.
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  #44  
Old 02-05-2015, 12:35 PM
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the brightness increase is due to the momentary short of the cap on the cathode of the video out. changes the bias of the tube, causes it to conduct hard, drops the plate voltage thru the load resistor, direct coupling to cathodes result in lower cathode (momentary) at the CRT, changes the bias to more conduction (less difference in G1 to K) so more eletron flow in the CRT.

I would start with the assumption that the problem is in the video out, so try a new video out tube. check voltages of that tube as well.

You should also try a new blanker tube since it is part of the crt bias circuit (unlike the CTC-12 this set uses G1 voltage adjustment to set CRT bias not the K's).
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  #45  
Old 02-05-2015, 12:36 PM
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if the capacitor i use to jump in on the contrast control has a charge in it the screen gets really nice and bright but for a second. it almost seems as if there is a source to the contrast thats missing.
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