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  #46  
Old 11-01-2014, 01:25 PM
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bright down the hv adjust does work and can get 23kv but only if the pot is maxed and on different scenes the hv drops off like it is not regulating and this is why i was wondering about the resistors. the hv adjustment dont have much gain to it and the reg tude does get hot like its working and in the dark if i raise and lower the hv adjustment the tube will glow with alittle blue to it depending on up or down adjusting and i have tried several reg tubes in the past and all the same result. but i will have to check the ma in that hv circuit.
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  #47  
Old 11-01-2014, 01:44 PM
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i had posted some pics of the crt in this set if you can find it or maybe you have seen them with the blue marks that start at the anode button and has traveled down the tube and when i first got the set the blue mark was nowhere as big then as it is now and yet it tests good and there is no blue or purple glow to suggest a gassy tube maybe there is something going on with this crt thats taking to much hv , making the lines, i dont know but i do know that the mark at the button was just that when i first got the set and now its several inches down extending from the botton and several members had said it was a manufacturing thing in the glass but why has it got worse is the question.
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  #48  
Old 11-01-2014, 01:48 PM
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bright down the hv adjust does work and can get 23kv but only if the pot is maxed and on different scenes the hv drops off like it is not regulating and this is why i was wondering about the resistors. the hv adjustment dont have much gain to it and the reg tude does get hot like its working and in the dark if i raise and lower the hv adjustment the tube will glow with alittle blue to it depending on up or down adjusting and i have tried several reg tubes in the past and all the same result. but i will have to check the ma in that hv circuit.
with the brightness all the way down what is the max HV you can get with the HV adj pot fully CW.
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  #49  
Old 11-01-2014, 02:10 PM
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i can get just befor the red mark on the hv probe i think its 25kv but the hv will droop down to 19-20 kv depending on the scene. but again with the hv adjust maxed and all my other sets setup on the hv the pot is just alittle over the half mark.
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  #50  
Old 11-01-2014, 02:13 PM
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ok with the brightness all the way down the max you get on the probe is 25kv?
with the HV pot maxed out correct?
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  #51  
Old 11-01-2014, 02:21 PM
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yes
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  #52  
Old 11-01-2014, 02:24 PM
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ok Now disconnect the lead from the top of the shunt tube, hang it so it cant arc to anything (it will have full HV on it).

CRT brightness all the way down are you still at max of 25Kv?
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  #53  
Old 11-01-2014, 02:29 PM
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well i will tell you i have done this befor with the reg tube cap off but now the chassis is on still on top of the cabinet and each time i have done this it did go to around 25kv and also did it with the crt plug off as well its only once the crt plug is put back on then the hv drops and it has been said that something is loading it down. either in the circuit or the crt itself.
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  #54  
Old 11-01-2014, 02:31 PM
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when you get it all back together if it is not working I will attempt to help you.
I can not with out going thru a specific series of steps in a flow chart like manner. Good luck with it.
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  #55  
Old 11-01-2014, 07:51 PM
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ok ill get this thing back together and see what i have and i will get back to you and i really appreciate all you are helping me with dave and the last thing i want to do is to waste your time or anyone elses for that matter. thanks
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  #56  
Old 11-01-2014, 08:07 PM
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No waste of time, you will get it, just sometimes a tough dog takes a very systematic approach to resolve. Hang in there.
I will be around to help when I can.
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  #57  
Old 11-01-2014, 10:08 PM
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well i will tell you i have done this befor with the reg tube cap off but now the chassis is on still on top of the cabinet and each time i have done this it did go to around 25kv and also did it with the crt plug off as well its only once the crt plug is put back on then the hv drops and it has been said that something is loading it down. either in the circuit or the crt itself.
If you are getting no more than 25KV with the reg cap OFF--then the HV ckt is not producing enough HV. With the reg out--it should make it to at LEAST 30K--unloaded or with no raster.

This might mean the drive is not good enough--or maybe the damper ckt is not working well enough, possibly that "boost cap" the one off of the damper tube--where the boost is taken from--is bad. BTW--I do NOT think the HV adj. will work at ALL--if the regulator is out of the ckt. BTW--not sure on this chassis--but SOME horiz. ckts, have a resistor that comes off of a positive supply, designed to keep the grid from going too negative. If it goes up in value--this happens...and you get low HV and other problems. It is likely to be a high value one--100K or more. I recall Jack Darr or someone, talking about this in an article--I think in a PF reporter magazine.

And--do NOT forget to check and see if the B+ is up to snuff. Not sure what it should be--but I would say at LEAST 375V...WITH proper load. Maybe more-much lower--and you WILL have problems ALL over the chassis.
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  #58  
Old 11-02-2014, 06:11 PM
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well this chassis is a ctc12 clone and it dont have a boost diode, why i dont know but i guess design but the 15 has it. i did disable the hv pot from within the circuit and got a scary little over 30kv.

Last edited by timmy; 11-02-2014 at 06:48 PM.
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  #59  
Old 11-02-2014, 06:55 PM
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The circuit rca2000 is a hold down circuit designed to limit HV output incase the shunt tube were to not regulate. It takes a negative voltage from the horz blanker grid and thru a voltage divider applies it to the grid of the horz output tube. was not used until the CTC-15, don't know about clones. the defect that would take place is a break in the trace on the edge of the chroma board, that would upset the voltage divider, providing too much neg voltage back the grid of the horz out, thereby limiting the power thru the tube and holding back the voltage.

You find this by checking the grid voltage of the horz out, should be about -50v if its a lot larger neg like -65v there is a good chance the problem with the broken trace exist IF THE SET USES THIS METHOD.

This would also show up in testing the horz out cathode current (it would be low).

This failure can also effect the brightness control as the too large a neg voltage also feeds the neg (dark) side of the brightness pot.
you can also check pin 2 of the horz blanking amp. this is the pin that has a 390k resistor to ground if its higher that 390k then the

A simple continuity check can be done by check from ground to the resistor that goes to blanker grid. Just look for the trace on side of the chroma board that runs next to the horz out. its pretty thin and is on the narrow side of the board.

I hesitate to mention all this as I would prefer to simply diagnose problems rather than jumping on every known problem in hopes of guessing right.

But if you have the chassis you may as well verify the continuity.

you can also check pin 2 of the horz blanking amp. this is pin to ground should not be more than 390k if so its likely the trace has cracked. the sams shows 220k on the resistance chart, but thats due to some other resistance in P with the 390k resistor that goes from the grid to the ground.

Last edited by DaveWM; 11-02-2014 at 07:05 PM.
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  #60  
Old 11-03-2014, 08:02 AM
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ok the 390k resistor checks at 250k and the ground trace is good. 250 seems alittle low dont they usually go up in value. as far as the damper there is 2 caps off the damper which has been replaced and its a .12 250v and a disc n1500 4kv and there is a small disc n760 1kv sams says it a 22mmf to ground off pins 2 and 7 was not replaced. and l31 and l30 check perfect .4 ohms.

Last edited by timmy; 11-03-2014 at 08:19 AM.
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