ctc12 clone beam current

[andy]

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[timmy]

Originally Posted by DaveWM

Did you ever check L14 (coil from service switch to cathode leads of crt) that I mentioned many many post and threads ago? if the swap shows the issue is with the chassis and not the CRT I would suggest you check that while the chassis is out.

yes i did check L14 the ohms, compaired to the sams. if im correct i didnt cut it from the circuit i just measured the ohms and it was where it should be so i didnt feel i should remove it from the circuit.

[timmy]

Originally Posted by andy

Does the HV remain constant until the regulator current drops to zero as you increase the brightness? If it doesn't, the HV regulator isn't doing its job. Blooming shouldn't start until the regulator current goes to zero.

If the regulator behaves, but it doesn't produce a bright picture at maximum beam current before blooming the CRT almost has to be bad.

the hv stays steady depending on the scene being shown on the screen because white scenes are the worst as during white scenes the hv drops and wont regulate to maintain until the white changes to some other colors. the brightness is always at max, but heres the kicker the blooming is so much worse if i do the grey scale the way it is said to do by putting in service mode and what ever color dont show up i would have to use the bias alittle and adjusting the rgb drives per the sams. this is when the blooming occurs so i have to leave the bias counter and the rgb drives counter in order to get any decent picture, and the white scenes are still a problem setting it up this way. so the result is a somewhat not bright picture although clear its not right. i didnt watch the ma during all of this but this is when it blooms as it seems to when a bigger demand is placed on the crt by raising the drives and or the crt bias, it cannot handle it as it will bloom and pull in on the right side screen. if i turn the brightness down and then turn it back up it does not bloom provided the rgb drives and the bias is fully counter clock.

[miniman82]

You have a HV problem, then. Start looking at the horizontal section or HV rectifier.

[andy]

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[Electronic M]

Perhaps the HV reg resistors or caps that tested good on low voltage test equipment break down and stop working at rated voltage.

[timmy]

well i already tried a solid state 3a3 rectifier, no difference. i also checked the hv regulator resistors and they checked at 1.6m and 1.59 close enough to 1.5 meg. the funny thing is first getting this set from the beginning the hv was a problem so since then i changed all the caps under the chassis with no change in the hv regulation including the flyback. i thought i found the problem when i changed the fly when i found the focus 1v2 was wired wrong but that didnt help after correcting that. i had thought there was a problem somewhere in the crt drive circuit chroma board or somewhere else affecting the regulation of the hv but im all out of options as to where to look. i was trying to cover as much as possible befor pulling the crt and swapping to rule it out because i am limited to room here and yet the crt in the set tests very good for the age.

[andy]

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[timmy]

lol,lol, thats just it i dont know anymore whats going on with the set. and yes i have to swap the crt and if another crt does the trick then ill be amazed at what may be wrong with the other seeing as it tests great. but it could be alittle gassy enough to create this problem and that would be a real shame because it does test good.

[miniman82]

Originally Posted by miniman in post #6

My guess? You probably have a bad picture tube (gassey), and you need to sub another one to confirm.

They can test good and be gassey...

[timmy]

well with my on going hv issue with this set i do have a question. with the set on hv present at anode crt plug off should there be any voltage at any of the crt pins. i checked with a dvom to ground and have no voltage at all except at the focus pin which was 7 volts , would this sound right ? and the hv with the anode wire off the crt is 19kv just at the wire. anode wire back on, crt plug off i was lucky to get 22 kv, thats it, picture scene changes and will dip right down to 19 kv or less. i didnt try another crt yet but was looking around for something concrete here that may give me an idea the crt is finished maybe due to gas. i read an article online about crts and what was said about getters is that a bright shiney mirror like getter is good no air or gas. however what also was said was that a white of course means it took on air but the last was a getter that is coal black no mirror shine at all indicates gas in the tube. has anyone heard of this coal black getter meaning a gassy crt ?

[Electronic M]

Unless white there is no sure indicator, looking at getthers, of gas.

[miniman82]

Well if it's 19kv with no load, you've got a chassis problem. It should shoot up to the setpoint of the shunt regulator and stay there with no CRT attached, does the HV pot do anything in that state?

[timmy]

Originally Posted by miniman82

Well if it's 19kv with no load, you've got a chassis problem. It should shoot up to the setpoint of the shunt regulator and stay there with no CRT attached, does the HV pot do anything in that state?

the hv pot adjust does seem to work but to get even 19kv the pot has to be maxed. there is nothing else i can seem to look at as i looked at what seems to be everything already and have not found anything wrong. so if its a chassis problem then i am overlooking something here. or it is infact the crt. i thought the hv without connected to a crt will be limited because the crt acts like a capacitor so being off the crt 19kv sounds maybe like thats all i would get, i dont know at this point. but then again hooked back up to the crt i would think it would shoot up but didnt. does anyone know the leads that come of the hv regulator tube as to which one if there is a specific lead that does the triggering of the regulation, maybe a specific lead from that tube i can trace if this lead is used as some kind of reference for the hv regulation. because this hv just sits dont raise up just dips as if there were such a wire were cut.

[DaveWM]

the HV adj should not "seem to work" it should work, in a very linear fashion.

Disconnect the pot from the circuit and confirm (preferably with an analog ohm meter) that it is working as it should (500k to near 0 resistance as you adjust).

Confirm the voltage readings at the shunt tube grid and cathode, make sure the grid varies with the pot.

Confirm the total bias of the shunt tube is within specs of the sams.

At some point I recall you saying the HV would go to 30kv with out the CRT anode attached.

If now you are saying the max is 19kv without the CRT attached then only 3 things can be wrong.


Remember you are working with high voltages all over the place (400v around the cathode and grid of the shunt, 30kv at the anode) so be careful.

1) bad shunt tube

2) bad shunt tube bias

3)no loner getting 30kv with shunt tube disconnected.