|
CTC 10 HV affected by brightness
Been stuck on this for weeks. Initially I thought it was a focus problem, but The HV on my 10 drops to around 14kv whenever the brightness is up, and it jumps around depending on what’s on screen, I have no idea what could be causing this. I’ve pulled the cap off the regulator tube and it made no difference, the rest of the hv tubes are fine. the power supply seems to be working fine. I even tried a different CRT but it made no difference, does anyone know how I could fix this??
All help is appreciated. Thanks again |
I presume the high voltage is normal when the screen is dark?
Have you replaced the tubes or only tested them? Tubes in the horizontal section can test good but be weak in actual use. |
Another thought: with a black screen, check the 640V boost voltage to see if something is pulling it down.
|
Does the picture 'bloom' (expand), go dim and out of focus with brightness turned up?
|
:oOOPs double post
|
Quote:
|
Quote:
|
I’m so lost I tried a few more things. None of the voltages or resistances look concerning. I checked the flyback it seems fine. Still no change
|
To repeat, is the boost voltage normal with a black screen? Does it go up and down with the high voltage as brightness changes?
|
Quote:
|
Quote:
|
Seems like the hv is not regulating or responding to the load.
|
Quote:
|
I had a silvertone ctc12 clone with the same problem hv would not go over 19 kv higher the brightness the lower the hv I checked and changed literally everything and was never able to figure it out. I basically gave up on it but it did work nice but was not right.
|
As old_tv_nut mentioned, more info would be helpful.
For example. HV reading at anode with brightness at low/mid/high 640v BOOST source with brightness at low/mid/high Damper plate (junt of L30 / C90) with brightness at low/mid/high This might give some clue as into what the problem is. |
The answer to the Boost voltage question carries some pertinent information.
|
Quote:
I change hundres of those over the years for blooming - it's the number one cause of HV drop when beam current goes up. Try another rectifier. Does the flyback get hot? A resistance check won't pick up a single shorted turn. If not, providing the boost voltage as requested will give the group more to go on. John |
The boost voltage is a most pertinent test. Another common fault is the HV Rectifier. How do you know it is good? Also is there a resistor in series with the HV Rectifier filament? They often go high reducing the filament current to a bare minimum and the low emission will cause the HV to sag.
|
You need to run the horizontal oscillator setup procedure outlined in Sams for that chassis. The horizontal circuit is the most finicky of all the circuits in a TV minus perhaps the tuner and IF strip, so if one adjustment is out of whack it will do funny things. Problem is- they're all related so it's difficult to pin down what exactly is causing the problem. When I troubleshoot horizontal circuit issues I do the following:
Begin with HV, is it high enough? If not, you must figure out why. Possible symptoms include HV pot needs adjusted, shunt tube is dragging down HV which is usually a drifted resistor in it's grid circuit if the pot doesn't get HV high enough, horizontal drive control not set properly (if so equipped, some chassis have one some do not), weak horizontal output tube, weak horizontal oscillator tube. If you initially have enough HV but you can't get reasonable brightness try rolling rectifier tubes, there can sometimes be a huge difference in how HV responds to various tubes because of their construction, emission and internal resistance. I've taken to installing solid state stick rectifiers in most of my sets, they make HV a bit stiffer. Lastly if you don't get some improvement, try the horizontal efficiency coil. If it's not set correctly, the circuit can struggle to push enough current through the flyback leading to sluggish performance. Sams will have the steps to follow to set it correctly, just download it and go through it. |
Quote:
|
Quote:
|
Quote:
|
What is the range of current? Does it go much over 200 mA?
|
Quote:
|
Quote:
|
Update, I adjusted the crt bias to the minimum and turned up the screens to compensate, it’s much more stable now. Focus is a lot sharper and it’s actually making a half decent b&w picture. The color is very weak though, almost nonexistent. I’ll need to figure out why that is, I messed with the color killer and got nothing.
|
Quote:
Current goes up because you have a heavy load on it, which is normal. What does “messing around all night” mean? Did you run the setup procedure? Did you verify 1ua cathode current on the shunt tube with a dark screen? Did you null the efficiency coil? Did you verify the double humped waveform with a scope? You haven’t given us much to help solve your issue... |
Quote:
|
Quote:
Nulling the efficiency coil especially should be done to all RCAs that have been brought out of decade long dormancies ...and might be all it needs if you haven't done that yet. |
HV is measured at "0 Beam Current" (black screen) this is when the guns are cutoff. This tells the technician how much HV the system can provide and should be able to reach spec. It is NORMAL for the HV to fluctuate a bit during brightness swings, if its severe- check the setting of the screen and drive controls that they are not too high- also as suggested monitor the boost.
Enjoy! Kirk |
A few things. First this set will never be bright ! Thats normal, most watched them with little or no room lighting. Trying to make it brite will cause trouble.
Ignore the color problem for now, turn it off & make it a good B&W for now. Do a set-up next by the book. G-2's, kine bias, HV, hoz efficiency etc. TUBES. Dont assume NOS are new & good. Many shops saved weak ones as test tubes. Find a dealer that looks at them first. Dont trust tube checkers ! They dont run the tubes under normal conditions. enuf fer now 73 Zeno:smoke: LFOD ! |
.
So you said that when you turn up the brightness as the picture blooms it jumps around. Does it begin to loose horiz. hold? (this was a few pages back) Or does it seem to loose Vert. & Horiz. hold?? Anyway, This blooming is a symptom of a bad HV Rectifier tube, So I hope you have more than one 3A3, and you can try more than one...... Same for Horiz. Output tube..... I guess you have by now got a schematic from Early Television website.... Can you check the voltages at the power supply 360V Source, 250V Source, 270V Source both when brightness is up, and when the screen is dark, and report voltages under both conditions. Also, V12 6DQ5 Horiz output tube, Can you report voltage at pin 1-5 G1 should be -40V & Pins 4-8 Should be 130V, Also 6CG7 Horiz Osc. Can you report voltage at pin 6, Should be 140V. Report these voltages at both High Brightness, & Blanked or Dark Screen.... Also, the color killer should not have any effect on weak color...... Did you replace all the capacitors in this tv? This morning, I'm thinking your statement "it jumps around" did not mean the picture jumps around, or the tv itself jumps around, but it means the HV jumps around as things change on the screen.. Yes, this sounds more like it..... But I'm still interested in the other points about voltage readings.... Thanks, & Good Morning! . |
If it's a sync jump it could be that AGC is set incorrectly and the change in brightness/contrast may be overloading the sync separator.
|
| All times are GMT -5. The time now is 04:03 AM. |
Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2026, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.