ITT CVC9 problem

[ljdavek]

Hi all..

I have just acquired this lovely ITT cvc9 colour TV.

It seems to work OK when I switched it on took ages to get the raster come up

BUT the problem is the brightness is very poor have to have it on max to get anything...

could it be just the PL509 needs replacing


many thanks

Dave.

[Nicklyons2]

It could be the tube, sadly. But before condeming it make sure the 1st anode supply is correct, the 1st anode voltages adjust and of course the Cathode voltages.
Does the contrast work? if so what does it do? smear picture? wishy washy? etc

If it's not been used for ages and the tube is low emission it may come up after a few hours use.

[HamishBoxer]

I also think it should be run a few hours and see what gives.Keep an eye on it though in case of any problems arising.

[slidertogrid]

Does it take a long time for the EHT to appear? In which case it could be a line output stage problem. I would expect though if one of the line output valves was low emission the width would be low.
If the crt base voltages are reasonably correct and the tube looks low emission check there is 6.3 volts across the heaters.
I can't remember if the CVC9 has a heater fuse, there is a fuse ISTR in the line output cage under the tripler, certainly in the cvc5, but I can't remember if it is a heater fuse or in another circuit.
I had a Korting way back that had a high resistance heater fuse, the picture took ages to appear and looked very "tubey" then it would slowly improve and then fade again, you could just see the difference in the glow of the heaters when the fault occurred, they faded from cherry red.
An odd fault with a simple cause, that took a bit of finding at the time!
good luck with the set!

Rich.

[Heatercathodeshort]

How long is a long time? You can switch off each gun with the slide switches on the convergence box. With the three A1 presets on full, this should give you a rough idea of the balance of the three guns. Does the dark picture have good contrast? You may have a beam limiter fault. J.

[ljdavek]

Hi all thanks for info i will try check voltages but only have a normal DVM..!! will that be ok i know i cant use it for the EHT though.

i will time how long it takes the screen to come up.

contrast seems ok i think.. its looks good ish when at max but gets rather grey when going down!!

i'm going to try connecting an old style VHS video recorder to it and try play a video or something.. i do have another tiny prob with this set how do you get the tuning thing out its got 8 touch buttons on this what seems to be a push panel at the top of the set i'm guessing you push in it a bit so it pops out so you can tune it but when i try pushing it it dose not pop out...

thanks

Dave..

[slidertogrid]

Yes the tuning drawer does (or should) press in and pop out to reveal the thumbwheels to tune the set.
A sharp prod might free it but if the latch is stuck you will have to remove the drawer and free it off, should be a simple enough job.
As far as the long time to come on is concerned, are there any signs of the line output valve overheating?
It could be a lazy line oscillator, are there any of those clear plastic polythene capacitors in the line osc? they were a bit notorious...

Rich

[Hybrid tellies]

Check the beam limiter circuit. Memory tells me that the transistor and diode, although DC tests ok, would go low gain and changing both cleared the fault restoring good clear bright pictures.

[Heatercathodeshort]

I will back you with that one Simon. I also seem to remember a resistor in the sensing circuit that went O/C J.

[ljdavek]

Hi, Well now I hooked up a video recorder to the TV the brightness has improved.
I got a good colour picture on it the other day. I just played a video through it and it seemed to work fine for over 2 hours. I tried it today, to find out the picture is now black and white, there is a kind of thin red line on all the edge of white bits though.

So why would the colour do what it did? ohh and it takes about a minute to warm up, so I guess that's about normal.

Thanks, Dave

[Nicklyons2]

The thin red line is probably convergence error; unless it is obvious at normal viewing distance and you are familiar with doing the adjustments - leave it alone, at least for now.

The UHF modulator of a VHS machine is not as stable as a broadcast transmitter and the black & white is most probably because the set has drifted slightly off tune; with a bit of fine tuning chances are, the colour will return.

[ljdavek]

It is obvious at normal viewing distance, but I only noticed it now its gone black and white.
I have tried retuning on 2 different channels. When I stop playback I normally get a blue screen, but its just black.

[Hybrid tellies]

It looks like you need to start with checking voltages and waveforms around the decoder. If you are lucky the fault might just be the 4.43Mhz reference oscilator has drifted and a slight tweak might clear the fault.