Packard Bell Color TV

[old_tv_nut]

Originally Posted by bhegges

I will give this a try and report back. Would there be any noise coming from the AGC keying or Noise Inv circuits (Q6 & Q7). Would it be helpful to disconnect these from where they tie into the sync amp?

They also are being driven by the video, not the other way around, so I think they are OK. I would try the amp without disconnecting them, and see if there is a problem. If everything works, you have saved some unnecessary work.
If you do have a problem with pulses feeding back, then of course you can disconnect them at that time.

[zeno]

A few comments.
1) the CRT tags look like Rauland ( EIA 1101 ) or Zenith ( EIA 343 )
Zenith owned Rauland. They bought them in the early 50's to assure good access to CRT's. Known to be very hi Q jugs.
2) blue screen w/retrace most likely blue G-2 is too high or one of the other blue gun voltages is way off. Turn blue G-2 down til the lines go away & see
if it gets better. Actual blanking problems are not common.
3) tuner / IF. Take signal off set. You should get very nice snow & a "waterfall" from the sound. If not we can dig in further.
good luck
Zeno
LFOD ! & that goes especially for the Ukraine !

\

Originally Posted by bhegges

After some further repairs I am questioning how well the RF/IF sections are working. My thought was to splice in composite signals to see what the set can look like.

I found a few posts with various ideas along with a few points of caution such as transformer isolation, inverted phase signal, and signal strength mismatch. It is not clear to me where I would splice in composite video. My first thought might be at the video detector diode cathode (X9). I am confused around if there is signal that is needed ahead of the pulse gate diode (X11) as this feeds the horizontal output tx and deflection circuit.

Next post has the relevant portion of the schematic.

[Telecolor 3007]

Who manufactured the picture tube?

[bhegges]

For this set I scored big and picked up a NOS Zenith 23VCMP22.

I did keep the old CRT but have not attempted to remove the cataract, it looks like a Rauland 1101 EIA code from my earlier picture.

[ARC Tech-109]

Oh that is a SWEET Packard Bell set, what a score!

[bhegges]

I built the composite video injection and it is working, kind of. A few notes and questions.

• I pulled power from the 18v supply off the IF/video/audio pcb board. Normal (stock) operations it measures 17.5 volts. For the composite video injection circuit I included a 12 power regulator to get a regulated 12 volts. I was surprised to see the IF/video/audio pcb board voltage pulled down to 15 volts. Is there any reason I cant provide an external 12 volts to power the composite video circuit and avoid tapping into the "onboard" power?
• I grounded the circuit to "chassis" ground via a ground test pin on the IF/video/audio pcb board. If I use an external 12 volt supply are there any grounding concerns I should be aware of?
• I used a pot for now to temporarily adjust the video signal voltage. The normal video signal measures 7.5 volts and I was able to adjust the gain to match. I couldn't make full sense of my scope, I expected to see that same signal voltage but there was a difference. Am I just looking at noise, see below pics.
• The injected video required tweaking of the horizontal and vertical hold to get a stable picture but depending on the input (DVD vs converter box) the picture just didn't look right. Further I have (what I think is an unrelated) bad convergence problems which makes it difficult to gauge how well this composite video injection circuit is working. Any thoughts would be helpful, pending no changes suggested I may put it all back and dive in for some help with convergence.

Original video feed


Composite injection

[old_tv_nut]

1) yes, you can use an external 12 volt supply.
1b) post a schematic of your circuit - it may be drawing more current than necessary depending on the resistor/pot values you used.

2) When you say you adjusted the amplifier to match the internal signal, is that a DC voltage reading of 7.5 volts? You need also to match the peak-to-peak voltage, and your waveforms look like the injected signal is much smaller.

3) the internal signal has much bigger sync than the injected one - your amplifier may be clipping sync. It would be good to buy a DVD with test signals like color bars that have known video levels instead of looking at program material where the video level varies scene-to-scene.

[bhegges]

I spent too many hours working on the color setup and convergence, but for now is acceptable. Back to the video composite injection circuit see below for the video signal when viewing a test signal. The video wave form shows about 10v pp. I should note the TV picture is using the tuner, I have removed the injection circuit for now.

Work in progress:


Video signal from above input using the tuner:


Here is the circuit I used for the injection:

[old_tv_nut]

I'm surprised that the detector output is that large, 10 Vpp. I was guessing something more like 4-5 v p-p.

The injection amplifier has a gain of 4.7x, so will only have 4.7 v p-p out. You can increase the gain by making the 470 ohm emitter resistor smaller, but it will be hard to get a 10 v pp signal out with a 12 volt supply. Your pot will have to be adjusted carefully, and because of the AC coupling, the DC will drift up and down with scene content, clipping whites in a dark scene or sync in a bright scene. To keep things stable, you will need a DC restorer.

[old_tv_nut]

The input of this amplifier shows how you could add DC restoration:
https://www.eleccircuit.com/video-amplifier-splitter/

[bhegges]

Ok I am bouncing between tinkering with adding a composite input and also still trying to dial in the color purity and convergence.

I am redoing the color purity and I am struggling to get an all red picture, note it has never been perfect yet. Is getting perfect color purity all a matter of mechanical adjustments of the yoke and convergence magnets? I can get an all red picture but the centering is way off. What else should I look for?

One other thing is I can get the purity better by playing with the horizontal hold which I guess moves moves an uncentered red screen back to center but then on restart the picture could not hold until I adjusted the horizontal back.

Also note the above purity adjustments I am trying are with the tuner, I have paused on the composite input for a bit.

[old_tv_nut]

Originally Posted by bhegges

... I can get an all red picture but the centering is way off. What else should I look for?

One other thing is I can get the purity better by playing with the horizontal hold

Horizontal hold should not affect purity. You may be seeing the effect of mistiming the burst gate. Set H hold to mid range and leave it there.

Strong interaction of the purity rings and centering may mean the rings are at the wrong position on the tube neck. Look for an illustration of the tube neck components and try to match it.

Hard to give advice without being there to see what you're doing.

[old_tv_nut]

Are you using an all-red video, or killing the green and blue guns? A video could produce an impure red if the tint/hue control is not set perfectly. Killing the green and blue guns by grounding the G1s is the best way to be sure only the red gun is emitting.

[bhegges]

I am using an all red signal via a setup DVD and then turning the blue and green guns all the way down.

[old_tv_nut]

Originally Posted by bhegges

... turning the blue and green guns all the way down.

That should be good.