Mighty Monarch of The Air

[old_coot88]

So what happens if you inject at pin 2, the grid of the 1st video stage (with the diode disconnected)?
Have you actually checked the diode with an ohmeter? It's a very elderly germanium diode, and should show a very high (though probably not infinite) resistance in one direction and a much lower resistance in the other direction.

[vts1134]

Originally Posted by old_coot88

So what happens if you inject at pin 2, the grid of the 1st video stage (with the diode disconnected)?
Have you actually checked the diode with an ohmeter? It's a very elderly germanium diode, and should show a very high (though probably not infinite) resistance in one direction and a much lower resistance in the other direction.

The diode reads 35k in one direction and 1.5k in the other.
There is no change in raster when I inject at pin 2 of the 12au7.

[old_coot88]

Originally Posted by vts1134

The diode reads 35k in one direction and 1.5k in the other.
There is no change in raster when I inject at pin 2 of the 12au7.

OK, so what happens if you inject at the plate of the 1st video stage (pin1)? It should show the same pattern and same amplitude as at pin 7 (grid of output stage).
There's a coupling cap, C28, which goes from peaking coil L12 to pin 7. Could this cap possibly be misconnected?

The reverse reading on the diode seems a little wonky to me, though that's not germaine to the issue at hand. When you get the video stages working, it might be a good idea to replace the diode on general principles. A second opinion on that from resident mavens would be appreciated.
oc

[vts1134]

I'll be damned if you weren't right about C28, the coupling cap. I had that screwed up . Pin 1 and 2 now give a change in raster when I inject there.
The picture below shows what the three vertical line pattern looks like on the screen.

You can see where the three lines are drawn on the screen, although they are distorted. Is there adjustments on the set that I can use to try and dial the picture in? The video is being injected just aft of the disconnected M4 btw.

[Electronic M]

Try tweaking the horizontal and vertical hold controls. You will need to become familiar with adjusting those controls anyway.

[old_coot88]

Originally Posted by vts1134

I'll be damned if you weren't right about C28, the coupling cap. I had that screwed up . Pin 1 and 2 now give a change in raster when I inject there.

WooHoo! So was C28 connected to the wrong pin or somethin'? Does the contrast control now work? For the heck of it, might as well reconnect the diode and see if anything's coming through the IFs. But be sure and keep your needlenose clamped on the diode's lead as a heatsink until the joint cools. Such an ancient diode may be prone to heat damage.
oc

[Electronic M]

Heat can fix them to I have a Zenith that had no video and almost no sound. Unsoldering and resoldering the detector diode fixed it.

[vts1134]

Originally Posted by old_coot88

WooHoo! So was C28 connected to the wrong pin or somethin'? Does the contrast control now work? For the heck of it, might as well reconnect the diode and see if anything's coming through the IFs. But be sure and keep your needlenose clamped on the diode's lead as a heatsink until the joint cools. Such an ancient diode may be prone to heat damage.
oc

I think the contrast control might be bad. When I rotate it in one direction it becomes shorted to ground. Adjusting the control does not give me similar contrast adjustment in the raster. If I adjust the control quickly the raster sort of flashes briefly and then goes back to the original level. I've previously cleaned the control with contact cleaner and the knob rotates freely. Is it possible to temporarily use a normal 1500ohm resistor in it's place for testing purposes?

[Electronic M]

I'd dismantle the control and go at it with an old toothbrush and contact cleaner as it sounds like it has tin wiskers.

[old_coot88]

Originally Posted by vts1134

I think the contrast control might be bad. When I rotate it in one direction it becomes shorted to ground. Adjusting the control does not give me similar contrast adjustment in the raster. If I adjust the control quickly the raster sort of flashes briefly and then goes back to the original level. I've previously cleaned the control with contact cleaner and the knob rotates freely.

If you put an ohmeter on the control, from the wiper to the 'top' end (which goes to pin 3 of the 12AU7) and rotate the control, the meter should reveal any rough spots or drop-outs. An analog meter is preferable as its needle will follow the control's rotation, while a digital meter just gives a bunch of hard to follow jumping digits.

Is it possible to temporarily use a normal 1500ohm resistor in it's place for testing purposes?

Actually the resistor will give you minimum gain (contrast), while shorting the 'top' end of the control directly to ground will give maximum gain.
oc

[vts1134]

Originally Posted by old_coot88

If you put an ohmeter on the control, from the wiper to the 'top' end (which goes to pin 3 of the 12AU7) and rotate the control, the meter should reveal any rough spots or drop-outs. An analog meter is preferable as its needle will follow the control's rotation, while a digital meter just gives a bunch of hard to follow jumping digits.

Actually the resistor will give you minimum gain (contrast), while shorting the 'top' end of the control directly to ground will give maximum gain.
oc

Sorry, I didn't look at the schematics close enough. The top end of the control SHOULD have low impedance to ground.

[vts1134]

The anticipation at the Estep house is building!!!
It's getting closer, so closer!!!
http://www.youtube.com/watch?v=XBa9o5VnNIY
The video is being fed from a VHS tape of Grease, one of my wife's favorite movies.

[old_coot88]

Say hey! Try the fine tuning. When you get some recognizable video, try the horiz. hold as the horiz. frequency looks to be quite a ways off. What does the raster do now when you turn the contrast control stop-to-stop?
Mayhaps some kindly soul will post the left-hand side of the schematic. It's hard to tell if there might be some kind of AGC control there or not.
oc

[vts1134]

I think the horizontal is seriously off. I'm sniffing around the horizontal osc tube right now. I'm getting some off voltages (even more so than my high across the board on the rest of the set.
Pin 1 should range from -1.8 to -2.5. If I adjust the horizontal afc to get -1.8 on the high side of the horizontal hold then I get -12 on the low side.
Pin 2 should range from 170 to 130. It's ranging from 210 to 125 so that doesn't sound too far off there.
Pin 3 should range 4.3 to -.8. It's ranging from 21 to 5.4.
Pin 4 should be -55. I'm getting a strange reading on this one. My meter keeps jumping from -73 to out of range.
Pin 5 should be 165. I'm getting the same meter behavior on this pin. It's jumping from 186 to out of range.
Pin 8 is the heater. It's spot on 6.3.
What do you thinks happening on pins 4 and 5?
Are the voltage problems on pins 1 and 3 a symptom of my frequency being totally out of whack.
The contrast control does change the raster, buts it's hard to tell how much it changes without a proper picture.

I don't know how to post the schematic short of just taking a picture of it, but I can't get a readable picture. If no one else can post it here then I can try taking several pictures close up to make it readable.

[old_coot88]

Don't worry about posting the rest of the schematic just yet. Need to get the horiz. sorted out first. Can you adjust B1, the horiz. frequency adjustment? Caution: if it's a powdered iron slug with an internal hole requiring a hex tool (which is doubtful), don't try to adjust it without that tool. If it's a brass screw shaft with a screwdriver slot in the end, you're good to go.

If the adjustment doesn't turn easily, don't force it.