Did you check the video detector diode (1N34) ?

jr

Yes that's odd because when I first got this set I couldn't get a pic and looked into the 1n34 only to find it was changed but wired in wrong so maybe I should look into that again.

Does checking a 1n34 with a Dvom in diode check mode is it normal to get readings in both directions changing polarity on the meter lead and getting different readings.

Did you disconnect at least one end of the diode, or is it still “in circuit” ?

What are you reading each direction?

jr

Out of circuit, Meg ohms one way and k ohms the other. I remember I had got 2 different kinds of 1n34 diodes when I restored this set,one had a red cathode end and the other a black cathode end so I just changed that diode to the black since I had the red one in there and the pic is better . But I do remember that someone had started the restoration and they used ceramics for hv filters and horizontal couplings and since finishing the set the picture flickers in different ways on scene changes so I'm thinking those caps have to go. The verticle couplings are correct. I believe the horiz ceramics used in here are doubled up for the capacitance changes when warmed up but they still may be creating problems.

On all digital meters that I have seen, the diode test mode measures the voltage drop across the diode in forward and reverse direction (when the leads are reversed). The foreword drop through a germanium diode is usually around 0.3 volts and “OL” in the reverse direction.

Your readings, IMHO, are inconclusive but I would expect more resistance than megohms (usually OL) in the reverse direction. :scratch2: Do you have a new 1N34 to test?

All of the HV caps in my set are ceramic, but higher than spec value...no problem. I suspect that your poor sync (flipping) is likely caused by the weak video signal... when you get decent contrast, sync should improve.

jr

Both the 2 different kind of diodes I have do have readings in both directions but the diode I took out of the set was the same as others i have, red band, and that one only had a reading in one direction, the extra red band diodes i have all have readings in both directions and the diode I took out of the set came from the extras, they're all the same. I kind of wonder I have a SAMs and it shows the cathode end of the diode facing up maybe it's a typo the way SAMs has mistakes but I didn't try the diode the other way. Is it possible the diode would work the other way around. I don't have another schematic to rule out the correct diode position .

Different diode better pic more contrast but still flickers. I would like to figure out why it flickers and repair it.

Rider shows the diode in the opposite direction... I don’t know which is correct. :scratch2:

http://www.earlytelevision.org/pdf/p..._rider_tv2.pdf

jr

I see that , so really if the way I have it in there now was wrong I don't think the pic would be that decent. So today I found the hv was Alittle low so I up the hv and it brightened up and I also changed the RF amp tube 12at7 to a 12ax7 and that helped get rid of most of the flickering and increased the contrast and it looks much better. So really who's the wrong one rider or Sam , it's always been SAMs being full of mistakes. What I should have done was reverse the diode to see if it worked at all and the quality of the pic but it looks much better and leaving it with an occasional flicker nothing like befor.

If the vid detector diode was in backwards, you would definitely know it. Vts1134 can tell you. He encountered exactly that problem in his Majestic 1600 "Mighty Monarch of the Air" resto.

:eek:

Highly likely but not completely guaranteed either. Electrostatic sets with weak CRTs particularly 7JP4s have been known to develop negative picture when overdriven...If someone installed the diode backwards with the CRT weak and cranked the brightness/contrast till the video on screen inverted then you have a double negative making a positive.............This now has me curious what that condition would look like on such a CRT VS under driven with correct video polarity. :scratch2: I wonder if that would be a way to milk more output from tired CRTs.

Problem would be the sync pulses will be in reverse polarity as well as the video being photonegative, which was the problem in vts1134's Majestic. The set couldn't sync at all.