Jagged hammer

[DaveWM]

any ideas what may be going on here?

[Sandy G]

Too blurry to tell much of anything, really.

[old_tv_nut]

Picture of the vertical blanking interval, rolled down into view with the vertical hold. Horizontal sync is pulling differently on different lines.

So, what is the question? Are there noticeable horizontal sync problems in the picture when the vertical hold is adjusted normally, or is there something else of concern?

[DaveWM]

its working fine, not issue at all except I just dont know why the hammer has those horz offsets, I have never seen that before, I can roll it back to normal vert lock. Just trying to figure out what is going on. I did put the scope on the pic test point, the blanking signal had some large spike in it.

[old_tv_nut]

Don't have an idea why you would see a spike on the test point.

The pulling could be because the sync separator or AGC is slightly out of spec, or because it's designed that way. The equalizer pulses in NTSC were designed under the bad assumption that the horizontal timing would be derived precisely from the leading edge of H sync, equalizing pulses, and vertical serrations. This was a dumb idea, because an analog H sync circuit with enough bandwidth to get those edges precisely right would be terribly susceptible to noise. Therefore, the input to the sync separator is filtered, which causes the H sweep to sync more towards the center of the sync pulses. This means that it normally pulls somewhat one way or the other during the three types of pulses. That is probably part of what you see - but I also see the video level change, which seems to say that the AGC voltage is changing some. You might try poking around in the sync and AGC sections, and see what happens when you adjust the AGC.

Any problems with streaking in the picture? If not, I would probably ignore this.

[DaveWM]

played with the AGC setting (has a pot) did not seem to have any effect. I did check all the caps and resistors in the AGC circuit (I was having agc issues before, turned out to be a bad cap).

it has those integrated networks for both the vert and horz sync circuits.

I have played with the idea of making new ones from discreet parts just for the heck of it.

Before I do all that I will try a different AGC tube.

[DaveWM]

Tried new tube, no help. The vert lock is a little iffy, critical (very narrow setting to hold), shifts some as it warms up, but once warm seems ok.

Horz lock is fine.

[old_tv_nut]

Time to check those networks, I guess - still wondering about the spike. Can you post a schematic of that part?

[DaveWM]

will do. I have been having fun looking at the various test points, I think I am begining to get a handle on how all this works, I can see the video amplitude along with what I presume is the horz sync, then the vert all riding below the video. Then after going thur the sync separater just the horz and and the vert. I assume the video is clipped off based on the bias of th sync tube, then the horz and vert use different band pass filters (the integraters) to isolate the correct sync (vert and horz) to trigger the osc (vert and horz). At least that seems to be the way its working. I am an accountant by trade so all this stuff is new to me, so please be patient if I ask any dumb questions, its all OJT for me.

I did check two TP's the video dector output and the vert amp output, besides being inverted (to be expected in a voltage amp) there was gain but not much, like 2.5X if my scope was reading right. I dont know what the gain should have been on that stage.

I am going to check the bias of the vert amp and if cathode bypassed I will check that as well.

The set is workiing fine, but I have a hard time leaving well enough alone, I just dont like the narrow range of vert lock, and that darn jagged hammer. I checked a couple of my other sets, same vintage diff make, and while there was some jagged edge it was very small.

[DaveWM]

here are the two networks, the one on the left couples the composite video signal to the sync sep tube and the other one is a low pass filter that passes the vert sync pulse to the vert osc.

[old_tv_nut]

not sure what you're referring to as vertical amplifier, but I presume the point where you see the clipped sync is TP-5. Does the schematic have a waveform for that point and does your scope show the correct amplitude?

[DaveWM]

opps, vert amp meant to say video amp, getting late, better knock off. No the TP's did not have any scope readings.

[DaveWM]

here is the video amp input and output where I get about a 2.5x gain.

TP2 and TP3

I will hook the scope back up again and see if there is any change when jumping C25 (the cathode bypass cap).

I check the voltages they were high by about 20v on the plate and screen (no signal) I swapped the tube out with another, and the voltage fell right back in line with the schematic. So Now I will check the gain again and see if that made any difference.

[DaveWM]

well duh, I had a 10x prob on one TP and a 1x prob on the other and did not take that into account (I was comparing by using a dual trace on the scope).

Going to take some more readings and compare to the P-P voltages that are given for various other TP's.