CTC-7 metal table top

[DaveWM]

I picked up a new 1 meg from rat shack, but before I installed it I tried cleaning the old one, that made a HUGE improvement (I must have missed that one in the 1st pass). I used the opportunity to demo the pot function both before and after the cleaning to my teen daughter, She enjoys watching dad work on stuff and we use it as a learning lab (both using digital and analog meters) on what a variable resistor is (in this case its configured that way) and the advantages of a analog device in some settings. working on the color code with her as well.

I think tv's make great labs, for troubleshooting, and general maintenance (like cleaning pots and switches etc....) of vintage electronics. I know its dead end tech but I still think there is an opportunity to learn some of the basics.

hope to get to the xtal later and the tube checks on all the rest (not much to be gained there as a working set is a better test, and other than the soft focus and the color lock being intermittent, its a working set.

[DaveWM]

new xtal made a little difference, I think its more a poor horz sync than anything else. both the vert and horz are pretty weak locks, so I think I will need to look into the sync sep circuits.

anyone have the setup procedure for the sine wave coil on a CTC-7?

[DaveWM]

never mind, found it, short the sine wave coil, gound pin 2 of the horz osc tube, adj the horz hold for somewhat sync pic, remove coil ground, adj sine wave coil to bring back in sync, jump the coil again to check.

did all that but I still have maybe 1/4 turn at most to flop the osc (using the hold adj), and since it does indeed flop my guess is its a weak sync pulse. I subbed in new sync tubes (sep and amp) but no real change, still very narrow sync range. I am going to have to scope the output from the separator and see whats coming out. My guess is some voltage issue from a drifted resistor. will check the video out as well, maybe something getting clipped before in the IF?

[DaveWM]

may have a break thru on the horz instability. while wiggling tubes (1st thing to do) I notice when I pushed the horz osc way over it went out of sync, by adj the hold while holding it over I was able to sync it back AND it had a lot more range once I got there. I will have to go over all the solder joints and tube pin connections, but at least I have something to shoot for now.

[DaveWM]

you guys that have predictas know the drill, broken tube socket right where there is a bridge between the pin socket and the pin insert to the pcb.

checking for continuity with the tube out (touch the probe to where the pin goes in and then the other side to the pcb shows good continuity. insert a tube socket extender with test points and try it again, now no continuity, moral of the story is if you see a predicta like tube socket, and something is not right, better check it with a tube socket extender to simulate an actual tube pin inserted. I have the correct tube socket so will replace it soon.

[DaveWM]

that was it. I put a new socket in (better q than the old predicta style). Reset the sine wave coil, Now has very good sync. I guess there was just a hint of sync getting thru the tiny gap (like a small cap) that made it work at all before.

The contrast is not that great, and of course the focus is a bit weak (but that may just be the test jig, its got a very dirty safety glass AND a bad cat, so not sure about a focus issue. the contrast is ok, I tried jumping the cathode bypass cap just in case it was weak, not much improvement. there is some video smear but again its hard to say with the lousy test jig. the color demodulation is good, and the tint range is perfect. I will need I will check out all the peaking coils later. I need to see if the filter caps are getting warm. I will prob go ahead and re stuff them since its coming along pretty well. I don't know the condition of the convergence assy, I just have the plug in the socket but not on the CRT.

Its full of those brown drops so I am sure they need to be replaced as well. I wonder if leaky brown drops on that board will be putting an undue load on the fly?

[DaveWM]

finally some working pics...

had to load again, goofed it as I ran out of space.
anyway the old angle of the screen shot is due to my test jig location, not the best, so I had to rig up a mirror just to see it.

there are a few brown drops left in, they checked fine, and I was out of new. I will have to order some more from mouser.

the filter caps seem to be doing just fine, not getting hot, but will keep any eye on them until I get around (if) to restuffing them.