CTC-7 metal table top - Page 2 - Videokarma.org TV - Video

DaveWM · #16 03-11-2013, 08:41 AM

I could not bring myself to doing a 1/2a$$ job on that cap in the IF board, so managed to remove the shield and replace it. That should do it so I hope to try it out soon. I know one of the filter caps have to be replaced as it still runs warm after my extended reform process.

DaveWM · #17 03-11-2013, 07:47 PM

whoo hoo whe got a raster!!

time to leave it alone for the night.

DaveWM · #18 03-12-2013, 09:00 AM

todays project will be to check all the tubes (yea I only did some subs on the HV tubes to get it working thus far), see about installing a cathode fuse on the HOtube (or at least a test point that is easy to get at).

there was some issues with the 1st start up, the drive to the HO tube was not right, very small PP and way to fast (like 8x fast) It seems to start out this way and then pops in as the H tube warms up. Not sure if its just a tube issue or one of the feed back caps in the H board may be an issue. I will check out some of those mica caps as well if a tube swap does not settle it down.

I need to get some correct fuses (the kind with the ears on one side) but at least I know the fly is ok, so I am willing to spend some more time on it.

the vert sweep was not full, about 4" short. I dont know if it was a mis adjusted pot (as I had cleaned them) but if not then I will need to check the electro in the cathode circuit, pretty sure its in a can as I could not see a single anywhere on the board.

My shop is in a bit of a state of flux, so I am having to work on the floor, in the garage, on top of boxes etc... not the best situation.

DaveWM · #19 03-12-2013, 11:28 AM

ah ha, a 1.8 meg plate load resistor in the H osc tube is reading 12+ meg. bet that has something to do with it. Turns out the is no cathode bypass electro cap in the vert out anyway. Since its a plate load resistor just another reason to get out the tube tester and check for shorts.

DaveWM · #20 03-12-2013, 09:32 PM

it was not that resistor, not sure what I was reading BUT there was a .01 brown drop that was very leaky. So I started checking... yep almost EVERY brown drop was badly leaky, and the one that was not was very lossy,

So I have completely recapped the vert board now, and I suspect I will end up dong a full recap of this one just like the 5.

Going to give it a rest for a while. Not looking forward to that point to point chroma section, plus I need to take stock of the caps I may end up needing.

IsthmusTV · #21 03-13-2013, 09:01 AM

Congrats on getting a raster. It's good to know the fly is good.

I had to replace all the brown drops on both the horizontal and vertical boards to get mine to sync. Here's the thread on mine:

HTML Code:

http://www.videokarma.org/showthread.php?t=252097

I went ahead and replaced all the other brown drops except the ones on the convergence board (I'll probably do those soon).

You're getting there

-Clark

DaveWM · #22 03-13-2013, 09:38 AM

yea I bitch and moan about replacing caps, but its therapy really for doing the books all day long...

Did you ever come up with a back for yours? I think I will see if I can find a source of the perf metal (I am missing one to), I would like it to be heavy gauge AND reinforced around the neck area with a metal cover for the neck as protection for the CRT.

DaveWM · #23 03-15-2013, 01:26 PM

it just keeps on going, leaky caps EVERYWHERE. so far I have about a 90% leak ratio. working the chroma section now. what a PITA. just replaced the .22 that couple the blanker tube plate (385vdc) to the cathodes of the -y amps, it leaked at 150v (would not open the eye at all). I have yet to look a the video board, I know there are some coupling caps there that if leaked would really upset the CRT bias thru the video out tube.

IsthmusTV · #24 03-15-2013, 03:54 PM

No, I never found a back. I'm thinking about going the perf metal route, too. I thought I read somewhere on VK that Home Depot may have something suitable. I probably won't have time to mess with it until the summer.

Recapping the color section was the biggest PITA but not too bad. Does yours have the metal shield over the color demod section? Mine is missing but it doesn't seem to cause any problems. Maybe it's more to keep the 3.58 MHz oscillator from radiating.

I had problems with intermittents on the video output board. The 12BY7 really cooks it. I reflowed all connections and that seems to have fixed things. But the tube socket for the 12BY7 has seen better days.

I look forward to seeing your progress.

-Clark

DaveWM · #25 03-15-2013, 04:16 PM

no metal shield over the chroma on this one. I just found another shorted cap across the shunt tube (.0033), that will booger up the HV regulation some.

its coming along, I will prob try it again after I replace that .1 in the grid of the video out. I just don't want to smoke any plate load resistors due to tubes cooking off with bad coupling caps. I got a couple more easy ones out of the way on the chassis bottom, some more .1's

You can see the fine cracks in the epoxy dip of a lot of the brown drops.

DaveWM · #26 03-16-2013, 05:02 PM

finished up the recap. put in the correct fuses, got a pic, but no color lock (rolling color bars). I never did check any of the tubes (just subbed in new HV tubes). So I will start there by subbing in a new chroma osc tube. if that does not do it I will try a new Xtal.

DaveWM · #27 03-16-2013, 08:34 PM

intermittent color lock after adj the fine tuning some (new color osc).

Has very weak sync lock (horz) but will lock just need to adj each time I start up.

Focus does not seem to change, I am getting focus voltage but was not able to check to see if the pot adjusted it or not. perhaps a new 1V2 is in order.

HOT current seems too high, but I need to check that again, I just realized I think I had the meter laying down, the needle may not have started at zero.

The HO tube seem s to have an intermittent filament so will need to deal with that. the HV reg pot seems to be working.

DaveWM · #28 03-16-2013, 10:52 PM

3 more things, I had replaced a power resistor (4.7k that was about 8.5k) and had failed to solder it (but it was neatly thru the term stip hole and wrapped completely around, it was part of the color osc circuit IIRC), 2 I noticed that one of the demodulator plate load resistors had been replaced in the past (poorly I might add), it was a 6.8k. I noticed the other demodulator plate load resistor was a 5.6k, I double checked the schematic and it was a 5.6k there as well. IF it had been a better installation I would have maybe chalked it up to a factory mod, but since it was poorly j hooked in I will replace it with the correct part (this is from a factory service manual not a sams). 3 I replaced the .15 cap that is connected across the eff coil. it tested very leaky but still was able to open the eye tube about 1/2 way when checking for value, but it was about .25 uf tested vs .15 marked. The initial test run I did not attempt to set the dip of that coil since it was inside the HV cage and I had no access to it. Now with that cap replaced (the 2 .1s on either side of it test like new) I will attempt another start up. this time with the set on its side so I can get easy access to that coil.

DaveWM · #29 03-16-2013, 11:35 PM

could not wait, 1st had to un stuck the eff coil slug, then turned it on, got tweaked it some and voila 185ma with a solid 24kv (adj pot working well as well on both the drive and HV) nice...

still a bit flakey on the color bars, but very happy with the HV now. Still got tubes to test, and a new Xtal to install but its getting late so will quit while I am ahead.

oh and the AGC pots is very crappy, that will have to get replaced. just touch it and it goes nutz.

DaveWM · #30 03-17-2013, 12:04 PM

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.