Repairing old 1951 sentinel 424 - Page 3 - Videokarma.org TV - Video

marty59 · #31 05-18-2010, 10:10 PM

Silly me for asking, but did you change the coupling cap for G1 of the HOT?

Patnukem · #32 05-18-2010, 11:22 PM

not silly at all looking at the voltage readings and the schematic it seems that should be where the problem is, I did not have suitable replacement so I made one with two in parallel, but the readings were the same. I am going to get a couple of replacement parts including that one for the horizontal circuit tomorrow, currently all minus two or three resistors are new, all the electrolytic and paper caps replaced about 3 years ago. I do need to get a new horizontal center control (it works but has a short, oops, in it so i can not adjust) as well.

Patnukem · #33 05-19-2010, 07:22 PM

well finally found the problem Marty59 was very close it was the capacitor next to that one (c72 Horizontal Discharge Capacitor) it must have been grounding out causing the lack of power needed for the horz. drive. I had a nice picture then would cut out small crackling sounds neat HV rect. tube I think it could be some of the re soldering I had to do on the two resistors under it. if the hv goes and I smack it lightly it comes back I can see the HV Rect. tube filament turn back on when I do this also witnessed blue in the bottom of it for a sec. or two when it comes back on could it be arcing on the other parts in the base?

anyway when I put it back in the cabinet the picture would not come in but I still have raster and sound so I think maybe the lug bolts hit something cause I had a picture before I put them in. anyway here is a picture of it working.

bandersen · #34 05-19-2010, 08:10 PM

Nice - looks like you're in the homestretch. I hate putting chassis back in. So many things that can get bumped or snagged.

Patnukem · #35 05-19-2010, 09:43 PM

I just looked at the schematic half of the morning then made up my mind that it was that one and went and changed it out with a good one. Then I was just testing the voltage when I heard the hv kick in and saw the screen it was a bit of a surprise for it being the first thing replaced today. I will pull it out tomorrow and hope to find what went wrong, i may have just bumped a tube.

I hope that sound is nothing to serious could it be the huge door nob cap arcing over a short inside of it's self, or could it be a loose wire or something arcing under the hv rect. socket, there is so much shoved up under there. I did switch the 1x2b tube out with another and it seems to only be affected by movement, I need to just redo all the connections under there wish, i could find my bottle of corona dope.

jeyurkon · #36 05-19-2010, 09:49 PM

Good progress!

Patnukem · #37 05-21-2010, 12:25 AM

well I found the one problem the new cap I put in was only lightly put in since I was just testing it, I must have gotten to excited to remember.

As for the HV arching I found a loose resistor under the HV rect. but fixing it did not help now there is constant arching in that area and hiss sound I could also see some arching inside the rect. tube and could smell the ionized air. I tried a new tube before fixing the resistor, but doubt that is the problem. any idea what could cause this?

Phil Nelson · #38 05-21-2010, 01:12 AM

With the HV cage off and all the lights turned out, you can play the set briefly and try to see exactly where the arcing happens.

If you have done soldering in that area, make sure the solder joints are smooth. No sharp clipped-off lead ends, pointy bits of solder sticking up, etc.

If there was continuous arcing in the past, that can leave a trail, or even tunnel through something like phenolic. If you haven't already cleaned the area, I'd do it now and look for anything like that.

Doorknob capacitors are pretty reliable, but anything can fail.

Phil

Patnukem · #39 05-21-2010, 01:37 AM

thanks you for the hints, I was not sure about the cage being off but wanted to so I could see if I could find the arcing so its good to know I can do that briefly, I did do some soldering down there and cleaned it up today finding a loose resistor that I might replace tomorrow it is a bit out of range but still ok I did notice a small crack in it so that could be the cause of all of this. It is also not a great place to try and work on since there are two resistors shoved under the base of the rect. and over the doorknob. I only asked about the doorknob because one of the leads turns but it is still very tight.

Patnukem · #40 05-21-2010, 12:52 PM

Took the HV cage off today and could see one of the problems right away, the thick plastic between the core of the flyback and the rect. base had nice black marks on it so I insulated it but still had arching inside the tube I changed out the tube and there was no more blue arc inside of it.

now I can only hear a very quiet click around the base of the HV rect. I think? and a hiss from where the HV connects to the picture tube I have no idea why it would be doing that the connections were cleaned and very tight under the cup. anyway left it on for a couple of minutes and it did not seem to do any noticeable damage but I am still weary of it and would like to figure it out before it is considered finished and put back in the cabinet.

marty59 · #41 05-21-2010, 08:10 PM

Are you able to tighten up the socket pins for the HV Rectifier? And make sure the pins are clean on the tube too.

This set has the 1X2B right? (seemed like I saw that here somewhere)

Patnukem · #42 05-21-2010, 10:42 PM

yeah it does have a 1x2b, I always try to clean the pins on tubes well before using. tomorrow I will try and tighten the socket it does seem a bit loose, and I might reflow the solder under the HV cup just in case there is a cold solder point there and I shall use a good amount of electrical tape to make sure arcs do not come back.

there is one more thing, I can not see arcing anywhere in there i could barely pinpoint the exact area since it is not that loud anymore and more of a clicking now. at least the picture and sound work.

thank you for your pointers.

bandersen · #43 05-21-2010, 11:04 PM

I'm curious - how exactly did you get that HV cage off ? Yours seems to have the HV anode lead threaded through the cage just like on mine. I couldn't figure out any easy way to deal with it and gave up. Luckily I didn't need to get in there but I might someday.

Patnukem · #44 05-21-2010, 11:15 PM

the board that the HV anode goes though is attached with these two little snap things and you can pull that board off and push it back on and it snaps right in. then I just slide it though. then there are the 10 mounting screws to take out. that cage is a pain to remove since there is all of that to deal with and the wires that run to the fuse need to be taken off, I wish the problem area was somewhere a little more convenient to work on

Patnukem · #45 05-22-2010, 06:20 PM

Today I made sure all the wires in the HV cage had plenty of room from the other wires, re soldered under the anode cup, and just in case it was the pins on the 1x2b arcing I snipped a little off all of them to make sure it was not that since they do stick out of the other side of the socket a little ways. it is still making that quiet clicking sound. I will check tonight when it is dark to see if I can see any arcing but I do not think there is any visible arcing. The flyback is fairly new with only about 3 hours max on it so I doubt there is any internal arcing in there not to mention it is covered with corona dope. it does not sound like it is coming from that area anyway. Is there anything near the HV Rectifier tube that would make such quiet clicking sounds under typical operation just to make sure it is not something I need to worry about?

thank you again for listening to my constant questions, this is my first electronic device with tubes in it and its a bit harder for me to work on then arcades and there monitors or vintage computers (two of my other hobbies) not to mention some of my solid state tv's.