Repairing old 1951 sentinel 424

[Patnukem]

That is a nice cabinet, to bad my tv will not fit. mine is in ok shape the outside got kinda scratched getting it down to KC from Omaha.

I have gotten the new coil in as well as a ton of parts the sound is working very well and tubes are all working and checked on my Jackson tube tester. I still can not get the HV to work with the neon test, it was working fine a couple of weeks back. Could the Fried Hor. Lin. coil when it shorted kill the flyback? I think I checked the Flyback windings for shorts and all seemed ok not sure if I did this before or after the coil short i may recheck them.

Also with the new Resistors I replaced the Vertical Output Transformer is still making noise but it is a lot higher pitched then before, the windings seemed ok here as well should I wonder what one I should replace first the vert. output or the flyback? or is there something else to try? I have switched out all the tubes in the HV box with others and that did not do it. I do not think I could see the filament in the HV rect. light up but I doubt it would with no HV.

Here is a picture taken when it was working


here are some current ones of the cabinet front that was protected thanks to the doors and the chassis.

[bandersen]

That's a nice cabinet. Maybe a little Howards's Mahogany restore-a-finish would help on the dings ?

I know that chassis all too well after spending hours staring at mine

Check the resistance readings on the flyback windings. Do the voltages on the horizontal sweep and output tubes check out ? Have you tried adjusting the horizontal drive and lock controls ?

[Patnukem]

I will check that out, would the Horz. Output. tube overheat if the flyback was dead? the cap melted right off of mine when i went to check it just now it is getting way too hot. I remember somewhere someone saying the horz. output can over heat if another tube fails (horz. osc. maybe?) also the lv rect tube is getting a little warm but I think it always does anyway.

[bandersen]

I believe it can overheat if either it's getting too much drive from the horiz osc. or if the load (flyback) is excessive.

[Patnukem]

I disconnected the flyback all the resistance values seem close to the original and no shorts to the other windings. Looking though the photofacts horz. sweep setup it says to connect a volt meter up to the green wire that comes up in the middle (connects to Horizontal drive adj) to ground and should read 20 to 28 volts it goes up to 3 or 4 then drops down and stabilizes around -27v so I should assume something is wrong before this in the circuit?

[Patnukem]

Wow the B+ was about 45VDC too high on all of them. Would this be from something not putting a big enough load on it or is it drawing too much of a load, or is it something in the power supply area causing these numbers to be high? well at least I kinda know whats wrong now it makes it easier to fix

Also would it be possible to make a solid state rect. to use while repairing so I do not kill my 5u4 tube I would hate to have to buy a new one, I was looking around and found this http://www.k6may.com/CollinsTip2.shtml and wanted to give it a try. I have a ton of the 1N4007 diodes and a base from a broken 5u4 I also have a resistor to put in there. I was thinking of starting off with a 300Ω 2 to 5 watt depending on what I have in the parts box.

My schematic now

and how it would look if I did this just to make sure I set it up correctly?


R88 was at one time replaced with a regular resistor I did not notice it until now so I will replace it with a wire wound one.

One last thing I was looking at your pictures bandersen, and they were a big big help I took some before pictures to reference and troubleshoot and I am very glad I did, I realized the thing i "fixed" moving R66 to the other side of the Horz. Lin. coil as in the schematics was wrong, R66 appears on the opposite side then the schematics in your set, from what I can see in the pictures, as well as mine before "fixing it"

I hope to get these bugs fixed tomorrow.

[Patnukem]

sorry for drifting to a completely separate question in the last post I was up to late I guess. I replaced some more resistors a lot of them are way off I think they are almost all replaced minus two in the HV cage and the sound/rf circuit since I am still receiving a signal fine and can hear it. I may start replacing them anyway. as right now I only have a very very cheap multimeter my good ones are in storage somewhere so the measurements I get may be a bit off but after replacing some more resistors the B+ seemed to drop 5-10v but still is about 385v and not 350v. I did notice that the HV filter cap had a lead that seemed a bit loose and spin a little but but very tightly. I do not have anyway to test it to see if that is causing the problem.

[Patnukem]

this may seem like a dumb question but the voltage at the Horizontal drive adjustment to ground should not be -25vdc right? When turned on it shoots up to 10 or 20 vdc then starts to fall to around -27 then it will start going back up very slowly the highest it would get was around -19vdc but I will not leave it on too long as I do not want to damage my HOT.

am I correct to assume the problem lies with in the Horizontal sweep circuit since I have no HV and my HOT is glowing red when on?

[bandersen]

Perhaps your B+ is a little high because the divider resistors have drifted in value ? That would be the 20 ohm vert. center, 50 ohm hor. center and 4K power resistors.

All 3 read a little high in mine.

I think that's a good assumption. IIRC my 6BQ6 was overheating at some point too until I got the horiz. phase inv. and horiz. mult. sorted out. There have been some production changes in that area so be careful. Do you have the Sams for this set ? If not, I can upload a copy.

[Patnukem]

I do have a copy of the sams I got a while back when I put new caps in it. I know I have a new 4k (r92) I tested the two centering pots. a while ago and they seemed to be in range but I shall check again just in case i messed up

Looking at the data sheet for the 6bq6gt i guess it is supposed to be a negative voltage going to grid 1 the sams just said in the horizontal sweep adjustment directions it should measure 20-28 volts I guess I just assumed it would be positive.

[Tubejunke]

Was this chassis done with Naval Jelly? It sure looks nice!

[Patnukem]

used some extra fine steel wool (stayed away from the magnets and sprayed it off with air) also used a nice metal polish that comes in wadding.

[cwmoser]

Nice finish on the chassis. Looks like Aluminum in the picture but I bet its a Steel Chassis? I like the looks of a fresh looking chassis.

Carl

[Patnukem]

some parts are aluminum, even though its not working yet, at least it looks nice!

I still can not seem to find the reason for the over heating HOT and the lack of HV. I do know power is getting to the HV from the B+ So I will start checking stuff in all of the Horizontal one at a time. Would it be possible that the Giant HV filter cap died if so would it cause this behavior I think I read somewhere that some tv's ran fine without one.

I wish I had a nice LCR meter (is Mastech an ok one? I can not afford a fluke right now) but for now I do not have anyway to test the capacitors.

[Patnukem]

I went though all of the horizontal circuit and all seems ok there, there are some capacitors I can not check and I changed out two of them with no change. I did get some readings The horizontal drive is now down to -0.2v and on the other side of C73 (the horiz. sweep coupling) one of the caps I switched with no change I get a reading that started out at 130v but now its around 70v on the other side of the line filter C80 I get +350vdc. the screen voltage of the HOT is about half of what it should be at 100v and the grid 2 is at -0.2 and not -20 to -27.

so any suggestions on my next move?