Repairing old 1951 sentinel 424
 

I am repairing an old tv got all new caps put in. The audio works now but still no picture, I suspect the HV transformer is bad. The back of the picture tube still warms up and lights all the tubes glow now too. I cleaned the HV transformer off and tried again this time I noticed the wire coming of the transformer to the HV rect. was arcing back to the transformer from about a millimeter away and started to smoke from the same area. the sound then stoped working after I cleaned the HV transformer, Possibly drawing to much power for the rest of the tv to work properly. I now need to find a new HV transformer, My photofact says it is a sentinel part 22E61 or merit part HVO-6. If anyone has some Ideas, That would be great The wire finaly fell off of the HV transformer So I am sure I need a new one know. I am also new here so I am so happy to finally be a member of this forum good stuff for vintage tv/radio hobbyist. Ive included the best picture of my HV transformer I could get. the wire that is missing was from the black ring in the middle of the transformer to the board where the black marks are on the other side from the red wire to the rect.

Thank you for your time
Patrick

http://www.audiokarma.org/forums/att...1&d=1181023104

Ouch! That flyback is cooked. This flyback also has an agc winding. When hv finally totally failed, so did your agc. Ran out of that fly myself. You should be able to find one. Good luck. Bill Cahill

I think I found a NOS transformer replacement. If I keep repairing this tv the parts are all going to be new, lol. What is a ring test? on a sencore, how is the readings on it interpreted? anyway he said the wax was in good condition and such so yeah awsome I will post back after I get it and install it and retest. Thank you again for your feedback on this.

Patrick

Are you still looking for an HVO-6 ? I have one in the box that I was given to use in my Zenith 23H22, the Sams says it will work but it's way different from what's in the TV. A couple of weeks ago I found an HVO-11 on ebay which is an exact replacement for all Zeniths that have the flyback under the chassis. If anybody needs the HVO-6 you can have it for what I've got in it $0.00. BTW the guy on ebay has another HVO-11 if anybody needs one for a Zenith.

Hey Patnukem, you need to check or better yet replace all of the capacitors in the High Voltage related circuits before you fry your replacement flyback.

Many transformers are bad only because some other part has caused a heavy load to be applied to it. So replacing only the most obviously ruined part will be a futile repair attempt. Take it from me!

Im with tubejunke on this , it most likely is a bad cap that cooked the HV .
did you do the HV caps ?
also check that there are no wires touching around the transformer .
best of luck .:thmbsp:

sorry to revive this thread (3 years later) but I had this tv fixed.... for a while then it died, then it sat for several years, and now I have time and a better place to work on it at. So as I am starting to go though it, last time it was on there was no sound, this time I found the sound problem and can receive audio from a rf modulated dvd player. The HV was working, but no picture. Replaced some bad tubes cleaned the chassis well and the HV cage (I guess I should have left it alone) now with the good tubes there is no HV and no picture, tubes still light up and sound still works. I have been testing the HV by setting a CFL bulb by the flyback to see if its working but now I do not even get a faint glow. While checking other things today I noticed L23 (Horiz. Lin) coil was shorted, I repaired it and it still shorted when powered on and the coil made a few small crackle sounds then I shut it off it was then at 100ohms, I think I could see where the coil shorted on the surface, cleaning it a bit and moving the shorts away from each other made the ohms drop back to 0 when turned on the same thing, The photofacts suggest is should be at 15ohms. Thank you to anyone wanting to help me with this headache :)

I found a Thordarson Linearity Coil that is IND .75 - 3.9 MH 16Ω do you think this is close enough to function in my set, the factory one was 15Ω but I do not know the IND. of it, I do know there is about 556 turns and the coil is 1 3/8 inch in length the overall tube length is 2 1/2 inches and the wire size is about 27AWG I can get the diameter of the tube it was on tomorrow I forgot to write that number down for some reason, the sentinel part is 20E524.

what kind of resistors are the best for replacement in tv's? I need to order a bunch while this tv is out. the schematics do not have a voltage rating but they do have power rating most at 1/2 watt I was thinking of getting 350v or higher 1/2watt metal film resistors do these sound acceptable?

That's what I generally use. Sometimes I get 1/2 watt carbon composition to preserve the original look.

thanks there are too many different kinds making my head spin a little! :thmbsp::thmbsp:

since the capacitors are new I started replacing some of the resistors and checking the circuit against the schematic got most of the video ones replaced and found at least 2 faults and 1 error on the schematic

one of the Horizontal Sync Coupling Caps were replaced with a resistor

a voltage divider resistor was placed on the wrong side of the Horz. Lin. Coil.

R41 incorrectly leads to +245vdc there is no +245vdc it should be +345vdc.

also I did find a NOS miller brand coil that is a drop in replacement for the coil that was dead in mine, it should be here tomorrow then I am going to fire it up with the dim bulb tester after triple checking the circuit and hope I did not screw anything up.

Good luck. I restored a 1951 Sentinel 430 recently. It's one of my favs.

I saw some pictures it is a very nice set, very similar chassis layout to mine. I wish mine would work again :)

The resistor I thought I found was an old ceramic cap with the old color code, this always throws me off I am glad I am double checking everything.

I can't view the image you attached - bummer. If your cabinet is in rough shape, maybe the chassis would fit in this cabinet :D http://chicago.craigslist.org/chc/fuo/1740283831.html

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
http://farm2.static.flickr.com/1130/...bd80e913_o.jpg

here are some current ones of the cabinet front that was protected thanks to the doors and the chassis.
http://farm4.static.flickr.com/3595/...5eea4fb1_b.jpg
http://farm2.static.flickr.com/1112/...3c8a2a52_b.jpg

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 :drool:

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 ?

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.

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

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?

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
http://farm5.static.flickr.com/4045/...c47616f1_o.png
and how it would look if I did this just to make sure I set it up correctly?
http://farm2.static.flickr.com/1225/...de8ae2d5_o.png

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.

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.

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?

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.

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.

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

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.

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

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.

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?

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

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.

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.
http://farm5.static.flickr.com/4043/...b8fc0acc_b.jpg

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

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.

Good progress!

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?

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

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.

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.