I started restoring my RCA 721TS and I'm not getting a raster on my screen. I've recapped the set, including all of the electrolytics. I have proper high voltage at the second anode (9000v) but my voltages at the crt socket aren't even close. Below is what I have:

Pin 1 -16.10 (should be 140V)
Pin 2 -25.4 (should be 75V)
Pin 10 377 (should be 290V)
Pin 11 62.6V (should be 220V)
Pin 12 -16.25V (should be 140V)

What am I missing here? Any help would be appreciated as this set is in nice condition and I'd love to have it as my daily watcher as I begin other sets!!

Thanks!

Scott,

It looks like your 150V supply is messed up. Looking at page 19 of the Rider's information, check your connections associated with C116C (30uF) that is connected to the voltage divider network between R153A and R154A. Maybe you shuffled something around there during the recap.

Here's the Rider's that I am referring to:

http://www.earlytelevision.org/pdf/RCA-721TS-Rider-TV1.pdfhttp://

Sean,

Thanks for your help. I couldn't open up the link...

Scott

There were some extra letters in there, try this one.

http://www.earlytelevision.org/pdf/RCA-721TS-Rider-TV1.pdf

Thanks Eric! I double checked my work and don't see any errors. I will dig into this schematic and try to figure it out.

Guess I should have tested that link before I posted. Did you test the resistors in the set? If R153A is open (1125 ohms) that would eliminate your 150V supply voltage and could drag it down negative which is what you are getting with the negative voltages on pins 1 (filament), 2 (grid), and 12 (filament). The voltage on pin 11 (cathode) will be dependent upon the setting of your brightness control.

Sean,

153A tests at 17.8k. Way off! Would being higher, not open cause these negative voltages?

I found a 30 watt, 1200 ohm power resistor and put it in in place of 153A and got a raster. After some adjustments with the focus cool and ion trap, I got a picture. I do have multiple overlapping images, so should I suspect failure with the mica caps on the horizontal controls? Any adjustments with the horizontal frequency, range and drive makes no difference.

Any adjustments with the horizontal frequency, range and drive makes no difference.

Are any of those adjustments the adjustable cores in the H osc. transformer can?....If not that is where I would look first.

If make sure resistors are good before trying the micas.

Yes, I would check resistors first. If no joy there, look at micas. There is a cluster of six micas near the horizontal adjusters.

http://antiqueradio.org/art/RCA721TCSMicasOriginal.jpg

I ended up replacing all of them on my 721TCS.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

the larger 'micas" there are probably paper caps, not mica. Only he small ones are mica

Are the images side by side or top and bottom?

In the picture you posted it looks more like the vertical is the problem (stacked top to bottom).

http://videokarma.org/attachment.php?attachmentid=188769&stc=1&d=1447311958

Eric,

The images are stacked vertically. I changed some out of tolerance resistors around the vertical hold control and vertical output tube, but no changes. I guess I will check resistors around the sync separator tube?

Thanks,
Scott

I would also check the capacitor values around the vert oscillator, an easy mistake is to use a cap of the wrong value, or a mislabled cap.

I changed a few caps in the vertical section and double checked my cap replacements. No changes, still double vertical images...

Often you can hear a faint buzz coming from the V.out transformer and/or yoke windings. If you can hear it, try turning the V.hold control stop-to-stop, and you'll hear the buzz change in pitch. The pitch change will usually tell you whether the osc. is running too fast or too slow.
This in turn can be a troubleshooting guide.

I replaced a few more out of tolerance resistors in the vertical oscillator circuit with little improvement. So I went to my 1950s tv repair bookshelf for some pictorial help. My book said split vertical picture is due to a few things, including misadjusted vertical hold control. I laughed and thought....no kidding! But I figured nothing else has worked and I didn't really spray this control. I rocked it quickly from one end to another and bingo, one picture!

Booyah! Say hey!:rockon:

Picture looks nice.

Nice, but a little odd. The image should be rectangular - not fill the screen. Something more like this. I wonder if the yoke is not pushed all the way forward or the HV is too low ?
https://farm1.staticflickr.com/750/22987062715_47546504fc_n.jpg (https://flic.kr/p/B2hGTv)

Nice, but a little odd. The image should be rectangular - not fill the screen... I wonder if the yoke is not pushed all the way forward...
Wouldn't that cause a neck shadow? :saywhat:

The last picture does have what looks like a neck shadow (I see a dark ring around the picture on the CRT face). Also, adjusting the height and vertical linearity for a "full screen" raster on a round CRT can itself cause the vertical-hold control range to be less than ideal. (Except on a round-bezel Zenith, of course.)

Nice, but a little odd. The image should be rectangular - not fill the screen. Something more like this. I wonder if the yoke is not pushed all the way forward or the HV is too low ?
https://farm1.staticflickr.com/750/22987062715_47546504fc_n.jpg (https://flic.kr/p/B2hGTv)

What kind of signal source is used? With my Zenith DTV convertor, I can get a small squared screen on some channels. With the caption, "set by program".

Over the air low power NTSC. We still have LPTV channel 6 in Chicago.

The darkness around mine is because I haven't perfectly adjusted the yoke and focus coil. I will do that when I get it ready to finally put back in the case. Getting the adjustable mounts at the proper depths will also help the centering.

Got it all back together....time to watch tv!

Do you always watch TV sideways? :D

Over the air low power NTSC. We still have LPTV channel 6 in Chicago.

I can only hear the audio from them here. Decently I might add, but even on a huge TV Beam aimed at Chicago I can't see their picture.

A couple times when conditions were exceptional and beyond good conditions for FM propagation, back in the Q87 days, I picked them up in Fon Du Lac Wisconsin, and kept a mostly stable signal all the way back to Lake Geneva.

Was pretty cool.

Do you always watch TV sideways? :D

I noticed that too. If he is using a Windows machine to upload, then he should use windows photo viewer to check for rotated photos, and use it's rotate 90 degrees buttons to get the pictures right side up prior to upload.....

Perhaps its in front of a couch and he likes to watch tv laying on his side?

SR