1960s Sweet 16 RCA television help
 

Hi all,

I'm looking for some guidance on a 1960s RCA Sweet 16 sportabout I'm in the process of restoring. It was working fine until just a few months ago, when it developed some disturbances, almost like an AC buzz but visual, in the picture. It would react to tapping on the cabinet, sometimes getting better or worse. Then, I noticed that adjusting the Horizontal Hold pot actually caused the picture to disappear entirely, but it would always come back when I moved it back.

So, with my AC theory in mind, I went ahead and replaced the electrolytic can and the glorified paper safety cap across the AC line. Those replacements appear to be fine, no obvious trouble. It's turning on faster than before, and I'm getting perfect sound.

However, my picture is gone.

I noticed that the HV rectifier tube in the cage was still cold after running it, and there was no high voltage whine, so I replaced that tube. Now, the whine is back, it gets louder when I adjust the horizontal hold, but the picture is still absent. Placing a screwdriver against the HV rectifier cap in operation is giving me a healthy blue spark, so I know my flyback is fine, and I've also verified that the resistor across the HV rectifier tube socket is up to speck, and that the lead to the picture tube appears to be fine, though my continuity there did seem to cut in and out at times, so perhaps that warrants another look. The tube is definitely still under vacuum.

I'm thinking my issue either has something to do with the Horizontal Hold pot, the picture tube HV lead, or how I'm installing that cable. The amount of clip that actually goes inside the tube is much smaller than I expected, but I also can't see any way for it to go further. Regardless, it's not falling out or sparking. Considering where I started, does anyone have any suggestions for where I should look next? I don't have a HV test probe, though I'm willing to get one if it's necessary.

Check for arcing at the CRT...Slip a screwdriver under the cup and see if it sparks decently.

Might be good to compare the horiz osc waveform width to sync pulse width on a scope to confirm it is on freq...If not severe reduction in HV can result.

Your pre-recap symptoms depending on exactly how they manifested could be attributed to caps or bad grounding of circuit boards, etc. Another possibility is bad solder joints on the osc coil.

Post the chassis number for us 1st KCS###
Healthy spark at plate cap leaves
1) bad tube
2) open filament winding or resistor. Check resistor with tube OUT.
3) open anode lead
4) bad CRT

Is this one of those early solid state sets ?? If so IIRC the anode lead has
resistors built into it, special OEM part.....

73 Zeno:smoke:
LFOD !

Chassis number is KCS152C. I'm including the SAMS schematic for reference.

I did a little more poking around, ran the same test with the anode lead disconnected from the CRT and received no spark from the end of the lead when I touched a screwdriver to it. Considering I already noticed that the continuity check on my multimeter seemed to go in and out on that wire, I'm leaning towards replacing it as my next step. I'll also go ahead and ohm out the resistor with the HV rectifier tube out to verify that it's good, but from what I saw in the wiring I believe my reading should be accurate.

This is not a solid state set, so fingers crossed that the lead is just a wire. No evidence on the schematic from what I see.

I would be surprised if the CRT was bad. It was perfectly bright just a few months ago, so to go from normal to no picture that quickly without something catastrophic happening would be bizarre. I'm no expert, though.

Is the schematic showing up? I'm not seeing it. I have to run but I'll post it later tonight if not.

Okay, here's a copy of the schematic.

Also, this slipped my mind, but I did notice one of the leads to the electrolytic can was broken off when I was removing it. I've fixed it, and didn't consider it worth noting since I was planning to move it to a terminal strip anyway, but if memory serves it was the positive lead to the triangle symbol. Either that or the semicircle. Either way, Unless the symptoms persist once I get a picture, I'm tempted to chalk at least part of the "percussive maintenance" response to that lead being broken or almost broken.

Does anyone have any recommendations for what kind of wire I should get to replace the anode? Are CRT anode leads still sold, and will a standard piece fit most CRT sockets?

Also, I was a little confused on some of the information regarding my 1G3GT HV rectifier. If I'm understanding it correctly, that tube is not part of the series filament string, and is powered directly by the flyback transformer. I verified that my old 1G3GT was bad by testing for continuity between pins 2 and 7, which I believe is where the filament is. Those two points tested no continuity, and further testing on a tube tester also showed no life.

Also, since I'm on the subject, and I apologize for asking these novice questions, what's the standard on numbering tube pins? If I've read correctly, I find the key on the center post, or gap on a miniature type tube, and count clockwise from there. Am I doing that right?

If everything I'm doing so far checks out, My next step is going to be to test that resistor and, assuming that checks good, verify that there is an intermittent break in the anode lead.

There's probably nothing wrong with the anode lead. The schematic shows a 1000 ohm resister in the HV rectifier socket, check that.

They used the same anode connector for most CRTs made throughout the years. If the lead somehow is bad one from a 1980's-2000's junk SS CRT set can be subbed. If your game to swap the connector to a new lead then non-resistive spark plug wire from an auto parts store could also work. Any wire with insulation rated 30-50KV will work in most B&W sets. The average CRT has 1mA max anode current so even thin conductor wire can handle that.

Pin numbers are read from the bottom clockwise. # 1 will
be the first one AFTER the gap or key.

The filament runs off the flyback not the regular string.
All of the HV stuff is running at 16 KV above ground so you need
20 KV or more wire. After that flexability helps. The anode lead
can be stripped if almost any junker. The 1 K resistor should be
carbon also. If you restring the filament try to keep it the
way the old one is.

73 Zeno:smoke:
LFOD !

Something you need to know here is that the CRT coatings form a capacitor that is charged by the short pulses from the HV rectifier. So with the lead disconnected from the CRT the HV will not develop, no spark.

Very few tube testers check HV rectifiers well. They don't apply high enough voltage and the tubes can't pass very much current even when good. The filaments are higher resistance than normal because they run on low voltage and draw little current.

You should check the voltages on the CRT socket, they have to be correct also in order to get light on the screen.
You might have got on the wrong track looking at the HV because some of your tests weren't conducted right.

Thanks for all the advice. I went back and did another filament continuity test of the original tube, and it looks like my original tube wasn't faulty.

I also went ahead and restested that 1K resistor under the rectifier socket. The results were mixed. An ohms test across the resistor with the tube removed is reading just about 1K, within tolerance, but a continuity test across the same resistor is showing no continuity. At the same time, doing another reading of the anode wire is showing stable continuity when I flex the cable, so I'm inclined to believe that's actually fine, but I'm also getting no continuity across that cable when I measure from the opposite side of the resistor. Is that normal, or is the resistor suspect?

If my high voltage turns out to be fine, will it be possible to be seeing the same results if I'm not getting a signal to the tube? I'll have to go back and check with the anode lead plugged into the CRT, though I'm not sure of a safe way to pull back the rubber cup and look for the spark. Gloves perhaps? If anyone has a method for that, I'd love to hear it.

Take a small thin bladed screwdriver, use a clip lead clipped to the blade and to the chassis and work the blade under the rubber cup. You should hear a arcing sound even before the blade is fully inserted, if HV is present.

Okay, I just ran that test, and I did see a blue spark at the anode cup, so it's passing high voltage. I didn't hear anything, but I saw it, so I presume that's enough of an indicator?

Anyway, I suppose my next step is going to be to pick up one of those tube extenders so I can check the voltage going into the base of the CRT. I'll go ahead and re-verify that I didn't screw up any wiring or values when I replaced the capacitors. I've checked it multiple times, but since it was working before I got in there and isn't now, it's worth taking another look at what I did.

Does anyone have any suggestions on where to check next, in case I missed something?

Alright, I just checked the pins on the base of the CRT while it was turned on and everything was plugged in. I removed the connector enough to wiggle a multimeter probe in there while maintaining electrical connection.

Most of the pins seem to check normal, but pin 3, which is listed as 260V boost, is showing closer to 90V. Could low boost voltage be causing my problem? I'm not actually sure what it does, but it doesn't seem like there should be that much variance. It looks like that's coming off of a lug on my flyback, and going through resistor R79. I suppose my next step is to verify that R79 hasn't drifted above tolerance.

I remember hearing that, when testing a resistor, the correct procedure is to unsolder one of the leads and isolate it from the circuit. Would that be correct in this case?

Time to back up a little...........
Remove the plate cap from the 1G3 & let it hang away from metal.
Take a well insulated screw driver & get it near the cap ( wire end).
You should get about a 1/2 inch arc, NOT just a spark if you touch
it or get very close.

Boost comes from the flyback. Its stacked on top of regular B+ voltage
( think of 2 batteries in series ) & filtered by C50 & C51. R79 must also
be good.
On your set if pin 3 of CRT goes to low it will kill the raster BUT not effect the HV.

Next is to get good HV ( that nice arc ) you need the following stages running.
1) horz osc
2) horz output
3) damper
Any defect will lower & or kill the HV & boost.

Bottom line it nice big arc = good till that point
Small arc = problem is before HV rect.

73 Zeno:smoke:
LFOD !

Gotcha. That's the first test I ran, so I can say with certainty that it was a very small spark. The screwdriver didn't have to quite touch the metal inside the cap, but it had to come very close to get a spark. I'd estimate a maybe 1/16" spark? Maybe less. So it sounds like my HV is low.

I keep thinking back to that Horizontal Hold control. It may be a red herring, but I was noticing some significant power supply defects when I adjusted that control before I recapped in. Specifically, a DTV converter box on the same outlet would actually reset itself as if the power were interrupted if I turned that control all the way up. Obviously I didn't repeat the test after I figured out what was happening, but I hope I didn't damage something doing it. A short somewhere, maybe? I checked the control, and it seemed to test fine, though I need to go back and make sure I'm testing the three leads correctly. I used to know how to do that, but it's been so long I've forgotten the specifics. I did notice that, at the extreme end, it drop from kohms down to ohms, which seemed extreme. I wonder if I've got a bad control, though that wouldn't explain the low voltage elsewhere.

I think I'll still give R79 a looksee. Worst case, I've practiced testing a resistor, and I might find a problem.

Resistors should be check with one leg lifted IF they check
bad in circuit. After a while you get the hang of which to
do & speed things up.

For now check pin 2 of the horz out tube & be sure its about -20 VDC.
If not its a dead horz osc stage.
Also check voltages on the 8FQ7 & 22JU6 & post them.

73 Zeno:smoke:
LFOD !

Is that continuity test on your meter a GO/NO-Go kind of thing? Is the indication a tone or light going on? If the test is this sort, then you must realize that the meter has a threshold to determine the result. If the threshold is below 1K then when you measure something with a resistance of 1K the meter will call it an open.
If the boost voltage on the CRT is that low it probably would prevent the beam from lighting the screen. It also would suggest that your HV was low. If the horizontal frequency is far off it would decrease the HV.

I looked this up after the fact, and yes it appears that my meter was probably responding to the functioning resistance of that resistor as if there was no continuity. That was my bad, but at least now I know that's how that works.

Sorry for the late response, all. I was out of town over the weekend, but I'll run those voltage checks sometime today or, if not, Thursday and see where I am.

Continuity is zero or near zero ohms. My fluke has a beep & a scratchy
tone. A beap is 0 ohms. If you wiggle something like a connector with
a rusty connector it will make the scratch sound.

Many meters have range select & auto range also so watch for that
when measuring,

73 Zeno:smoke:
LFOD !

Usually a continuity test is for things where you expect the resistance is very low, maybe no higher than 10 ohms. It is really for testing wire, contacts and switches. You can also use it on things like filaments and modern speakers. If it is a resistor use the ohms measurement, otherwise you will just confuse yourself.

Okay, so I may have broken something, but it may not have been something I did.

I got the voltage measurements. For my 22JU6:

1: Unused
2: -20V
3: 0V
4: .3V
5: .15V
6: Unused
7: 120V
8: 37V
9: Unused

For the 8FQ7 (I checked then all because it's easier to access the pins above the chassis):

1: 0V
2: 5V
3: 8.6V
4: 109V
5: .04V
6: .06V
7: 5V
8:2.3V

Then, I measured Pin 9 on my 8FQ7, and the yoke started squealing and sparking. I see no indication that I shouldn't measure that pin on the schematic, and I fact, looking underneath, I don't even see anything hooked up to that pin, nor any mention of it at all on the schematic.

It looks like a wire may have broken on my yoke. I'm attempting to attach a picture, but I'm on mobile so I may have to do a separate reply for that.

So basically here's where I am: I don't think I should go any further without looking this yoke over. Is there a way to check if it's okay? If I do have a broken wire (it's accessible, but small) what are my repair options? If the yoke was having trouble, could that be causing my low high voltage problem? Also, from the schematic, should I be safe to measure pin 9 of my 8FQ7? How do my other voltages look? Some of them seemed off to me.

Your 22JU6 voltages are fine except pin 8, you got 37V but it should be 25V.
You should measure on the other side of R77, the voltage should be near 145V. Also check the value of R77, should measure 47K.

Your 8FQ7 are nearly all wrong! Did you measure the wrong tube?

Yes, check out the yoke. Perhaps there is a short or maybe is arced because the voltage got too high somewhere.

When you measure the filament pins you need to use the AC volt ranges.

I just double checked. Unless someone rewired this thing and moved one of the tubes, which I don't see any evidence of, it was definitely the right one. That being said...

I had my multimeter on DC. Maybe that's part of the problem? I'll rerun my tests, but I'd better check out that Yoke first. Looks like Moyer Electronics has a replacement, but I think I'll try and resolder that wire first. Assuming it's just the lead that's broken off, would splicing a new wire onto that lead and running an extension to the terminal be alright? I get the impression that the winding pattern on the yoke is fairly significant to its operation.

While I'm at it, I suppose it would be a good idea to measure the resistance on the yoke. I imagine I can do that from the plug, but I'm not sure how to tell which lead is which. Any ideas?

Maybe the arcing at the yoke when you were measuring pin 9 was a coincidence.
The yoke plug pin out and connection is shown on the schematic. The coil resistances also. Unplug the yoke to make the measurements. Make sure that the resistance between the horizontal and vertical coils is basically infinite.
From your picture it is hard to tell whether there is a strand out of place that is causing a short or close gap that may have arced, or maybe a wire has opened.
The filaments are fed AC, the rest of the tube pins should DC measurements.
The filament string voltages are shown in the lower left corner of the schematic but are seldom the problem.

If the yoke is open or shorted it will greatly reduce the HV and throw off everything else in the horizontal section...Ever pull the H yoke leads on a CTC-15 and power it up?..I have.
Check your yoke like tolooz sayz. That magnet wire is coated in lacquer or some such translucent insulator and you'll need to scrape, melt, or dissolve it off before you can solder it...A short jumper if a section burned off will be fine...Just don't make it longer than it needs to be and don't place it where it could arc to other things.

It could be that pin 9 was being used as a terminal/tie point for other things in the horizontal osc or that it shorted to another pin...Sometimes if the osc is tuned close to the point where it screams adding a small bit of load to the circuit from a meter can push it over the edge in to the scream zone.

Looks like some carbon was created when the arc occured.make sure you scrape and or sand that black stuff off.its conductive.RonL

You have -20 volts on the G-1 of the output so the osc
is running. Testing around the osc will often throw it off
freq so that may be the scream you got.
If yoke wire broken you may be able to patch it if you can dig
out both ends. After that you are pretty much don to a bad
flyback, yoke or damper tube.

HINT ! When yokes get a shorted winding its usually on the
inside windings. Pull the yoke back off the bell. That will give
it air to burn better & you will see it often. Saves time !
If its not burning you may see on the CRT where it was burning.

73 Zeno:smoke:
LFOD !

Hold on, I think I need some clarification here.

I'm seeing the pin output for the Yoke on the schematic, but my confusion is arising from the fact that it lists a different resistance for the horizontal and vertical windings. How can I tell which winding set I'm measuring?

I'll double check, but from what I Pin 9 on the oscillator isn't used for anything. I looked underneath and it appears that it was soldered to the board for stability, but there are no traces on it, and no wires connected to it, so I'm fairly certain that in itself was not the cause of my yoke going bad.

As far as I can tell, the only wire that broke on the yoke is the lead going to the terminal strip on the side. I'll have to trace where that's supposed to solder and reconnect it, then do an ohms check to see if I'm okay. At least, that's what I'm figuring. I'm confused on your suggestion to dig out both ends, though. Can I not just reconnect that one blown lead and test from the pins on the socket? That will at least tell me if I've got worse problems before I start tearing into anything else.

That being said, is a yoke really supposed to be receiving enough voltage to spark like mine did? These were big sparks - think the size I'm supposed to be getting from my flyback, but from the yoke. If I were to pick up a replacement, or repair this one, what's to say something else wouldn't immediately blow it? Is there somewhere else I could be testing to check for that, or would a shorted yoke be enough to do what mine did?

I'm probably going to have more questions before I move forward. I'm a bit out of my element here, and I don't want to blow anything else.

There's often several KV sized spikes on the h yoke winding... meanest shock I ever got was off one.

If you trace the wiring on the schematic you see that the horizontal output circuit is connected to pin 4. The yoke coil connected to pin 4 ends at pin 8, so the horizontal coil is between pins 4 and 8, resistance should be about 33 ohms. That coil is also center tapped and connected to pin 5, so from pin 5 to either pin 4 or 8 you should measure 16-17 ohms. Likewise you can trace the vertical connections on the schematic to pins 1 and 2, and measure about 26 ohms. You don't have to just go by the diagram of the the yoke as a separate unit, you can use the rest of the schematic to give you clues. The sparks were a result of the current jumping a gap, it could be were the wire broke or because the voltage rose so high the current jumped to somewhere it should not have. Do remove any carbon tracks you find.
The way the horizontal output works is that the current passing through the flyback and yoke that scans the beam across the screen suddenly stops at the end of a line. The flyback and the yoke are inductors, when you stop the current through them suddenly they react by producing a voltage spike (several thousand volts) that tries to continue the current. This voltage spike is stepped up further by the flyback transformer to provide the anode CRT anode voltage. It also generates the boost voltage. The narrow spikes is why there has to be some capacitance to smooth them out to a level DC voltage after they are rectified. BTW, the ignition on a car engine use the same technique of cutting off the current through a coil to generate the spark.

Alright, so I went ahead and ordered a spare yoke from Moyers. I'll have to pull this one apart and see if it's salvageable, but considering that I was already having High Voltage troubles, part of me is wondering if the origin of this whole thing - the horizontal issues, flickering on the screen, power draw issues, and now the lack of picture - isn't because the yoke was failing. Would that be possible?

Part of me wants to see about running additional voltage tests without utilizing the yoke, original or replacement, to protect myself from any further problems. If I were to jumper some resistors to mimic the picture tube filament and yoke resistances, would I be able to remove those from the circuit for the time being?

The flyback depends in inductive resonance of the yoke to opperate correctly... you would need another yoke or a correct size inductor to have the fly work correctly.

Understood.

Here's my issue, though. How can I tell if the yoke blew because of an existing short, or because of something wrong in the circuitry around it, without running another voltage test with the yoke hooked in? If it was something around the yoke, don't I risk blowing it again? Seems like a catch-22, unless I'm not understanding what to test next.

I have NEVER seen a yoke in a tube set be blown by something.
The enemy here is heat & humditity plus high voltage spikes.
Put the new one in without worries........

73 Zeno:smoke:
LFOD !

Okay. Finally some good news. The yoke came in a few days ago, and I finally had a few minutes to sit down and swap it in. Sure enough, my picture is back! Everything seems to work appropriately now, though I haven't tried running a signal through it. I never had a problem with that before, but my next step is to hook up some sort of stable signal so I can adjust the yoke, those two magnetic rings on the collar, and the various controls along the back before I button it up.

So basically, here's what I think happened. Again, I'm no expert, so if this seems wrong please feel free to correct me.

I believe that the yoke began to fail a few months ago. Perhaps some of the material on the inside had begun to deteriorate, which caused the flickering and noise in the picture. I pulled it down to my workbench, opened it up, and got sidetracked for a few months. During that time, the yoke deteriorated further, or perhaps the improved startup from the new capacitors pushed it over the edge. Regardless, that was my culprit the whole time, and I should be good to go now that it's out of the picture, no pun intended.

By the way, does anyone have any recommendations for a good basic RF adapter? Tim sent me a test pattern DVD eons ago, but I can't use it since none of my DVD players have RF out. I picked up a Heathkit linearity pattern generator sometime back, so I suppose I could restore that to get a picture on the screen, but I'd honestly like to go ahead and just fire up something I already have ready to finish this up. Once I get that figured out I'm essentially minutes away from being able to put this set back into use.

Thanks again to everyone for your help. I couldn't have done this without you.

Get a blonder tongue AM40 (AM60 or BAVMz if you want to transmit) those are among the best around though they often need a bit of work.

One thought if the dag is flaky and the yoke terminals are unprotected then flaking dag could have caused shorts and damage.

The Dag on the CRT? It doesn't look flaky to me. It doesnt cover the whole CRT, but where it is, it's solid and has clear borders.

There is a lot of grime back there, not sure from what, not sure if I'll ever know. Maybe that caused some issues?

I actually already have a few blonder tongues. I have this dream of setting up multiple in-home broadcast stations. I need a manual, but if I understand correctly the company will still supply them if I provide the serial number. Ill try and tackle that today.

Speaking of which, I tried to use one of them a while back, and didnt get much luck. Just some red color. If I need to tear into mine, I'll post a new thread, but what sort of work usually needs to be done on them?