Are these things I should consider bad

[andy]

...

[TinCanAlley]

Originally Posted by andy

It doesn't look that bad to me. I think your scope is showing more of those sharp negative going pulses than what ever scope Sams used. If you ignore that really fine negative pulse, it ends up being around 8-10 volts which is well within reason. I doubt Sams would have used a 100MHz oscilloscope because no technician in the 70's would have had anything even close to it.

I can just about guarantee nothing in the HOT base drive circuit is causing your jail bars. Generally, if there's anything wrong with the base drive, the HOT will overheat and fail. The HOT acts as a switch. It's either completely on, or off.

I think you need to be looking around the flyback, and yoke. Something is causing the flyback, or yoke to resonate at about 10x the horizontal scanning frequency. It's not going to be caused by a slightly wrong drive signal, or slightly off voltage.

Have you looked at L218 and C274?

Okay, just to make sure, is this attached pic of the L218 you're referring to (the brown cylinder with the coil around it)? It took me a moment to find, but it is connected to tie points 3 and 4. I should check its resistance and see if it matches what Sams has across tie points 3 and 4? Also, I can't find the capacitor shown (the .047).

You have any tips on checking the yoke? I've been trying, but I can't see to get any meaningful results. I've tried checking pin pairs, but according to the schematics, each has multiple connection points. So how am I supposed to check the resistance? All I can really do is check continuity. The first pair I tried should have a resistance of 220ohm, but my meter shows me 8ohms.

[TinCanAlley]

Originally Posted by andy

Have you looked at L218 and C274?

Okay, I checked L218 and I got .7. It's supposed to be .12, but I checked and my leads are .6. So subtract the leads and I get .1 (my meter doesn't show anymore places to the right).

I think I found the capacitor. It's red and axial and there are actually two of them. Is this them in the pic?

[TinCanAlley]

Okay I finished the testing of the FB. I don't know how accurate it is as my leads seem to have .6 resistance of their own and I don't know if that should be disregarded or subtracted. I usually disregard it, but the numbers I'm looking at for the FB are pretty low and if .6 is added by the leads, it could easily triple some of the results. So if anyone knows what should be done in this situation, let me know.

I'm attaching the FB section of the schematic so you can see where/what I tested.

Below are the connections, the results w/out subtracting me leads and the values on the schematic. The first three are at the tie points on the board next to the FB. The rest were done at the chassis connections of the FB leads.

Connections Results Sams
3 - 9 / .8 / .1
4 - 8 / 2.2 / 1.6
9 - yoke plug / .12 / .5

G - R/W / .10 / .5
R/W - Blk / .8 / .7
Y - Blk / .7 / .1
Y - Vio / .8 / .2

I don't know if anything is thrown off by all the leads being connected to the chassis still. Nothing in the Sams says anything about tolerance, so I don't know how close or dead on they have to be.

[TinCanAlley]

Originally Posted by Username1

At this point, I am going to assume your 125v source may be 140V.
You are also seem to be having different readings on your two pieces of test equipment. You will have to figure out how you want to deal with that.

I would check through the low voltage power supply where the 125v comes from, and check through the voltages listed there, there should be 4 or 5 low supply spots you can test, Use both your dmm, and the scope on DC, see which one you are more willing to trust. If that 125v is way off, then your HV may be using too much power and creating that ring just because the voltage is too high....

If you can, please post the power supply circuit, lets see if its a doubler with a possible bad part making too much voltage.....

I'm sorry to be casting doubt on your test equipment, but I have been there before, it may seem to be a stupid step, but we have to follow the evidence we have to find the real problem.

I'll check all the points of the 125V from the point it leaves the transformer to various points using both DMM and scope.

I've attached a pic of the power supply section.

[Username1]

Well, that 16v is generated in the coupling transformer. So for that to be too high, all other stuff being good, the primary has to be getting too large a signal, and you have evidence of that. So the thing to do is try and figure that out....

Is the power supply too high?

or

is there something making the primary signal too high?

I am leaning towards double checking the power supply, that 125, and what else may be associated with it, be it larger or smaller sources that may be there.... Please post the power supply section when you get a chance, ( Isee it thanks ! ) and measure the different sources available....

And just in case the power supply is pumping out too much voltage, lets limit how long you keep the set on to just 10 minutes or so during each measurement period.

Be careful when measuring the power supply, if its regulated, you don't want to accidentally short anything that will fry anything in there....

[Username1]

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

[TinCanAlley]

Originally Posted by Username1

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

I'll do these next. I've been going over the 125V sources and they all show up as 129V. The DMM and scope are in agreement there. I also checked the 125VAC and did the math. The DMM showed 128V and the scope had 126V after doing the calculation given me for RMS.

I'll let you know the voltages asked for.

[jr_tech]

Originally Posted by Username1

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

I have been looking at the schematic and scratching my head over that cap... what does it do? Is the transformer somehow set up to be a constant voltage device?
jr

[Findm-Keepm]

Originally Posted by jr_tech

I have been looking at the schematic and scratching my head over that cap... what does it do? Is the transformer somehow set up to be a constant voltage device?
jr

That transformer supply is ferroresonant - an L-C tank, and causes the transformer to provide some level of regulation itself. If the 440V cap goes bad, you'd know it, with a dead set, or really low voltages. If you get B+ and other transformer secondary voltages, move on, as the ferroresonant circuit is working. Zenith stressed this after seeing a spike in folks ordering the cap. Reliability testing showed the cap had a 40+ year life, and shops that didn't understand the circuit would order and replace the cap to eliminate that as the cause of whatever problem they had. I've only seen one go bad- and a dead set was the result, with the blown input fuse as well.

We always kept the caps from the sets we junked, and I used one two summers ago as a makeshift run capacitor in my HVAC Gaspack to keep the AC going in July 2011. Date code on the cap is 1979....

Cheers,

[TinCanAlley]

Originally Posted by Username1

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

The voltage to and from the regulator (Q212) is correct. I get 23.4V and 24V. Each is only off by .2, but that's most likely my DMM. The scope also showed the proper divisions from baseline for DC.

I thought that 3.5uf canister wasn't soldered in, but it is. It's also 440V. What size resistor will I need to discharge it?

[TinCanAlley]

Originally Posted by Username1

128v at the diode there just before the filters and choke.

Okay, on the AC side of the diode I get 131VAC and on the other side I get 131VDC. According to the schematics, the Red-Blk is supposed to be 100VAC. So if I test directly to where the Red-Blk connects, I shouldn't seem much more than 100VAC, right?

Here's a pic of the red-blk connection and the 3.5uf 440V cap. If you think this cap needs to be checked, let me know. I'll have to unsolder one of the leads.

[Username1]

I'm happy your check of the low voltage power supply went well. As long as the 125v is not as high as 140v and your measurement of the 24v regulated showed the same readings on both test instruments, lets go back to tp5. I know there are not many who believe something can be wrong here, but there has to be a reason the drive voltages are so far off. I'm posting 2 more pictures. In the horiz osc, driver, I would like you to measure the voltages of the driver transistor and post them. I believe its q803. I would also like to check the caps attached to the coupling transformer between the driver and HOT.

Also check that 2200 ohm resistor between 124 and 123 is it ok....?
If the emitter voltage of the driver is too high, you'll have to check that 40 ohm resistor in that circuit.

In that picture you posted of the flyback, is it melted or is that some repair made to it ? its not running hot is it?

Sams gives an emitter current for the HOT on that schematic, I think it say 1.8A, if you think its running hot, it may be worth measuring that.... You have to use the 10A DC current scale on your DMM, - to ground + to the emitter. Only if you think its running hot..... or the FB is melted....

[TinCanAlley]

Originally Posted by Username1

I'm happy your check of the low voltage power supply went well. As long as the 125v is not as high as 140v and your measurement of the 24v regulated showed the same readings on both test instruments, lets go back to tp5. I know there are not many who believe something can be wrong here, but there has to be a reason the drive voltages are so far off. I'm posting 2 more pictures. In the horiz osc, driver, I would like you to measure the voltages of the driver transistor and post them. I believe its q803. I would also like to check the caps attached to the coupling transformer between the driver and HOT.

Also check that 2200 ohm resistor between 124 and 123 is it ok....?
If the emitter voltage of the driver is too high, you'll have to check that 40 ohm resistor in that circuit.

In that picture you posted of the flyback, is it melted or is that some repair made to it ? its not running hot is it?

Sams gives an emitter current for the HOT on that schematic, I think it say 1.8A, if you think its running hot, it may be worth measuring that.... You have to use the 10A DC current scale on your DMM, - to ground + to the emitter. Only if you think its running hot..... or the FB is melted....

The two caps you noted between the coupling transformer are new and were tested before installation (jail bars were there before the replacement).

I think you're looking at the blob of RTV covering the lead so it doesn't arc from the top of the flyback to any metal in its surroundings.

The HOT runs around 81 degrees and cool to the touch (well not cool, but barely registers to the touch as it's no hotter than my fingertips).

I'll pull the horizontal board today and check the values of the cap and resistors noted. If they are okay, I'll put it back and scope the H-OSC transistor.

Gotta catch up on some other duties this morning, but will be back inside the set in a couple of hours.

[TinCanAlley]

[QUOTE=Username1;3084085]I'm posting 2 more pictures. In the horiz osc, driver, I would like you to measure the voltages of the driver transistor and post them. I believe its q803. I would also like to check the caps attached to the coupling transformer between the driver and HOT.

Also check that 2200 ohm resistor between 124 and 123 is it ok....?
If the emitter voltage of the driver is too high, you'll have to check that 40 ohm resistor in that circuit.QUOTE]

Okay, finished testing what you noted. The 20pf (C814) is 19.8, the 2Kohm resistor (R821) is 2.5Kohm (this one has no percentage band so I don't know if that's too far off), the .22uf (C811) is .23uf and the 40ohm resistor (R819) is 47ohm.

Do you want me to test the voltage of all three legs of (Q803)? Do you just want DMM readings, scope or both? This little bugger's a pain as it's right behind the large capacitor and it's a pain to get the hooks on the legs.