Just got this one the other day from a friend. Turns on with sound and backlit channel selector but no video. What year would this one be? I figured somewhere between 68 and 72. If more pics are needed, lmk. Really want to see this one working.

B is 1972. Does it have raster?

B is 1972. Does it have raster?

Ok, thanks. Nope, nothing. Just the heater.

Don't run it for more than a minute like that. Check grid voltage on the horizontal output. Should be around -75V. If not your horizontal oscillator isn't running.

Don't run it for more than a minute like that. Check grid voltage on the horizontal output. Should be around -75V. If not your horizontal oscillator isn't running.

Isn't that the 6U10 tube? Set needs to be on or just plugged in?

Clean set. Tubes I can see are OEM. White or yellow = OEM, red labeled are replacements.
Hoz out usually fused with a Bel-Fuse Those 2 green squares are examples
Hoz will be black & say 500-1. Center rear on top or under chassis IF it uses one.
Careful of that HO tube, VERY expensive !

Zeno:smoke:

Clean set. Tubes I can see are OEM. White or yellow = OEM, red labeled are replacements.
Hoz out usually fused with a Bel-Fuse Those 2 green squares are examples
Hoz will be black & say 500-1. Center rear on top or under chassis IF it uses one.
Careful of that HO tube, VERY expensive !

Zeno:smoke:
I don't recall seeing a fuse for that but I'll get in there tomorrow and look.

Zenith bel fuses are plastic rectangles.

Zenith bel fuses are plastic rectangles.

Yeah I seen the two green ones but didn't notice any others.

I'm gonna get in there this evening and look to see if there is a fuse near the oscillator. Also I'll test for reading. Where should I put my leads? Just wanna make sure I get it right.

By convention use the steel chassis for ground ( - or black lead).
Newer sets may have several ground points. Voltage is measured
at the Hoz out tube G-1 (6LB6 ? ). If the voltage in NOT very
negative ( @ -70 to - 90 VDC ) it will eat the H out & in some cases
melt it ! So keep testing under 1 mn til you get a raster.
You can measure from the top, you just need to count the pins CCW.
Pin out is on any data sheet for the tube.

Zeno:smoke:

By convention use the steel chassis for ground ( - or black lead).
Newer sets may have several ground points. Voltage is measured
at the Hoz out tube G-1 (6LB6 ? ). If the voltage in NOT very
negative ( @ -70 to - 90 VDC ) it will eat the H out & in some cases
melt it ! So keep testing under 1 mn til you get a raster.
You can measure from the top, you just need to count the pins CCW.
Pin out is on any data sheet for the tube.

Zeno:smoke:

Ahh ok, number 5. I'll get in there tomorrow and see what I get. I'll check for that belfuse as well :thmbsp:

One pic shows a fuse nearby. I couldn't get a reading. Did I do it right?

Looks right. See if the fuse is open.It goes between the hoz out cathode & GND.
If blown you can just jump it out for a FAST check, < 1mn.
Things can get complex now so take it slow, one thing at a time. NO shotguns !

Zeno:smoke:

Looks right. See if the fuse is open.It goes between the hoz out cathode & GND.
If blown you can just jump it out for a FAST check, < 1mn.
Things can get complex now so take it slow, one thing at a time. NO shotguns !

Zeno:smoke:

If I did it right on meter, it showed open. I'll jump it for a few secs. If jumping it, what will it do? Work normally or?

Is somewhat difficulty to see in the photos, but I have the impression that the fuse near the Hout tube are blown...

I couldn't find my alligator clips so I just hooked a wire to both ends. I tried it twice and I'm not getting any changes.

It's hard to see, but it doesn't look like your wire jumper is contacting the fuse leads, just the insulating spaghetti.

If I did it right on meter, it showed open. I'll jump it for a few secs. If jumping it, what will it do? Work normally or?


If everything is fine it will work normally.

Tubes are more forgiving than solid state - a SS horiz output will fail in 1/15K of a second, but you have more time to experiment with tubes. If you have insufficient drive to the output tube or if there's a load on the flyback, the tube will begin to "red plate".

In a dark room, jump the cathode fuse and watch the output tube as the TV warms up. If you see the plate begin to turn red, shut it down. If there's no red and the TV lights up with full raster and no nonlinearities or compression in the raster, it's probably good, but there might also exist an intermittent loss of horiz drive that will stress the output tube and open the cathode fuse, which is why you don't want to leave it jumped without constantly watching it.

John

If everything is fine it will work normally.

Tubes are more forgiving than solid state - a SS horiz output will fail in 1/15K of a second, but you have more time to experiment with tubes. If you have insufficient drive to the output tube or if there's a load on the flyback, the tube will begin to "red plate".

In a dark room, jump the cathode fuse and watch the output tube as the TV warms up. If you see the plate begin to turn red, shut it down. If there's no red and the TV lights up with full raster and no nonlinearities or compression in the raster, it's probably good, but there might also exist an intermittent loss of horiz drive that will stress the output tube and open the cathode fuse, which is why you don't want to leave it jumped without constantly watching it.

John
I'll get the clips today so I know it's jumped and I'll watch it.

I'll get the clips today so I know it's jumped and I'll watch it.

The other thing you can do instead of jumping out the fuse is to put your DMM set for reading milliamps (requires a lead change on the meter) in place of the fuse and watch the current. You should be getting a reading in the 200ma range somewhere give or take after 20 seconds or so.

If it stays low, the output tube is safe or the tube itself could be very weak, but if it goes over 250ma and keeps climbing past 300ma, shut it off.

John

The other thing you can do is to put your DMM set for reading milliamps (requires a lead change on the meter) in place of the fuse and watch the current. You should be getting a reading in the 200ma range somewhere give or take after 20 seconds or so.

If it stays low, the output tube is safe or the tube itself could be very weak, but if it goes over 250ma and keeps climbing past 300ma, shut it off.

John
Lead change?

Lead change?

Yes, you remove the red lead from the V, diode, ohm hole and move it to the ammeter side. Depending on your meter, it may have one or two holes for the ammeter side - one low (like below 400ma typically) and a higher one for several amps or more.

The black lead stays put.

John

EDIT: make sure to remove the lead from the ammeter hole when done as it presents essentially a dead short across the leads and you don't want to measure voltage in that manner.

Yes, you remove the red lead from the V, diode, ohm hole and move it to the ammeter side. Depending on your meter, it may have one or two holes for the ammeter side - one low (like below 400ma typically) and a higher one for several amps or more.

The black lead stays put.

John

EDIT: make sure to remove the lead from the ammeter hole when done as it presents essentially a dead short across the leads and you don't want to measure voltage in that manner.

Ah ok, move the red to top one. I've never used that one. First time for everything 😂

Not sure of setting on meter but I moved red lead to other port and I'm getting readings up to .46 or .50. plate in tube starts to glow so I shut down.

Not sure of setting on meter but I moved red lead to other port and I'm getting readings up to .46 or .50. plate in tube starts to glow so I shut down.

That's a half amp of plate current - too much.

Horiz output tubes are pretty forgiving but don't run it under load until you figure out why it's red plating - it's either too little drive or too much load.

Leave the cathode fuse open and scope the horiz drive signal to the tube. Without the horiz cathode connected the waveform will be more of a square wave but the amplitude and frequency will be the same.

If there's no horiz drive, that's your problem. If you do have horiz drive, you have a load issue, and that can be a problem with the flyback, damper, yoke, etc.

John

That's a half amp of plate current - too much.

Horiz output tubes are pretty forgiving but don't run it under load until you figure out why it's red plating - it's either too little drive or too much load.

Leave the cathode fuse open and scope the horiz drive signal to the tube. Without the horiz cathode connected the waveform will be more of a square wave but the amplitude and frequency will be the same.

If there's no horiz drive, that's your problem. If you do have horiz drive, you have a load issue, and that can be a problem with the flyback, damper, yoke, etc.

John

I don't have the means to do that.

Or at least I don't have a scope 😔

Or at least I don't have a scope 😔

Check the grid of the horizontal output with the cathode fuse out - you should get a negative DC voltage with respect to ground. On most Zenith horizontal outputs, that's pin 5. Look for at least -50VDC.

If that's missing, try a horiz osc tube and check all the voltages on the tube and the parts around it.

If your negative voltage is there, you have some kind of dynamic load on the flyback.

Most output red plating I can remember was due to insufficient drive.

John

Check the grid of the horizontal output with the cathode fuse out - you should get a negative DC voltage with respect to ground. On most Zenith horizontal outputs, that's pin 5. Look for at least -50VDC.

If that's missing, try a horiz osc tube and check all the voltages on the tube and the parts around it.

If your negative voltage is there, you have some kind of dynamic load on the flyback.

Most output red plating I can remember was due to insufficient drive.

John

So I need to remove that fuse? Pin 5 is G1 right?

So I need to remove that fuse? Pin 5 is G1 right?

Yes on both.

When troubleshooting red plating, it's best to avoid running the circuit until the problem is solved, but if you need to run the circuit to make voltage and waveform measurements, then running without the cathode fuse is one way to prevent the plate from dissipating too many watts and weakening it. Removing the plate cap is another, but sometimes the lead drifts back to the tube and arcs.

Pin 5 is the first grid on most typical Zenith outputs like the 6LF6, but if you have a different output (not familiar with your model number), then you can look up the datasheet for the tube on line and identify the first grid.

John

Yes on both.

When troubleshooting red plating, it's best to avoid running the circuit until the problem is solved, but if you need to run the circuit to make voltage and waveform measurements, then running without the cathode fuse is one way to prevent the plate from dissipating too many watts and weakening it. Removing the plate cap is another, but sometimes the lead drifts back to the tube and arcs.

Pin 5 is the first grid on most typical Zenith outputs like the 6LF6, but if you have a different output (not familiar with your model number), then you can look up the datasheet for the tube on line and identify the first grid.

John
My horizontal out is 6LB6.

My horizontal out is 6LB6.

Then yes, pin 5 is G1. Should be a large negative voltage on pin 5 to ground - maybe -60 or so.

If that's missing, that's good. Loss of horiz drive is easier to troubleshoot than a secondary load issue.

Is there a schematic on line for your TV?

John

Then yes, pin 5 is G1. Should be a large negative voltage on pin 5 to ground - maybe -60 or so.

If that's missing, that's good. Loss of horiz drive is easier to troubleshoot than a secondary load issue.

Is there a schematic on line for your TV?

John

No idea. Put on 5 and ground. Got nothing. If I put it on right setting...

If you dont get the neg voltage on pin 5 of the 6LB6 either the
hoz osc is dead (6U10 ) or associated parts, OR the 6LB6 is dead
shorted.
BTW NEVER measure the plate of the 6LB6 OR the damper unless you like
fire trucks. Your meter will go up like a Tesla !
BTW #2 the HV regulator ( 6HS5 or 6HV5 ) must be matched with the
right damper tube. Look for tags on HV box or layout chart. Wrong
pair will work BUT not right & not for long.
Good you are taking it slow....

Zeno:smoke:

If you dont get the neg voltage on pin 5 of the 6LB6 either the
hoz osc is dead (6U10 ) or associated parts, OR the 6LB6 is dead
shorted.
BTW NEVER measure the plate of the 6LB6 OR the damper unless you like
fire trucks. Your meter will go up like a Tesla !
BTW #2 the HV regulator ( 6HS5 or 6HV5 ) must be matched with the
right damper tube. Look for tags on HV box or layout chart. Wrong
pair will work BUT not right & not for long.
Good you are taking it slow....

Zeno:smoke:

Will a dead tube still light or no?

Will a dead tube still light or no?

It's absolutely possible for a tube to have a good heater (part that lights) and a dead cathode (signal tubes and CRTs alike get this) or a short. Got a tube tester or know somebody with one?

It's absolutely possible for a tube to have a good heater (part that lights) and a dead cathode (signal tubes and CRTs alike get this) or a short. Got a tube tester or know somebody with one?

Unfortunately no :(

Unfortunately no :(

You really should if you want to work on tube era sets. The alternative is to buy 2-3 examples of each tube (unless the seller has tested them there's no guarantee that they aren't used duds being sold) that you suspect is bad and try each of them... this is a bad approach on color horizontal sections as the 6LB6 is a $25-50 tube and 3 are more expensive than a basic tube tester.

You really should if you want to work on tube era sets. The alternative is to buy 2-3 examples of each tube (unless the seller has tested them there's no guarantee that they aren't used duds being sold) that you suspect is bad and try each of them... this is a bad approach on color horizontal sections as the 6LB6 is a $25-50 tube and 3 are more expensive than a basic tube tester.

I'll have to see if I can get one. Never thought I'd really need on but I've acquired more tube sets than expected.

We had good luck with the B&K. Just be sure it has the set-up book
& be modern, @ 1970 + REMEMBER checkers are NOT the final word.
Good tubes can check bad & bad tubes good.

Zeno

We had good luck with the B&K. Just be sure it has the set-up book
& be modern, @ 1970 + REMEMBER checkers are NOT the final word.
Good tubes can check bad & bad tubes good.

Zeno

I hear that. I'll see what I can do but not sure I can get one.