Chassis 16H27, black and white, that I got from Dwight :)

Great sound, no raster. Ran through the tubes and replaced a shorted 6EA8 in the tuner. Here's a couple of questions:

1. For a set to form a raster, does the rubber insulator on the HV anode on the picture tube have to fit tightly against? While the anode is securely in place, the rubber boot is kind of floppety.

2. I can hear what might be the oscillator running, but what could also be described as light rapid snapping from inside a shorted transformer (councidentally, there's a transformer right there). The frequency increases with clockwise rotation of the vertical hold control.

Sams on this set is 575-2 according to a note on the inside of the set. Remember guys I'm a noob at tearing into these beyond tubes and radio restoration, and I'm committed to get a working knowledge of set repair!

Tim,

Make sure the pins are good on the crt. Lots of the cemented crt plugs loosen up and result in poor connections. If the filaments light in the crt, try lightly rocking the plug left and right to see if a picture flashes, if so, you need to resolder the pins of the crt, and also make sure you have good non corroded contact the crt socket. I run into this many times with the early 60s zenith b/w portables.

Should all that check ok, make sure you have good hv. If you have a probe, check to make sure you have HV in there, like around 20KV. IF you dont have a meter hold the anode about 1/4 inch from chassis, it should arc if you have proper HV. The rule is, for every 1 centimeter of spark gap = 30KV, so the arc should be less than 1 cm. Most of the zenith anode covers will dry up over the years and dont seal to the crt like they once did. It wouldnt have any effect in your case. If all this fails, and tubes are lighting then you probably dont have any horizontal drive (from the horizontal oscillator) or your flyback is toast. (burnt up flyback is uncommon though for this type of set). That set probably has a 6GH8 h. osc. If you have a 6GH8 around, try subbing it to make sure. Those things are nothing but trouble. zenith sets are known for having corroded tube sockets even if the set is perfectly clean. What I normally do is shoot some contact cleaner into the pins of all the minature tubes sockets and work the tubes in and out. IF tubes in perticular are the worst, this will cause loss of sound and video resulting in just a blank raster.

Just to note, that rappid "snapping" you hear is the vertical oscillator and is comming from the vertical output transformer. It changes the rate of the noise as you turn the vertical hold like you said. This is kind of a clue that your set will have vertical trouble once you get to see the raster!! Your picture will probably be rolling rapidly. Luckily Vertical problems are about the easiest TV fix.

Make sure the pins are good on the crt. Lots of the cemented crt plugs loosen up and result in poor connections. If the filaments light in the crt, try lightly rocking the plug left and right to see if a picture flashes, if so, you need to resolder the pins of the crt, and also make sure you have good non corroded contact the crt socket. I run into this many times with the early 60s zenith b/w portables.

Funny you should mention that, the phenolic wafer board on the inside of the plug is toast! It's cracked and pieces are missing, but it is still functional. I'll verify all of the connections when I get the back back off, which will be later this morning if the kids behave :D

Should all that check ok, make sure you have good hv. If you have a probe, check to make sure you have HV in there, like around 20KV.

I do have a HV probe that I've never used.....the clip goes to chassis ground, correct?

That set probably has a 6GH8 h. osc. If you have a 6GH8 around, try subbing it to make sure. Those things are nothing but trouble. zenith sets are known for having corroded tube sockets even if the set is perfectly clean. What I normally do is shoot some contact cleaner into the pins of all the minature tubes sockets and work the tubes in and out. IF tubes in perticular are the worst, this will cause loss of sound and video resulting in just a blank raster.

I remember the 6GH8 discussion, this one checks out good, it was the first thing I thought of actually.

Just to note, that rappid "snapping" you hear is the vertical oscillator and is comming from the vertical output transformer. It changes the rate of the noise as you turn the vertical hold like you said. This is kind of a clue that your set will have vertical trouble once you get to see the raster!! Your picture will probably be rolling rapidly. Luckily Vertical problems are about the easiest TV fix.

I was pretty sure this was the case, but thanks for clarifying that :)

Thanks for the tips, let's see what damage I can do here ;)

Couldn't find my probe, so I did as you suggested. No spark at all, not even when held about 1mm away.

Here's a pic of the flyback....didn't realize while testing tubes yesterday that it seems like it's kind of baked. Not sure, but at the very least, it's overheated as the black coating melted off, some of which is lying around the surrounding area on the bottom.

So what would be the next step? :) I supposed I ought to do as you recommned with the tube sockets, but after pulling the tubes last night I did work them back and forth in their sockets just in case.

That flyback looks pretty sad. I think its safe to say its fried! I will get you a part number so you can let moyer know if you want to get a new fly for the set.

That would be great as I do intend to fix this thing :)

Do flybacks usually go on their own, by that I mean is a toasted fly the symptom or the whole problem?

Here are some additional suggestions:

1. Use a neon bulb tester to check for AC high voltage. Hold the
bulb (attach to a pen or other non-conductive device if needed to keep the HV leads away from your fingers) against the insulation of the HV output lead (plate lead of rect.) and the horizontal output tube--no direct connection. There is enough RF radiation from the leads to light the bulb if there is AC HV.

2. If no AC HV is indicated, remove the plate cap from the horiz. output tube. Attach the voltmeter to the disconnected plate lead. You should get the B+ voltage. If you do, the damper and flyback are working well enough to pass DC plate voltage on to the tube.

3. If plate voltage is indicated at the HO tube then hook the plate lead back up and measure the negative grid voltage. No negative grid voltage equals no input signal from the oscillator.

If none of this turns up anything then I would check the flyback w/ohmmeter...from the horiz plate lead to the HV plate lead is usually 400 ohms.

Another thing I do is to use a lamp bulb in the HO cathode circuit--from cathode to ground...a 200 MA 6.3 volt if I remember correctly. This will act as a fuse if there is a heavy overload and also allows you to set the cathode current in sets with horizontal efficiency coils by adjusting for minimum lamp brightness. If the lamp is positioned where you can see it glow through the back, you can also check it periodically and therefore detect abnormal increases in current by an increase in lamp brightness.

I think the biggest cause of flyback fry-ups is excessive HO current. Sets made in the 60's generally have no overcurrent protection in the HO circuit. A lot of 50's sets have a fuse in series with the damper and some 70's sets use a thermal fuse, circuit breaker, or more rarely a fuse in the HO cathode circuit.