Howdy!! DuMont failure it seems....

[CaryLee]

It's been a while since I was on. Several years ago, I chronicled the restoration of my grandparents 1950 DuMont Ardmore here in the forums.

I've watched that television off and on for years now, and eventually, the digital converter failed. I recently purchased a new one, and hooked it up today. I had some issues with the connector on the back of the CRT. A couple wires needed to be soldered....

First, the brightness control wouldn't work. I found a wire had come off the connector. Resoldered it, and everything worked fine.

Then, another wire came off the connector. When I was was removing the connector from the back of the CRT, disaster struck! The entire bakelite connector came off the neck of the CRT! The wires remained intact in the glass of the neck of the tube, and I was able to reattach the bakelite connector. Each wire lined up with the pins on the connector, and I was able to resolder them, at least so it seemed.

I soldered the wire that came off the connector back onto it.

However, currently, it appears something very bad has happened. I have sound. The filament in the neck of the CRT is glowing just like always. However, the screen is currently dark. There is no picture.

It's hard for me to believe the CRT could have failed so suddenly. It was working a couple hours ago. Now I have no picture.

The set uses a 19ap4 CRT. I know those aren't easy to come by.

Any thoughts?

[MadMan]

Possible that the crt pins didn't take the solder?

[CaryLee]

Originally Posted by MadMan

Possible that the crt pins didn't take the solder?

I resoldered just to be sure. Seems they are all connected.

I do not have a CRT tester. Is there a way to check the tube with a multimeter/ohm meter for internal failure?

I'm at a loss. The picture tube was working great just hours ago. Bright as always. It will be a real shame if it's a goner.

[old_coot88]

Have you confirmed that the CRT is getting high voltage?

BTW, I remember that resto thread.

[Kevin Kuehn]

Any chance you bumped/moved the ion trap?

[CaryLee]

Originally Posted by old_coot88

Have you confirmed that the CRT is getting high voltage?

BTW, I remember that resto thread.

Well, I did confirm the metal cone of the tube was getting high voltage, with a quick touch of the metal cone...

Is it getting the PROPER high voltage? Not sure yet.

I had purchased an old time do-it-yourselfer type repair book a while back, and it does seem to indicate that my condition is related to the high voltage section not working...Dark screen, filament glowing, etc. I switched out the two 1x2 tubes just to be sure.

Since this TV has an FM radio as well, and a switch that shuts off the screen..but not the filament...when one wants to listen to FM, I'm wondering is something could have gone haywire with that switch. I noticed that when I switched it to FM tonight, the FM sound would drop off. Working the switch some brought the FM sound back up, I suppose it's possible that it's not turning the screen back on when it's switched to TV.

From what I've read, the "getter" turning white is a telltale of the tube losing vacuum...I'm going to have to remove the deflection coil to get a clear view of the "getter", as from what I've seen, it's up close to where the neck meets the cone. It looks like I can see part of it at least, and it still looks dark, not powder white.

I'm puzzled. I suppose it's very possible when the bakelite "base" came off the neck of the tube, one of the wires pulled and broke the seal...but from what I've read, along with the "getter" turning white, the filament wouldn't last long if the vacuum was lost...

[CaryLee]

Originally Posted by Kevin Kuehn

Any chance you bumped/moved the ion trap?

I was hoping that was it...but I moved it around, and nothing changed.

Darn it.

[old_coot88]

If the CRT lost vacuum (went to air), the heater would not be glowing a normal healthy orange which it appears to be doing. Instead, the CRT neck would become sizzling hot very quickly because the heater is immersed in heat-conductive fluid (air), and will not be glowing visibly.

Also if it lost vacuum, it would lug the HV down and you wouldn't have got that unnerving ZZap.

[Electronic M]

Got a schematic? check the voltages at the CRT socket (srick the DMM probe in the hole for the CRT base pin) and compare with those listed on the schematic. If the voltages jibe (may require brightness contrast adjustments to match) then either the CRT base solder ain't right, the CRT has some other problem or the HV ain't right.

[CaryLee]

Good morning folks!

Thanks for the further tips! Much appreciated!

After sleeping on it, I see I'm going to have to start a more methodical diagnostic process other than the panicky/scattered/disasterous issue driven stuff I did yesterday...

I'm going to have to dig out my Photofact on this set..hopefully I put it in the files with the rest of the schematics..when I did this TV it was pretty early in my restoration days and I didn't have the file yet. If I stashed it somewhere else, THAT might be a challenge!

One issue I've always had with this set is not having the proper connector for the CRT...or perhaps I only have the "inner" part. The bakelite housing has always been missing, so there is no stress relief on the solder joints. Thus, the wires have always been prone to coming off. That's what happened yesterday when I was moving stuff around. It didn't help that when our cat was younger, a couple years ago, he would get up in there and knock stuff around.

When a wire came off the connector yesterday, the tube went dark, and that's what started the whole "tube base coming off the neck" snowball..the tube has never come back to life since. But yes, the heater is glowing and continued to do so for well over an hour, and the neck never got hot beyond what I ever experienced. It gets warm, but one can hold onto it forever if one wants to. What I'm hoping is that perhaps when that wire fell off, it touched something that took out that circuit..hopefully it did NOT touch something and take out the CRT!

And I had such a good picture until then...

So, yes. My next step will be to check voltages at the connector and make sure they are correct. I'd MUCH rather it be a circuit within the TV than a bum CRT! Even with my very limited experience, I can likely fix the TV...but if I'm correct, there is still nobody on the planet that can rebuild a CRT.

Last I'd read, the Early Television Museum had decided not to rebuild tubes commercially.

It might be a couple days before I can get back to it. My wife and I are taking our RV out to Navajo Lake State Park today until Thursday to try to get some fishing in while we still have some nice weather, before winterizing the thing for the season. We've already had a few nights below freezing (it's 25 as I type this), but the next few days are supposed to be warm and sunny (high 60's). Fall is definitely upon us here in northern New Mexico!


PS: That red stuff between the tube base and the glass neck is nail polish. I'd read that nail polish makes a good glue to re-attach loose tube bases. My wife doesn't know where her clear nail polish is...so red it is!

[CaryLee]

I've been looking, but can't seem to find....

Is there a proper forum to post "buying/selling"...I'm going to start my hunt for a CRT whether mine turns out to be good or bad..this set is pretty sentimental to me and I need to keep it working.

Thanks.

OK...nevermind...I found it. Apparently I just couldn't see the "Classifieds" and "Curbside" forums until I was logged back in.

[old_coot88]

Originally Posted by CaryLee

... The entire bakelite connector came off the neck of the CRT! The wires remained intact in the glass of the neck of the tube, and I was able to reattach the bakelite connector. .

Any thoughts?

If you're positive none of the wires broke where they come out of the glass, the CRT should be OK.

Just a tip - when you go to take voltage readings, pay special attention to the voltage on the cathode and G1. If G1 is overly negative with respect to the cathode, the tube will be cutoff (no raster). Just as an off-hand example, if G1 reads 100V and the cathode 140V, the tube will be cut off.

[Eric H]

If you could get hold of a 5AXP4 test CRT it would tell you for sure if the set is working. No Ion trap needed and it can handle 18kv on the anode which I'm guessing is in the range of that set?