RCA 630TS maiden voyage -- sploosh!
 

Finally replaced the last cap in my RCA 630TS and powered it up. All good/new tubes, including CRT. Rewarded with a faint ghostly blur on the CRT which I could somewhat move around by fiddling with the ion trap and focus coil.

No sound, or any semblance of picture. Then . . . nasty spitting noise from the HV area, followed by instant power-off.

Rats!

Ideas? I'm taking a break until tomorrow, but would appreciate any tips about known weak points in this set.

Did it have a bright raster before it went Ppphhhht!
I hear peaking coils can give problems on those sets. Some folks have been saying the Mica caps in the 621's & 630's are having problems too after 60 years.

I haven't had the pleasure of working on a 630 yet so I don't have any specific ideas.

Hopefully you'll be able to see what let go, maybe a cap hooked to the wrong place. Seems like I always get at least one wrong on every set! :sigh:

BTW, I have a junk chassis if you find you need a part.

Well, it had a moderate raster before the poof. See http://antiqueradio.org/art/temp/RCA630TS16.jpg .

That's a little hard to judge when you have absolutely no signal, a problem I traced down to a failed 6J6 in the RF section. (It tested OK before, but nothing lasts forever.)

I spent a long time checking my work and poking around. Found one last paper cap that I had overlooked before -- and discovered that one end was not soldered! The lead was just lying in the terminal. In another area I had found a pair of resistors "connected" in the same fashion, so some sloppy serviceman had his hands on it once, but what else is new.

I then remembered that I had seen evidence of arcing from a h-v lead to the chassis, so I disconnected one end and slipped spaghetti tubing over the lead. I also did more cleaning of things in & around the h-v cage.

Oh, and also cleaned the picture adjustment pots on the back panel, something I had skipped before.

I brought it up on the variac and it looks like we're back on track. Raster is back and no spitting, at least for the time being. After some fresh 6J6 tubes arrive in the mail, I'll be able to do some more intelligent diagnosis.

Good to know there's a junk chassis out there -- you never know what odd unobtanium part you might need one day! Reminds me of my Hallicrafters 505, which was complete except for three little coils that someone had "borrowed" once upon a time.

Hi Phil,

Do yourself a HUGE favour and replace the filament winding on the flyback transformer
with new wire. If one point was willing to arc over to the chassis, there's sure to be others as the wire insulation has broken down. Make sure you round off the solder joints on the 1b3 socket to discourage corona discharge and potential arc over.

Bob

Pardon my ignorance, but what does this mean, exactly? Taking apart the flyback? And if so, where would I get the right sort of wire?

The filament winding is just a few turns of heavy insulated wire wrapped around the flyback's ferrite core. Usually physically separate from the other windings.

I gather this is the two or three turns of white wire pointed to by the red arrow in the photo at http://antiqueradio.org/art/temp/RCA630TS17.jpg ?

I tried to attach the same photo to this message, but haven't done that trick before, so my apologies if it is hosed somehow.

Is the type of wire critical?

It looks like a fair amount of work to pull things apart to replace that wire. I think I will bring up the TV one last time in the dark, in hopes of (quickly) spotting the arcing source.

Meanwhile, I need to do more detective work to find the no-signal problem, which did not improve as hoped with the substitution of 3 new 6J6 tubes in the RF section. One of the coupling caps in that section is mica, so perhaps that's the culprit. The others are ceramic, which I am assuming (ha-ha) is very reliable.

Tried that, staring at flyback in the dark, and didn't see any sparks. Which only means it might be arcing in a place where light doesn't leak out, I guess. Or maybe the Bad Thing is happening under the chassis in that area. I can't get it to spit unless I turn Brightness up pretty far. (Beyond that point, the brightness diminishes.)

Hi Phil.

The filament winding looks to be in pretty good condition, I don't think I'd risk damaging the flyback by trying to replace it at this point.

HV arcing is usually of the faint hissing type rather than a sharp crack, unless perhaps it came from a source where the HV might accumulate like maybe the doorknob cap or a poor ground on the CRT.

B+ seems more likely to me if it was a sharp noise, perhaps a bit of solder lodged somewhere under the chassis? I know I always have tons of stray solder bits when I'm done recapping.

I spotted the spark, under the base of the 1B3GT tube, which is mounted above the chassis on a little phenolic "table." Looks like a pain to lift that assembly out, but you gotta do what you gotta do :-)

I'm still puzzled by the behavior of the brightness control. The CRT reaches maximum brightness -- which isn't all that bright, even tho' this is my precious brand-new CRT -- about midway as you turn up the control. Then it decreases and goes back to dark as you turn farther. The sparking doesn't occur until it's turned up all the way and the CRT is completely dark again. Oh well, perhaps this will become more clear after I get things pulled apart.

Look for and remove any carbonized traces in the phenolic table.

Be aware that the very high voltage will be higher when the picture tube is at low brightness. Low brightness makes for less load on the very high voltage source circuit.

Is there an ion trap? You may need to adjust its position to get more brightness.

Speaking of ion traps, is it where it's supposed to be? Seems to me there are two spots on the neck where you'll get a raster but only one is recommended (and brighter).

Thanks, I cleaned up with rubbing alcohol and a toothbrush and didn't see any obvious traces, although the insides were covered with a uniform black dust, like everything else inside the h-v cage had been. Maybe the lazy-man solution would be to put it back together and see if that helped at all :-)

Yes, there's an ion trap, but adjusting that for best brightness, I still got the odd up-and-down response from the brightness control.

I attached photos with a snip from the schematic and a view of the 1B3GT socket. Resistor R235 (1 meg) tests normal on an ohmmeter, but note how it's assembled with its body resting against the terminal to which R233 (3.3 ohms) is connected. Maybe that was the arcing spot . . . ?

Which brings up my real question. In this photo, the upward end of R235 connects to one of those beautifully rounded-off solder joints. With things as they are -- i.e., hanging sideways with no way to turn the table any farther -- I doubt I could replicate that joint.

In other spots, I'd be content to snip the old resistor lead to the big rounded joint and do a J-hook connection to the new resistor. Just wondering if that's asking for trouble here, since lead dress looks important.

Phil,
Your symptioms of diminishing brightness with advancing brightness control sound like either inadequate high voltage, or low B+ to the HV section. Check the B+ at hte damper.
Try unpluging the high voltage capacitor, sometimes they can fail and overload the high voltage. Disconnect the CRT anode an measure the high voltage, then reconnect it and measure it as you advance the brightness.

Try replacing the damepr and hv rectifier tubes.

One of these things should lead you in the right deriction.

replace that large resistor under the 1b3 tube. it looks as if it has been hot. if cracked it will arc. steve

r253 i meg reolace that resistor

Thanks, that is on my to-do list. Also the second resistor in that photo. I might as well replace the little one, too, as long as I'm in there.

I don't have any 3.3 ohm resistors in the house, but perhaps a 3.0 ohm will do here.

If anyone votes for using a 4.7 ohm in place of a 3.0 ohm, speak now or forever hold your peace. That's all I've got on hand, and I don't feel like waiting 3 days to order one resistor thru the mail :-)

That will be close enough.

Wahoo! Replacing the bad 1 meg resistor cured the arcing.

Now, on to the next problem. Thx for the advice :-)