Recapping a 1955 RCA KCS92d
 

Hello all, this is my first recap job and I am not having much luck. I replaced all the caps in my tv and seem to have made matters worse. Before recapping I at least got a tiny bit of screen action, but now the screen no longer lights up. The rear of the tube does light up however, so I guess the picture tube is alright.

The flyback sounds a bit strained which is worrying, and the tube inside the flyback housing is not lighting up. Voltage is going through the wire that attaches to the top of the tube though.

Any ideas on this? I do not have a tube tester so I am mostly looking for a way to troubleshoot this if the tube is not the issue. I got this tv from the original owner and have really been trying to fix it to show it to him. His health is declining so I am trying to get this project done as soon as I can.

Also keep in mind I have never really messed with tubes. I do repair on vintage solid state audio so this is a bit of a stretch.

Where do you live? Maybe someone here lives nearby and can come over and give you a little help...

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If you have the schematic check the voltages in the set against the ones on the schematic...
How much of a recap did you do? If you have been powering it up every few caps changed it is possible that your work is okay and one of the old unreplaced caps died.

The HV rectifier heater is powered by a winding on the flyback transformer...If the transformer is not being driven properly by the H output/osc system there will be no heater voltage to the HV rect. Most HV rects are hard to impossible to see any glow from even when working properly...So don't worry if it is dark. If you can get 1/4"+ of arc from the top cap of the HV rect, but no arc from the HV connection to the CRT then the HV rect is suspect. You can look up the data sheet of the tube and check if the heater filament is open with the ohms function of a DMM. Substitution with another tube is also a valid test.

If you don't get an arc from the to cap of the HV rect then make sure you change all caps in the horizontal output and osc sections as well as the B+ Boost rail. then check resistors in those sections and check voltages.

QUOTE:

"If you can get 1/4"+ of arc from the top cap of the HV rect,..."

To expound a bit for a newbie, use a metal screwdriver with an insulated handle. The screwdriver is ungrounded. It draws the arc due to its innate capacitance in the air.

Recapping is best done in stages.
When first testing, you have to observe the operation!
With a signal: Is there sound and some kind of image on the screen.
Knowing that set, the horizontal will be off frequency, the vertical circuit will be producing a miss-shapen screen, both common problems with that set.

I live near knoxville, so it is very unlikely anyone around here would know much about something like this. Very few people around here mess with electronics. In this area I'm the "electronics guy" so I'm mostly on my own.

As for recapping, I shotgunned the thing. The only original caps left are the big metal multicaps. Parts still need to be ordered, but I forgot about it due to having a million projects.

I did not do the screwdiver test, but instead used a grounded multimeter to get a precise reading. On the top of the tube, the cap archs and reads really high. Enough to max out the meter. The plunger that attatches to the tube only reads around 20v, so that is certainly a problem.. Guess the tube is the issue, but it worked before to an extent.

Also I do not have any schematics for this tv, but have been looking for something I don't have to pay a ton for. I have to admit, this isn't the best hobby for a collage student.. It sure can be fun though.

the "big metal multicaps" are electrolytic capacitors and are usually the most important ones to replace, usually replace those 1st. Keep at it and learn from it.. thats what i did at first and still do. these other guys know their stuff. im just a rookie.

That multimeter is probably ruined (or you are not getting enough voltage there). NEVER measure voltages on the top caps of tubes connected to the fly or the HV with a normal multimeter. Damper elements and the HV to the CRT are also points not to measure with a DMM. The top cap of the HV rect usually has 10KV-20KV AC spikes, the top cap of the H output 1KV-5KV AC and the CRT HV is usually 8KV-25KV (increases with screen size)....Most multimeters are rated for 500V-1KV max input. If you don't have a HV prove designed to measure over 20KV don't try to measure....Another reason to have the schematic it will tell you where NOT to measure voltages.

I'll check my duplicate sam's...If I have the service info then you can have it for $3 plus postage.

I figured those metal caps were important, but I just got excited and wanted to see if this tv had any life. Those metal caps are probably why the audio makes such horrible noises.

I wasn't aware about places not to measure voltages, but the meter is a pretty decent one and it still does fine (for now anyways). I'd appreciate the manual if you can find it.

I also ordered a replacement tube for $4.99 free shipping. Figured might as well, even if the original isn't bad. It'll probably need it someday.

The set is a little harder to troubleshoot because the CRT is mounted separately in the cabinet. I never give it a second thought because I can use a test CRT.
The OP would have to remove the CRT from the cabinet and have it on the bench with all the connections made, as the yoke plug has to be in to complete the B+ circuit.

Hello everyone, still working on this tv and have finished recapping. I am still getting no action from the screen, and the plunger that connects to the CRT is giving off nothing at all. The HV screeches and I get an arch off the tube when using a screwdriver. With the plunger there is no arc, and with a meter it reads no voltage.

Sounds like the HV rect tube is bad. Also worth checking is its heater lead and any series resistors connected to its socket.

I went through the tv again with a tube tester and found the vertical output tube was bad. This wouldn't cause no voltage on the plunger would it? The audio tube is also missing. Everything else looks fine and I keep going over this thing over and over again looking for mistakes.

Today I fired it up and gave it full voltage with no luck. The flyback sounded strained compared to a newer tv. Not sure if this is okay or not.

The audio output tube is a key part if the power supply in some TV's. Make sure you've got a good set of tubes installed

I just ordered the two tubes I needed, so hopefully they help out. I am mostly confused by this HV tube. Off the top of the tube I get voltage arching when using a screwdriver, but nothing from the plunger which is attached to the bottom of that same tube. The tube tests good, so I'm not sure what is happening. Maybe not enough voltage is going through or something. It's been driving me crazy for quite a while.

The vert tube is usually not able to take out the HV... granted some sets take boost voltage from the flyback to feed the vert and if the vert stage has an issue causing it to overload the boost that can also load down the HV indirectly.

The fly sounding strained sounds like a more telling lead... if the h osc is too far off the correct frequency then the HV output and sweep will collapse. The entire h output/fly/yoke is a big tuned circuit and needs the right frequency to work. Also the waveform and amplitude need to be at least close to the right for the system to work... when it it right it should be a high pitched whistle tone no screeching or crackling.

Make sure to get a schematic...TVs are complex and diverse so flying blind without a schematic is going to waste more money in burning through your valuable time than buying 10 schematics will cost.

I will certainly try adjusting to see if I can get the flyback to sound somewhat correct. Would the adjustment being off cause no voltage to go through the plunger though? Like I've mentioned before I'm really new to TV's so there's quite a bit of confusion on my end. Dang audio repair is so much easier.

Just ordered the schematic, so that'll help hopefully.

The "plunger" (I presume you mean the suction cup at the end of the HV lead) that connects between the side of the CRT and HV cage is the HV lead so yes off freq can kill the HV. Hard to tune it without an oscilloscope, Best to get a scope, measure dist between h sync pulses on video sign then hook the scope to h osc and tune it to match.

Here is one of my favorite diagonstic tricks that newbys can try. I doesn't take any special exotic equipment. The fluorescent bulb doesn't have to be good, the glass tube has to be still sealed though.
If the bulb lights when held near the horizontal output, flyback or yoke leads then the horizontal output circuit is working. Before compact fluorescent bulbs were available neon bulbs were used. I guess now the compact fluorescent bulbs are being phased out.
The horizontal circuit has to be working before the CRT High Voltage (HV) will be produced.
The filament voltage for the HV rectifier tube comes from the flyback transformer. The filament usually can't be seen anyway on that tube.
Do get a schematic and learn how to read it.
Do be very careful around the B+ and Boost voltage. Stay at least a couple of inches away from the tube caps, the voltages there can jump when the set is working.

There are generally three sources of schematics for products of this vintage.
Sams, Riders and Beitman published schematics. Sams usually has the most info like parts lists and photos. Many times you can download Riders and Beitman for free.
Go to the link below. Click on the top check under 1955 of the TV Diagrams section. That will download that pdf file. Look on page 149 of the manual (page 145 of the pdf file). What is the model number by the way?
http://www.americanradiohistory.com/Beitman-Manual.htm