RCA 621TS restoration -- in pictures
 

I've got an RCA 621TS on the bench, which I'm restoring for someone else. I thought I'd show some of the progress in pictures as I work through the process. This one has turned out to be relatively easy, so it's not as challenging as some, but perhaps still interesting to follow the progress on.

Someone else will be refinishing the cabinet on this one, so I'll only discuss the chassis work here.

First thing I noticed when pulling the chassis out of the cabinet was some grass coming out the bottom. I worried a bit, expecting the grass got there by means of a little critter, which would likely have left urine and feces as well (what a mess!). This one is a bit different, however. Just a single stalk of grass that grew up through a hole in the bottom of the cabinet, wound its way around inside the chassis, and came out through the top in a few places. I wish I had taken a picture before I pulled it out, but here are some of the remains:

http://www.videokarma.org/attachment...4&d=1486624254

The top of the chassis was pretty clean, although someone had pulled all the tubes they could easily recognize and get to. Notice how they missed a metal 6H6 (doesn't look like a tube to some folks), tubes with shields, and a few tubes that were hidden from view from the rear:

http://www.videokarma.org/attachment...5&d=1486624254

http://www.videokarma.org/attachment...6&d=1486624254

I've removed some of the covers in the above photos; all the covers are in fact present on this set.

The 7DP4 CRT came to life in just a few minutes on the tester and tested very good (great news!).

Missing tubes were replaced with tubes from my stock (I had all of the ones needed, and even managed to find RCA tubes for almost all of them).

http://www.videokarma.org/attachment...7&d=1486624254

Since bad power resistors are often a problem on this set, I checked all of them -- both the ones in the HV cage and those in the chimney on the back. Good news -- they're all good!

The owner of this set requested that I restuff the electrolytic and paper caps. I don't normally do that for my own sets, but I'm actually looking forward to doing that on this one. First a set of pictures like this from various angles to document the underchassis component positions (I'll refer to this later as I put the restuffed caps back in original positions).

http://www.videokarma.org/attachment...8&d=1486624254

Since I don't want to go through all the trouble of restuffing caps at the very start, and put off the actual bring up of the chassis until all that is done, I'll do things a little differently than some of you might at this point.

First I thought I'd see if the electrolytics could be reformed. I seldom bother trying to do this, but have noticed that a few other restorers do this and leave the caps in place. I don't intend to leave them; I'm just looking for a temporary short cut. So I ran the set at low voltage on a variac for 30 minutes or so while monitoring the B+. The entire time I tried this, it was evident that the B+ was too low, indicating something drawing way too much current.

So I gave up on reforming, and temporarily subbed new caps under the chassis. Since these new caps are going to be stuffed inside the original cans later, they are literally lap joint soldered with full length leads and various connections hanging in mid air (see picture at very bottom of post). Everything made to come apart again once the chassis is up and running.

With the new electrolytics, the B+ comes up just fine for a moment. After a few minutes of observation - POW! One new electrolytic explodes. Hmmm... Why?

Four of the five electrolytic can capacitors have no markings, since they are covered with featureless black sleeves. So I'm relying on the schematic for values and voltages. Shame on Rider! (or possibly RCA) They have the voltages for C128A and C128B reversed! Rider shows both at 40 uF, with C128A at 450 VDC and C128B at 150 VDC. Quick inspection of the schematic shows this can't be right. C128B is the first filter after the 5U4 rectifier. It gets the full B+ voltage -- POW! C128A is the one that only needs to be 150 VDC. I bet I'm not the only one to have this happen, since Rider is the only schematic out there for this set.

After putting a 450 VDC cap in place of the one that exploded, I bring the voltage on the variac up to 100 VAC or so, and check the horizontal oscillator to see if it's working. It is, but very erratically, and at the wrong frequency.

So I replaced the paper capacitors (and a few micas) in the horizontal oscillator and output stages. Firing up the set again, we see a nice horizontal drive waveform:

http://www.videokarma.org/attachment...9&d=1486624266

And better yet, there is some high voltage. The flyback is working OK.

http://www.videokarma.org/attachment...0&d=1486624345

So how lucky am I going to be here? Let's try putting the CRT in and see if we get a raster. First attempt: No raster -- a completely dark screen. Naturally I suspect the problem is the ion trap. I try some permanent magnet ion traps with no luck, thinking that perhaps the ion trap is open or not properly powered. Checking the original ion trap reveals it is OK.

By luck I manage to notice that at the moment of shutting off the set, I get a little glimmer of light in the CRT. I checked the cathode grid voltage on the CRT, and the grid is way too negative. That's why the screen is black. I add a socket extender with test points, and short the grid and cathode together. Viola! We now have something on the screen, but it's just a horizontal line.

http://www.videokarma.org/attachment...1&d=1486624345

The vertical deflection is not working. Seems reasonable, since I have not recapped that section yet. After recapping, it works no better. Time for some real trouble shooting. Checked the resistors and found none to be way out of whack. Started probing voltages, and find that the grid voltage on the first triode of the vertical oscillator is too negative. Further tracing isolates the problem to the horizontal hold control. The wiper is shorted to chassis with a 330 ohm resistance (on a 1M pot). Seems like a whisker problem. I brushed the area around the lugs with a toothbrush, which is often enough to cure this problem. No luck.

Removed the control. Still shows the short. Disassembled the control. Can't see anything wrong with it. It had some whiskers on the outside of the housing, but inside looks very clean, and this one even has an insulating ring of bakelite on the inside of the housing, so it's not obvious where the short could be. Anyway, once it's apart, whatever was causing the short is gone. Reassemble and test again -- still OK. Remount back in the chassis. Vertical deflection now works fine.

http://www.videokarma.org/attachment...2&d=1486624345

At this point, I'm still running with the CRT grid and cathode shorted; otherwise the picture is black. A little checking reveals that the HV bleeder resistor stack (which plays a role in the brightness circuitry) has bad resistors in it. These are a string of 2 watt carbon comp resistors, each with value in the 10+ megohm range. Most are high, and one is completely open (although it looks perfectly nice to the eye). I don't have any suitable 2 watt resistors, so I create some subs with 1 watt resistors in series and install them. Still no raster unless I short the cathode and grid on the CRT.

I have not recapped the video amp at this point, and a quick check of the circuit reveals that I need to do so. After recapping the video and IF sections, we have a nice raster. Feeling lucky, I connect a signal source. How lucky can you get? The set happens to already be on channel 3, and tuned well enough for a very nice picture.

http://www.videokarma.org/attachment...3&d=1486624345

A little fiddling reveals that in fact the tuner contacts are extremely touchy, all the front panel controls are touchy, and the sound is rather weak (although there is some). All that can wait until tomorrow. This set is now ready for restuffing the caps.

All the paper caps have been labeled as to where they came from. Other components replaced thus far are also visible here.

http://www.videokarma.org/attachment...4&d=1486624345

What does the bottom of the chassis look like with all those caps temporarily hanging there with long leads and temporarily soldered lap joints?

http://www.videokarma.org/attachment...5&d=1486624358

It may not look bad from a distance, but close up it's ugly. More to come in the next few days as we do the restuffing to get things back to the original appearance.

Great story. It's fun to see a restoration step by step, since who knows when I might get a chance to work on one of those. I look forward to the next installment.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Tom, that's great. Nice to see yet another set working again. I stuff electrolytic cans because it only takes about an hour or less each and then I don't have to find a place to mount a terminal strip etc. I have stuffed some paper axial capacitors but not many. I am with you, I don't usually do that. But for something that is significant to history, I will do it. It does take work and I have not quite yet found the correct sealing wax for the ends. I did get some hot glue that is sort of amber but still not "brown" enough.

Waiting for more pictures...

Said it before, but I'll say it again, as someone who has almost ZERO technical prowess, this never fails to impress me...Still think you fellers that do this kind of stuff are magicians of some sort...

Tom- I had the same thing happen to me with my restoration here http://videokarma.org/showpost.php?p...6&postcount=43. I hope every one here who will perform a restoration on one of these reads our warnings. I had unfortunately already restuffed the electrolytic before it blew up so I had to do it all over again.
Set looks good, I'm looking forward to seeing it's progress until the end.

Tom, The underside of the chassis seems pretty clean. (aside from the Bermuda Grass that is) Doesn't look like there were any other attempts to restore would you agree?

The "out of my dreams"picture looks great even at this early stage! Given that those CRTs are hard to come by I'd say there was a real stroke of luck involved. Not to mention the wizzard behind the curtin that brought it back to life after being asleep all these years.

At least the previous owners had the good sence not to meddle with it or perhaps even plug it in. So hats off to them.

You make the restoration sound all to easy but I'm with Sandy, it all looks like magic to me.

Keep up the good work. I'm sure you'll find some more good bugs to work out as you get into the fine tuneing.

Hi vts1134,

You've done a nice job of documenting the problem with the parts list. Hopefully a few people will see that in the future before their capacitors explode.

I guess I was lucky in that I chose to temporarily wire up the new caps without restuffing them from the start. It would be much more frustrating to have to rebuild a restuffed can. In my case, it was just one cap down the drain, a moment of head scratching, and about 10 minutes with the door and windows open to air out the shop!

I don't remember this happening on my previous 621TS restoration (the one in my avatar: http://www.antiqueradios.com/forums/...p?f=3&t=114614 ). Maybe I used all 450 VDC caps in that one (I could easily have done that if I didn't happen to have a 160 VDC cap on hand at the time).

John Q,

The only evidence of prior tampering (other than the missing tubes) was one added resistor in the horizontal oscillator, which was put in to change the range of the horizontal hold control (I took it out and it works fine; was probably done to correct a drifting cap at the time) and one capacitor that looked like it might not be original (the grey Bumblebee-looking cap in the photo above). Everything else appeared original.

This one will definitely get more tweaking. The sound IF needs attention, since the sound is weak, and may not be quite aligned with the best picture in terms of fine tuning control position. The raster width is a bit narrow and the horizontal linearity is not too good, so there may be some drifted resistors in the horizontal output stage. Controls and tuner contacts need cleaning. I'll burn this set in for many hours over the next couple of weeks, so a few more issues may pop up with usage.

Why the Bermuda grass? Was it in a barn with grass or hay?

Very nice project, Tom! Your previous 621 experience means this one may go easier. At the least, you already seem to have a problem-free CRT (unless that is a test one).

Meticulous work.
I wish you were paid top tech rate by the hour - but
realistically I doubt you were:-)

Good read.
Thanks,

Carl

Hi Lee,

This TV must have been sitting on bare ground for a time. The cabinet is not bad, but the bottom shows a little dampness damage, with a little delamination of the plywood. Overall, the set is quite clean, so this must have been a temporary thing at some point, and the grass grew up inside it during that time.

Hi Carl,

I keep the charges pretty low, so that more people can get things restored. It's just a hobby. Day job pays the bills! I really enjoy restoring TVs. Doing it for others means I don't have to find room in the house to display the item when I'm done. :)

Some pictures of restuffing electrolytic cans:

There are five cans with black sleeves on them. These are easier to do, since the final replacement of the black sleeve will cover up the way I cut the can. For this method, I don't even need to remove the cap from its mounting. The wires to the negative terminals (can) have not been disturbed.

First, I pulled off the black sleeve. Fortunately on these, no heat is needed -- just a good pull and it comes off. Sometimes a bit of heat is needed to get the adhesive to let go, but in this case not. I then removed nearby items on top of the chassis, so I can get a Dremel tool in there to cut around the circumference of the can, about half way up:

http://www.videokarma.org/attachment...6&d=1486624945

After pulling the can apart, the guts come out easily:

http://www.videokarma.org/attachment...7&d=1486624945

For this cap, the replacements are tiny compared to the originals, so room is not an issue:

http://www.videokarma.org/attachment...8&d=1486624945

The top is put back on the can and taped with Gorilla tape:

http://www.videokarma.org/attachment...9&d=1486624945

The sleeve then goes back on. There is enough friction on this one that no adhesive is needed:

http://www.videokarma.org/attachment...0&d=1486624945

One of the can caps doesn't have a black sleeve. To keep the final appearance the same as the original, I won't cut the can in the middle. Often I see people uncrimp the bottom of the can, but this can leave the bottom of the can a little ratty looking. So I'm going to elect to slice off the crimp at the very bottom so I can remove things from the bottom without affecting the appearance of the can from the top at all. For this operation, the can is completely removed from the chassis:

http://www.videokarma.org/attachment...1&d=1486624953

I used a Dremel tool to carefully cut around the lip on the bottom of the can. I cut from the bottom, not from the side:

http://www.videokarma.org/attachment...7&d=1486625075

As you can see, a little ring of aluminum (which I discarded) comes off when I do this. Next, the ring with the tabs is removed:

http://www.videokarma.org/attachment...8&d=1486625075

The wafer with the lugs is pulled out. Next comes the job of getting the innards out. This turned out to be a little bit of a challenge. I heated the whole works with a heat gun to soften the tar. However, it was tricky to grab the innards in any way to pull them out. Finally I came up with the idea of driving a screw into the center and pulling on the screw:

http://www.videokarma.org/attachment...9&d=1486625075

Unlike the first cap mentioned above, fitting the new caps into this one (with four sections) was not easy. Most of the caps I had were too large. I finally found a combination that would fit. For the 20 uF section, I ended up using two 10 uF in parallel, since the 20 uF cap I had available was too large in diameter:

http://www.videokarma.org/attachment...0&d=1486625075

Everything was reassembled, and I used a little bead of JB Weld to hold everything together:

http://www.videokarma.org/attachment...1&d=1486625075

The bead of epoxy won't be visible after the cap is mounted back in the set. This is obviously not as strong as the original, but as long as no one uses the cap as a handle to pick up the chassis, it should be OK.

A few more electrolytic cans to go, and then the paper caps will have their turn.

Very good thread, Tom: eagerly awaiting the next installments.

Wow NEAT!

Always heard the term "stuffing caps". but never seen anyone do it. I'd be happy to just replace the cap, but THIS is pretty cool!!

Nice work, Tom.

Have you tried those Nichicon and Panasonic narrow diameter electrolytics? You can get them with great life and temperature ratings (105 C), high voltages, radial leads, and they are just the trick for restuffing cans.

They are long and narrow, say 12.5 or 16mm diameters, and I habitually use the 350v and 450v versions, for a margin of protection.

At Mouser Electronics, naturally.:smoke: