Sentinel 430 restoration
 

1000th post :banana:

What better way to celebrate than another restoration project ? This one's a real doozey!

Here are a bunch of videos if you'd rather watch than read :D
Sentinel 430 restoration - part 1 (Overview)
Sentinel 430 restoration - part 2 (Time to start recapping!)
Sentinel 430 restoration - part 3 (Finally, some real progress)
Sentinel 430 restoration - part 4 (More steady progress and a few surprises)
Sentinel 430 restoration - part 5 (Time to finally test the full size CRT!)
Sentinel 430 restoration - part 6 (A final twist and putting it all back together)


I received a tip on a picture tube that's compatible with this set. I'd never really checked it out other than determining that the CRT is weak. So before dropping some money on a replacement I figured I'd do a quick recap and slowly power it up. What I thought would take a few hours turned into four long, late night sessions :drool:

Here's the set. I got it a while back in Skokie, IL from the nephew of a woman that had worked in the Sentinel plant in nearby Evanston during the war. It had been in the same house all this time and it's in great condition. The only minor flaws being the 'piece sign' stained speaker cloth and a break in the CRT gasket.
http://farm4.static.flickr.com/3394/...58351a09_b.jpg

Weak CRT
http://farm4.static.flickr.com/3339/...76e45395_b.jpg

Here's the chassis. Copper plated so no rust to remove for a change!

http://farm4.static.flickr.com/3409/...fe846e46_b.jpg

http://farm3.static.flickr.com/2783/...a6c22f9e_b.jpg

I had to use a heat gun and some vaseline to get the CRT out. There's probably a joke or two in there somewhere :rolleyes:
Then I dug right in and tacked in new electrolytics beneath the two cans. I also replaced all the big yellow ones below. I slowly powered it up slowly and all the tubes lit up nicely :D
http://farm5.static.flickr.com/4026/...dafd8a26_b.jpg

My excitment was short lived though: no sound - not even a hum, no video, no HV. What could the problem be :scratch2:

I measured B++ it was about 75v too high. I remembered leadlike had a similar problem and I checked the filter choke. No voltage drop across it. I tested the choke and it's around 100 ohms.

I started tracing the path after the choke and discovered that it runs through two low valued wire-wound pots for vertical and horizontal centering. I checked the vertical pot - bingo it's open!

I didn't have any replacements on hand so I built a little substitute using 10 ohm resistors.
http://farm5.static.flickr.com/4018/...66528908_b.jpg

Making progress
 

I powered up the set with my little patch and was treated to some nice white noise from the speaker that responded to the volume control :D Instead of HV though I got a loud squeal. Time to check around the horizontal circuits. I replaced a bunch of caps and resistors, but still no luck :(
http://farm3.static.flickr.com/2738/...01f4c20d_b.jpg

I checked out the flyback and it seemed ok so I widened my search and replaced a few more caps. Finally, I got rid of that bug, ugly bumble on the far left and got 10KV :thmbsp: Still no picture though. I was going to call it a night until I noticed a flash of light on the 8XP4 test CRT as I turned the set off.
http://farm3.static.flickr.com/2701/...99085cc7_b.jpg

A little more work and I had the first image of sorts.
http://farm3.static.flickr.com/2779/...fa39d6ba_b.jpg

That was it for day 2.
On to day 3 and more recapping and resistor checking. Making some real progress now.
http://farm5.static.flickr.com/4020/...fe22c25f_b.jpg

Good enough to pop the full size CRT in and see if it has any life left.
So close!
http://farm5.static.flickr.com/4052/...d2172f04_b.jpg

A little more work and :rockon:
http://farm3.static.flickr.com/2778/...5457f53f_b.jpg

However, that's with brightness and contrast at 100% with all the lights off. If I back off on either, the picture quickly fades to black. It's not very pleasant to watch so I fear the CRT really is weak.

So much for a quick recap, but I do know for sure that the set is viable and worthy of spending a a little money on.
I really hate those bumblebees - they look cool but cause so much trouble :uzi:
http://farm5.static.flickr.com/4055/...3ac4c5f8_b.jpg

...An' ANOTHER one about to spring to life...

Cabinet restoration
 

Now for the cabinet. Luckily there wasn't much to do. Just some Weiman's furniture polish took care of the "colorfast Blond Korina" wood. Here's the original sales brochure: http://www.tvhistory.tv/1951-Sentinel-Brochure.jpg

I found a date scribbled on the back that confirms it's from 1951.
http://farm3.static.flickr.com/2796/...e38242eeb6.jpg

Here's that stained speaker grille.
http://farm3.static.flickr.com/2705/...98fd8509_b.jpg

http://farm3.static.flickr.com/2764/...e51f0f45_b.jpg

I used some detergent, stain remover and bleach to clean it. No more peace sign.

http://farm5.static.flickr.com/4026/...ae629bb3a4.jpg http://farm5.static.flickr.com/4064/...a2a78832f5.jpg

I hooked up the internal antenna and did a test with my agile modulator.
http://farm4.static.flickr.com/3337/...e6157176ed.jpg

http://farm3.static.flickr.com/2598/...36cbb86c_b.jpg

Not the best picture, but there's still some work left to do.

Yep, nothing like being snowed in to get loads of sh*t done :yes:

GREAT!:banana::banana: That is one fine looking set!

Have you tried to re-activate the CRT yet? What is the tube, a 16KP4 ?

jr

Thanks! No, I haven't. I've never used that function before and I'm a little wary to try. Plus, I have another idea or two to test out. If all else fails, I certainly will use it.

I don't know what CRT this is - it's unmarked. The schematic states a 16KP4 or 16RP4.

http://farm5.static.flickr.com/4010/...f80a242b_b.jpg

...re.

Roger that! I have a Sencore CR70 now. Back when I took that picture a year ago or so, I only had the B&K.

Nice work. Good to follow the steps. And I'm amazed that speaker grille came back to life, I would have thought you'd have had to replace it.

but wait - there's more!
 

While I pondered my next step with this set I remembered I do actually have another 16" set. It's an Airline/Monkey Wards GSE-3020 I picked up last spring.
http://farm4.static.flickr.com/3579/...06a0c9e3_o.jpg

The previous owner said he had been watching it up until it gave out shortly before he sold it to me.
I did get a decent raster on it when I briefly powered it up last year. It has a CRT marked 1-3-64.
http://farm3.static.flickr.com/2797/...f0d0c186_b.jpg

http://farm5.static.flickr.com/4030/...7fa2cc96_b.jpg

Hmm - something looks awfully familiar about it :scratch2:
http://farm3.static.flickr.com/2787/...02f55805_b.jpg

It's the same freakin' chassis :eek:
A couple minor differences like the speaker field coil instead of a dedicated choke and a hybrid module instead of discrete for the vertical integrator.

How weird is that ? I wonder if both of them outsourced to the same manufacturer. I wish I had doubled up on my capacitor order to cover this set too!

Here's a closer look at that CRT. Hey, it's been rebuilt. Check out the angle on that gun.
http://farm3.static.flickr.com/2752/...0edc30ca69.jpg

http://farm3.static.flickr.com/2774/...fbf0ce7a_b.jpg

I popped it in the Sentinel and discovered the dimensions are a bit different. That caused the focus and center to be a bit off, but I'm not going to adjust that stuff for this test. It's definitely brighter but seems pretty harsh no matter how I set the contrast :scratch2:
http://farm5.static.flickr.com/4020/...615e4382_b.jpg

I may be all wet here (the mind is the second to go...I don't remember what the first was), but I think somebody posted a picture of another brand set that was determined to have the same chassis as your Airline... does that thread ring a bell?:scratch2:

jr

I'm not sure, but I did a little search of 'Airline' on this site and found my own from when I found this set. Apparently, it originally used a 16TP4 CRT. I'm not sure what the current one is.

Thanks. I thought I would too. I tried two different stain removers, but bleach is the only thing that really had an effect. Maybe it's whiter now that it was originally, but I'm OK with that.

There's nothing like a little flash of light on the screen to mess up a night's sleep!! I've done that, too. About to call it a night, and then something positive happens unexpectedly... "Oh geez, can't go to bed now... I'll never get to sleep!"

That's awesome the way your speaker cloth came out! On the other hand, I think the peace sign was kinda cool! :D :beatnik:

Making progress... getting close! Won't be long now! :banana::yippy::yippy::banana:

LOL - I was until 4am that night http://www.jawaspot.com/smilies/tired.gif I kinda liked that piece sign too, but the stain had to go.

Although I haven't given up on this CRT, I couldn't resist picking up this Motorola chassis with a 16RP4A for $15

I hope it arrives in one piece!

Does anyone have a schematic specifically for a Sentinel 430 ?

I'm currently working from Sams set 124 Folder 9 which covers models 420, 423 and 424. That's the best they had to offer. It's close, real close, but I'm encountering subtle differences in the sync separator, dc restorer and horizontal circuits.

I also checked Beitmans 1951 which has 412-416, 420, 423, 424. Beitmans 1952 has 438-444 :dammit:

It's been a couple very, very frustrating weeks, but I think I'm in the home stretch. First, I liberated a replacement pot from my Airline set. Then, I discovered that not only did the sync/dc restorer circuit differ markedly from the schematic, but some parts were only connected at one end! Apparently, someone was tinkering with it way back when. I decided to rebuild it from the ground up according to the schematic.
Now I had a much brighter picture, but the horizontal sync went to hell :smilemad:
It appears I was wrong about this CRT - it still has some life in it :thmbsp:
http://farm5.static.flickr.com/4022/...6b55f43f_b.jpg

So, I started putting old parts back in (or new parts with the old values regardless of what the schematic called for) following the reference picture I had taken. Finally, when I got to the horizontal phase inverter, I got my sync back :D
Only problem now is the retrace lines are very prominent.
http://farm3.static.flickr.com/2740/...5e429daf_b.jpg


I remembered seeing an article at the ETF on a retrace mod and dug up this page. I was surprised to find that this mod was already in this set, but it wasn't doing the job. I experimented with the RC values and finally, got a bright, stable picture with no retrace lines :banana:
http://farm3.static.flickr.com/2762/...ba448d49_b.jpg

Time to fire up a test pattern and get that picture all squared away!

Hey that's awesome!!
:banana::yippy::grnbounce:yippy::banana:

Yeah, sometimes it seems there's simply no mercy, and then when you least expect it, it works!

Congrats! :thmbsp:

I have one of those B&K 440's it always show the crt as worse than my Sencore CR-70. And always the CRT seems better than what the 440 says.

Also the Sencore seems very good at the rejuv mode, have had good luck with it.

just something to think about.

My parts chassis with a 16KP4A arrived today. It was really, really well packed!
http://farm5.static.flickr.com/4039/...fd74ed238e.jpg

http://farm5.static.flickr.com/4065/...3f5698b6_b.jpg

It turns out this a very nicely restored Motorola chassis. Does anyone recognize the handy-work ?
http://farm3.static.flickr.com/2753/...40982407_b.jpg

I wonder what happended to the cabinet :scratch2:
http://farm5.static.flickr.com/4011/...b4e591f8_b.jpg

Here's the GE 16KP4A.
http://farm5.static.flickr.com/4017/...13c5b452_b.jpg

Unfortunately, it reads absolutely 0 on both my CRT testers :( :tears: :dammit:
Maybe it's just a loose cathode connection inside the base cap ?
http://farm5.static.flickr.com/4001/...246d3f89_b.jpg

I suppose worse case scenario I have a really nice parts chassis for my Motorola 12K2 and a tube for Hawkeye to rebuild.

Thread jack: That's a pretty simple mod, I'd like to use it on my Philco which shows retrace lines at high intensity. Problem is on the Philco, the pic tube cathode is used for brightness and the grid is driven by the video amp tube. How could I change this simple circuit to work with the grid vice the cathode, if that's even possibe? I assume I'd need a phase inverter, and a coupling cap at the very least.

Looks like someone's done all the hard work for ya on that one! Yes, one of the pins in your socket could need resoldering. I had a NOS 21EP4 that gave a dead element on one of the pins and feeding more solder in the pin fixed that... then tested like new.

And if resoldering the pins doesn't help you can always try the re-weld the cathode trick as a last resort.

John

I'm glad you asked - I had the same problem with this set!
What I did was feed the vertical pulse into the cathode along with the brightness control and leave the video grid alone. It wasn't working at first because the 0.05 cap on the cathode was filtering it out. So i cut that down to 0.02 and reduced the resistor to 3.9K.

I hope this helps.

I took the base off - it was loose already. It's not a bad solder joint :tears:

Here's the best photo I could manage. To my eyes it looks like the cathode connection is OK, but I can't see all of it. What's the cathode re-weld trick ?

http://farm5.static.flickr.com/4022/...9f1605c5_b.jpg

:grnbounce
:yippy:

Every once in a while I get lucky!

Thanks, I'll have to give it a shot.:thmbsp:

that chassis looks a LOT like the motorola TS-14 I am working on.

It's a TS-60. I have a TS-23 that looks the same too. They made a bunch of chassis that were all very similar.

This is from the Sencore CR31A SuperMack manual, so I don't know if it works with all rejuvenators.

John

:banana: :banana: :banana: :yippy: :grnbounce :guitar: :boink:

I cannot friggin believe that actually worked!

I followed your directions about 30 times with no luck. Just as I was about to give up I saw a brief flash. Still no emission though.
About 6 more blasts, whacks and flashes and I finally got it welded back on. The emission is really strong too!

I think it would have been easier if I had a 3rd hand :scratch2:

Thanks you so much for those crazy instructions. What a great forum :D

Time to try it out in the set. I'm kinda afraid to move it now though :para:

http://farm3.static.flickr.com/2737/...ff8ffaef_b.jpg

How cool is tthat! :banana:

Great success story! Thirty times NO and then a big YES. :beerchug:

I admire persistance!

My old boss had a poster on the way, "never give up" with a frog choking a bird that was in the process of swallowing the frog.

In contract negotiations the idea was aways the same, "out last'em"

WOW! it is nice to know that works! :banana::banana::banana:
A few months ago, I gave up on a 14" tube in a small DuMont portable... the cathode would connect on occasion if the neck was tapped, especially if the heater voltage was elevated, but it would not "stick". Since the set came with a spare jug, I just went ahead and changed it out. When I autopsied the gun, I found several additional welds that were very poor...somebody was having a bad day at the CRT plant. :sigh:
Does Scotty (or anybody else) have the equipment to do a Laser rework?

jr

More good news :) Here's a preliminary picture with the 16KP4A in the Sentinel chassis. I still need to do some tweaking of the focus coil, yoke etc. I'd say it's about 15% brighter and sharper than the other tube. I wonder if some of that is due to the dag coating which the other tube lacks.

I'm not sure which tube I'm going to leave in the set :scratch2: Either way it's nice to have a spare :yes:

http://farm5.static.flickr.com/4008/...390df3ae34.jpg http://farm5.static.flickr.com/4052/...4888c7cec5.jpg

Nice, good to hear you were able to re-incarnate it!:thmbsp:

I hooked it up to my B&K 1077 and tweaked as best I could. There are a few issues to resolve:

The top is clipped.
The brightness increases from top to bottom. You can see that in the earlier pictures too.
The upper-right corner is dim.

I've done the best I can with the ion trap magnet, focus coil and yoke. Any thoughts ?

I think I'll poke around the vertical circuitry first to fix up the top of the picture.

http://farm5.static.flickr.com/4063/...6dcc1a095a.jpg

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