Sentinel 430 restoration

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1000th post

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
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

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.


Weak CRT


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





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
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


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

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.

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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 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


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 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.


A little more work and I had the first image of sorts.


That was it for day 2.
On to day 3 and more recapping and resistor checking. Making some real progress now.


Good enough to pop the full size CRT in and see if it has any life left.
So close!


A little more work and


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

[Sandy G]

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

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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.


Here's that stained speaker grille.




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



I hooked up the internal antenna and did a test with my agile modulator.




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

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Originally Posted by Sandy G

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

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

[jr_tech]

GREAT! That is one fine looking set!

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

jr

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Originally Posted by jr_tech

GREAT! 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.

[andy]

...re.

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Originally Posted by andy

I bet a modern CRT tester would brighten up that CRT with little to no risk. Don't try with the B+K 440 I see in the picture.

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.

[Reece]

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.

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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.


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.




Hmm - something looks awfully familiar about it


It's the same freakin' chassis
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.




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

[jr_tech]

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?

jr

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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.

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Originally Posted by Reece

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.

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.

[Charlie]

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!

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