SC1224 version 3 Questions

[+DrVenkman]

So I got this new-to-me SC1224 today that appears to be the less-common third version, manufactured by Samsung. It's in pretty good cosmetic condition aside from the inevitable yellowing case. I intend to use it as a display for an RGB-output for a VBXE board in an Atari 8-bit, not with an ST.  I don't have the VBXE in hand yet, let alone installed, so I obviously can't really test it yet.

 

But that said, I do seem to have an issue with the control knobs. The are all three frozen and unable to move. I sprayed Deoxit through the gaps behind the knobs in toward the shafts and allowed it to sit/penetrate for a bit, but still no movement. I also tried WD40 but again with no result. I expect that at some point I may have to take it apart to get at the controls more readily, and possibly even perform some kind of surgery there. 

 

I've scoured the 'net this afternoon for a service manual but I don't seem to find one. I see plenty of links and copies to the SC1224 version 1 (which is actually the model I had as a young adult with my 1040ST back then) but nothing for this one. I have never disassembled a CRT and I'm very leery to do so for the first time without a service manual of some kind. And yes, I'm very well aware of the inherent danger, the need to discharge the tube safely, etc. 

 

Of course I'd rather avoid that altogether if someone can provide some tips on freeing up these adjustment knobs. Barring that, if anyone has a service manual for this particular version of the monitor, it would be appreciated. 

Thanks.

 

[+DrVenkman]

After liberal spraying of Deoxit and WD40 through the vent slots and around the knob shafts, I've managed to get the Volume and Brightness knobs to move freely and easily again. I have gotten just the tiniest bit of movement from the Contrast knob but that's it. I'm spayed the knob and pot liberally with WD40 again today and will let it marinate all day to see if it loosens up like the others. 

 

Have I mentioned I *really* don't want to open up this CRT?

[+Mitch]

Just stay away from the section cup on the side of the tube and you will be fine. I used to be nervous about opening them up too but now that I've worked on them many times it is no big deal. You just need to be careful, even more so if you work on it when it is powered on.

 

Mitch

[tjlazer]

Yes I had the same issue, Deoxit Fader F5 got them loose but it took me a while as the knobs were seized up completely. (I didn't use WD-40)  They are buttery smooth now and still holding well after a few years.

 

I had to open mine up as it made it so much easier.  I didn't have to take the case off completely though.  Just enough to get access to the knobs.

Edited July 4, 2020 by tjlazer

[+DrVenkman]

9 minutes ago, tjlazer said:

Yes I had the same issue, Deoxit Fader F5 got them loose but it took me a while as the knobs were seized up completely. (I didn't use WD-40)  They are buttery smooth now and still holding well after a few years.

 

I had to open mine up as it made it so much easier.  I didn't have to take the case off completely though.  Just enough to get access to the knobs.

 Good to know!

 

I worked up enough nerve to remove the four screws that appeared to hold the top/back part of the case on (two on the bottom that join the font part of the base to the rear) and two on the sides. But all that did was allow the picture tube and front panel/bezel to move forward. There are two small black machine screws on the back that I didn't remove - you can see one above in the third picture. They look like they support the power and video cable panel where the cables pass through the case and do not appear structural. There are also two chrome machine screws on the bottom that look like they secure the front part of the main board to the RF cage that surrounds it, and again don't appear structure. The only other screws are four short screws that hold the rubber feet in place. That's it. 

 

So anyway, when I tried to see if I'd freed anything, it seemed that the front part of the case and CRT were pulling out of the back but not really easily. Without a service manual or good pics of the disassembly process for this particular version, I chickened out and put it back together. I don't want to pull anything loose. I also don't know if I should try separating parts with the screen horizontal (i.e., the monitor in the normal operating position), or if I should tilt it glass-down on a towel on my bench. 

 

Anyway, still no real loosening of that stubborn contrast knob. I've got some different penetrant/cleaner coming from Amazon tomorrow as well. 

[+DrVenkman]

Okay, in the interests of documenting this version of the SC1224 - which, again, seems to be far less well-known or documented - and since AtariAge has been around so long it's essentially the single best Google-searchable resource for all things Atari, I've figured how to get inside this case, though I have not fully disassembled the monitor. 

 

First, the bottom view. The monitor is here shown face-down, glass on the towel. So these four feet are attached with four very small screws. These are not, in fact, structural and serve only to hold the feet. Similarly, those two chrome screws there secure the board and RF shield to the bottom part of the case. To begin the disassembly, these screws also do not need to be removed.

 

 

However, there are two additional screws on the bottom - there are threaded transversely, back to front, and serve to hold the bottom of the back/top part of the case to the forward portion. There is one like this on either side of the bottom.

 

 

Next, there are also these two screws - on on each side of the case near the top/front of the case toward the screen. Removing these two screws will allow you to separate the case halves by a couple inches but not more than that.

 

 

Turns out these two black screws much also be removed if you want to fully remove the back/top portion of the case and expose the guts. That's because these screws secure the back feed-through panel where the power and video cables pass through the case and into the monitor. There is very little internal slack in these cords and if these screws are not removed, the case halves cannot be separated by more than a couple inches. Once these screws are removed, the feedthrough panel and cables will drop back into the back of the monitor and the case halves can be pulled apart as far as necessary.

 

 

All I wanted access to was the inboard-most potentiometer, that for the contrast control. As it happens, the controls for this version of the monitor are on the left as viewed from the front. Unfortunately, as I discovered when I separated the case halves, the CRT anode cap is *also* on the left. And given the relatively small size of the monitor (12" diagonally), I didn't feel comfortable pulling the back off completely. I was still able to get the flex-tube for my Deoxit far enough in to flood the exposed portion of the pot housing where the contacts exit the pot and the wires are soldered. So I did that and left it sit again for a few hours. I will check it again later tonight and repeat further if it's still necessary.

 

If worse comes to worse and I absolutely cannot get the pot to move, I'll break down and make a CRT discharge tool, remove the anode cap and get full access to the pot to either replace it or take it apart and try to clean it that way.

[tjlazer]

Yeah I only just cracked the case open enough to get access to the knobs and put some paper towels under or behind the knob in an effort to not get it everywhere inside when spraying.  I also had to spend a while working the knob and applying a lot of Deoxit to finally break them loose and get them smooth.

Edited July 4, 2020 by tjlazer

[+DrVenkman]

17 hours ago, tjlazer said:

Yeah I only just cracked the case open enough to get access to the knobs and put some paper towels under or behind the knob in an effort to not get it everywhere inside when spraying.  I also had to spend a while working the knob and applying a lot of Deoxit to finally break them loose and get them smooth.

Sadly, no luck getting the Contrast control knob free yet. I finally sacked up, made a CRT discharge tool and removed the anode cap - I didn't die.  (Also, no snap or spark - dunno if this model has bleeder resistors or it's just been turned off long enough and the air here humid enough that no additional charge had built up). 

 

Anyway, with the case halves much further apart, I can now access the potentiometers more easily and remove them if necessary. 

[+DrVenkman]

Victory. I freed up that f@#$!@!! Contrast control knob finally, though it took removing the little potentiometer panel off the front panel to do it. I just didn't have enough moment arm to get generate enough torque on the shaft to start it moving. Since the only part of each knob normally exposed by case is just a short arc (chord) on the very bottom, if there's any serious resistance to movement inside the pot it's just not gonna want to turn. But once you have the panel out, you can use the full diameter of the knob to get it started turning. And once I got it started, it began spreading the lubricant and solvents I've been trying to get into the pot across all the sliding surfaces. I rotated the knob across the full range 2 or 3 times and it became nice and smooth again. 

 

So then I took the opportunity to spray all three with Deoxit again and worked them all across their ranges of motion again. When I was done, I left it all open to dry. I'll clean up any excess spray inside the case from my earlier efforts tonight or tomorrow after work and then I'll put it back together. I still can't test the image quality but it was sold to me by a friend as tested and working so I expect it's basically fine. It is very clean inside as well - very little if any dust, the caps all look good, and the cables all look clean. So I'm optimistic.