CRT TV / Monitor repair

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CRT TV / Monitor repair

Postby FuzzyLogic » 2019-6-23 @ 14:17

I finally got around to fixing my teen years 1991 vintage 19" Magnetbox set. This was my main TV until 2009 when I finally got an HD set. And it worked fine until I moved it from one spot on basement's concrete basement floor to another. From then on the screen had a red cast to it.

1-red.jpg
Red with retrace lines

2-red-c64.jpg
Sad C64 screen.


After watching many shango066 videos on youtube, an learning nothing about how to fix black plastic crap sets, I decided to go for it a few weeks ago. I hoped it was just a broken solder joint. And it was, sort of.

BTW, this TV set was assembled in the U.S. (Tennessee) has all Nichicon caps. Even the tube was made in the USA. The yoke was made in Mexico. Maybe it's a decent black plastic crap set. It does have simulated wood grain.

The solder joint on the collector on the C2482 for the red gun had broken. I reflowed it and it worked for a bit, but it turned red again after a few minutes when the set warmed up.

I ordered a few 2N6517s on digikey, got them, and proceded to desolder. And the damn pads came loose when I did. The area was a bit brown from the transistor heat. Ugh.. I ordered tiny rivets from China to do a "proper" repair. Another week and a half goes by and they arrive in time for the weekend.

3-pads.jpg
Son of a!


The rivets were a bit smaller than I expected and flanging them out took a while. But it'll do as I'm not waiting another two weeks to get the next size up.

4-rivets.jpg
Fix

5-tran.jpg
Fix


Five attachment limit. Continued on next post.
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Re: CRT TV / Monitor repair

Postby FuzzyLogic » 2019-6-23 @ 14:22

Continued...

The solder mask crumbled off in that spot and it looks like a mess, but it works! Commodore 64 looks good through composite. I'll worry about the geometry later when I figure out what pots to adjust. It had shifted up gradually over the years.

6-c64.jpg
Good colors


TD;DR: TV fixed. Purdy Skeletor on a C64 for Skeletor lovers.

7-skelly.jpg
Skeletor



Next up: my 1994 15" VGA monitor that is super dim.
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Re: CRT TV / Monitor repair

Postby keropi » 2019-6-23 @ 14:32

great repair!
I would not bother with geometry much - it looks as good as these sets can do
maybe mess with V.PHASE to center the image better
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Re: CRT TV / Monitor repair

Postby FuzzyLogic » 2019-6-23 @ 19:12

keropi wrote:great repair!
I would not bother with geometry much - it looks as good as these sets can do
maybe mess with V.PHASE to center the image better


Thanks! I'm glad to have it working and I'll take your advice on the geometry.

I hope others with successful CRT repairs will tack on to this thread and share their successes. There isn't too much out there for modernish CRT TV and CRT monitor repairs.
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Re: CRT TV / Monitor repair

Postby SirNickity » 2019-6-24 @ 18:34

So true. It's amazing how quickly obsolete technology just vanishes from the greater economy. It's like the Planet X3 video where David talks about having difficulty finding a place with 3.5" floppy label templates. How does ANY print shop not have a template for labels that were in massive demand only like five.. six.. geez.. 20-something years ago. Ugh. I'm getting old.
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Re: CRT TV / Monitor repair

Postby FuzzyLogic » 2019-6-25 @ 13:52

SirNickity wrote:So true. It's amazing how quickly obsolete technology just vanishes from the greater economy. It's like the Planet X3 video where David talks about having difficulty finding a place with 3.5" floppy label templates. How does ANY print shop not have a template for labels that were in massive demand only like five.. six.. geez.. 20-something years ago. Ugh. I'm getting old.


I haven't seen any of 8-Bit Guy's videos in a while, but took the time to watch his latest on Planet X3. A while back he made a video on adding RGB to his childhood TV. I'm not sure I want to do that with my TV. I'm in my 40s and yes I feel old. Especially so when kid call me "sir."

For me, CRT's are a must for retro computing. LCDs have lag, the colors are off, aspect ratios are different, and the scalers blur the image badly. CRT's will get more expensive once more go to the landfills.

I'm going to start working on my teen years 15" monitor this weekend. Last time I turned it on it was very dim. Now I'm thinking that it's not generating high voltage. I don't think the tube when bad. I hope it's just some capacitors in the SMPS that need replacing. The VGA cable also needs replacing. But the connector is glued to the neckboard with some green high strength adhesive. This one might end in failure.
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Re: CRT TV / Monitor repair

Postby SirNickity » 2019-6-25 @ 18:10

Meh, it may not look as pretty when you're done, but hey.. the PCB goes inside the case, so if it works then it's good enough.

I was doing some preventative maintenance on a 386 motherboard this last weekend. Battery leakage, of course.... I removed the AT connector, some diode-shaped inductors around it, and a couple of SMD caps and resistors that had all corroded a bit. I cleaned it all, replaced some of the worst, and put it back together. And that broke the keyboard. Turns out, the +5V trace was JUST hanging on through all the damage, and didn't survive the rework. You couldn't see it, but it had cracked right at the pads in two places. Ended up having to put in some new jumper wires. It doesn't look as nice, but it's a heck of a lot more reliable at this point. Sometimes that's gotta be enough. Get in there. :-)
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Re: CRT TV / Monitor repair

Postby oeuvre » 2019-6-26 @ 15:40

FuzzyLogic wrote:Continued...

The solder mask crumbled off in that spot and it looks like a mess, but it works! Commodore 64 looks good through composite. I'll worry about the geometry later when I figure out what pots to adjust. It had shifted up gradually over the years.

6-c64.jpg


TD;DR: TV fixed. Purdy Skeletor on a C64 for Skeletor lovers.

7-skelly.jpg



Next up: my 1994 15" VGA monitor that is super dim.


excellent! MYAAH!
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Re: CRT TV / Monitor repair

Postby FuzzyLogic » 2019-7-01 @ 01:09

Here's the next victim, My Mag Innovision 15" CRT.

mag-01.jpg
Mag


I haven't turned it on in years, and took it apart for the first time only a week ago. Of course I grounded the anode to make sure I live and started poking around today. Everything looked alright. The diodes for the rectifier were fine. No bulging caps in plain view. No cracked solder joints.

mag-02.jpg
Innards


Anyway, I plugged it in and hooked it up and turn it on. Only the blue shows up. I kink the cable some and now only the red shows. Twist it just right and I get the R, G, and B working. Now I crank up the brightness. It's works! Although a bit dim, a bit blurry, too much contrast, but it works.

mag-03.jpg
Working


Last time I used this monitor it progressively got dimmer the longer it stayed on. Today it stayed as bright as when I turned it on. Maybe because I had the cover off and it wasn't heating up.

I'll have to find a way to soften the glue on the neck board connector and swap out the bad VGA cable. Maybe play around with the focus an screen controls. And possibly test and swap out some of these CapXon capacitors.

This might be doable. More to come.
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Re: CRT TV / Monitor repair

Postby SirNickity » 2019-7-01 @ 17:10

Good start. :-) I used to swoon over the Mag ads in the computer magazines of the 90s. I was always torn between them and Viewsonic. I didn't really know at the time that Sony pretty much had a lock on the tube market with Trinitron, nor that many other vendors used them in their better models.
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Re: CRT TV / Monitor repair

Postby oeuvre » 2019-7-01 @ 18:56

skeletor approves!
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Re: CRT TV / Monitor repair

Postby FuzzyLogic » 2019-9-14 @ 23:52

Update:

Last week I took apart the Mag 15" to see what caps I need to buy. And last night and today I recapped the PSU board and the neckboard. The high voltage caps on the neckboard were shot because they were sandwiched between transistors and hot resistors. One had 1400ohms ESR another had 350ohms ESR. I plan on recapping the whole neckboard later, that's not too important at the moment.

Can we put Humpty Dumpty back together again?

mag-set2-2.jpg


mag-set2-3.jpg


We we can!

mag-set2-4.jpg


Not exactly poka yoke. Some plugs fit in multiple places. I'm glad I took a lot of pictures and labeled them.



mag-set2-5.jpg


Holy crap. It didn't blow up, and you probably can't tell by this picture, but there is a massive improvement in focus. But it is still a bit dim and the cable is shot. I had to fiddle with the cable for five minutes to get all three colors working at one time.

mag-set2-6.jpg


I got a new VGA cable (couldn't find a white one) and a few connectors for the end that attaches to the neckboard. As soon as I figure out how to remove that damn strain relief I'll get the old cable out and figure out the pin out.

Anyone got any tips to get strain relief grommets out? Is there a special tool for that?
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Re: CRT TV / Monitor repair

Postby Vynix » 2019-9-15 @ 11:16

You could try adjusting the G2 voltage to increase the brightness, but keep in mind that it is a last ditch effort, the tube might be already on its last legs :dead:
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Re: CRT TV / Monitor repair

Postby oeuvre » 2019-9-15 @ 12:43

Hmm one of my IRC friends did a CRT TV repair recently. I can connect you two if you wish.
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Re: CRT TV / Monitor repair

Postby FuzzyLogic » 2019-9-15 @ 16:40

Vynix wrote:You could try adjusting the G2 voltage to increase the brightness, but keep in mind that it is a last ditch effort, the tube might be already on its last legs :dead:


I was planning on increasing the screen voltage after I sorted out the cable. The odd thing is that the monitor started getting dim very quickly until it was almost completely dark. I'm not sure why it has brightened up, but I hope that means the tube is okay. The tube also doesn't have a lot of hours on it.

It could be that I'm not remembering that this monitor was never that bright to begin with, eve when the brightness knobs was turned up. And I am comparing it to the blindingly bright monitors of today.


oeuvre wrote:Hmm one of my IRC friends did a CRT TV repair recently. I can connect you two if you wish.


He's welcome to chime in here on Vogons if he feels like it. We definitely need more CRT knowledgeable people here.
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Re: CRT TV / Monitor repair

Postby duga3 » 2019-9-15 @ 17:22

Yeah, most people forgot how dim CRT monitors were. The spec for them is around 90-110cd/m2 on full-white signal which you can measure with a colorimeter (DTP-94 is cheap and good enough). You can overdrive it to around 150cd/m2 on some monitors but it will be a bit blurry with less accurate colors. If I can I like to go for 100-120cd/m2 as a happy medium. New LCD monitors are usually around 200-400cd/m2 for comparison.

You should adjust G2 so that full-black signal is pretty much black in a dark room and full-white signal produces around 100cd/m2. That is basically where you want to be for best overall results. If you go over 100cd/m2 you will have grey black level, if you have black level too dark you will not get the 100cd/m2 on white, etc. The exact number (100) will vary so adjust black level, then measure white level and repeat this procedure a few times until you know the best range. You can then fine tune this with OSD brightness option if needed. You should also reset all OSD settings before doing this. After that you will want to mess with color settings in OSD, full-green should be around 75cd/m2, and all grey scale should track your desired white-point coordinates such as 6500K or 9300K (you will really need a colorimeter for this). And if your CRT happen to have those, BIAS settings control color mixing in dark areas and GAIN control the lights.
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Re: CRT TV / Monitor repair

Postby FuzzyLogic » 2019-9-16 @ 02:51

Duga3, thanks for the tips. I'll pick up a calibration tool to see what the brightness is on this monitor. Oh and this monitor is so old it doesn't have an OSD. Only a brightness and contrast knobs and a few buttons for height/width/position.

I had a little more spare time today and got the old VGA cable out,got the pinouts, and measured the resistance on the RGB lines. The red was 1.5ohms, blue was around 2, and the best I could get green was 4ohms. I don't know how much that attenuation would affect the brightness, but I have a feeling that it might just be the cable is all that's wrong.

new-vga-cable-1.jpg


Here's the new cable. I need to get a decent wire cutter and shrink wrap tubing.. I also have to decide how I'm going to wire the ground lines. On the old cable/plug, all of the grounds were tied together somehow.
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Re: CRT TV / Monitor repair

Postby SirNickity » 2019-9-16 @ 18:49

Just a thought: Why not put a female VGA port on your monitor? I never liked that CRTs had a tail you couldn't detach anyway.
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Re: CRT TV / Monitor repair

Postby duga3 » 2019-9-18 @ 17:06

The new cable looks similar to what I have and it is just fine, never felt the need to buy one of those overly expensive "pro" VGA cables (or BNC if applicable). Adding your own female VGA port would be a very good idea, making it more future-proof, even if it would just dangle instead of being screwed tight to the chassis somehow.

Lack of a better OSD is a bummer, you will need to figure out how to adjust colors directly on the hardware - I have no experience there so I cannot help you with that. See if you can find a service manual for it though, perhaps you will find some pointers there.
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Re: CRT TV / Monitor repair

Postby FuzzyLogic » 2019-9-22 @ 02:50

SirNickity wrote:Just a thought: Why not put a female VGA port on your monitor? I never liked that CRTs had a tail you couldn't detach anyway.


I thought about doing this, but decided against it because I don't want to mod this monitor. I would have to hack some steal, and I would probably do it sloppily. Also, it would probably degrade the signal a tad; I can't have that :)

Anyway, I finished it the cable and it looks great.

mag-fixed-1.jpg


mag-fixed-2.jpg


And here it is working.
mag-fixed-3.jpg


It's definitely brighter then with the bad cable, but not much. I jacked up the screen a tad and it will do! I messed with the focus some, but that is the best it could ever do. Turning off cleartype in Windows helped a lot with text. I do remember this monitor was disappointingly unsharp. And I used to marvel at my friend's near pixel perfect Gateway 2000 Diamondtron (Mitsubishi's Trinitron clone.) But I couldn't keep my eyes off the damper wire.

This puppy is about to have its 25th birthday and it's fixed. Really happy about that. I'll pair it up with the P90 soon.
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