M1438 Pictures

[jbenam]

Here we are, I have finally cracked it open.

C3 220n 250V
C4 220n 250V
C23 100uF 400V
C215 47uF 250V
C17 47uF 250V
C20 470uF 35V
C214 470uF 35V
C7 100uF 25V
C404 100uF 25V
C405 100uF 25V
C8 100uF 25v
C301 470uF 35V
C317 100uF 63v
C601 10uF 50v
C311 2.2uF 63v
C307 10uF 50v
C501 3u3 160V
C216 4n7 2000V
C217 1u 250V
C500 15n 160V
C313 1000uF (I think?) 25v
C306 1000uF (this is for sure) 25V

I have missed some, as they were difficult to reach. I hope these will be enough.

I have also got some pictures, which I have attached to this post.

Please let me know if you need anything else

BTW, I have attached the other M1348's tube on the other M1348s, no purple issue after a few hours... It looks like it's the tube I wonder if I can get a replacement or if there are any places which can refurbished them?

[Retrorepair]

That's the third version I've seen of this board! It looks quite different to mine in a lot of places but it would seem the circuit is actually very similar, just a different layout.

The cap values are invaluable, thank you for that! I'll update if I can get this thing doing what I want it to

Regarding your tube that's bad luck, I would usually suspect the tube last. Sounds like one of the guns has had it.

You can get (quite expensive now) a tube rejuvenator but you may be better off sourcing an Acorn AFK-50 monitor as the tube should match. Actually they are good for spares as they are almost the same monitor.

[jbenam]

Originally Posted by Retrorepair

That's the third version I've seen of this board! It looks quite different to mine in a lot of places but it would seem the circuit is actually very similar, just a different layout.

The cap values are invaluable, thank you for that! I'll update if I can get this thing doing what I want it to

Regarding your tube that's bad luck, I would usually suspect the tube last. Sounds like one of the guns has had it.

You can get (quite expensive now) a tube rejuvenator but you may be better off sourcing an Acorn AFK-50 monitor as the tube should match. Actually they are good for spares as they are almost the same monitor.

Luck had it that the same day I did this at my friend's house I had also brought another CRT I had bought (which I decided not to keep) for 10€. It was an offbrand CRT (Yang / Colorsonic) and while leaving my friend suggested to crack it open and... Voilà, it was the same exact tube as the Microvitec!

I did a tube swap and it has now been working for a few days with no issue. Fingers crossed that it will stay like that

If I knew about this before I might have avoided purchasing another 1438s

I hope those infos will be useful to you

[Retrorepair]

Well I think I've changed all I need to and yet I still don't seem to have auto switching. In fact, I don't have 640x480 anymore either, I'm now stuck in 800x600.

If anyone else has a M1438s and fancies opening it up for some pictures it would be appreciated.

[jbenam]

Originally Posted by Retrorepair

Well I think I've changed all I need to and yet I still don't seem to have auto switching. In fact, I don't have 640x480 anymore either, I'm now stuck in 800x600.

If anyone else has a M1438s and fancies opening it up for some pictures it would be appreciated.

If you need any more pictures I might open the M1438 again soon, it went purple after a month or so I am gonna to recap it this time.

Any idea on what might be going wrong with it? It's definitely not the tube, because the symptoms are the same as last time.

[Retrorepair]

It could be a bad connection on the neck board, sounds like green is missing. I actually didn't have a picture when putting it back together this evening, wiggling the neck board connector brought the picture back so it could be worth a look.

But yes, if you could I think I'm out of ideas as to what's happening now (or not happening).

The area where the neck board ribbon meets the main board would be good to see. Every picture I've seen has this area covered up by the ribbon so I might have missed something there.

I've discovered 800x600 will display fine, if a little narrow. All other resolutions seem to be doubled or trippled on the horizontal though. I assume the relay should click when is switches resolutions?

[Retrorepair]

You know, I could repair it for you and in the process document all the differences. Help us both out

[jbenam]

Originally Posted by Retrorepair

It could be a bad connection on the neck board, sounds like green is missing. I actually didn't have a picture when putting it back together this evening, wiggling the neck board connector brought the picture back so it could be worth a look.

But yes, if you could I think I'm out of ideas as to what's happening now (or not happening).

The area where the neck board ribbon meets the main board would be good to see. Every picture I've seen has this area covered up by the ribbon so I might have missed something there.

I've discovered 800x600 will display fine, if a little narrow. All other resolutions seem to be doubled or trippled on the horizontal though. I assume the relay should click when is switches resolutions?

I thought the same, that's why I have resoldered the entire neck board, didn't help I have also resoldered the ribbon, still nothing.

It's an extremely temperamental issue and it almost always only happens if the unit is hot.

Could it be caps?

Yep, the relay clicks when it switches resolutions.

Originally Posted by Retrorepair

You know, I could repair it for you and in the process document all the differences. Help us both out

Sure, I will send you a PM and see if we can arrange something Thanks!

[Retrorepair]

It could still be a cold joint somewhere, if it heats up and the problem presents itself. Doubtful it's caps but anythings possible.

Yeah shoot me a PM and we will sort it out. I'll post my eventual findings for anyone else looking to fo the same too

[rjd324]

I also have one of these and it seems to work fine... except... when I turn the monitor on the screen is just black. I have to turn it off and then turn it on again and then I get the picture. This can happen from cold or from hot and it does not always happen. Probably >50% of the time it just turns on fine.

My only skill set is being able to solder/desolder, look for any "suspicious" component and replace them. I have good LSR meters and can check for ESR reading etc, but even those cannot be trusted from what I hear. Anyway, a capacitor right near the flyback, C702 (which for some reason I cannot find in the list of components in this thread), is a 35v 470uF (EUROCAP brand) and it looks fairly clean but it is bulging at the top. I have checked ESR in circuit and out of circuit and it is reading fine. What would you suggest? There is no harm in replacing it, but would you? And, would this possibly explain the reason why sometimes I get a black screen and have to turn off/on? I have also noticed -very occasionally - screen artifacts, but they just flash on and go away almost immediately.

I really like this monitor so I want to treat it right and try to keep it alive. As I say, it general it seems to be working okay. What would you advise? I can supply more pictures too.

For anyone on the internet at all who is wondering how to open their M1438 there are holes to press the latches at the top which is why it seems like it is stuck! I have read a few forum posts where people are stuck on this:

[jbenam]

I am not a big CRT expert, but recapping won't certainly harm If it fixes the issue you are seeing, good, otherwise you will have done something that will most certainly prolong the life of the entire monitor, even if it didn't fix the issue you are seeing.

Actually I should do the same on mine as well...

[rjd324]

Well, I did replace the capacitors and the issue with pressing the power switch and the monitor not showing anything on the screen requiring me to press the on power switch off and then back on again seems to have went in way. In other words, the monitor just comes on every time now.

I still see a slight glitch every few minutes. It is literally like a horizontal scan line glitch that lasts about 0.1 seconds. So it is just a flash.

I see this glitch on more than one machine in different screen modes.

Could it be the flyback ? If so I would look for a replacement.

Ty.

[kold666]

Resuming this topic to ask if anyone knows the part number of the flyback transformer (EHT).