Problems with MS9

[IPD]

I have two Toshiba A68KJU96X tubes with MS9 chassis in storage so today I decided that it was time to test if they still work. Both were working when I last used them, around two years ago.

First one starts up fine, no problem. Using a Craftymech TPG to cycle through some RGB patterns, and it seems to be working like it should. Image is really good.

Second one however, appears to be dead. Nothing happens when I turn on the power. I see no neck glow. So I try on/off a few times, but no change. Interesting. Tried changing the remote board to another one, but still no change. I did notice however that once I turn power off, after a minute or so I hear a "chirp".

Google found https://gamerepair.info/hardware/35_nanao_ms9_29 which suggests replacing a MOSFET at Q901? Also, the chassis is very dirty so I'm contemplating giving it a good ISO cleaning. Not sure if that's a good thing to start with however.

What should I do next? I have never attempted to repair any monitors before (except for recapping a chassis once) so I need some advice.

 

[nem]

You could swap the mosfet from the working chassis.

I don't expect it to be the problem, but worth a try in any case.

 

[IPD]

That doesn't sound too promising. Is there anything else I can do if replacing the mosfet has no effect?

 

[nem]

Of course there is. It just depends on how much effort you want to put in to it.

Start with the mosfet, then if still not working, check the horizontal output transistor.

 

[IPD]

Not much real progress yet, but I do have a few questions for the CRT wizards here.

Had some free time yesterday, so begun removing the chassis. After discharging and disconnecting the anode cap, a small metal clip fell out. Can't remember this happening the last time (and only time) I've done this before. What is it and is it required when reassembling everything? Looks like this:

Also, the tube neck and neckboard is protected by a metal cover. I guess it's just there for preventing someone to accidentally necking the tube or touching the neck. Or does it serve some other purpose?:

Anyway, removing the chassis only took a couple of minutes. But it was filthy, almost entirely black in some parts. Decided to clean it with ISO and used some SafeWash and De-Ionised water. Much better. Now it's at least clean enough for me to actually see what I'm working on:

And that's it for today.

 

[nem]

Can't remember this happening the last time (and only time) I've done this before. What is it and is it required when reassembling everything?

It's just a small washer that the end clip for the anode wire goes through. Not an important part, but since you have, might as well include it when you put the anode cap back on.

Also, the tube neck and neckboard is protected by a metal cover. I guess it's just there for preventing someone to accidentally necking the tube or touching the neck. Or does it serve some other purpose?

No other purpose. I threw mine out.

 

[IPD]

Thanks @nem

Maybe some progress today, but not much. I noticed that the capacitor on the neck board looked a bit suspicious. I removed it and yes, it was leaking. Checking the main PCB and I find more caps with similar problems. Looks like I'll have to recap the entire thing. Probably doesn't fix the original problem(?), but might as well do it anyway.

Also, I see a lot of dry solder joints. I'll reflow them when I replace all the caps.

One more thing. Removing the black plastic frame from the PCB wasn't as easy as I thought. I removed the 6 screws, but the PCB is still stuck. Tried pressing on the black "buttons" in the image below but they won't move. I guess I have to press all of them and slide it out somehow. Frustrating.

 

[kikaso]

Removing the black plastic frame from the PCB wasn't as easy as I thought. I removed the 6 screws, but the PCB is still stuck. Tried pressing on the black "buttons" in the image below but they won't move.

As the plastic ages it gets brittle and less flexible. Might be a two-person job lest you break the tabs.

 

[nem]

You have to slide it first, and afterwards press the two tabs. Then it will come out.

 

[IPD]

Came back to this today and maybe made some progress. I started with changing out all the capacitors, it was about time anyway. Took me a couple of hours. Double and triple checked everything, and compared it to a known working chassis. After that I took a look at some dry solder joints, especially around the power area. Reflowed about 10 of them.

Put the chassis back, connected everything and made sure everything was exactly as before.

Connected my TPG, and turned the power on. And I have neck glow again! And the monitor shows the standard TPG grid. That's interesting, looks like it works again.

For about 8-10 seconds, and then it just turned itself off. NO!

Tried to power it on one more time, but now it's just dead again. No neck glow. Not really sure if this was progress or if I messed it up. It appears I'm back at square one with the original problem.

Not sure if the next step really is to swap the mosfet and/or HOT from a working chassis, but right now I'm not all that excited about touching stuff that works.

 

[Mukuro_W]

Start with the PSU section but first recheck all caps again, theyr values, theyr position , just check every cap you have installed for right direction, check for cold solder joints on v. Ic and expecially near the HOT under the little grey driver trasformer, then check the B+ at tp2 point.