Suddenly no video on a MS2930

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Ioncannon
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Suddenly no video on a MS2930

Post by Ioncannon »

Was testing out my new Blast City and just got an I/O Board for my Naomi when suddenly the monitor stopped working. One moment I was booting into Virtua NBA (Naomi) for the first time, turned the machine off and then back on.... black screen. Board works since I do hear audio.

- Given it's a Blast City Nanao with no autosync it looks like a MS2930.
- I don't see any arcing in the neck so tube looks fine.
- HV doesn't sound like it's turning on; no static on the screen and no whine.
- This chassis doesn't have any black goop.
- Orange heater is turning on.

There was a suspicious thing going on earlier where the screen was flashing randomly. I can't recall if it cause the FL to also flicker with it.

Here are videos of before and after:



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grantspain
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Re: Suddenly no video on a MS2930

Post by grantspain »

it might be as simple as bad solder joints,in particular on crt socket
it could be bad flyback or some bad caps, the fact its showing tube heaters is a good sign as it means its not kicking in the ocp
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

grantspain wrote: April 1st, 2021, 5:26 am it might be as simple as bad solder joints,in particular on crt socket
it could be bad flyback or some bad caps, the fact its showing tube heaters is a good sign as it means its not kicking in the ocp
Cool, thanks for the places to look! Will be pulling the monitor once I'm done recapping the PSU and can take a closer look. I assume OCP = Over Current Protection?

Any hypothesis on what the flickering could have been? It almost seemed like the monitor was shutting down momentarily. Might have been a component failing. Wish I captured a video of it.
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grantspain
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Re: Suddenly no video on a MS2930

Post by grantspain »

yes on the ocp

could be anything causing that flicker, all the things i mentioned will or could cause it
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

Grantspain, was going through the MS2931 manual for neck glow + no HV and was able to match most of the ref codes. Most things look good but checked the HOT and there is a 0 reading (diode test) on the base and emitter pins both ways. Shorted out?

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grantspain
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Re: Suddenly no video on a MS2930

Post by grantspain »

you will read short base-emitter in circuit, best to remove and read
i doubt the HOT is short as usually a short HOT will take out the FET in the power supply section as well
I would suggest replacing the vertical deflection ic and the caps on its immediate circuit
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

Replaced all the caps and resoldered the crt socket pins (nice and shiny now). Any other places I should resolder or check for damage before putting it back together?

HOT out of circuit looks good. Is there anyway to test the vertical deflection chip beside just putting in a new one in? If not I'll try turning the monitor on and see if it works. Will buy a new one if it still won't start.

I wasn't able to remove the daughter card to replace the two caps there, is there a trick to it?
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grantspain
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Re: Suddenly no video on a MS2930

Post by grantspain »

on the deflection ic you could check for short between ground and vcc
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

Ah, so pins 1/8 (+vcc1, +vcc8) with pin 11 (gnd)? I get around 560ohms on pin 1, and 1100ohms on pin8. Is this a short or is it fine? Similair tests on the diode reading (around 520 and 1000+).
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Re: Suddenly no video on a MS2930

Post by grantspain »

sounds ok but its not a dead cert, try the chassis and see how it goes
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

Awesome! Will report back when I have it reassembled.
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

Welp still no video or raster :cry: :cry: :cry: :cry:. Was really excited to play this machine.

I did notice that the HV squeal does return when setting the remote board to 15khz AMP. No video from my MVS board though. No static on the screen surface either so HV might be still missing?

In terms of other things: Heater still turns on, no arcs that I can see or hear in the neck, and the only other noise I hear is some static and noise in the yoke; probably from loose convergence strips inside.
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

Did another test; tried turning the monitor on in pitch black darkness.

Oh no don't tell me the tube ended up necked. The flash is happening on the anode cap and infront of the yoke. Hence why I didn't see any arcs.

Did I screw up installing the cap? Seemed hooked and sealed with grease.

https://youtube.com/shorts/ipbjPiLGbdM
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grantspain
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Re: Suddenly no video on a MS2930

Post by grantspain »

next step would be to test the eht with a hv probe, i have seen these flybacks fail where the eht goes very high and the chassis protection kicks in
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

So it isn't a necked tube? Phew. Googling around, seems EHT is the red cable (was wondering what the proper term is). Alright will probe to see what's going on.
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grantspain
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Re: Suddenly no video on a MS2930

Post by grantspain »

a proper hv probe connected to a multimeter and then set at the correct range, it will allow you to see if hv is present and what level it is- pretty sure more than 27kv will cause chassis to shutdown on this particular model

no idea about your video, i could not see anything
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

Yep, got a Fluke HV probe I have been using to discharge the anode; though from the lack of reading I don't think there has been HV unless the bleeder resistor is that fast.

Yeah it was the only way I could get the spark to appear on camera. You can see two quick blue flashes; the left one is the anode, the right one is from the yoke. At the end you can also see the orange glow of the heater tube (I guess the protection circuit does not shut off the heater?).

I'll also try cleaning out and reapplying the dielectric grease. One thing I forgot to mention was I finally see something on the screen; a small white spark at the edge of the screen for a quick second (like when a CRT shuts down). So the original problem might have been fixed causing this new issue.
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nem
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Re: Suddenly no video on a MS2930

Post by nem »

The grease won't make a lick of difference. As long as your cap is hooked inside the hole, that should be enough.

There's something wrong with your chassis.

Also, when I killed my Blast tube there was a similar spark outside, near the yoke. When I connected a working chassis to it I had sparking inside the neck.
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

Would the heater still glow if the tube was necked? Doesn't need a vacuum?

Well that just ruined my day =\. Will double check with my other chassis (that works) to make sure.
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Re: Suddenly no video on a MS2930

Post by Ioncannon »

Ok, update! Reinstalled the EHT/anode cap and the zapping disappeared. I must have somehow screwed up the installation the first time. I do still see a flash in the yoke but no "tsk tsk tsk" noise or anything like that.

Next, when I start the CRT; I see a white screen for a second before it fades away. Static is felt on the screen as well. This only appears when a video input is plugged in. Nem can a necked tube even produce an image? I'll post a video soon.

This is actually better than before where *nothing* happened.

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