[SOLVED] ms9 loud ringing after recap

[wabbylegs]

Hey everyone I recently got a NAC with a ms9-29a that I had to send the chassis off for repairs since it wouldn't turn on when it arrived. Once I got it back in, despite some burn in on the tube, the display looks amazing. The problem is it has a really loud ringing, not like the 15khz whine, it's definitely lower frequency. I've been doing research for a couple weeks and I can't figure out where it's coming from. For the record, I don't think it's from the PSU since I've had this cab on when the monitor was dead and there was no ringing.

Things I've tried based off my research:
1. Tightened the screw that holds the flyback to the chassis. It was already super tight.
2. Took a wooden plunger handle and pushed down on every component I could see, including the flyback, neckboard and the safe parts of the yoke. Didn't hear any difference.
3. Checked B+ voltage which is at 75v, that's normal for 15khz mode right?
4. Adjusted the knobs for focus/screen on the flyback as well as the ones for horizontal/vertical but the noise was happening even before I calibrated the display.
5. Used one of those spectrum analyzer apps on my phone which seems to point to the flyback as the origin, or at least where it's loudest.

What else can I do? I saw there's some trick with sticking wooden toothpicks into the flyback but I didn't see anyone attempt this on the ms9's flyback. I must be missing some other component that could be the cause right? I'm really new to all of this so I don't know what else to do but make a thread.

 

[wabbylegs]

Tonight I raised B+ voltage and it now sits at about 76.5, didn't hear any difference but figured I should have it higher than lower. Lowered the screen knob on the flyback all the way to see if it would affect anything, nothing. Using a paper towel tube and my spectrum app again, it's hard to tell but I think the sound is definitely loudest around the flyback/HOT area. This week I'll try reflowing the flyback, HOT, and the little transformer thing next to the HOT as well as anything else that might look suspicious, I'll be careful. Was hoping I could find the culprit by bopping it on its head while the cab was running.

Is there anything I can do to fully rule out the yoke copper windings? It's like exposed copper so I don't think it's safe to prod it with anything. Maybe unplug the yoke connectors to the chassis one at time then power it up, see if the whine goes away?

 

[trashedcabs]

The yoke windings are not exposed copper, it's enameled magnet wire, same as used inside transformers. Beware of the exposed terminals on the top, otherwise it's fine to touch. I am not a lawyer and this is not professional advice so don't sue me.

I have had a yoke in my blast city whine loudly in a similar way and I used insulating varnish (MG 4226A) to quiet it down.

 

[wabbylegs]

Just wanted to give an update. I did some reflowing in the area the sound seemed to be coming from as well as any other joints that looked suspicious. It was recently reflowed but I saw a few that could use a bit more love.

The yoke windings are not exposed copper, it's enameled magnet wire, same as used inside transformers. Beware of the exposed terminals on the top, otherwise it's fine to touch. I am not a lawyer and this is not professional advice so don't sue me.

I have had a yoke in my blast city whine loudly in a similar way and I used insulating varnish (MG 4226A) to quiet it down.

Hey thanks for the tip. I ended up prodding the wires and even disconnected the yoke connectors one at a time to see if the noise went away and unfortunately it didn't. I went ahead and applied the varnish just in case, might as well do some preventative care.

I got a link to a video recording of the sound. It's more prominent about halfway through. This isn't a normal sound right? I'll keep digging and see what else I can try.
https://streamable.com/y5zguv

 

[wabbylegs]

Alright I found the cause. For any other noobs out there in a similar situation I highly recommend a mechanic's stethoscope to better investigate this kind of stuff.

 

[nem]

Alright I found the cause.

Which was?

 

[wabbylegs]

I wanted to make sure before i went too deep but it turned out to be a component on the power supply! Putting the stethoscope on the transformer (I believe that's what it is, looks like coil that's heat wrapped and filled with some kind of varnish) I get the ringing loud and clear. Putting considerable pressure on it would stop the noise so what I did was applied a bit of heat and then injected varnish into it. It seems to have quieted it down a bit but it's still pretty noticeable. I'll have to research other ways to quiet it down cause it's really annoying and from quick research it doesn't look easy to find replacement components/power supplies.

I'm curious why the PSU would make this kind of noise once the chassis was operational. When the chassis was dead the PSU was quiet, I thought the monitor wasn't powered by the PSU.

 

[wabbylegs]

Last week I ordered a cap kit for the 400-5198-01X PSU from arcadepartsandrepair.com and it arrived today. After replacing the caps the coil whine was gone! I'm guessing a few were knocking on death's door and giving the transformer a harder time. With peace and quiet at last I can finally enjoy this cab. It's been a three month journey getting this thing to a comfortable state to finally enjoy some gaming. After a break I'll get a kick harness wired up, maybe some painting done if I'm feeling brave.

Oh yeah, there's a giant plastic covered 200v cap that wasn't included in the kit, should this have been replaced too?

Here's the cab in all its glory: https://imgur.com/cmCEoI9