Wavy corners - blast city 2931

[mRCaESaR]

Just wonder if anybody has seen this behaviour before?

Backstory:

The blast city had some "buzzing" that got louder as time went on. After reading a thread on AP, it pointed to some stuff inside the yoke and would need "cleaning" but to do so would mean removing the yoke - something I was absolutely petrified of doing due to the risk of damaging the neck.

Fast forward to today:

I received convergence strips and finally worked up the courage do the maintenance.

Upon removal of the yoke, a few crusty bits came off and some permalloy strips also came off the tube



I gave the yoke a good dust with a dry brush and got it to a reasonable state



After putting back everything, the buzz was mostly gone - still a little buzz, but nowhere near as loud.

I started mucking around with the convergence strips and you can see the difference.

Before convergence strips



After



Only problem I have now is I seem to have introduced "wavy" corners and I have no idea how or why they've been introduced.

I don't believe it can be "caps" as I don't recall this previously and this chassis has been serviced back in October with very minimal use. They seem more prominent on the right side versus the left side, but it's definitely there.

Would loose windings cause this?

If you look at the top there's probably a couple of loose copper.



Any suggestions would be great as I really want to stop that "wavy" part and it only appears to be on the corners

[grantspain]

looks like some kind of interference, possibly earth related or signal related or a regulation issue on the chassis

[mRCaESaR]

Thanks for the reply. If there was someone I was hoping for that would reply, it was you

Definitely looks like some sort of interference.

I'll take out the yoke again on the weekend and see if I can see something.

I'll also take out the ground pin on the neck board and re install.

[grantspain]

i would try an external 640 x 480 signal source from a laptop or pc using a different vga cable as well- to rule out anything related to power supply or cab wiring

[mRCaESaR]

Yeah good idea, I'll whack my DC in there

[grantspain]

do not use cab power or cables, try to eliminate all possible points of interference

[mRCaESaR]

How will I power the monitor if I don't use the cab? I might have to create a cable for the monitor to go into my step down tranny

[grantspain]

i meant don't use cab power for the pc or laptop

[mRCaESaR]

A lot of trial and error this weekend but still haven't gotten to the bottom of it unfortunately

I tried plugging in the vga (31khz) to my naomi universal and I didn't get any wavy corners. Monitor is powered via the blast city, everything else is on the naomi



So I thought, I'd try it on my Blast in 31khz - same result, no wavy corners.

Tried it on my Astro City in 15khz with a new 15 te amp up cable and totally separate from the blast city (didn't use the blast city at all) and unfortunately the wavy corners are still there even when using the astro city



Confirmed that the wavy corners aren't there when using the MS8 on the astro city, so it's definitely related to the monitor and the gut feeling is something in the yoke.

I took out the yoke again for further inspection and couldn't really see anything outside of some residue from the tape





Upon putting the yoke back, I introduced MORE buzz



I also reached out to Jomac who stated this:

That appears to be caused by some sort of coil vibration, probably not something you hear though. It would be causes by loose coils windings or convergence strips vibrating against the coils, I would find something plastic you can get between the yoke and tube and see if putting pressure on different spots stops it happening, when you find it try putting some silicon on that part to absorb vibration.

After taking out the yoke again, inspecting it some more, this fell out and I thought bingo! This vibrating is what's causing the buzz and interference on the corners.



Unfortunately, upon installing back it got rid of the buzz, but wavy corners are still there.

Going back to what Joey said, I thought those couple of windings that appear to be loose could be the cause, so I tried securing it with electrical tape to see if it had any effect



Unfortunately no effect

So right now, there's still a slight buzz and the wavy corners still exist.

I'm really out of ideas exactly trying to "secure/seal" the yoke as best as I can with silicone as outlined here - http://www.albyhus2.se/_eget/monitors/MS-2930-S/

One side of the yoke has "movement" when you press down on it unlike the outer side that has no movement

[nem]

I don't think the tape will be enough to secure the windings to rule that option out. I would try the silicone thing.

[mRCaESaR]

Well this one will be the final update for a while

Purchased a can of PCB Lacquer to tighten the windings up and used up almost 1/2 the can - she was pretty secured!



After the initial test, there was no change to the wobble, so the last ditch effort was to impregnate the yoke with silicone.



There was no way this the windings were vibrating!

Still no difference. I decided to live with it as it wasn't present on 31khz and in 15khz it wasn't all that bad once playing a game. I was fixing the corners and then for whatever reason, I decided to do one more removal of the yoke and when I installed it back, I forgot to plug the yoke connectors to the chassis. I turned it on, heard some buzzing and no pictured. Quickly turned it off and then I realised the yoke wasn't connected. After connecting the yoke back, turned it on, I got this



BOOOO!!!!

What do you do, it is what it is unfortunately. Hopefully I can get this fixed.