MS9-29 chassis ground, and other problems with grounding.

[notsonic]

I have an OK Baby cabinet that I've been rewiring. It has an MS9 tube and chassis that are not original.

The CRT is mounted to a custom frame for the cabinet which is isolated from any of the other metal parts. The chassis sits separate on a wooden shelf. There's no single metal frame around it like in an Astro City.


The MS9 chassis has a little ground connection that's supposed to connect to the metal monitor frame.


If I tie the chassis's ground to FG and CRT frame to FG I get horizontal bands at the bottom of the screen and diagonal noise flowing across the screen. If I remove the two connections to FG, no problems.

1. Is it safe to float the monitor? I assume so since the frame in my Astro isn't grounded either. So far after disconnecting the connection to FG I just notice a little static buildup which seems normal.
2. Should I connect the chassis ground to the monitor frame? This seems like a good idea to replicate the connection that would be there if it was mounted on the normal metal frame. There's already continuity through the ground strap around the monitor though.
3. I have a Meanwell power supply. There is no continuity between FG and Com (logic ground). I've seen threads suggesting jumpering FG and logic ground. Thoughts?

 

[notsonic]

I did some poking around my Cyber Lead cabinet which also has an MS9 and found a few things. The monitor frame, chassis, all metal parts, etc. are tied to FG. There's an FG connection being made on the 3 pin connector with the degauss button wires. Also, logic ground has continuity with FG.

 

[dos]

I've never not had interference grounding a monitor frame. Leave it floating

 

[nem]

Agreed.

Also, you don't have the tray for the chassis? The board will warp over time if you don't have enough support underneath. MS9s have a crapload of SMD components on the solder side. It will be a PITA to diagnose if one of them loses contact.

Honestly, I suggest you just make a WTB for a tray.

 

[notsonic]

Yeah it was a bare chassis from eBay (China). I've got it on 6 pcb feet (the 4 corners, one near the flyback and one in the middle). I was hoping to print something for it but it probably would be easier to just see if anyone has one for sale.

I still seem to have one anomaly with this monitor. The lower 1/5th of the screen is ever so sightly darker or shadowed. It's similar to the interference from the ground connection but much taller.

 

[nem]

Have the caps been replaced?

 

[dos]

Have you tried degauss?

 

[notsonic]

I just wired up the degauss button and it wasn't that. If I knew any better I'd assume it's burn in. I don't know the history of this tube (I literally don't remember why I have it, I just found it in my basement years after I must've picked it up) and I used to use it rotated 180* which would put it at the top of the screen, further away, where you're not looking too much when playing shmups. Maybe it was always there with the previous chassis.

Considering the chassis has some repairs on it I can assume that some of the caps have been replaced but maybe not all. It's from a Chinese ebay seller so who knows.


Nothing makes you feel like more of a crazy person than trying to take a picture of CRT interference and explain it to someone.
Here's a pic. I circled the line.

 

[nem]

Some of the caps in the power section have definitely been replaced.

Easy to check for burn in. Power it off and point a flashlight at it. If you can't make out the line, then it's not burn in.