TV monitor assistance needed urgently.

[Walkinshaw]

Hey guys,

Just looking for some advise on a problem I have encountered with a friends machine.

We are making a mame system with a TV using S-Video out.

When the cabinet was given to me to put the controls in and wire everything up, my friend had already installed a brand new 51cm TV into the unit, decasing and mounting the chassis inside the cabinet. The chassis is on a plastic base and only wood underneath. The problem comes when any cable from the PC is connected to the TV.  When this happens the safety switch to the house is tripped.

I have gone through a lot of the trial and error procedures and have found the following:

1. The TV works fine plugged into the mains power by itself
2. The computer works fine plugged into the mains power by itself
3. The computer works fine using S-video out and running into another TV (which is cased and all original)
4. I have changed the power supply in the computer as a precaution.
5. The safety switch is only tripped when either the S-video lead or the PC Audio lead is connected into the ports on the chassis of the decassed TV. Both will run off the same powerboard and work fine until they are joined together.

From this I understand there is a short somewhere. The TV is double insultated but I am not sure where the problem is.

One thing my friend did say to me was when he put the TV into the cabinet the earthing strap that runs around the monitor(not the degauss wire) would not reach to where he mounted the chassis so he spliced into this and made it longer (the one that plugs onto the chassis not the neck). I am not sure if that is a problem but thought I need to mention it.

Does anyone have any suggestions? He is at the point of buying another TV now.

Thanks

[Ken Layton]

Sounds like your tv is of a "hot chassis" design. You probably must run it from an isolation transformer.

[Walkinshaw]

Thanks Ken.

Why would it work just as a normal TV de-cased or even if I was to put it back in the case? only when a computer is connected to it does it fail. Is there something I can measure here if there is a earth leakage or something.

I am just curious to know that. In the past I have build atleast 10 of these using different types of TV's but the one my friend purchased is the first time I have used that particular brand.

[Dennis]

It's more than likely what Ken Layton said.  Connecting the PC to the unit is causing a "hot ground" to "cold ground" conflict.

[Rickn]

Ok- not sure, but I think your friends comment is a clue, along with the comments of a hot chassis.

There was an a bit of a Hy-brid that had some parts of the set hot and others "Cold".

This required the CRT Earth wire/ground - not to be connected to the metal frame or actual AC power ground.

It must be make contact to the Aquadag ground of the picture tube- this means that the braided ground wire must make contact to the "Grayish part" of the back of the tube- this is conductive and is internaly connected to the picture tubes ground.

In most cases this ground wire would connect directly to the ears of the picture tube- in the case of the television cabinet- there was likeliy an additional component that was between the connection to the ears- tjis looks like a ceramic capacitor- but it is what is called a "capisitor" your friend may have inadvertently left it out.

Take some pics of the original connectionsto the CRT ears...

or try me at the office during eastern standard time and I will try to help - if this is the case.

Meanwhile good Luck

Rick Nieman
Nieman Video Dipslays - NVD
Niemandisplays.com
Rick@niemandisplays.com
519-621-1722