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The Monitor FAQ
AndyWarne:
--- Quote from: menace on June 09, 2004, 02:42:20 pm ---Question: What is the specific function of a 1:1 Isolation transformer? Isn't it supposed to keep the AC at a steady 60hz? Keep the spikes out so the monitor doesn't blink?
Answer (courtesy of Ken Layton): As pertaining to commercial arcade games the function is solely to isolate the monitor's "hot" chassis from all other components in the cabinet and keep you from frying if you touch the chassis. Only the monitor is connected to the output side of the transformer and nothing else. The transformer was not designed as a voltage regulating/spike protecting unit. It is a safety device for sure.
--- End quote ---
I think Ken must have been misquoted here as this is not really what an isolation transformer does. In fact its the opposite. The function is to render the monitor chassis "cold" as opposed to "hot" and allow it to safely be connected to ground along with all other compnents in the cabinet. It does not isolate the chassis from the other componets in the cabinet, it isolates it from the AC power input. One side of the output of an isolating transformer should always be connected to ground and to the monitor chassis. The game board or PC ground is connected to the monitor ground by way of the video harness and so the monitor chassis must be grounded and definitely not "hot".
Early TV sets were designed in the same way as older arcade monitors and did not have isolating transformers. This meant the chassis was directly connected to one side of the AC mains supply. This was OK as the chassis was completely contained within an outer insulating cabinet with no external connections (apart from the antenna which was easy to isolate using coupling capacitors). Later TVs and all arcade monitors have external connections so cannot be allowed to have live chassis.
These days providing isolation from mains is easier with switch-mode power supplies which are isolated by design.
In many cabinets the isolating transformer feeds everything in the cabinet especially in 240 volt regions where it also drops the voltage to 110v.
What would happen if a monitor which needs an isolating transformer was used without one? It depends on which way the AC power cord is connected. It would either result in building neutral being connected to ground which is against every electrical code in the book and dangerous or it would result in 110 volts AC being applied to the ground of anything connected to the monitor ie the PC casing and the controls in a Mame cab, which would instantly destroy the PC and maybe the user!
Level42:
For the very brave of heart only: How to set-up purity and convergence:
http://personalpages.tds.net/~rcarlsen/cbm/converge.txt
This is about the best walk-through I've seen on the net. Text only, but pretty clear and complete IMHO.
Only do this if you have a poor convergence !!!!
DeLuSioNal29:
I recently contacted the author of the Powerpoint tutorial (discharge.ppt) and he gave BYOAC permission to post the file here for archival purposes. (Attached as a .zip file)
A big thanks goes out to Russ from www.arcadegames.net for letting us use his great file. :applaud:
~ DeLuSioNaL
AndyWarne:
The Powerpoint tutorial is good and note that it mentions to do this when the CRT has to be disconnected from the main board. This is the only time you should discharge a CRT, ie when you need to remove the anode cap.
There is no need to discharge in any other situation. But be aware there are other dangerous charges held in the power supply capacitors on the main board, especially under some fault conditions (eg open fusible resistors on the power supply outputs) where the charge is not drained away and can stay there for hours.
On a working monitor, the power supply caps would drain fairly quickly.
Andy
Level42:
--- Quote from: menace on January 12, 2004, 07:55:34 am ---continued...
Q: You said you would help me identify my monitor, so identify already...
A: Ah the impatience of youth... ;D
The best thing to do first is look for a tag or sticker that explicitly says what model you have. Please note that only manufacturer's and a few gifted arcade guys can identify using serial numbers --please find model numbers (it will say model:_____). Failing that, look for identifying marks on the boards themselves (chassis and neckboard) Sometimes there are numbers, sometimes there are letters that can help identify what it is you have.
Last bet, take as good a top down picture as you can--this may require you to discharge the monitor and remove it from the machine but since it's likely not working anyways you will be doing this regardless (more on this later)
Armed with your picture, visit:
www.jomac.net.au/mon.htm OR
Bob Roberts-big bear bulletin board and see "whats my monitor" about halfway down the page.
--- End quote ---
That link to Bob Roberts' Monitor ID page is dead: Use this one instead:
http://www.therealbobroberts.net/monitor.html
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