TECH: isolation transformer confusion.

[erikthecat]

[ukvac] TECH: isolation transformer confusion.

afternoon.

a simple question, i hope someone has the time to assist, thanks in advance.

i was under the impression that it was dangerous to remove an isolation transformer,
its purpose in life is to prevent main voltage somehow being present on the chassis of the monitor in a cab?

as far as i can see the so isolation transformer in my table just steps 240v down to the 110v that the monitor required. there would only appear to be a live and neutral feeding the monitor, the chassis is just earthed in the regular fashion.

there are other tap off's that were feeding a PSU regulator board, but that died ages ago and has been replace with a regular arcade PSU.

i would like to remove the isolation transformer and replace it with a USA - UK voltage converter.
the reason i would like to do this is that the i believe the cause of the 'wobble' of the image is something to do with the magnetic field generated from this 8 inch cubic monster due it's proximity to the monitor.

clear as mud?

any pointer / URLs to a site that has some technical descriptions, would be fine.
Yahoo, returns, nothing of any use (not simple enough

thanks for your time.

GaRy:? still a newbee

 

[Zektor]

RE: [ukvac] TECH: isolation transformer confusion.

You could always replace it with a similar transformer but shielded like the
ones used in the Taito cocktail machines. I had the same problem with
picture wobble and it took ages to figure out what was wrong.

 

[guddler]

RE: [ukvac] TECH: isolation transformer confusion.

As you say, clear as mud

I'm not totally convinced from your description that the transformer in
there that you're describing is even an isolation transformer. More often
than not, a monitor's isolation tranformer will have just the one voltage
coming out (again, most commonly 128v, but far from always) and one going in
(either 240v or 110v depending on whether it also steps down).

If there are other voltages coming off this transformer - or were when it
was fully functioning - then I would question it's isolation.

Now then, this also assumes that the monitor is not a modern one (such as
some, maybe all Polo monitors) that has it's own isolation built in.

Anyways, regardless of whether it has other windings or not and whether it's
isolating or not, the wires that you describe sound fine to me. 240v in,
128v (less maybe depeding on monitor make model) out live and neutral from
the transformer going to the power input of the monitor, earth's all
commoned up back to the pin on the 3 pin mains plug with one attached to the
metal of anything in the cab. Normally, including the metal of the monitor
chassis.

Does the table use a switching psu or a linear that wants all funny
voltages?

If it uses a switcher then just bung a UK switcher in wired direct to the
240v mains and a 240v->12xV* isolation transformer, again wired to the mains
to power the monitor. Make sure it's isolating though!

If it uses a linear psu then first add your stepdown transformer, then
either use the transformer that's in there to get your voltages for your
linear supply, followed by a 110v->12xV* isolation transformer for the
monitor.

If it uses a linear psu and the transformer that is supplying the linear's
input voltages is the suspect for the wobble then you're going to either
need to source a xformer with the same windings on it, or see if the linear
can be replaced with a switcher.

Add a mains filter in before any of the transformers for good measure.

*Match this voltage to the voltages required for the monitor. 128v is a
generalisation. For instance, while I don't have much experience of them I
believe monitors typically used in Taito's used 110v input and the Sega one
in my Monaco GP was 100v input, so double check this. Obviously it's also
subject to a +/- percentage difference too.

I should add as well, that if all of this is being done to convert from US
to UK mains via the step down then I have absolutely no idea if the
difference between 50 and 60Hz will have any impact on things. I think it's
a case of most transformers will be specc'd for both 50 or 60Hz, but again,
probably worth checking.

Anyway, hope that's reasonably clear(ish).

Plenty enough typing from me for now.

Cya,
Martin.

 

[junofirstman]

[ukvac] Re: TECH: isolation transformer confusion.

One of the best articles on the subject is by Randy Fromm

http://slot-tech-ftp.serveftp.com:8080/techdept/monitors/isolation%20transformers/isoxfmr.htm

Definately worth reading for the definitive reasons why an isolation
transformer is required for all monitors except for newer ones that
are specifically designed to not need one.

Chris