Aurora Question

[mark pirate]

Hi all, i have just bought myself an aurora, in the instructions it states "If the television is of the 'hot chassis' type where it is connected to one side of the ac mains, then an isolation transformer should be used between the converter and the television"
As all the tv's i have are ac/dc sets, i was wondering what do others use for isolating thier Aurora?

Mark

[ppppenguin]

This is an extra precaution in case the TV chassis is actually live and the aerial isolator breaks down. If you ensure that the chassis of your set(s) is neutral then there is really no risk in connecting the Aurora directly. A small box with isolating caps (Class Y 2n2 or 4n7 is ideal) in both centre and screen is all you need as an additional isolator.

[mark pirate]

Thanks Jeffrey, i just wanted to be sure before connecting it up, as i have to make up a lead from the aurora to the tv, i will fit the caps as you suggest.

Mark

[oldticktock]

As Jeffrey says I assumed the aerial socket on the TV should be isolated from the chassis and I always replace the components which do so to be sure and ensure the chassis is at neutral. Maybe this is wrong but my Aurora also sits behind a dist amp with further circuit prevention, am i'm wrong but is this also a good method should anything fail.

[ppppenguin]

Originally Posted by mark pirate

...as i have to make up a lead from the aurora to the tv, i will fit the caps as you suggest.

You could make a lead with an F plug on one end and a small plastic box (35mm film container?) on the other. The box has a co-ax socket and 2 caps inside. Strictly there should be a bleed resistor (1M or greater) across each cap.

[murphyv310]

Originally Posted by oldticktock

Maybe this is wrong but my Aurora also sits behind a dist amp with further circuit prevention, am I'm wrong but is this also a good method should anything fail.

Hi Chris,
Yes it can help, but really only if the distribution amp is earthed, I run four channels here, three with programmes and one continual test card.
If your isolator caps are duff you will soon know about it, if faulty your RCD will trip and if the chassis is live no doubt there will be some fuse blowing.

A little tip try to always fit a 1 or 2 amp (dependant on the set) fuse in the plug top. If you cannot get them locally CPC do them.

[oldticktock]

Hi Trevor, yep it's earthed, perhaps another option Mark can consider too.

Chris

[Dave Moll]

Originally Posted by murphyv310

If your isolator caps are duff you will soon know about it, if faulty your RCD will trip.

Just to emphasise that this is true even if the chassis is neutral.

[mark pirate]

I have found a tiny diecast box & some suitable caps, so will get the soldering iron out
I am very carefull to check that chassis is connected to neutral, i also have an rcd, the sources i will be using (freeview/dvd/video) are all double insulated.
Better safe than sorry....

Mark

[ppppenguin]

Originally Posted by mark pirate

I have found a tiny diecast box.....

A plastic box is a better bet since it could go live under fault conditions. A 35mm film canister is ideal.

[murphyv310]

Yes, the aerial socket & Coax plug would go live too with faulty caps!
I always replace the caps in the aerial isolator now after being caught out before!

[BGmidsUK]

My converters are isolated by virtue of filtering, slight amplification and an air gap so no danger of them being blown up by a vintage set!


Brian

[mark pirate]

A plastic box is a better bet since it could go live under fault
conditions

Good point, i was just thinking of the screening properties of the diecast box, i think i have a similar sized plastic box that will do the job.

Mark

[Dave Moll]

I suppose that you could line the plastic box with foil if screening is a concern.

[McMurdo]

You can also buy commercially-built units that just fit inline, anywhere from 5-15 quid

[Boom]

There was no such warning with my Aurora. Maybe a few have been blown up?

Mine is fed by a 12V PSU of the wall type which uses an isolation transformer. I assume that such PSU's are approved for isolation? The sets are always plugged in with neutral to chassis anyway.

Just a thought. How about a few turns of a coil with another few turns interwoven in the lead from the Aurora to the set to isolate?

[murphyv310]

I personally have never has a problem and being honest I really doubt anyone has.
For many reasons any set should have the aerial isolating caps replaced with suitably rated caps, remember the aerial socket is easily accessible to non technical personnel on most sets, and if children are near your TV's and get a belt, well you wouldn't forgive yourself.
Changing the caps to decent X rated types or suitably rated ones will also render the Aurora safe and obviate it from damage.
Always make sure the chassis of the TV or TV's are connected to neutral.

[ppppenguin]

AFAIK there have not been any incidents. However there is the possibility of an accident so it's best to issue the warning. For my own usage I'm not sure I can be bothered with an isolator. My main precuations are making sure the chassis is neutral and using an RCD.

[julie_m]

Originally Posted by murphyv310

Changing the caps to decent X rated types or suitably rated ones will also render the Aurora safe and obviate it from damage.

I think you mean Y-rated.

X-rated capacitors are intended for wiring across the mains, and will never catch on fire.
Y-rated capacitors are intended for wiring between mains and earth, mains and exposed metalwork or mains and SELV circuits, and will never fail in a low-impedance state.

(This probably should be stickified somewhere.)

[murphyv310]

Hi.
I have had problems with both X & Y types of caps, I have a nice little box of nasties!
The failure rate is tiny but of the faulty X types they mostly suffer with low value, I have three Y types here that have a nice brown burn mark on their bodies, and all three are dead short!

I fit X types and have not had a failure here but that is because I have hundreds of X types I also have some 47nf marked XY so what is that all about?