Trying to match small AC transformer - 240V primary 12.8V secondary

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Hi all,

Having found an open primary in the small transformer providing standby
power to a Yamaha home theatre receiver, I want to source a replacement
of course.

The transformer is marked on the side:

XW608  AO
TAM M 0118

and has no voltage or power specs on it. On the schematic there is a
voltage shown across the secondary of 12.8V AC; the primary is 240VAC
since this is an Australian unit.

The transformer is physically small (about 30x30x30 mm, or roughly an
inch and a bit on each side) so I am guessing it has a rating in the
milliamp range for the standby switch, IR receiver and a relay to switch
on the main PSU.

Can anyone offer me guidance on sourcing a replacement?  Searching for
the markings via Google hasn't turned up anything useful.

      Thanks for any help,

         Matthew.

Re: Trying to match small AC transformer - 240V primary 12.8V secondary



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That's strange.  Transformer primaries don't open very often.  I would be
inclined to dig deeper to find out why there's an open circuit (internal
fuse open?  Bad connection?  Melted wire?) and whether there is any fault
downstream of the transformer (shorted component?).

Re: Trying to match small AC transformer - 240V primary 12.8V secondary



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Don't know the reason, but I have removed it from the board and there is
infinite resistance across the primary terminals and no visible damage
to the transformer or the board it's on.  Fuse is intact.  The unit
would be about 5-6 years old I reckon.

Re: Trying to match small AC transformer - 240V primary 12.8V secondary



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Mebbe it has a faulty or tripped thermal protector ?

--
Cheers .......... Rheilly P



Re: Trying to match small AC transformer - 240V primary 12.8V secondary


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Thermal protectors are fitted to prevent overheating etc. Usaully you
can by pass same, and "fix" them, but as theyre fitted for a reason( not
used to our extreme heat?) they often fail. The tranny suggested is
probly close enough.

Re: Trying to match small AC transformer - 240V primary 12.8V secondary


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Small transformers are impedance protected, the windings can be damaged
by power surges or an overloaded secondary. If the unit works after
replacing the transformer, it was probably just a surge that popped it.

Re: Trying to match small AC transformer - 240V primary 12.8V secondary



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In my professional repair life, I replace trannies in hifi units all the
time, that have primaries that have gone open for no apparent reason. Yes,
sometimes there is a thermal fuse in the primary, and yes, sometimes it's
connected across a couple of external pins so can be temporarily bridged for
test purposes, but I find it rare to then come across a fault downstream,
that has caused a genuine overheat that has led to the failure.

Arfa



Re: Trying to match small AC transformer - 240V primary 12.8V secondary


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very small 50/60Hz transformers can be a right pain, as the wire gauge
is so damn fine. Its extremely hard NOT to slightly damage, say, 44AWG
magnet wire when winding such a transformer.

Low power transformers must have extremely high magnetising inductance
AND low volume, so require silly numbers of turns of astonishingly
(vanishingly more like) fine wire.

One I used in an OEM UPS' had, IIRC, 11,000 primary turns, of (again,
IIRC) 44AWG. Now 41AWG is about 0.09mm outer diameter; 11k turns is thus
around 70mm^2, ie 8.4 x 8.4mm, which is about the cross-sectional area
ISTR for the primary winding.

And we had quite a bit of trouble with those - although they were made
in Mexico, for a very low price - all of which was related to the
termination.

Cheers
Terry

Re: Trying to match small AC transformer - 240V primary 12.8V secondary


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Any small transformer with an approximately 12V output should be fine.

Re: Trying to match small AC transformer - 240V primary 12.8V secondary


On Sat, 03 Mar 2007 15:19:49 +1100, Matthew Kirkcaldie

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The markings will be house numbering, either from Yamaha or their chinese part
supplier.  The 0118 will be a date code - week (probably) 18 of 2001, and
googling that will not uncover anything helpful.

As others have said, any comparable unit with a 12v6 secondary will be fine.
Any downstream elctronics which are voltage sensitive will have some supply
regulation, to guard against mains input variation.

Apart from the Jaycar unit mentioned, Altronics have one which has dimensional
info at http://www.altronics.com.au/index.asp?area=item&id=M2851L ..  'tis a tad
weightier, implying to me that it has more iron or copper - both good things.

Even Trickie Dickie has one
http://www.dse.com.au/cgi-bin/dse.storefront/45e9221405120d9e2742c0a87f9c06b9/Product/View/M2851

Which one is for you depends on how critical size is, and how near you are to
the supplier.

Re: Trying to match small AC transformer - 240V primary 12.8V secondary



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**Yamaha are usually pretty helpful and not stupidly priced for spare parts.
Try them. The part will fit like a glove.


--
Trevor Wilson
www.rageaudio.com.au



--

Re: Trying to match small AC transformer - 240V primary 12.8V secondary


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I've not had cause to use them for audio parts, but their computer side is
one of the worst I've ever come across and put me off them as a company.

--
*Can fat people go skinny-dipping?

    Dave Plowman         snipped-for-privacy@davenoise.co.uk           London SW
We've slightly trimmed the long signature. Click to see the full one.
Re: Trying to match small AC transformer - 240V primary 12.8V secondary



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**Your lack of local knowledge is duly noted. Matthew posts from Australia.
The local Yamaha distributor provides an excellent backup for their
products.


--
Trevor Wilson
www.rageaudio.com.au



--

Re: Trying to match small AC transformer - 240V primary 12.8V secondary



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**Again: The Yamaha distributor in Australia is pretty good.


--
Trevor Wilson
www.rageaudio.com.au



--

Re: Trying to match small AC transformer - 240V primary 12.8V secondary


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Is there just the one for all Yamaha products? In the UK I found the one
which dealt with their pro audio fine but not the one for computer stuff.
It was some time ago when CDW was newish and expensive. But I've got a
long memory. ;-)

--
*If God had wanted me to touch my toes, he would have put them on my knees

    Dave Plowman         snipped-for-privacy@davenoise.co.uk           London SW
We've slightly trimmed the long signature. Click to see the full one.
Re: Trying to match small AC transformer - 240V primary 12.8V secondary



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**Yep. Hi fi, computer and instruments. One big company. Japanese owned.
Good service and reasonable prices.


--
Trevor Wilson
www.rageaudio.com.au



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