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

As a follow up, would this do if I can't get the same component?

The output on the original is 12.8V but this is 12.6 - I don't know what the tolerances are but I'm guessing it would be regulated in some way.

Matthew Kirkcaldie wrote in news: snipped-for-privacy@news.sydney.pipenetworks.com:

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?).

Near enough. What about Dick Smiths?

"Matthew Kirkcaldie"

As would the similar DSE M2851

BTW both unit are made to " class 2 " or double insulation requirements.

Important if that Yamaha receiver is " class 2 " - as I bet it is.

.... Phil

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.

Thanks Phil - there's no ground on the plug so I would guess double insulated is the way to go.

The DSE part is cheaper and available locally - thanks!

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

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.

Mebbe it has a faulty or tripped thermal protector ?

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.

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

Even Trickie Dickie has one

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

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

That tranny will work just fine. The only thing that I would say is that power transformers in domestic equipment are usually what's known as a "designated safety component". This means that they formed part of the original design approval which declared the unit physically safe - it won't set fire to your house in the event of it failing - and electrically safe - it won't make the equipment live in the event of a breakdown of the insulation on the winding wire or terminations. You can identify components which form part of a safety spec, and are thus "designated", because they have an exclamation mark inside a triangle, marked by them on the schematic.

If you do substitute a non-Yamaha transformer for the original, this would almost certainly compromise the original safety approvals for the equipment, and if there were any unforseen unfortunate consequences down the line, Yamaha would have no liability at all.

Almost certainly, replacing this tranny with a substitute, will cause no problems at all, but I think that you should be aware of exactly what you are doing for your own peace of mind. For what its worth, as a professional repairer with a legal duty of care to the public, I would never substitute a transformer that is going to run 24 hours a day, as a standby tranny is, nor would I recommend others to do so. At the very least, I would try to check, through the suppliers or even directly with the manufacturers, that any tranny you intend to use is rated for continuous operation. I would also contact a Yamaha spares agent to check the price and availability of a genuine replacement, after you have proven that all is well by checking with your substitute in place. Not trying to put you off or anything, just advice ...

Arfa

Thanks Arfa, wise words there and I will certainly think it over.

Problem is, Arfa is right 99.9% of the time.

"Meat Plow"

Someone who is also wrong 99.9% of the time.

....... Phil

Also meaning you included?

Just killfile him Arfa. His signal to noise is about the highest of any newsgroup contributor so really not worth wading through for the 1% of useful stuff he posts.