Amp toroidal transformer

[brakel]

Replacing the toroidal transformer inside a logitech z5500 sound system. The input is 110v and need output, according to old transformer, 2x26.4V and 1x14.5V. It also has two more wires with 0v output. Any idea on where to find a replacement transformer/transformers?

[Mooly]

Any transformer with multiple secondaries (as opposed to a centre tapped or twin secondary) is normally a custom job for a particular application.

Can we ask why you think it needs replacing ?

To replace with off the shelf items would need knowledge of physical size and va rating etc

[brakel]

The transformer over heated and something melted in the transformer. It no longer has any voltage coming out of it. Just wanted to try and see if it was possible to replace it with a single or multiple transformers.

[Mooly]

I would suspect something has caused that failure then... maybe shorted rectifier/s or shorted output stages. No secondary fuses for protection ?

Is the primary winding reading open circuit ? Its such a rare failure mode for a toroid tbh...

[indianajo]

antekinc.com seems to stock stuff in New Jersey. If you are in New Zealand that is no help. 120 VAC primary, 2x28v and 15V secondary are pretty common windings, but you won't find them on the same core. You better put a fuse on the secondary before you install a new transformer, to avoid burning it again. Hint- electrolytic caps often short, taking the rectifier with them. Cheap short life electrolytic caps are the curse of consumer electronic devices.

[dchisholm]

Yes, the first order of business is to determine why the transformer failed. Transformers by themselves are inherently rather rugged and forgiving devices, so I'd go looking for something else as the root-cause for the failure. Like "indianajo" said - electrolytic capacitors are high on the list of "the usual suspects".

(And having said that, I know that occasionally a power transformer will have some kind of overload protection device buried inside the windings under several layers of insulation tape. IF (and that's a pretty big "IF") your transformer includes such a device, replacing the overload protector may restore the transformer to like-new operation. The details of the task are up to you - and may, in fact, consume more time, effort, and money than replacing the transformer. You're still left with the problem of determining why the protector operated in the first place.)

I agree that you're VERY unlikely to locate an exact replacement as an off-the-shelf catalog item. Logitech may sell a replacement as a repair part, but even that's a long shot. The folks in your area who install and service home theater systems may be a source of help, or even replacement parts, but their standard operating policy probably instructs them to declare your unit "unrepairable" and sell you a replacement.

I'm guessing that the main load is on the 26V windings, and the 14V winding supplied a few watts of power to the controls and preamp stages. If you obtain a standard unpotted transformer with a pair of 24-, 26-, or 28-volt windings and suitable power rating you may be able to create a 14V winding with a little effort. Several incarnations ago, on a one-off piece of production test equipment, I had good success with adding a winding to a stock toroid transformer. I needed a few watts at roughly 6V to power some relays, control logic, and indicator lamps. A few dozen turns of wire-wrap wire, wound around the toroid core on top of the standard windings, did the trick. A quick experiment gave me the turns-per-volt constant for that particular transformer.

Dale