Stern transformer issue

[illawarra_steelers]

Hi Guys,

This isn't mine and have no idea on Stern SS....so will hand it over to you:

Basicly the issue with machine is that the transformer smokes on it when power up but i have been through the whole machine and cant find a short or anything that maybe casuing the issue. Rebuild the whole power supply section and every pcb in cabinet is reading correct voltage without cpu/eproms fitted but as soon as i refit the eproms and cpus bang smoke again so its got me beat. The pinball did come with 2 transformers and both seem to work without load on bench but i have a feeling that there both worn out and cant handle the amps anymore that the machine requires

[Pinball Fixers]

I came across a Bally a while ago with an internal winding short to the metal frame of the transformer, and when inside the machine it would smoke due to this - on the bench it was fine.

So, check if there is any short to the metal frame...

[Retropin]

Could well be as Owen states - windings should be isolated from metal surround.. on the bench it has nowhere to run to ground and so will read OK - once mounted to game it has path to ground.

Another possibility is that the transformer is in fact on its way out - i come across this a few times with iron core neon transformers. Transformer will test OK without load but put load across it and current draw is much higher than it should be and transformer runs hot.

Just to add though that the fault above is normally created by transformer running open circuit. In other words power is applied and current is drawn through internal resistance of the windings etc. A power step down or up tranny will continue to convert 240V even when not under load. Eventually, it starts to run hotter - laminations start to break down and so the cycle continues till it burns out.
If you have a step down transformer in your machine that is close to the wattage required youll notice it gets warm even with the game switched off at game switch.... always switch off at the wall

[illawarra_steelers]

Thanks guys, have sent your suggestions to the Stern owner (and asked him to join AP)