Power supply problem.

[brianj]

I had a Stereo (tuner/amplifier) that went dead on me. No lights, no sound. I opened it up and started searching for the problem. The fuse was good and I had line voltage at the primary side of the power transformer but no voltage on any of the secondary windings. I then unplugged it and used an ohm meter to check the resistance on the windings. The primary side has 4 terminals marked 0V,120V,220V and 240V but only uses the 0 and 120V. I assume the others are for when the product is sold in other countries. I found that the windings between 0 and 120 were open. It occurred to me that the 0 to 120 winding should be identical to the windings between 120 and 240 so I reconnected the supply mains to those post on the transformer. I powered it up and it works again.
Is this an acceptable practice or should I expect some problems with it?

 

[MikeMl]

Should work for another 20 years.

 

[Diver300]

It will almost certainly be fine. It's likely that the winding broke where it connected to the terminal, as the primary of the transformer is quite thin wire.

It is just possible that the 0 - 120 V winding was larger diameter than the 120 - 240 V winding, as your amplifier would take less current when running on 240 V, so smaller wire could be used. However, on small transformers that would add to the cost of construction, and would only save a tiny amount on the wire so it wouldn't be worth doing.

On larger transformers, it's quite common to have two 120 V windings, and to run them in parallel for 120 V supplies, and series for 240 V supplies. On those, only using one primary winding could cause a problem at maximum load. As whoever made your transformer didn't think it was worth having two separate windings, they probably used same wire for all of the primary windings.

 

[brianj]

This transformer wasn’t designed to run two parallel windings. They have the four post that tap into a series winding to allow for voltages of 120, 220 or 240. The one power lead is soldered at 0V and the other one has a solderless connector so you can easily select the proper voltage. It did cross my mind that they could have possibly dropped to a smaller gage wire after the 120V tap. If they did I’ll find out soon enough because it’s going into service where it’ll be at full volume for 20 hours a day (I’m donating it so we can have some tunes at work).

MikeM, you have amazing powers of perception. Although I revealed nothing about the age of this stereo you were surprisingly close when you guessed 20 years. When I bought this Sansui system it came with a dual cassette drive and a phonograph.

 

[MikeMl]

...
MikeM, you have amazing powers of perception. Although I revealed nothing about the age of this stereo you were surprisingly close when you guessed 20 years. When I bought this Sansui system it came with a dual cassette drive and a phonograph.

My 20 year old stereo tuner is dying. I've been looking for a replacement at garage sales. Seems like all I can find in stores is this weird 5.1 and 7.2 crap?

 

[crutschow]

My 20 year old stereo tuner is dying. I've been looking for a replacement at garage sales. Seems like all I can find in stores is this weird 5.1 and 7.2 crap?

**broken link removed** (bottom of page) does sell a couple of stereo only receivers but you probably have to go on-line to find them for sale.