Sansui au 717 transformer help

[jFF_Bulbo]

hello.
working in a au 717 wich need tons on TLC.
short on DBT .
i rebuid amp modules, short on DBT
i removed power supply and disconected the amp boards. short on DBT.
transformers, maybe blown?
it is a multivoltage unit, once removed from amplifier, how could i conect or configure them to test each one in 120v?

 

[Hyperion]

There are a number of things that could cause the symptoms you are seeing, without it being a transformer problem - which is extremely rare for Sansui. Damaged rectifiers for the high current supply, or reverse mounted or wired main filter capacitors is another but somewhat more remote possibility.

Firstly, don't remove the transformers just yet, as it is not necessary.

You might find this thread and the discussion interesting

AU-719 on the bench

With collection of the transformer expected very soon (Wednesday), I decided to remove it and see what I could discover, as you can see no need for any more guessing, this says it all. So just the excitation of the mains in one lead seems to have been enough for the transformer to work...

audiokarma.org

And for transformer testing - read from post #165

 

[jFF_Bulbo]

There are a number of things that could cause the symptoms you are seeing, without is being a transformer problem - which is extremely rare for Sansui. Damaged rectifiers for the high current supply, or reverse mounted or wired main filter capacitors is another more remote possibility.

Firstly, don't remove the transformers just yet, as it is not necessary.

You might find this thread and the discussion interesting

AU-719 on the bench

With collection of the transformer expected very soon (Wednesday), I decided to remove it and see what I could discover, as you can see no need for any more guessing, this says it all. So just the excitation of the mains in one lead seems to have been enough for the transformer to work...

audiokarma.org

And for transformer testing - read from post #165

i´m going to study that thread, thank you
i also suspect the multivoltage conection terminals... it unit was very very damaged for some one with no sense of how to work....

 

[Hyperion]

i´m going to study that thread, thank you
i also suspect the multivoltage conection terminals... it unit was very very damaged for some one with no sense of how to work....

Do please be careful, you'll be working 'up-close-and-personal' to mains voltages - work safely, don't leave anything to chance.

 

[Tom B]

I agree with John. Transformers are usually the last thing to fail. And when they short (usually as a result of someone defeating a fuse) they only short for a short time and then they open. Burnt smell becomes apparent at the wire openings. Probably shorted rectifiers, or reversed caps

 

[mcgjohn]

hello.
working in a au 717 wich need tons on TLC.
short on DBT .
i rebuid amp modules, short on DBT
i removed power supply and disconected the amp boards. short on DBT.
transformers, maybe blown?
it is a multivoltage unit, once removed from amplifier, how could i conect or configure them to test each one in 120v?

its takes quite a bit to short out the transformers.

might want to consider disconnecting the rectifiers and PS caps from the transformer secondary, leave the transformer secondary unattached and try the dim bulb test again. More likely cause is a shorted diode or an old shorted cap in the power supply. Therre is also that power supply board that resides next to the transformers. Its quite common to have shorted caps on this board, or OEM glue that has shorted out the cap leads over time. I have worked on quite a few of the 717s and was not uncommon to see a few caps on that large board which had exploded.

 

[jFF_Bulbo]

Hello all.
Well.....

A little toasted...
Wires also...

The other one works pretty fine. No shortcut on dbt... Just a little high voltaje in the output.. 44vac instead of 39vac in the service manual..
Some Transformers available on eBay, but shipping Is very expensive.

I'm going to try a major rebuild on them.

Regards AND thank you for your commnets and help.

 

[jFF_Bulbo]

Just for the record.

 

[mrk229]

Wow that got so hot before it blew the fuse the solder melted on the copper strap. Did somebody put a nail in the fuse holder?

 

[jFF_Bulbo]

Hi, I don't know what could have caused such a spectacular failure. I bought this Sansui because it is a unit that I have wanted to have for a long time. I knew it needed repair, although I didn't think it was something with the transformer. I hope to be able to fix this nice unit soon.