Sansui AU-X1 transformer T702/4002970 wanted

[Knut1]

Hello,

I am (with help from a service shop) restoring a Sansui AU-X1 integrated amp, and have found that the transformer referred to as T702 in the service manual, model no 4002970 needs to be replaced. (The one in the unit says 4002971, by the way, not sure why.)

Any ideas where to get this? If not, does anyone know if the same transformer was used in any other sansui amps that might be easier to come across than the AU-X1? TIA!

Regards, Knut (Norway)

 

[Harolda]

Are you sure there is a problem with the transformer? To my opinion the likelyhood of transformer failure is very low.
I am sure that this transformer is only used in the X1! So you would need to find a company that can make a new one or find a spares unit.

Does your tech have experience with this amp? Why does he think the transformer is faulty?

 

[Hyperion]

As I understand it, 4002971 is the part number of the smaller 100V only transformer used in Japan domestic models.

If you are expecting yours to have 4002970 - this may be the part number of the multi voltage transformer?

The 2 Japanese domestic 100V transformers are P/Nos 4002961 (main T-701) and 4002971 (auxiliary T-702)

However the service manual says the P/Nos are 4002960 & 4002970. - so the mystery remains.

As Harold says it is quite rare to have a Sansui transformer fail, a lot more common to have a 'would-be' Sansui tech fail

As regards having a replacement wound, this should be a piece of cake! - you may even be able to buy a similar spec transformer 'off-the-shelf' however physical size may be an issue.

 

[Knut1]

Hello,

Thank you for your replies. The tech has measured infinite resistance in the primary winding of the transformer, indicating an open circuit in this winding. He is a professional technician, has serviced a lot of vintage gear including Sansui, and also has an AU-X1 himself, so I have no reason to doubt this. But we are all humans, so if any of you have any pointers or hints on what other things could cause these measurement results, please feel free to share. The power switch was also found to be broken (open circuit also in on position), but here I have ordered a replacement, and I assume this problem does not influence the transformer measurements.

But any hints are welcome, it's always good to have an open mind.

Regards, Knut

 

[Hyperion]

Knut, at a guess those transformers haven't been made for at least 30 years, the only source would be from someone parting-out an AU-X1.

Or from the very small possibility that they have one here:- http://www.sansui-parts-shop.com/index.php?page=main

My quick look says no.

If you are in a hurry and can't wait for one to turn up, I suggest you pursue getting one wound - good luck.

Please excuse the scepticism regarding transformer failure, Sansui (as you may know) made their name making them in the beginning, hence very good quality and not prone to failure. Add to that, if an untalented tech sees a vintage piece and couldn't be bothered to repair it, the standard response is "the transformer is blown" - picking one of the most unavailable and expensive parts so as to make the repair uneconomical. (or simply because the tech does not understand 'soft start' circuitry so often found in vintage pieces, including the AU-X1).

 

[Knut1]

Hello,

Again, thanks for your reply. Most people (including myself) make mistakes or overlook details from time to time no matter how skilled they are, so a second opinion or sceptic remark to any statement is always welcome.

To my surprise it turns out that I have actually had two offers on used transformers of this kind today. They are not cheap, plus shipping will also be expensive, and who knows how long they will last. But I still fell it's worth a try. The tech says the amp otherwise appears to be in good condition. I am aware of the AU-X1 oscillation problems, and this is a Fairly early model (October 1979) so I am aware that there may be other issues waiting. But still it's very tempting to have a working AU-X1, having followed Sansui for so many years. Any advice or opinions regarding transformers? Buy or fix?

Regards, Knut

 

[Hyperion]

Any advice or opinions regarding transformers? Buy or fix?

Not sure what you mean here, you want a working AU-X1? - get a transformer! - 'how' is up to you.

 

[Knut1]

Hello,

Sorry about not being precise. My question is if you would advice to buy a new (that is, used) original transformer, or have someone rewind the coil of the transformer I already have? Or could trying to get a Brand new transformer with the right specs be an option?

Regards, Knut

 

[avionic]

Does your tech know how to trouble shoot a "softstart circuit". Rookies usually point at the transformer as being the fault. Usually it ends up being a shorted output transistor.

 

[avionic]

I'd have a close look at R621 on or around the F-2781 board. R621 is a 20 watt ballast resistor for the "softstart" ( 3.9Ω). If it is toast. Then start checking the output transistors.

 

[avionic]

Please excuse the scepticism regarding transformer failure, Sansui (as you may know) made their name making them in the beginning, hence very good quality and not prone to failure. Add to that, if an untalented tech sees a vintage piece and couldn't be bothered to repair it, the standard response is "the transformer is blown" - picking one of the most unavailable and expensive parts so as to make the repair uneconomical. (or simply because the tech does not understand 'soft start' circuitry so often found in vintage pieces, including the AU-X1).

Sad but so true.

 

[rcs16]

FYI, I have a open primary transformer for a G-7500, it just blew one day for no apparent reason. started to take it apart trying to find a thermal fuse. Would have to take off the insulation to dig into it, so I gave up and used a different p/s(Pioneer sx-1050) in the g7500. Not so easy for a AU-X1 however
You can easily verify/confirm if the primary is open with your DMM.

 

[Overundr1]

snip from Hyperion---

" Add to that, if an untalented tech sees a vintage piece and couldn't be bothered to repair it, the standard response is "the transformer is blown" - picking one of the most unavailable and expensive parts so as to make the repair uneconomical. (or simply because the tech does not understand 'soft start' circuitry so often found in vintage pieces, including the AU-X1)."

Just finished a Sansui amplifier that was diagnosed exactly with this condition by another shop, it was not, not that we are trying to rain on your tech's parade, just being helpful.
-Lee

 

[miromustang]

My tech can revind it for you with all specs you need if you are willing to ship it to Slovenia. I've made one for AK member for his au-20000 this summer.

 

[Ronito6]

My tech can revind it for you with all specs you need if you are willing to ship it to Slovenia. I've made one for AK member for his au-20000 this summer.

Wow. Didn't think that could be done.

Any pictures of the re-wind man's work anywhere?

 

[Ronito6]

Also... there must be a contemporary toroid available that would serve.

These guys did it. (Not for an X1, but still...) The second vid shows the toroid installation in place.

 

[slon06]

Я могу предложить трансформатор Sansui AU-X1 T702
Только не сейчас летом - осенью

 

[Hyperion]

Welcome to AK slon06 !

I know you are just trying to be helpful, but please note that you are not allowed to offer items for sale in this part of AK, please read the forum rules.

If you subscribe you will have access to AK's 'Barter Town' in which case you can offer items for sale.

Here is a translation of your post:

"I can offer a transformer Sansui AU-X1 T702 Only not now in the summer - in the autumn"