Change 230 V to 115 V power transformer

[Bompata]

I have a Bose AM-8P Acoustimass speaker system that I bought in Europe. It continues to operate fine in the US if connected to a large external step-up transformer. I want to use it without the external transformer (which creates a hum and wastes energy). Can't I just replace the internal 230 volt power transformer (Billion #192252) with a 115 volt power transformer (Billion #182577)? If the answer is yes, then how could I locate such a transformer? No luck so far finding one on-line. Or is there someway to re-wire the 230 volt transformer (which has 5 primary wires leading into it and 5 secondary wires leading out of it -- I can send a photo once the server cooperates)?

I asked Bose customer support and they wrote back that "It is not possible to internally transform this unit to 120V by installing a 120V power supply. Bose does not offer power supply conversions on this product, and the internal parts of the product are not available to be purchased by end consumers for self-installation."

Thanks for any advice.

[sreten]

Hi,

It should be trivial. Though your primary should have 4 wires not 5.
4 wire primaries are two 115V primaries you wire in series for 230V
and in parallel (maintaining correct phasing) for 115V.
That simple, you convert the series connection to parallel.

The 5th wire may be just a ground wire for the core, totally isolated
from the primaries. Secondaries may be different, a centre point
as earth / ov, and than two different taps, above and below, one
pair for high power and the other pair for preamp circuitry.

rgds, sreten.

[Bompata]

Thanks Sreten,

I will give it a try and let you know how it works out.

By the way, I located the relevant section of the Bose circuit diagram. I hope that the attached photo is legible.

According to the diagram, to convert a 230 Volt Model to a 120 Volt Model:
a) Close Y602 to connect White (the curious 5th wire you were wondering about) to Brown;
b) Open Y603 to disconnect Orange from Brown; and
c) Close Y601 to connect Brown to Neutral.

This, as you say, will change the two primary coils of the transformer from being in series to being in parallel.

I'll let you know how it works out.

Regards, Bob

[SoNic_real_one]

The black wire is connected to an integral thermal overload protection. Hopefullly self-resetting.

[Bompata]

It works!!!

The system is playing beautifully as I type.

This was my first experience re-soldering a circuit board. All it took was to remove one half cm wire and insert two others.

I have written back to Bose technical support asking them to comment on whether the modification should work (without telling them that I have already carried it out).

Thanks

[stratus46]

Originally Posted by Bompata

It works!!!

The system is playing beautifully as I type.

This was my first experience re-soldering a circuit board. All it took was to remove one half cm wire and insert two others.

I have written back to Bose technical support asking them to comment on whether the modification should work (without telling them that I have already carried it out).

Thanks

They know it works but insurance / liability issues prevent them from telling you it's OK. I predict they'll give you the 'no user serviceable parts inside' and 'you'll void the warranty' lines. Enjoy

G²

[AndrewT]

Originally Posted by Bompata

I asked Bose customer support and they wrote back that "It is not possible to internally transform this unit to 120V by installing a 120V power supply. Bose does not offer power supply conversions on this product, and the internal parts of the product are not available to be purchased by end consumers for self-installation."

does this confirm that Bose Customer Support will write any lies to persuade the Customer to buy another model of their equipment?

[Don Hills]

No, it confirms that they are like any other business. It costs them to tell you how to change the wiring, it voids your warranty, and it leaves them exposed to litigation should you electrocute yourself. It's not worth it to them. The strictly correct way to do this is to take it to a service agent and have them change the settings. They have access to the service manuals, they have the skills, qualifications and certification / registration, and they have their own liability insurance. Of course, this is diyAudio...

[AndrewT]

"It is not possible to internally transform this unit to 120V by installing a 120V power supply.

this turns out to be untrue.

That to mean means the Bose actually lied in their reply.

[Bompata]

After a couple of emails to Bose, one of their Technical Support staff wrote back to suggest that I call their technical support phone line.

The person I spoke to on the phone offered to sell me a new and updated unit at a 50% discount. When I explained that the Bose circuit diagram showed that the modification was quite simple, he said that Bose could work on it for $259 if I shipped the unit to them. He was not willing to comment further on what was required because, he noted, Bose no longer maintains the relevant circuit diagrams. In fact, he added, Bose has stopped selling Service Manuals because Bose now requires that all servicing be done at Bose HQ.

This is problematic for someone like myself who bought the original unit to take with me to Africa. I ordered the service manual because the system malfunctioned while in Africa and I couldn't even figure out how to open it up. When the service manual arrived and I succeeded in opening it up I discovered that a simple fuse replacement was all that was required.

Ten years later the system is still functioning beautifully -- even after my novice voltage modification. I have to give Bose credit for that. But I will let each reader draw his/her own conclusions about Bose's approach to servicing.