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Audioengine A5+ transformer replacement
Audioengine A5+ transformer replacement
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Old 18th June 2019, 12:02 PM   #1
Daeveren is offline Daeveren
diyAudio Member
Join Date: Jun 2019
Default Audioengine A5+ transformer replacement


I'm looking for a replacement for the toroidal transformer in my Audioengine A5+ active speakers.

I've had no luck reaching Audioengine Support, nor my local distributor. Basically I'd need to either find a transformer replacement, either use the speakers completely passive, hooked to a 4 ohm stereo amplifier.

Based on what I can understand from the photo I've taken of the transformer, its specs are as follows:

230v input

What I'm looking for is help with pointing me towards a place where I could order online a similar transformer which will meet the voltages needed.

link to a photo of the transformer
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Old 19th June 2019, 10:34 PM   #2
Mark Tillotson is offline Mark Tillotson
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Join Date: May 2018
Location: Cambridge UK
You need the VA rating for each winding to be safe.
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Old 19th June 2019, 11:29 PM   #3
MAAC0 is offline MAAC0  Portugal
diyAudio Member
Join Date: May 2010
Are You sure the transformer is busted ? Do You get infinite reading on the primary ?
Unpeel the insulation and try to find a small fuse inside. The label on the upper left side tells You it's thermally fused .
Short it just to test and then try to find one. There is one fuse on the back plate also.

If it's busted..

First determine the power of the speakers for finding a suitable transformer.
Based on size, look at transformer manufacturers datasheets for example.

(I presume 17V is Your rail voltage, Check were the wires connect on the board .. rectifier bridge with big capacitors ?)

Say You need a 17+17V / 6A transformer. 2*70W speakers 17*1.4 (rail voltage rectified) / 4Ohm=5.95 A -- 23.8*5.95=141.61 W

You will need a 250 or a 300VA one. (1.5* rated power) Go for the 300 one if it fits.
If You can't find the correct voltage transformer (only 2*20V) for example, unwind a few turns and measure until You have the correct Voltage. Make sure Your mains voltage is between tolerance before measuring.

Now that You have Your main rails powered, You'll need those auxiliary voltages.
Wind a few winds on it (10-20) and measure the output voltage. Look at the wires on the old one for finding the correct gauge.
Compute winds needed. Say You measure 1V AC with 10 winds connected to 230V in spec Voltage mains.
You need 10*15 for a 15V output. You will need to wind 5 windings (2*15+2*17+10)

Voila Problem solved.
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Old 25th December 2019, 10:16 PM   #4
hijdoetut is offline hijdoetut
diyAudio Member
Join Date: Dec 2019
Hi Daeveren, I may have had the exact same issue you had, and if so then you're in luck as I fixed it. Well, bypassed it would be more accurate ;-)
My toroidal transformer was broken. There's an AUPO M-3A-F thermal fuse inside it, right on the primary coils. Between the white and the red wire. Mine was broken. I did not replace it, but chose to live without a thermal fuse there :P
So if you measure infinite ohm too between white and red wire (when desoldered from the switches) then yours is broken too.
If you are on 240V then you can just move the red wire to where the red one is soldered to. If you are on 120V then you need to add a wire between white and red.
ps. Yes I had to unwind the entire toroidal transformer to find this, but I was able to put it all together, working.
-- Hans
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Old 25th December 2019, 11:04 PM   #5
sgrossklass is offline sgrossklass  Germany
diyAudio Member
Join Date: Nov 2004
Location: Germany
If you had the xfmr unwound to find the thermal fuse, it would have been easy to replace it at this point. Typical values for trip temperature I've seen include 125 and 150C.

For a thermal fuse attached externally, try 73C or thereabouts.
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Old 28th March 2020, 04:30 PM   #6
joghurt is offline joghurt
diyAudio Member
Join Date: Mar 2020
Hi Daeveren and Hijdoetut,

My A5+ died just a few days ago (doesn't seem to have any power anymore), and after some google searches I found your posts. What you describe sounds very familiar, so I might also be facing a broken thermal fuse.
I'm not scared to try to repair something (my A5+ is 6 years old, so out of warranty anyway), but I've never done something like opening up a transformer before. So before I do so, I just want to double-check.
@Hijdoetut: did you physically cut the primary wires (5 ones) to the transformer before taking it apart (to solder them together afterwards again), or were you able to leave those intact? And when I completely dismount this transformer (peeling off all plastic and isolation), and remove the thermal fuse, how do I assemble and isolate the transformer again? Wrap it in duct-tape or so?
If you would perhaps have some pictures from your repair process, it would be highly appreciated!

I guess this will be a nice activity for the next few days, now we're forced to stay home due to this corona-crisis anyway :-)
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