So my AT8612 arrived on Friday, direct from HK via DHL. It wasn't double boxed, and slightly damaged in shipping (the banana jack got pushed in and broke the plastic on the front panel a little). It did arrive with a US (110V) power plug, and the 110V/220V selector switch set to 110V on the back! So, was it actually ready to roll on 110V... probably not (but I never actually tried it). After reading a previous post in this thread that the 110 / 220 v switch wasn't connected, I did what Dave would do, and didn't turn it on, but took it apart!!
So, what do we have... yup, indeed the 110V / 220V selector switch IS NOT CONNECTED AT ALL:
Also, a bit of a design flaw with the ribbon cable of the display rubbing on the corner of the transformer mounting bracket... not good... hopefully the screen will still work...
Looking at the transformer, it indeed has 2 110V primary windings, and 2 secondary windings: a 13vac winding, and a +/- 13vac winding with center tap. A little common sense and looking at the secondary wires from the transformer leads to decoding the Chinese characters for Yellow Black and Green. A little googling to look up the Chinese symbol for Red and Blue, and you can easily figure out all the labeling on the transformer:
So originally on the primary, there's a plug that comes from the board and has blue and red going to the transformer, and yellow and black are tied together under a piece of heat shrink. Just out of curiosity, I plugging it in with 110V and measuring the open circuit voltage on the secondaries. You'll get 8vac on the green pair, and 16vac on the yellow pair, when we're expecting 13vac and 26vac respectively as per the label on the transformer. It's probably not going to work as is on 110vac input...
To reconfigure the transformer primaries for 110V operation, both 110V coils must be wired in parallel. I cut the red and blue leads going to the connector, and cut the yellow and black apart that were connected initially on the transformer. I connected red from the plug to red and yellow on the transformer, and blue from the plug to blue and black on the transformer to put the 2 110V coils in parallel. It's important that red and yellow be tied together, and blue and black be tied together so that the coils are actually in parallel. Now connecting it to 110V input and measuring the secondaries, I saw 16VAC on green, and 32VAC on yellow. Slightly higher than the transformer label, but to be expected as I'm measuring the windings open circuit with no load.
So, ready to go with 110V operation. Let's hope the display still works...
Yes, it does luckily! I put some tape over the damaged ribbon cable to prevent it from rubbing on the transformer mount in the future. I also fixed the contacts to the banana jacks and got that straightened out, but didn't take a picture.
In the end, it's quite easy to convert this unit from 220V input to 110V input, but don't trust what line cord it comes with, or the input voltage switch on the back!!