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Prying Eyes: Shocking 12V AC adapters

26 Apr 2016  | Michael Dunn

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Removing the plate reveals the simplest circuit of the batch: No EMI filter (though space for one), no controller. The caps are 400V & 25V, "105°".

The third adapter I opened provided a real surprise. Can you spot it before reading the caption?

The "LY1205". Tacked wires. Tacked LED. Whoa – name brand! It's made by PSU biggie Delta.

Note R43-R46 in the lower left: 88MΩ bridging HV(-) to 12V(-).

Definitely higher quality than the other units. The model number is EADP-18GP.

This is good quality guts paired with a botched repackaging job. The original operation of this PSU was intermittent, responding to jiggling of the output wire. I now see it wasn't because of a loose connection, but because the wires of the original, cut-off connection are essentially touching! Fortunately, the original AC wires aren't touching, because they're right on the line input of course – no fuse but the one in my breaker panel! Yikes.

Otherwise, it looks good. The input cap is a 400V 105° UCC/NCC part. Output is 25V, 105°. Both are unfortunately close to hot spots though.

As far as I can tell, the production date is ca. 2000-2001 (board:0093, AC rectifiers:0062). Ugh. Wonder if the board had seen service before being repackaged.

The two blue caps at the upper left are 2.2nF parts in series, bridging primary to secondary sides in parallel with the 88MΩ of resistance. What's the goal here? Preventing charge buildup on the otherwise isolated output? EMI control?

None of the boards have isolation slots cut in them between primary & secondary sides, but this one has a few elsewhere: between the main transistor leads, and between the leads of the input fuse.

There you are. A look at a very dirty side of Chinese manufacturing. One wonders how deeply this sort of thing permeates the industry, or does it only turn up to bite cheapskates like me who enjoy living dangerously and buying stuff from the big retail Websites and eBay?

Now to decide if I should teardown some of the better-performing adapters from my collection. Are they simply better repackagings, or are they real PSUs?

About the author
Michael Dunn has been messing with electronics almost as long as he's been walking. He got his first scope around age 15, and things have been going downhill ever since. The scopes now vie with wine racks, harpsichords, calculators, and 19th century pianos for space. Over the years, he's designed for the automotive, medical, industrial, communications, and consumer industries, as both freelancer and employee, working with analogue, digital, micros, and software.

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