I need help identifying these parts, which I believe are SOT89-3 packaged, and I'm guessing are regulators. I have a board which is not working and my troubleshooting leads me to want to replace this part. They are marked only as "A6 55" and "A6 66".

They are each from different generations of the board. It may be that both chips are the same, and that 66 is just an upgrade/replacement of 55 - I don't know.

A6-55 A6-66

Note: these are two separate images. Ignore the apparent size difference between the two parts.

  • Edit: Using a working board, it appears that pin 3 (right pin) is attached to a 12V supply, pin 2 (and 4) is connected to ground, and pin 1 (left pin) measures approx. 6.1V.
  • \$\begingroup\$ 6.1 V? That's odd. DC or switching? \$\endgroup\$
    – winny
    Commented Feb 11, 2017 at 7:41
  • \$\begingroup\$ DC. There are only 3 leads: one to vcc, one to ground, and an output. Take 6.1 with some tolerance. Certainly not 5v but it's an old board and I wasn't using clips. Could be 6v. \$\endgroup\$ Commented Feb 11, 2017 at 13:09

1 Answer 1


KIC3201S-16, a 1.6 V LDO regulator.

Datasheet: http://www.datasheetcatalog.com/datasheets_pdf/K/I/C/3/KIC3201T-17.shtml

55 or 60 is strangely not the week code but lot code.

  • \$\begingroup\$ Hmm - actually, it doesn't seem to add up. The datasheet shows pin 1 as ground and 2 as the input, but my board has pin 2 tied to ground, pin 1 has 6.1V and pin 3 has 11.9V (roughly) \$\endgroup\$ Commented Feb 10, 2017 at 22:37
  • \$\begingroup\$ Maybe this is why you have to replace them :) \$\endgroup\$
    – user76844
    Commented Feb 11, 2017 at 6:40
  • \$\begingroup\$ @BlairFonville Then probably 7806 with that pinout. I can't get Digikey to sort out SOT-89 for me, but there are plenty. You just meed to find which manufacturer makes their chips that way. \$\endgroup\$
    – winny
    Commented Feb 11, 2017 at 8:09
  • \$\begingroup\$ @GregoryKornblum No, I made the measurements on a working board. The same measurement on the board with the faulty chip read something like 2.3V. \$\endgroup\$ Commented Feb 11, 2017 at 12:59
  • \$\begingroup\$ @winny I'm sure you're right, winny. I searched for hours but couldn't come up with an exact match, but I'm sure something will turn up. I'll go ahead and close this since, in all fairness, your answer was a perfect match to my original post. It wasn't until afterwards that I probed the board and found the discrepancies. Appreciate the research. \$\endgroup\$ Commented Feb 11, 2017 at 13:03

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