Identifying a SMT regulator (long)

[Franc Zabkar]

Well, I'm tentatively reporting success. Focusing on the
K4D551638H-LC50 RAM, I was able to determine it got power from U8 a
UTC1117. THAT turned out to be a 3.3V regulator. WTF??? The
K4D551638H-LC50 requires 2.6 volts! The I discovered that YOUWANG
ELECTRONICS makes variants with other output voltages. There are
three UTC1117s on the board, the one powering the K4D551638H-LC50 has
B25 on it (this is not the date code per the data sheet). The others
have B33 (near the Flash memory) and B18 (near the LGDT3303).

There are many variants of the UTC1117 linear LDO regulator.

I see this one quite often:
http://www.diodes.com/datasheets/AP1117.pdf

It comes in an adjustable version and fixed versions - 1.5V, 1.8V,
2.5V, 3.3V, and 5.0V. The part number incorporates the voltage, eg
AP1117E18 is a 1.8V device.

Your Bnn numbers would be voltage ratings.

Here's an NS version:
http://www.national.com/dt/lm1117.pdf

.... and another:
http://www.icbase.com/hotic/html/docs/LM1117.pdf

I haven't been able to find a data sheet for the LGDT3303, but 3.3 volts
appears to be right for the flash memory.

This LG Innotek VSB/QAM + NTSC tuner datasheet refers to a "3.3V
supply voltage for LGDT3303" and a "1.8V supply voltage for LGDT3303":
http://www.haluyatech.com/down/lgtunner/TDVS-H066F.pdf

See pages 21 and 22.

And all of the UTC1117's were from YOUWANG ELECTRONICS.

The next problem was locating a replacement for the dead chip.

Fortunately, Mouser Electronics came to my rescue. They stock only
one adjustable bucking regulator in the SOT23-5 package. It's the
Exar SP6669AEK-L, and it has the correct pinout. The best news they
will sell in quantities of 1.

That looks right for a 1.2V supply:
http://www.exar.com/Files/Documents/SP6669_DS_RevC.pdf

Now to make up an order (I need caps, transistors, and a fuse for a
dead LCD monitor). Then a weeks wait for the pars to come in.
Finally, solder in the regulator and give it the smoke test.

PlainBill

Good luck.

- Franc Zabkar