On Jun 19, 1:42 am, Doug Smith W9WI wrote:
Anyone know if this is on the Web somewhere? A Google search returns a
pile of Asian-language sites, one of which might have the information if
only I were literate in Chinese/Japanese/Korean...

It's the logic chip in a cheap mini FM transmitter, sold for use with MP3
players. I'm trying to change the frequency selections, as none of the
factory choices (88.1/88.3/88.5/88.7MHz) are usable here.

I did find a schematic for the transmitter as a whole on the FCC website
but changing the logic level of a pin that *seemed* appropriate caused the
unit to stop working altogether. (or shifted the frequency out of the FM
BCB...)

My notes, based on a ripping into a unit I got from Wal-Mart a while
back, disagree with your factory choices. According to my notes, pin
18 to Vcc selects a band which has choices of
88.7/88.9/89.1/89.3/89.5/89.7/89.9.
And pin 18 to ground selects a band which has choices of
107.7/107.9/108.1/108.3/108.5/108.7/108.9. Maybe due to this
disagreement you've got some customized or different variant version
of the chip. I think my chip was a BH1417-something or other (Rohm?).
Is HY Hyundai or something else?

The unit I was playing with had a varicap and a small coil for tuning
the VCO of the synth. I had to remove a few tunes from the coil to get
it onto the 107-108Mc band as opposed to the factory 88.7-89.9Mc band.
It didn't stop oscillating when the coil was out of range, but it
didn't lock either.

Tim.