"Jack" wrote in message
...
You probably corrupted the EEPROM when you read it. I just learned about
this when I was reading an article about security chips. If you try to
read
them with normal reader/writers, they get corrupted due to the fact that
during the read process, the reader tries to write something on the chip,
to
test it out and this corrupts the chip.
Probably the only way out of it is a new head unit, since you probably
cannot get just a replacement chip.

What's weird is I can scope the EEPROM lines (CS, SCLK, etc) and I'm not
seeing the micro making any kind of queries.

FWIW, the programmer is of my own design. It's been thoroughly tested and I
don't have it set up to write to EEPROMs to "test" them. I realize asking
for repair help is a bit like asking, "...my engine is making this
noise...what is it?"

But if anyone has a dump of the EEPROM, I'd appreciate it!

-Tim


"Tim H." wrote in message
newsiFob.56248$275.141733@attbi_s53...
Hello,

I took on a friend's Kenwood head unit (KDC-PS909) with the intention of
reparing it. It would power up correctly, ask for the security code
(which
I
have) and turn on but no audio. I cracked it open and noticed a chip,
TC7662, pretty hot Turns out, this is a DC-DC converter. Upon power-up,
it
would output roughly -8VDC but soon drop off. Odd, I thought. There was
also
a ground PCB track on the solder side that was toast. It's in the
vicinity
of the DC-DC converter chip. I have a new chip coming to me in hopes
that
that will fix it.

However, I've created a new problem. While waiting on this chip, I asked
myself, "where is the security code stored? Internal EEPROM, external?"
Then, I noticed an 8-pin chip sitting next to the NEC MCU marked KKZ01.
After a little research, it turns out that this is a 93C46 EEPROM.

Long story short, I removed the eeprom, put it in my programmer and
proceeded to dump the contents. I solder the chip back in and now I have
NO
display whatsoever. So, if the chip was inadvertently written to, would
this
cause the MCU to not display anything in an attempt to fool a would-be
thief?

I've also noticed that there's a transistor used as the +8VDC supply
(2SD2396). If I put my meter on it, power up the unit, it'll show about
+7.5VDC for maybe 11 seconds and bam, it dies out. I'm thinking is
probably
related to the DC-DC chip not doing its thing. Although, it seems to be
under microprocessor control because if I reset the chip, it'll come
back
to
+7V and zero out after 11 seconds.

So, the only thing I'm after is a copy of the EEPROM's contents so I can
re-burn it. However, if a corrupt EEPROM won't prevent the unit from
even
turning on, I'll pursue other avenues.

Thank You and Good Night,

-Tim