"Franc Zabkar" wrote in message
...
On Wed, 2 Mar 2005 22:34:13 -0000, "N Cook"
put finger to keyboard and composed:
"Franc Zabkar" wrote in message
.. .
On Wed, 2 Mar 2005 13:30:22 -0000, "N Cook"
put finger to keyboard and composed:
I repaired a guitat tuner today - blown 78L05 as
no supply reversal protection.
I was intrigued by another 3 pin TO92 device marked
8054
HN
3C31
Presumably working order - just wondered what it did.
Probably 8054HN not 8054 datecode , by Seiko,
activation voltage 3.8V to 4.2V, battery monitor.
One line is connected to INVERSE READ of the 80C51 micro
Are you sure it isn't connected to the uC's reset pin?
, I didn't trace any other lines. But what would it
do presumably when 5V drops to 4V or so. Just kill
the LED drives or shut down completely via some other
undiscovered trace. Seems odd having this sophistication
but no diode protection against battery or ext ps reversal,
especially in a product destined for musos.
I think it's a PSU supervisor IC used to hold uPs in reset mode in the
event of low Vcc. I believe the output pin should be high if Vcc is
OK. IIRC, I've seen an S8053ALR used in an Akai VCR for this purpose.
- Franc Zabkar
--
Please remove one 's' from my address when replying by email.
So what would happen to a microcontroller without such an IC
and low Vcc state. It wouldn't corrupt the internal ROM.
I originally suspected it might be a negative rail inverter or negative
v.
reg.
I think these supervisor ICs are used where loss of sanity in the uC
can have serious consequences, ie a mechanism jam in a VCR. I wouldn't
think a guitar tuner would have this kind of requirement, though. Have
you confirmed whether the 8053 is connected to the uC's RD* or reset
pin?
- Franc Zabkar
--
Please remove one 's' from my address when replying by email.
Guitar tuner back with owner, so nothing else known.
I agree that by the time 9V had dropped to 4.2V , LEDs would be decidedly
feint
and whole unit will not
operate much longer and no consequential damage anyway if it did, compared
to
lack of power reversal protection.
|