On Fri, 24 Feb 2012 23:43:18 -0500, "John Smith"
put finger to keyboard and composed:

Has anyone encountered fake TA7317P devices?

Before I replaced the chip I checked the voltage at all pins as follows.

1. -0.7
2. 0.7
3. 0.1
4. 0
5. -0.8
6. 76.5
7. 0
8. 0.6
9. 3.2

I concluded that The 0.7V at pin 2 must be coming from within the chip
because there is near 0V at the other end of the series resistor on that
pin.

After replacing the TA7317P, meter readings show only 1.8 V at pin 9.

I believe pin #3 is being used to provide thermal overload protection.
That said, I can't see how it could possibly work, even with the
"correct" supply voltage at pin #9.

Here is the relevant section of the circuit:

pin #3
o
|
pin #9 o-|-- R366, 15K -- TH301 --|-- R367, 3K --o pin #4, Ground
| |
|-- R365, 180K ----------|


TH301 is an NTC thermistor, Panasonic p/n ERT-D2FHL503S:
http://www.panasonic.com/industrial/...arg0000ce2.pdf

It's resistance at 25C is 50K.

AISI, in order for the thermal overload to activate, pin #3 would have
to exceed 0.6V (the B-E voltage of Q15 in the datasheet). However,
even if we allow the resistance of TH301 to fall to 0, then the
voltage at pin #3 is still only 0.57V, assuming a voltage of 3.2V at
pin #9. At 1.8V, the voltage at pin #3 would be only 0.32V.

C316, R371 and R374 appear to provide a dethump delay at switch-on.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.