On Mon, 5 Mar 2012 18:44:57 -0500, "John Smith"
put finger to keyboard and composed:

I was going to try the battery test but first I used a resistance meter
between pin 4 and pins 2 and 3. I was expecting these two pins to look the
same but they didn't no matter which pin I assumed to be pin 1.

Nice idea.

With nothing to lose I fitted an unused chip backwards.

At power on there was a click and:

1. 0.22V
2. 0.32V
3. 0.6V
4. 0V
5. 0.82V
6. 3.49V
7. 2.38V
8. 1.35V
9. 3.16V

R366 (15K) has 2.53V at the thermistor end.

That means that the current through R366 is ...

(3.16V - 2.53V) / 15K = 42uA

The current through R367 is ...

0.6V / 2.85K = 210uA

The current through R365 is ...

(3.16V - 0.6V) / 180K = 14uA

Therefore pin 3 of the IC must be sourcing 154uA (= 210 - 42 - 14).
This is inconsistent with the equivalent circuit in the IC datasheet.

Also, the fact that pin #5 is at a higher potential than ground would
suggest that the IC has an internal open circuit between pin #4 and
Q20.

Assuming capacitor C316 is not leaking, then pin #7 of the IC must be
sourcing 72uA (= 2.38V / 33K). This is also inconsistent with the
equivalent circuit.

R369 is 28mV at the end not connected to the chip.

My next move was to connect a 100K resistor between the rail end of R372 and
pin2.
This took pin 2 up to 3.11V but the relay didn't turn off.

My conclusion is that whatever I bought in SIP9 packages marked TA7317P
can't be TA7317P

It sure seems that way. :-(

- Franc Zabkar
--
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