Crown PSA-2 - Page 114

SAZPSAZOT 3081
PSA-2 IOC Low level triggering modification
Any PSA-2 Display Module
In early production of the PSA-~2 amplifier, a low level signal would
cause the I0C LED's to illuminate. This was caused by crosstalk within
the LM339 used for both the 10C as well as the signal presents indicator
(Q100 and U200 on the PSA-2 display module)... for this reason, 0113 and
0213 were added to limit the size of this spike by (at .6v greater than
the -15v supply) shunting the spike to the -15v supply.
In Hovember of 1980, we used LM339 chips purchased from a different
vendor to be used in this cireuit and the problem reappeared. To cure
is as follows:
UANTITY. CPN DESCRIPTION
2 C 3447-1 IN270 diode
2 € 2631-7 TOK ohm & w
1) Remove the diodes presently being used in positions O113 and 0213
{CPN C 2851-1) on PSA-2X display module
2) Replace with CPN C 3447-1 (1 N270 germanium diode)
3). Install from the base to emitter junction of each transistor
(Q101 and 0201) a 10 K ohm & w resistor (CPN C 2631-7)
We have found this problem exists only when using the National LN339
chip for U100 and U200 on the PSA-2X display board (problem does not
exist on the SA-2 display board).
If you have any questions, please call or write.
a . Eagstrom
Product Specialist
Jao