Date: Wed, 27 Jan 88 08:58:58 est
From: mac@idacrd.UUCP (Bob McGwier)
To: ka9q.bellcore.com!n4hy@bellcore.UUCP
Subject: 56K modem fixes


              56 kilobaud modem bug report  (1-10-88)



TRANSMITTER ENCODER BOARD (110386):

     Some of the 110386 transmitter encoder boards have a missing 
trace between U10 pin 21 and pin 24.  This problem exists only in 
the  second  batch of boards and was due to tape falling off  the 
artwork.  To fix it just solder a wire between U10 pin 21 and 24.


RECEIVER DECODER BOARD (021987 rev A):

     There  have  been reports that various brands of  555  timer 
chips don't work well (or at all) in socket U7.  I have discoverd 
the cause of this problem.  The ground side of capacitor C1 needs 
to  be  DIRECTLY connected to pin 1 of U7.   You need to cut  the 
trace  that goes between component carrier N1 pin 9  and  ground.  
Solder a wire from N1, pin 9 to U7 pin 1.  All non-CMOS 555 chips 
should  work with this mod.   The next release (rev B) will  have 
this fixed.



from Dale A. Heatherington  WA4DSY
 
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