Woo hoo! I fixed one :-)
Came to me as "Used to work, then the screen went black".
With my logic probe I looked at the sync. Good! RGB - Bad!
Nothing to 6L, the prom.
CMP BLK to 6M was stuck.
161 counters at 5s,4s,5r,4r not counting.
fed by *MLD, stuck low.
*MLD driven by 4C - 4C had stuck input on pin 13, fed by 7474 at 3D
3D had no clock, fed by 139 at 4C
4C looked to have good inputs, but no outputs.
Swapped it, nope, still no outputs.
Just when I told Simon, that I rarely use my scope, I pulled it out, and
found that the enable for the 139 was not swinging the full ttl range, even
though the logic probe was triggering. This is fed by a 7474 at 5C.
Swapped 5C and she roared to life!
So a scope can be usefull!
Mike
---------------------------------------------------------------------------
** To UNSUBSCRIBE from rasterlist, send a message with "UNSUBSCRIBE" in the
** message body to rasterlist-request@synthcom.com. Please direct other
** questions, comments, or problems to neil@synthcom.com.
Received on Fri Aug 18 09:34:02 2000
This archive was generated by hypermail 2.1.8 : Tue Dec 02 2003 - 17:28:59 EST