arp@mordor.UUCP (04/12/84)
++++++++++++++++++++++++++++++++++++ Before anyone starts cutting traces on their boards it should be noted that the 820 used a TTL monitor ie. seperate HS,VS,and VIDEO. If you do a bit of reading you will find that TTL monitors have no horizontal oscillator and require a 25-30 microsecond HS pulse to sync them while COMPOSITE monitors, having their own oscillator, require only a 5-8 micro- second HS pulse to trigger the oscillator. If you use a circuit to combine the sync and video signals to drive a composite monitor you should indeed use the shorter HS signal. This does not require any trace cuts since there are unused pins on J7 and an unused IC position on the board next to U34. I used that IC position for my combiner circuit and brought out the composite signal to an unused pin on J7. This gives both TTL AND COMPOSITE video output so you can use either type of monitor. I prefer the TTL type since it has a greater bandwith thereby giving a sharper display. The circuit I used appeared in the Oct. 6, 1982 Electronics Magazine page 113. Al Pierce L-276 P.O. Box 808 Livermore, Ca 94550