backflipper
Active member
Fault: Ball would not reverse direction when hitting the top of the screen in attract mode. When playing it would do the same but also there was no downward motion when the ball hit the bat.
Remedy: First off there are some really brilliant resources for pong out there now. After looking at the schematics I was first drawn to the 7474 flipflop at A2 as it will flop when the ball vertical position(VVID) and vertical blank are the same but after checking the output with my logic probe it was functioning properly.
I then looked at the inputs on the 7450 @ B6 and the input at pin 13 was constantly high. This made me think the flipflop @ B5 that feeds it had failed. So I removed it and replaced it but the fault persists.
I then removed the 7450 and it failed the test in my ABI with an input pulled high. So I ordered some modern replacements from Tesla in Bulgaria, fitted it an it works a treat.
So the 7450 @ B6 was the problem.
If anyone needs a 7450 I had to order 30 so I have a few spare.
I have attached a schematic which has been marked up with colour codes showing each section which was super handy.
backflipper2013-11-24 15:15:18
Remedy: First off there are some really brilliant resources for pong out there now. After looking at the schematics I was first drawn to the 7474 flipflop at A2 as it will flop when the ball vertical position(VVID) and vertical blank are the same but after checking the output with my logic probe it was functioning properly.
I then looked at the inputs on the 7450 @ B6 and the input at pin 13 was constantly high. This made me think the flipflop @ B5 that feeds it had failed. So I removed it and replaced it but the fault persists.
I then removed the 7450 and it failed the test in my ABI with an input pulled high. So I ordered some modern replacements from Tesla in Bulgaria, fitted it an it works a treat.
So the 7450 @ B6 was the problem.
If anyone needs a 7450 I had to order 30 so I have a few spare.
I have attached a schematic which has been marked up with colour codes showing each section which was super handy.
backflipper2013-11-24 15:15:18
