tech: Do I need a pull up resistor.

[John Bennett]

Hi

I am fixing an original Galaxian PCB. I have nearly fixed, just down to three faults;

There is a graphics glitch on the missile sometimes and on scrolling text (i.e. the points on the attract screen).

I managed to track this down to the 74ls273 @ 4L, I piggybacked the chip and the fault was fixed. So assuming the outputs weren't strong enough I removed the chip and replaced it expecting a new chip to solve the problem.

However the new socketed chip displayed the same graphic glitches, when I piggy back this new chip the problem goes away!.

I am guessing that the outputs aren't strong enough (no ossci) do I need a 'pull up resistor', or should I just solder on the piggy back?.

Thanks

Rob

DATA Imported from archives: originally posted by Rob Walmsley (rob@walmsley.ws)

 

[cliff_poole]

Rob,

Are you only having the trouble with certain outputs ?, I would
suspect the next device in the line. Do you have a 'scope to look at the
outputs with ?, are the levels really too low in voltage or are you seeing
spurious harmonics or peaks ?.

Cliff.