Printer spacing issue little bit of further testing

LOOKING FOR CAUSE OF LOW PULLUP OF -LINE SPACE LATCH AND FAILURE TO RESET

Yellow trace is the -Carriage CB which pulses as the carriage reaches the next vertical position where a print line would be placed. This pulse should cause the line space latch to reset. The green trace is +Line Sp Latch which goes down about one volt during the CB pulse then returns to full on. The purple trace is the -Line Sp Latch signal which is trying to pull up which is the action that will drop the latch. It only reaches about .5 V before falling back to zero when the CB pulse ends. 

TESTING BEHAVIOR OF THE 6250 CARD THAT PROVIDES THE PULLUP

While I don't have any schematics for the 6250 card, I do know the use of the pins on the card and the role in plays at various points in the printer controller logic. Three pins are pullup functions and hopefully the one I suspect will behave differently from the other two. If so, I can then trace out just the wiring of this pin and look for a bad component. 

CARD BEHAVED JUST FINE, NOT THE CULPRIT

All three pullup pins, B05, D05 and B10, deliver +6V as a pullup. The diode oriented circuits that these signals feed are actually insensitive to logic high input voltage. Thus, while +3 is the nominal logic high level, it can be 6, 9, 12 or more, up to the breakdown specs of the diodes involved. All that matters to those inputs is whether they are pulled down to ground through the diode, not whether there is a high voltage; even an open circuit is logic high to those gates. 

I used a debounced pushbutton on my digital testbench to pull the pin down to ground and watched the signals. All three pullup pins behaved exactly the same. I put a 5K resistor in series with the pushbutton, which caused all three to still work fine although the voltage was a bit above 0 due to the voltage drop of the resistor. 

I have swapped every other card involved in the circuit and this card only participates as a pullup. Not a problem on any card. All pins involved in the logic net have infinite resistance to +3, +6, -3 and ground power rails. 

There must be a hidden connection to some other net that is pulling this down to ground. I will have to keep probing.