Re: Falcon on the launchpad.

Craig Sawyers <c.sawyers@...>

Does anyone have suggestions for how I should begin debugging
timebase A?
OK. First try free-running the timebase by setting the "Stability" control
fully clockwise. If there is still no trace when the "Horizontal Display"
switch is in the "A" position, then there is a fault in the A timebase
generator circuit. Here is what the manual says (you absolutely *must* get
a manual! It is the only way to ensure sanity with one of these units)

"No Horizontal Sweep
If the Time-Base "A" generator is not producing a sawtooth sweep voltage
when the Stability Control is adjusted for a free running sweep, some defect
in the generator is holding the Miller Runup circuit. Depending on the the
on-off states of the Disconnect Diodes V152 (6AL5), the Miller Runup circuit
may be held at either the high end or the low end of the sawtooth. The
manner in which it is held may be determined by measuring the voltage at the
Sawtooth A binding post. If the Miller Runup circuit is held at the high
end of the sawtooth the front panel binding post may measure about +300V; if
held at the low end the voltage at this point will measure anywhere between
ground and -20V, depending on the cause. If it rests at -20V, the trouble
probably is non-conductance of V152A, and it should be replaced. It could
also mean that R151 (1k, between pins 7 and 8 of V152) is open.

If the Miller runup circuit is held at the high voltage end of the runup,
replace V152 as it can mean that both heaters can be open or its cathode can
have low emission and give the same effect. Usually if V161 (6CL5) is not
conducting, B167 wil be glowing brightly.

In the event the front panel Sawtooth A connector voltage rests at +350V,
there is probably a plate to grid short within V173 (6DJ8); replace it.
When this occurs B167 glows brightly at the electrode attached to pin 6 of
V161. If this reverse conduction condition is permitted to contine for
longer than about 15 minutes it may be necessary to replace B167 with a new
neon glow tube. The reason for this is that B167 may be unstable

If the heater of V173 is open, both neon glow tubes will be glowing brightly
and there will be no sweep.

If all the tubes have been checked, then check for open plate or cathode
resistors in the Sweep Gating Multivibrator circuit, the Hold-Off circuit or
the runup CF circuit. Also check that the Stability control can vary the
voltage at the grid of V135A"

Good luck!


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