Base Voltage Generator Troubleshooting - ConMed Sabre 2400 Operators & Service Manual

DISPLAY MODE
1 Normal
2 Late
3 Early
4 Lockup
*on initial entry to Mode 4
feature not checked automatically is lockout,
which is extremely reliable due to its simplic-
ity. If the unit declares a HLP-4 error in RUN
mode, then the timing is incorrect. Select Late
Mode 2 to observe timing of both WDT one-shot
stages at their test points. Stage 1 should go high
for 16-20 mS after each WDSTR, and Stage 2
should run from 32-36 mS. Slight timing errors
are most likely due to a faulty timing resistor or
capacitor. Failure of the pulses to respond at all
are more indicative of an IC failure.
A HLP-7 indicates that the WDT did not shut
down RF when Stage 2 timed out. This may be
caused by failure of any of the components carry-
ing the WFAIL signal to the WFG and VBASE
circuits.
Most WDT faults can be diagnosed in
Diagnostics 1 using a simple logic probe, but
an oscilloscope will yield better timing measure-
ments. The general health of the WDT can be
confirmed with no instruments simply by observ-
ing the behavior of the Return Monitor Lamp in
the various modes.

4.7.4 Base Voltage Generator Troubleshooting

Remove all collector and base fuses on the A1
Power Board Assembly before checking a suspect
Base Voltage Generator (BVG). Enter the dIA
2 mode (see Section 4.6). Check that A2U11 is
producing the proper VDAC voltage at pin 2.
Do this by selecting the Monopolar Pure Cut
mode, and increasing the power setting from 0 to
300W . Monitor the pin to see that VDAC goes
from approximately 5.0 Vdc at 0W to 2.8 Vdc
WDSTR PERIOD
25.0 mS
38.0 mS
15.0 mS
25.0 mS
Table 4.8 dIA 1 Modes
RYLEN RETURN MONITOR ERROR
Unaffected Dark
Unaffected Flashing
Unaffected Bright
Set Dark*
at 300W . The VDAC voltage at 300W will vary
from unit to unit, the important factor is that the
voltage changes in small increments.
Next monitor A2TP6 and repeat the above proce-
dure. Confirm that TP6 voltage increases from no
more than 0.4V at 0W to approximately 5.0Vdc
at 300W . If it fails to do so, check that VSENSE
and ISENSE are both less than 0.6V (this is true
only if the PA fuses have been removed). Confirm
that A2D2, D3, and D8 are good.
Confirm that A2U12 pin 3 is approximately
3.42Vdc.
Other problem sources could be one of the resis-
tor divider chains in the BVG, a bad RFEN or
WFAIL signal. Also check that the other com-
ponents in the BVG chain are correct and func-
tional.
If the BVG performs correctly as tested so far, and
the Power Amplifier and Waveform Generator
both test good, proceed with the following test.
Turn off the unit, confirm that RFSUP has
dropped to less than 15 Vdc, and replace
the fuses in the PA. Reenter dIA 2 and select
Monopolar Blend. Monitor A2TP7 (VSENSE)
and slowly increase the power setting on the
front panel. When functioning correctly, TP7
will increase with power setting up to about 4
Vdc. At that point, there should only be a slight
increase in TP7 voltage. If TP7 fails to increase
towards 4V , do not proceed with this test; find
the failed components and repair them.
R
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