Waveform Generator Troubleshooting; Aspen Return Monitor (A.r.m.) Troubleshooting - ConMed Sabre 2400 Operators & Service Manual

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After successful testing of the VSENSE circuit,
connect a 300 ohm 250W load resistor to the
unit's RF outputs. Select Monopolar Pure Cut
and slowly increase the power setting while
monitoring TP8. The dc voltage at TP8 should
increase as power increases, but should not exceed
4.2 volts at full power.
Units that have passed the troubleshooting steps
so far should be checked for properly oriented
diodes, mismarked resistors, and correct divider
voltages. If the unit has passed these BVG checks,
then the problem is likely elsewhere.

4.7.5 Waveform Generator Troubleshooting

Remove the base and collector fuses from the
Power Board Assy before checking a suspect
Waveform Generator (WFG). Enter the dIA
2 mode (see Section 4.6.1.) Check that a 10.0
MHz clock appears at A2U25 pin 12. Select a
power setting and mode that corresponds to the
photos in Fig. 3.2 and confirm the waveforms are
similar to that at TP23 (use TP14 to trigger the
oscilloscope to get comparable results). If they are
not, suspect one of A2U23-U27 or U29 as being
bad. Another problem could be in the waveform
select lines WV0-WV7.
4.7.6 Aspen Return Monitor (A.R.M.)
Troubleshooting
The overall functionality of the A.R.M. cir-
cuitry may be checked by selecting DUAL
FOIL in Run Mode and connecting an accurate
decade resistance box or selected resistors to the
Return Electrode Jack on the output panel. If
the Resistance Indicator vs. resistance appears
to match Figure 3.1, then the circuitry may be
assumed to be operating properly.
If this test passes, but the unit still declares a
Return Fault in operation with the ESU activat-
ed, interference from electrosurgical current is the
4-18
likely cause. Check the A1T5 shield lid for
good electrical and mechanical contact with the
shield cup, and capacitors A1C55 and C56 for
proper value and connection. Also check bypass
capacitors A1C65, A2C27 and low pass filter
capacitor A2C23.
If the Resistance Indicator vs. resistance test fails,
check 2VARM at A2TP13 with 10 and 150 ohms
connected to the Return Electrode Jacks. With
10 ohms connected, 2VARM should be +0.88 to
0.98 Vdc and with 150 ohms, it should be +1.89
to 2.18 Vdc. 2VARM should also be twice the
voltage at VARM (A2TP12). If this test passes,
then the trouble is most likely in the A2U15, one
of the resistor values, or A2D11.
If the VARM vs. resistance test fails, check the
dc current source U15 and D11, by connecting
a dc milliammeter from A2TP12 to ground. The
meter should read from 0.47 to 0.53 mA. Read
the dc voltage across D11. It should be approxi-
mately 1.235 Vdc.
If VARM test reads near zero and the dc current
is low, check for a short circuit in the harness,
shorted bypass capacitors, or shorted transistors
A1Q14 or Q15.
With the Return Electrode Jacks open-circuited,
check the waveforms on the A.R.M. oscillator
collectors, A1Q15 or Q14. They should appear
as half-wave rectified sine waves with a frequency
of 34.5 - 38.1 KHz. If the frequency is too high,
A1C53-C56 may be open. If the circuit is not
oscillating and VARM is 0.6 - 0.8 Vdc, check the
feedback resistors A1R49 and R50, transformer
A1T4 for opens or shorts and transistors A1Q14
and Q15 for opens. If the circuit is oscillating
at the correct frequency but VARM does not
respond to resistance changes, check the cir-
cuitry from the secondary to A1T4 to the Return
Electrode jacks for shorts or open circuits.