(3) Troubleshoot using a procedure from column three of the troubleshooting
guide. Use the schematics to locate the area of the unit where the cause of the problem is
likely be found.
Continue to use the chart and schematics until you find the malfunction.
Decide what corrective action should be taken (column three).
b. Locate the Cause of the Malfunction (Example 1). SYMPTOM: The
monitor/defibrillator is attached to the heart rate output tester via a five lead patient cable
with 60 bpm selected. There is a flat line (trace) displayed on the CRT. The heart rate
meter is not counting, but the 1mv calibration button shows a square wave on the CRT
when it is depressed.
(1) Identify malfunction (column 1). Notice that a similar problem exists in
section 16.1.4 (Trace present but no QRS. Rate meter not counting).
(2) Select a probable cause (column 2). You suspect the problem is caused
by the patient cable (number 1).
(3) Troubleshoot (checking procedure--column 3). You replace the cable with
a known good patient cable either from another working unit or from stock. However, the
symptom is still present. Therefore, you refer back to the Probable Cause column to
select another probable cause.
(4) Select another probable cause (column 2). You suspect the problem is in
the monitor circuitry prior to the QRS signal separating into the CRT circuit and the heart
rate counting circuit, but before the 1mv calibration circuit. You refer to the C7-B8 section
(U101 and U102) on the monitor schematic in Appendix B. The problem is probably with
U112 or U101 (number 3).
(5) Troubleshoot (checking procedure--column 3). Check for 1.25v QRS on
pin 8 of U101. With an oscilloscope referenced to a ground, you expect to see a 1.25v
QRS signal at U101 pin 8. You discover this signal is not present. Follow the circuit back
to U101 pin 7. You expect to read a positive going triangular shaped 1.2v wave. Again,
this signal is not there. You follow the circuit back U101 pin 1. You see a QRS wave on
the oscilloscope and trace it through the shaper network and back into U101 pin 5. It is
present at U101 pin 5, but not at pin 7.
(6) Determine corrective action (column 3). You should replace the faulty