Troubleshooting Table - Welch Allyn SureTemp 986 Service Manual

3. Troubleshooting
3.2

Troubleshooting Table

Symptom Possible Cause
No operation Dead batteries, no batteries,
battery missing, battery
incorrectly installed
Broken battery wire
Short circuit preventing
operation
Failed component
Display LCD frame loose
problems
Dirty LCD elastomeric
conductor strips
Failed Component
Cracked LCD
Display Microprocessor failure
problems
(Continued)
No beeper Defective horn
sound
Broken connection
Defective U1
Normal/Monitor
Ambient above 33.9
Mode switching
(93.0
problems
22
If the unit fails to operate properly after completing the suggested
procedure listed in the following table, contact Welch Allyn
Customer Service at 1-800-535-6663.
°
C
°
F)
Procedure
Refer to Battery Removal and Replacement
section on page 15. Check that all batteries are
installed in proper direction.
Reset electronics. (See Instrument Reset/Self
Tests section on page 6)
Open instrument case, install batteries, check
for voltage on main PCB at battery wire
connections.
Remove batteries, press mode button 5
seconds, set DMM to Ohms, measure
resistance of electronics at battery contacts
("+" to bottom right corner, "-" to top left corner)
Resistance should climb to more than 2 Mega
ohms as C25 charges.
Check oscillator at U1-68 for 2.4975 MHz sine
wave. If not present, suspect X1, U1, C6, and
C7.
Check that all 3 plastic hooks for the LCD
frame are tight and not broken. The frame
should not be lifting off of PCB.
Remove LCD frame by unlatching plastic
hooks. Clean LCD elastomeric strips, LCD
glass contacts, and PCB contacts with lint
proof cloth dampened with alcohol.
Check R17 for open component
Inspect LCD for hairline cracks
Check for improper soldering of pins, crystal
operation on O-scope, proper reset.
Replace horn.
Check continuity from U1-50. to horn pin 2 and
from ground to horn pin 1.
Check for signal with O-scope at U1-50.
Replace microcontroller U1.
Will cause auto switch to Monitor mode.
70995-0000B M986