Lcd Display Is Blank - A.O. Smith 100 Series Service Handbook

DISPLAYED MESSAGE/CONDITION/INDICATES

LCD Display Is Blank

The LCD on the UIM is not showing any data.
Possible causes for this include:
• On/Off switch is turned off.
• Tripped breaker - blown fuses.
• 120 VAC power supply problems.
• 24 VAC power supply problems.
• Defective transformer.
• Wiring or plug/socket connection problems.
• UIM communication cable defective.
Important Service Reminder:
When performing any troubleshooting steps outlined in
this manual always consider the wiring and connectors
between components. Perform a close visual inspection
of all wiring and connectors to a given component before
replacing any electrical part or component.
Servicing should only be performed by a Qualified Service Agent
CHECK/REPAIR
• Ensure the Boiler's on/off switch is in the "on" position
and is working properly and supplying 120 VAC to the
on/off power relay coil - replace switch if defective.
• Ensure the on/off power relay contacts are closed,
see Figure 10 on page 17. Check for 120 VAC between
terminals 8 and 9 on the PDB's TB1 terminal strip -
replace relay if defective.
• Ensure the circuit breaker/fuses is supplying power to
the Boiler.
• Ensure 7.5 amp fuse on MCB is not blown/missing -
replace fuse, see page 20.
• Check communication cable connections between
the UIM and the MCB's Internal Comm Ports. Plug
the UIM communication cable into the other Internal
Comm port on the MCB, see page 25. Ensure the
communication cable IS NOT plugged into one of the
External Comm Ports.
• Turn off power to the Boiler and install a new
communication cable (standard Cat 5/6 network
cable) between the UIM and the MCB's Internal
Comm Port, see page 25.
• Closely inspect communication ports on MCB and
UIM for damage or wear.
• Ensure 120 VAC power is properly connected in the
junction box on the back of the Boiler.
• Ensure 120 VAC is supplied to TB1 terminals 8 and
9 on the PDB. Hot wire to terminal 8, neutral wire to
terminal 9, see page 29.
• Ensure F3 fuse on the PDB is not blown/missing -
replace fuse, see page 30.
• Check for 120 VAC to transformer at the primary
winding terminals on the transformer.
• Check for 120 VAC at the PDB J1 Socket pins 3 and
6 that supply power to the transformer, see page 31.
• Check wiring between PDB J1 Socket pins 3 and 6
and the primary winding on the transformer - repair/
replace any disconnected or damaged wiring.
• Check for 24 VAC output at the transformer
secondary winding terminals - if 24 VAC is not
present AND the checks above were performed and
the results were successful - replace the transformer.
Check all primary and secondary transformer wiring
for shorts before powering up the new transformer.
• Check for 24 VAC between pins 1 & 2 and between
pins 4 & 5 of the J1 Socket on the PDB, see page 31.
Perform this test with the wiring harness plugged into
the J1 Socket.
• Ensure the pins in the J1 Socket/Plug on the PDB
are in good condition and making good contact, see
page 31. Repair or replace any parts that are worn,
damaged, or failing to make a good connection.
• Call the toll free support phone number on the back
cover of this manual for further assistance if the
problem has not been corrected after performing the
procedures outlined here.
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