Troubleshooting - Honeywell 7800 SERIES Manual

c. Start the system. Startup should be normal and the
main burner should light normally.
d. After the sequence is in the normal RUN period for
at least ten seconds with the main burner firing,
close the manual main and pilot fuel shutoff
valve(s) to extinguish the main burner flame.
e. The flame signal should drop below 1.25 Vdc
within .8 or 3 seconds (depending on the FFRT of
the amplifier) after the main flame goes out.
f. Safety shutdown will occur.
RM7890 SYSTEM DIAGNOSTICS
Troubleshooting control system equipment failures is
easier with the RM7890 self-diagnostics and first-out annun-
ciation. In addition to an isolated spst alarm relay (audible
annunciation), the RM7890 provides visual annunciation by
displaying the ALARM LED.
Self-diagnostics of the RM7890 enable it to detect and
annunciate both external and internal system problems. Ex-
ternal faults such as flame failures and false flame signals are
annunciated by a lockout of the RM7890 that energizes the
ALARM LED by using the optional Keyboard Display
Module or 7800 SERIES System Annunciation Diagnostics
and Troubleshooting, form 65-0118.
The RM7890 provides diagnostic information to aid the
service mechanic to obtain information when troubleshoot-
ing the system, see Table 6.
The optional Keyboard Display Module displays se-
quence status messages indicating: INITIATE, STANDBY,
SAFE-START CHECK, PILOT IGN and RUN. The select-
able messages also provide visual indication, current status
and historical status of the equipment such as: Flame Signal,
Total Cycles, Total Hours, Fault History, Diagnostic Infor-
mation and Expanded Annunciator Terminal Status (if used).
With this information most problems can be diagnosed
without extensive trial and error testing. Information avail-
able in the Diagnostic Information file includes: Device
Type, Device Suffix, Software Revision, Manufacturing
Code, Flame Amplifier Type, Flame Failure Response Time,
Selectable Jumper Configuration Status and Terminal Status.
Diagnostic Information Index
The RM7890 with the optional Keyboard Display Mod-
ule can monitor input/output terminals and can display the
status of the terminal at the VFD (e.g. Pilot Valve T8 ON<),
see S7800A1001 Keyboard Display Module Specifications.
A complete terminal description and terminal number are
provided. The display will show the actual status of the
CHECKOUT • TROUBLESHOOTING
IMPORTANT:
1. If the RM7890 fails to shut down on any of these tests,
take corrective action (refer to Troubleshooting,
RM7890 diagnostics and return to the beginning of all
Checkout tests).
2. When all Checkout tests have been completed, reset all
switches to original states.

Troubleshooting

terminal. If voltage is detected at the terminal, ON is dis-
played; but if voltage is not present at the terminal, OFF is
displayed.
Historical Information Index
The RM7890 has nonvolatile memory that allows the
Relay Module to retain Historical Information for the six
most recent lockouts. Each of the six lockout files retains the
cycle when the fault occurred, the hour of operation when the
fault occurred, and the fault message and burner status when
the fault occurred. The Historical Information can be viewed
by the optional S7800A1001 Keyboard Display Module.
SERVICE NOTE: A restart of an RM7890 can be accom-
plished by pressing the reset pushbutton on the RM7890,
or by pressing a remote reset pushbutton wired through an
optional Keyboard Display Module, DATA
CONTROLBUS MODULE™, Extension Cable As-
sembly, or Remote Reset Module. A power-up reset will
cause an electrical reset of the RM7890 but will not reset
a lockout condition.
SERVICE NOTE: Remove the access slot covers on the
sides of the Q7800A,B to check voltages.
CAUTION
!
Reinstall access slot covers on the Q7800A,B Sub-
base after performing voltage checks.
SERVICE NOTE: Maximum ambient operating tempera-
ture of a C7012E,F Series 1 through 6 will be reduced to
125° F because of the duty cycle operation of the
RM7890B Relay Module.
25
RM7890A,B,C
65-0126—2