2120 Multiplex
B$implex
FABT McCulloh
Loop
Board
Trouble Isolation Procedure
Disconnect electrical power when making any internal
adjustments or repairs. Installation and servicing
should be performed by qualified Simplex Representa-
CAUTION
POWERING REQUIREMENT
When removing power from this system, disconnect
batteries FIRST and AC powar last. When connecting
power to this system, connect AC power FIRST and
batteries last.
This publication provides trouble isolation procedures for the FABT McCulloh loop board.
The McCulloh loop board is used on FABTs to provide McCulloh loop (Class A) operation for FABT monitor point
circuits 1 through 4. Monitor point 5 on the associated FABT is used to report McCulloh loop troubles; monitor
points 6 through 8 may be used as normal.
Because of the way that the McCulloh loop board operates, a special procedure is required to locate the McCulloh
loop monitor point that is actually in trouble. (The BMUX only knows that there is a M,cCulloh loop trouble being
reported by an FABT.) This procedure is outlined below.
IMPORTANT!
Before proceeding, notify appropriate building personnel and local authorities (fire department,
etc.) that you will be working on the 2120 system.
UPON RECEIVING A MCCULLOH LOOP TROUBLE REPORT:
1. Determine which FABT reported the McCulloh loop trouble via the BMUX trouble report.
2. Go to that FABT and observe the McCulloh loop board.
3. Look at the LEDs on the McCulloh loop board just located to isolate the troubled zone(s). LED 1
indicates trouble on monitor point 1; LED 2 indicates trouble on monitor point 2; etc.
4. Repair the trouble in the indicated monitor point circuit’s wiring.
5. Press the BMUX DETECTOR RESET pushbutton.
6. The McCulloh loop trouble will clear, and the McCulloh loop board will resume normal operation.
IMPORTANT!
There are two versions of the McCulloh loop board that you may encounter:
l
The 562-318 McCulloh loop board,, used only with 562-312 FABTs. This board is now
obsolete.
l
The 562-550 McCulloh loop board, used only with 562-531 FABTs.
Although these two McCulloh loop boards look the same,
THEY ARE NOT INTERCHANGEABLE!
Ed 9 86
0
1966
Simpler Tlme
Recorder Co.. Gardner, Mass. 01441.0001 U.S.A.
MUX2-61-001
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