AT&T UPAM-K 9, Default Timer Modifications, Important Centrex Modification

Installation Manual

Default Timer Modifications

Inhibit default timer

A field modification is available to inhibit the default timer. Do not inhibit the timer if jumpers

have been removed as outlined in

Important Centrex Modification,

below, and the VOX delay timer has

been disabled

(S5

is OFF). This situation may cause the UPAM to remain off-hook indefinitely.

Also, do

not inhibit both timers unless the station line has CPC capability.

Some older UPAM equipment may not have jumper J3 (refer to the illustrations on page 11 to

determine the revision level of the pc board and the location of the jumpers). Do not inhibit the default

and VOX disconnect features and rely solely on CPC to provide disconnect control on these models. If

this is unavoidable, then replace the UPAM with one showing a date code of 90A or later. (The date code

is the first two numbers and letter of the unit’s serial number, printed on a sticker on the rear panel of the

unit. The code is also stamped on the outer carton below the UPAM-K name.)

To inhibit the default timer, proceed as follows (note that the other disconnect methods are still

available when the default timer is inhibited):

Open UPAM by removing 4 screws. Lift cover straight off while tilting up the left side of the cover to

clear the punch block.

Locate and remove capacitor C4 mounted in a 2-pin socket on the upper left corner of the printed

circuit board (refer to the illustrations on page 11 for the location of the capacitor).

Replace the capacitor with the 10kilohm resistor (color code: brown-black-orange) supplied in the

parts bag. The parts bag is either taped to the inside cover or wedged between a large capacitor and

the upper right-hand corner of the chassis. Bend and cut the resistor wire as shown below.

Replace the cover and screws.

Changing default time

To change the timing of the default timer, replace component C4 (located in the upper left-hand

corner by the transistor with the black heat sink) with the 100

µF, 6.3V Tantalum capacitor supplied in the

parts bag located inside the UPAM enclosure. This capacitor will change the default time to 17 seconds

minimum to 2 minutes maximum. First follow steps 1 and 2 above and then install the capacitor by cutting

its leads to approximately 1/4 inch and inserting into the socket at C4 so that the lead marked with a ( + ),

or with a vertical bar is in the lower socket hole, as shown: ¼"

Important Centrex Modification

Some phone systems (in particular, Centrex-type systems) may produce open-switch-intervals

(OSIs) when the UPAM first answers the line. OSIs are short breaks in loop current resulting when the

central office switches equipment on and off the line. The UPAM may misinterpret these OSIs as

disconnect signals. It may be necessary to remove jumpers

and

from the printed circuit board (see

the illustrations on page 11 for the location of these jumpers) if the UPAM exhibits any of the following

symptoms during station mode operation. Do not remove the jumpers unless you are confident that

an OSI problem exists, and the UPAM has been verified as functional by following the troubleshoot-

ing procedures in Section 4.

Symptoms:

UPAM disconnects from the line immediately after answering.

2. UPAM answers and remains connected to line but the page audio does not come through the paging

system. This condition is verified if the UPAM external contact closures are still open during a page.