Bell System 177A Test Set

Introduction

The 177A test set is designed to monitor the voltage polarity and levels provided to the coin telephone set from any type of Central Office (CO), test desk, test console, test cabinet, line status verifier, or mechanized loop testing system.

The 177A test set Light Emitting Diodes (LED) respond to negative or postive potentials across the loop, or to either side of the loop to ground.  A third wire is also provided with LEDs for tip to ground tests.  Alternating Current (AC) and superimposed potentials can also be determined and identified.  The 177A test set may be used for monitoring on an in-service basis without interfering with the circuit operation.  It can also be used to determine trouble conditions when circuits are in the idle state.  Foreign Electromotive Force (FEMF) trouble conditions are readily identified without fear of burning the trouble condition clear.

Listed are sample test procedures and the signaling threshold required for Dial Tone First (DTF) service.  From this it can be determined the signaling application to be monitored.  The test set can be connected at the station, central office terminal locations, or any location where tip, ring and ground can be accessed.

Signaling Threshold for Dial Tone First

  1. Coin Present Test for Initial Deposit:  -48 VDC battery on the tip side with the ring side open.
  2. Stuck Coin or 5 Cent Overtime Test:  +48 VDC battery on the tip side with the ring side open.
  3. Transmission and Coin Deposit Readout on Local Call:  -48 VDC battery on the ring side of line and ground on the tip side.
  4. Transmission and Coin Deposit on Toll Call and Totalizer Homing Before Coin Control is Applied:  +48 VDC battery on the ring side of the line and ground on the tip side.
  5. Coin Return:  -130 VDC battery on the tip side of the line with the ring side open.
  6. Coin Collect:  +130 VDC battery on the tip side of the line with the ring side open.

Sample Test Procedures Using the 177A Test Set

Test Set Lead Connections

GREEN and RED from the 177A test set connecting cord to the TIP and RING of the line.  YELLOW lead from the connecting cord to the central office or station GROUND.





Dial Tone First Mode (Local Call)

Local Overtime Call

Test set connected to a DTF line appearance in the central office or at the station.

Step Action Verification
1 With handset on-hook. No. 1 LED (-48 VDC) lights brightly, indicating battery and ground from the line equipment.
2 Go off-hook. No. 1 LED (-48 VDC) goes dim, indicating battery and ground (dial tone) from the CO or test desk.  No. 5 LED may light (dim) on loops equipped with Dial Long Line (DLL) or Signaling Range Extenders (SRE).
3 Deposit initial rate and dial local charge number. No. 1 LED follows dial pulses.  At completion of dialing, No. 6 LED (-48 VDC) lights momentarily, indicating initial rate ground test.
4 Call answered. No. 1 LED (-48 VDC) now lit.

Automatic 5 Cent Overtime

Step Action Verification
1 At the end of 4-1/2 minutes. No. 4 and 5 LEDs (+130 VDC) light and go dark, indicating a coin was collected.
2 Trip hopper trigger to simulate local overtime deposit.   
3 At the end of first 5 minutes. No. 2 LED (+48 VDC) lights momentarily, indicating totalizer homing battery has been applied.  No. 5 LED (+48 VDC) flashes, indicating coin present test.

Dial "0" and Call (TSP, TSPS, Cord Board)

Step Action Verification
1 With handset on-hook. No. 1 LED (-48 VDC) lights bright.
2 Go off-hook.   
3 Dial "0" + (local charge number). Just prior to operator answer, No. 3 and 6 LEDs flash, representing coin refund.
4 Operator answer. No. 2 LED (+48 VDC) lights, indicating positive talking battery for totalizer homing.
5 Trip hopper trigger and request operator to collect. No. 4 and 5 LEDs flash once, indicating +130 VDC coin collect pulse.

continued...



Step Action Verification
6 Request operator to ring back and hang up. No. 1 and 2 LEDs glow following 20 cycle ringing supply, indicating ringing current applied.
7 Trip hopper trigger and request operator to refund. No. 3 and 6 LEDs flash once, indicating -130 VDC coin refund pulse.

Incoming Toll (Collect)

Step Action Verification
1 Have operator initiate call to coin test station. No. 1 or 2 LED lit prior to ringing.  Both diodes are lit during ring.
2 Go off-hook. No. 1 and 2 LEDs go dark.  No. 2 LED lights, indicating +48 VDC talking battery on line.
3 Request operator to identify deposit.  Deposit less than initial rate. No. 2 LED remains lit, totalizer homes, operator can identify deposit.
4 Request operator to refund. No. 2 LED goes dark, No. 3 and 6 LEDs flash, indicating -130 VDC coin refund pulse.  No. 2 LED lights.
5 Trip hopper trigger and request operator to collect. No. 2 LED goes dark, No. 4 and 5 LEDs flash, indicating +130 VDC coin collect pulse.
6 Request operator to disconnect circuit.   
7 Hang up. No. 2 LED goes dark.  No. 1 LED lights.

















Recycle

Step Action Verification
1 At coin station, block coin relay armature (non-operational).   
2 Lift handset.   
3 Deposit initial rate and dial a local test number for audible ring (busy). No. 1 LED lights, follows dial pulses.  Audible heard.
4 Hang up. No. 1 LED goes dark, No. 3 and 6 LEDs flash, indicating a -130 VDC coin refund pulse.  No. 5 LED lights, indicating +48 VDC stuck coin test.  No. 3 and 6 LEDs flash, indicating a second coin refund pulse.
5 Remove blocking tool. No. 1 LED lights.
6 Go off-hook, then hang up. No. 1 LED goes dark momentarily, No. 3 and 6 LEDs flash once, indicating a -130 VDC coin refund pulse.