TROUBLESHOOTING THE SX20


Dead system
Voltage test points and limits
Weird problems
Trunk problems
Extension Problems
Console Problems

Completely dead
Lightning can kill systems - always confirm that this is not the case.

In the first instance check that power is reaching system - disconnect the mains lead and plug into a kettle or any appliance that uses a similar lead.

Then switch on and see if display on system cabinet flashes ???????? during start up.  Yes   No

If the display flashes OK - check to see whether the system clock starts after about 30 seconds.  
If the system clock shows 00:00 then check the first extension for dial tone.  The picture below explains what the LED's are on the system display board.


If no dial tone - do you have transmission?
Does the console work?

Check the system voltages on the system backplane.  Also check the circuit breakers (one is inside the PSU).
If voltages are not right then remove all cards from the system and check the voltages again.  If they are correct then replace the cards one at a time, checking the voltage each time a card is replaced.  Do not remove or insert the CPU or MISC cards without switching off the power.

The pictures below show the voltage test points on the backplane and the voltage limits.

Now, with only the CPU and MISC cards in the system, power up the system and watch the display (ensure that cards are pressed well home - make sure card handles are laying flat when inserting the cards).  If 00:00 finally comes up then the system cards should be OK.  Now start replacing the extension cards and see if these drop the system.

The picture above shows the correct positions of all cables and ribbons.

If the customer database has been lost then remember to default the system before inputting customer changes.

Loading Default data

  1. Open cover
  2. Set CPU switches 1 - 8 to required positions
  3. Set battery switch on PROM board to ON (PROM board is fitted to CPU card)
  4. Turn power on
  5. Set CPU switch 8 on CPU card to closed
  6. press RESET button (below DIP switches on CPU card)
  7. Console display shows 88888888
  8. Console display shows ????????
  9. Within 6 seconds set CPU switch 8 to open
  10. Console display shows --------
  11. Set CPU switch 8 to closed
  12. Console display shows 00-00
  13. Default Data has been loaded

CPU DIP switch settings

OFF ON
1 Wall mounted
2 Diagnostic inhibit
Always closed 3
Always closed 4
Always closed 5
Port 1 normal extn 6 Port 1 test extn
3 digit extn range 7 2 digit extn range
review only customer data 8 data access allowed

Weird things happen after a power outage
RAM batteries are most probably dead or low voltage.  Check with a multimeter and replace if dead or of low voltage.  After replacing the system will have to be defaulted and all the customer programming retyped.  Remember to switch the batteries on after placing the RAM board onto the CPU card (switch is under RAM board - slide switch).

Extensions dead
If all the extensions on one card are dead then the most probable cause will be the cable plug having fallen off of the card connector or jumped out of the MDF connector.  The connector at the MDF end should have a cable tie around the cable end of the connector.  At the system end ensure that the clamp plate behind the fan is secure and clamping the cables.

Trunks don't work
If a loop line then the usual cause is a line reversal or line fault on the network providers line.  Prove the line reversal by reversing the trunk wires on the MDF.
If an earth calling trunk then the most usual cause will be a line reversal.  Reverse the A & B wires and test the trunk.  Remember - if you use a test telephone to check the line, then an earth must be temporarily connected to the line to get dial tone.

Console problems
If the console is dead then check that the console cable connector is pushed home in the base of the console and that the cable (where it leaves the console casing) is fixed to the console with a cable strap.

If the handset cord breaks or is partially broken then the console will stay on Night Service and no buttons will work.

If the console is dead then an MF telephone can be used to do programming changes.
Use port 1 and set the CPU switch 6 to ON.