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Noise Problem in C-DOT MAX-XL Exchanges

                In C-DOT MBM-XL Exchanges, when the equipped configuration exceeds 16 BMs, and more RBMs are configured without co-located BMs in the same IFC cards the following observations are noticed.

•          Disturbed ring back tone or furred R/B tone while dialing a c-dot subscriber from other exchanges.

•          Random Noise in inter BM calls.

•          Once IFC is made out-of service and bring  in service, then the noise is arrested for some time. 

•          Even though the C7 working is normal, threshold alarm for LS status appears in OOD.

Reasons:

•          More number of RSUs are equipped.

•          Only even numbered BMs are equipped as RSU and odd numbered BMs are equipped as co-located BMs.

•          In our network conditions, there are not so many co-located BMs as that of RSUs.

•          As the ODD number of BM positions are left vacant, Noise is getting introduced..

Solution: Certain engineering changes are to be implemented in the CM hardware

And they are explained below.

1. Loop Back Connectors:Unequipped co-located BM’s slots in the BTU of CM-XL are to be provided with this loop back connectors. These connectors need to be put in the unequipped BM slots. These connectors have to be put in the slots in the PSM or ESM cards where there is one equipped  and one unequipped BM are there. In case of PSM, it can be either the BM or even BM and in the case of ESM, it is only the odd BM slot.

2. ACP change: (ECP-ACP190/F-S02) The Z1 – BUS Terminator THT 330-470 RA (EHY-HMC00103-002) in the ACP card, which is sitting on the back plane of SSU should be changed to new part ERN-14103XXX-D10. All the 32 ACP cards are to be changed.

3.  EPLD Change in the ESM Cards:    The EPLD prom at position U14  having checksum 81D5 is to be changed as 6E2D.

            Buffers in PSM card:

Presently 74ABT821 is used in position U16 , U17 , U27 and U28 at the PSM card.

         These buffer ic’s are to be changed as 74FCT2821.

Similarly 74ABT821 at U42 , U43 , U46 and U47 at the ESM cards are also to be changed as  74FCT2821.

Loop Back connectors wiring details:

• Two numbers of 3 X 7 connectors are needed  to prepare one loop cable.

• c1 , a1 , b2 , b3 , c4 , a4 , a5 , c5 , b6 ,b7 should be shorted and to be connected to black wire and this black wire is  taken to pin c6 of connector 2  ( ground)

• b1 , c2 , a2 , c3 , a3 , b4 , b5 , c6 , a6 , a7 should be shorted and to be connected to red wire and this red wire is taken to pin a7 of connector 2  (VCC)

        Position of connector in the BTU Frame:

                Case :1 Odd BM equipped and Even BM not equipped

                                Connector 1 at B connector TAB 1 of respective back plane of IFC card.

                                Connector 2 at B connector TAB 4 of the above slot.

                Case :2 Odd BM not equipped and Even BM equipped (ESM card)

                                Connector 1 at A connector TAB 3 of the back plane of ESM card

                                Connector 2 at B connector TAB 4 of the above slot.

        NOTE: This ECN implementation can be done by yourself after procuring the materials in

                the market or get the help of C-DOT, Bangalore or C-DOT, New Delhi.