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I believe you are correct, and that the problem is between the DDS-R and the DS0 DP, but unfortunately the DS0 DP STATUS LED only shows green for "Normal" or yellow for "In Test".
On the TA 850, go into MODULES, and then the DS0 DP module and look at STATUS. If it shows "All Zeros on Drop Side Yes" then the DS0 DP is not receiving the DDS circuit (instead it is all zeros), and it may be a simple wiring issue. If the "All Zeros" is YES, then try swapping the Tx and Rx pair from the DDS-R at the 66-block. You can also try doing a DDS loopback by shorting the Tx to the Rx, and having the Cisco connected off the OCU DP to verify the signal loops up going through all the equipment.
Took a look at the status on the DS0Dp card and it indeed shows all zeros on drop side as being "yes" I also swapped tx and rx to see if that changed anything and it didn't. It seems as if there should be voltage across the pairs measured tip - tip, ring - ring. When you measure the OCUDP end of the circuit, with the router unconnected there is 52v and with the router connected, 25V. And when you look at the OCUDP status within the channel bank when the router is connected you get a Yes for sealing current, and a No when the router is disconnected. When you measure on the office end of the circuit across the TX and RX pairs on the DS0DP, you get 0 volts. There is the typical 9.86 volts across the pairs on the Total Reach DDS-R.
Shouldn't there be voltage on the DS0DP pairs on the 66 block with nothing connected to it like the OCUDP card? This really seems to me that this is the problem. No matter what I do, we can't get rid of the "No DSU" light.
I have been in touch with our carrier network support, and have learned that the Total Reach DDS-R will not work with the DS0-DP/OCU-DP equipment used to extend the circuit. The NO DSU LED stays on at the Total Reach DDS-R because it doesn’t see terminated DSU/CSU connected to it. The DSU/CSU terminates the sealing current and basically give a path back so we see the sealing current coming back which extinguishes the NO DSU LED. The OCUDP/DSODP’s don’t do that.
Th final word is that you cannot use the DS0-DP/OCU-DP to extend a circuit being dropped off from a Total Reach DDS-R.