Brother DP-525CJ Service Manual page 115

Troubleshooting
2) The test connector to be used in the echo-back test is indicated below.
(Output)
(Input)
(Input)
(Output)
(Input)
(Output)
(Input)
Machine Terminal
RTS
7
8
CTS
1
CD
4
DTR
6
DSR
3
TXD
2
RXD
3-52
SERVICE MANUAL
Test Connector
7
8
1
4
6
3
2
REPAIR