Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 244)

A N 9 3
244 Rev. 1.3
 Connect Evaluation Board to Prototype System
Completely disconnect the embedded modem from the host interface in the prototype system. Connect the
ISOModem evaluation board to the host interface using JP3 as described in the ISOModem evaluation board
data sheet section titled Direct Access Interface. This connection is illustrated in Figure 40. Be sure to connect
the evaluation board ground to the prototype system ground. Power up and manually reset the evaluation
board, then power up the prototype system and send AT<CR>. If an OK response is received, make a
connection to the remote modem as in the previous step. If no OK response is received, debug host interface
and/or software. If a connection is successful, go to the next step to isolate the problem in the prototype
modem.
An alternative approach is to connect the prototype modem to the ISOModem EVB motherboard in place of the
daughter card and use a PC and HyperTerminal to test the prototype modem. See Figure 41 for details.
10.1.5. Isolation Capacitor Troubleshooting
Connect the evaluation board isolation capacitor to Prototype Modem Si3018/10. Remove C1 on the evaluation
board and on the prototype system. Solder one end of the evaluation board, C1, to the ISOmodem-side pad
leaving the other end of C1 unconnected. Next, solder a short jumper wire from the unconnected side of C1 on the
evaluation board to the Si3018/10-side C1 pad on the prototype system. This connection is illustrated in Figure 42.
Connect the phone line to the prototype system RJ-11 jack.
Power up and manually reset the evaluation board, then power up the prototype system. Attempt to make a
connection using the host processor and software, the evaluation board ISOmodem, and the prototype system
Si3018/10 and associated external components. If this connection is successful, the problem lies with the PCB
layout, the external components associated with the ISOmodem or the ISOmodem device itself.
If the connection attempt is not successful, the problem lies with the Si3018/10 and/or associated components.
Proceed to “Si3018/10 Troubleshooting”.
This diagnosis can be validated by connecting the Host ISOcap capacitors to the Si3018/10 on the evaluation
board as shown in Figure 43.
10.1.6. Si3018/10 Troubleshooting
Start by measuring the on-hook and off-hook voltages at the Si3018/10 pins with respect to IGND (pin 15).
Compare these voltages to those in Figure 44. This may indicate an area of circuitry to investigate further using the
Component Troubleshooting techniques in the following section. The voltages measured should be reasonably
close to those in the figure.
If any of the on-hook or off-hook Si3018/10 pin voltages are significantly different than those in Figure 44 and
nothing seems wrong with the external circuitry after using the Component Troubleshooting techniques, replace
the Si3018/10.
10.1.7. Component Troubleshooting
A digital multimeter is a valuable tool for verifying resistances across components, diode directions, transistor
polarities and node voltages. During this phase of troubleshooting, it is very useful to have a known, good
ISOModem evaluation board to compare against measurements taken from the prototype system. The resistance
values and voltages listed in Tables 148, 149, and 150 will generally be enough to troubleshoot all but the most
unusual problems.
Start with power off and the phone line disconnected. Measure the resistance of all Si3018/10 pins with the
Ohmmeter’s black lead on pin 15 (IGND). Compare these measurements with the values in Table 148. Next,
measure the resistance across the components listed in Table 149 and compare the readings to the values listed in
the table. Finally, using the diode checker function on the multimeter, check the polarities of the transistors and
diodes as described in Table 150. The combination of these measurements should indicate the faulty component
or connection. If none of the measurements appears unusual and the prototype modem is not working, replace the
Si3018/10.