Apple Data Modem 2400 Troubleshooting Guide

Main logic board of the Data Modem 2400 in its bottom case: (1) volume lever, (2) light pipe assembly, (3) speaker cable, (4) mounting screws (Apple Technical Procedures, Figure 7)

Apple serviced the Apple Data Modem 2400 by swapping modules: the power adapter, the main logic board and the speaker. Its tests are a power-on self-test, a communications check, an analog loopback test and the ModemTest diagnostic disk. Neither document gives a schematic or component values for the board.

Settings come first

Most modem problems turn up during installation. Others appear only at certain speeds, in certain modes or on certain telephone lines. The Data Modem 2400 has no switches for speed, parity, word length or duplex. All of them are set in software, and Apple notes that many modem failures come from a communications program (or, on an Apple II, an interface card) set differently from the remote system.

Apple warns that ModemTest fails a modem whose stored parameters are wrong, so a modem with bad settings can look like a modem with a bad board. If the modem will not connect to a bulletin board, reset its stored parameters to the defaults before doing anything else:

1. Hold down the mode switch on the front panel, between the two lights. Apple's procedure calls it the Select button.
2. Switch the modem off, then on again.
3. Release the button once the modem is on and the green light is lit.

Typing AT&F does the same from software.

Power-on test

At switch-on the modem lights the amber LED, runs a short self-test, sounds two tones and then lights the green LED. If it gets through that sequence it has power and has passed its self-test. Apple's flowchart for a modem that stops part-way:

Power-on faults (Apple Technical Procedures, Figure 11)

Symptom	Check or cure, in Apple's order
Amber LED does not come on	Check that the modem is plugged in and the power connector is firmly seated. If it is, replace the power adapter, then the logic board.
Amber LED on, but no two beeps	Turn up the volume lever, check that the speaker is connected, replace the speaker, then replace the logic board.
Beeps heard, but green LED does not come on	Replace the logic board.

The Service Source symptom chart says the same in shorter form.

Service Source symptom chart, Apple Data Modem 2400

Symptom	Cures, most likely first
Modem lights are not on	Replace the power supply; replace the logic board
Both lights on or blinking, or the yellow light stays on after power-on	Replace the logic board
No sound while the modem is operating	Move the volume lever towards the front of the modem; replace the logic board; replace the speaker

The Data Modem 2400's power socket is the same as the one on the Apple IIc and the AppleFax Modem. Their adapters fit it, but the modem will not power up from either of them; Apple says this does no damage. Check that the adapter is Apple's own, service part 600-0455, before condemning the logic board.

Line problems

Only the inner two wires of the RJ-11 jacks (tip and ring) pass through the modem. Some PBX systems use the outer pair for special features and misbehave with the modem in the line; Apple's advice was to give the modem its own line. The line and telephone-set jacks are not interchangeable, because the telephone-set jack is disconnected while the modem is in use. The two serial ports are not interchangeable either.

Communications test

This checks that the computer and modem are talking.

1. Load the communications software, turn on the computer and check the configuration settings.
2. Enter terminal mode, type AT and press Return. The screen should show OK.
3. If several tries give no OK, check the cabling and set-up against the owner's guide.
4. Check that the software or interface card is set to 300, 1200 or 2400 baud, with either 7 data bits and odd, even or no parity, or 8 data bits with 1 or 2 stop bits and no parity.
5. If it still does not answer, replace the main logic board.

Analog loopback test

The modem must be on a known-good telephone line for this test.

1. Connect the modem to the line and the computer, attach the power adapter and plug it in.
2. Turn on the modem, load the communications software and enter terminal mode.
3. Type ATS16=1D and press Return. The speaker turns on and you hear a dial tone or a high-pitched tone, and the screen shows CONNECT.
4. Type a short message. The modem loops the characters back, so if you can see what you type, the modem is working. Return may not move the cursor to a new line during this test.
5. Wait one second and type +++ to return to command mode. The screen shows OK.
6. Type ATZ and press Return to leave self-test mode. The screen shows OK.

If the loopback fails, confirm the telephone line works, then replace the main logic board.

ModemTest

ModemTest is Apple's disk-based diagnostic for the Data Modem 2400 and the Macintosh Portable's internal modems. It runs the modem's own self-test (RAM, ROM and microprocessor), command tests of each Hayes-compatible command, register tests, analog and digital tests, a speaker test that plays the tones for 0 to 9 followed by a carrier, a pass-through mode test and a ring detect test. It does not test the circuits that connect the modem to the telephone line. Apple checked those by calling a known-good system, normally AppleLink.

Set-up

Use any Macintosh except the 128K, 512K or 512Ke, a peripheral-8 (mini-DIN-8 to mini-DIN-8) serial cable, and a second peripheral-8 cable for the pass-through test.

1. Connect the power adapter to the modem and plug it in.
2. Connect the serial cable from the modem port on the Data Modem 2400 to the modem port on the computer.
3. For the ring detect test, plug one end of a telephone cable into a wall jack, but leave the other end free. Connecting it to the modem now gives unpredictable results.
4. For the pass-through test, connect the second cable from the printer port on the modem to the printer port on the computer.
5. Turn on the modem, boot the Macintosh, and run ModemTest from its floppy disk. Choose Data Modem 2400 in the Modem Selection window, tick the tests and click Start Tests.
6. When the ring detect test asks for it, plug in the telephone cable, wait about 30 seconds, then dial the modem's number from another telephone or modem.

A clean run ends with "All selected tests passed". A failure brings up an alert naming the module to replace.

When ModemTest itself misbehaves

• No communication with the modem: check that the serial cable is on the correct ports at both ends.
• The cursor freezes when the Test Selections window appears: replace the modem and retest. If it still freezes, try a different computer.
• Run ModemTest from floppy. ModemTest does not work under MultiFinder. To run it from a hard disk, switch to the Finder, remove third-party INITs and desk accessories, and make sure 12-point Monaco and 10-point Geneva are installed.
• For the final call, set the communications software to 2400 baud or below and to the port the modem is on.

Disassembly

Apple's take-apart needs a flat-blade screwdriver, a No. 2 Phillips screwdriver and an earthed mat and wrist strap.

Top case

1. Turn the modem off and disconnect the power, telephone and interface cables.
2. Push in the two plastic tabs at the back with the screwdriver until the top case lifts.
3. Lift the back of the top case up and forward until the latch at the front lets go.

To refit it, push down the front until it snaps in, then press each back corner down until its tab clicks. If the second tab will not go inside the bottom case, press it in gently with the screwdriver while pushing down.

Main logic board and speaker

1. Lift out the volume lever.
2. Lift out the light pipe assembly.
3. Disconnect the speaker cable.
4. Remove the two Phillips screws and their star washers.
5. Lift the main logic board out. The speaker then lifts out of the bottom case.

On reassembly, lay the speaker with its cable towards the right of the case, route the cable through the slot at the upper right of the board, and refit the screws before reconnecting the speaker. The light pipe has small clear tabs at the bottom front that go into holes in the case. Forcing the larger tabs behind them into the holes breaks the assembly.

Related pages

• Apple Data Modem 2400
• Apple Modems Documentation
• Apple Modem 1200