When replacing the volume control in a TR-2400, certain precautions should be observed to insure against inducing new problems to either the control or the radio.

When installing a replacement volume control R05-2409-05, soolder the leads to the potentiometer sparingly, to prevent flux or solder from running down the tabs and into the joint between the tab and the deposited resistance material. If this precaution is not observed, future failure of the new control is possible.

Secondly, when reassembling the radio, tape insulate the PCB ground pathe directly adjacent to the power switch tabs on the volume control. This will prevent accidental shorting of the battery to ground, and loss of the B+ RF choke, L101.

Note:
Reference page 2, Service Bulletin #808, issued 2/12/80 for a picture of the PCB/Vol control insulation.



19-07-1998 TR-2400 Battery Charger Failure
Author: Trio-Kenwood Communication, inc.

The stock charger (W09-0307-05) supplied with the TR-2400 may be rapaired and/or tested as necessary.

Open circuit, the charger should deliver 18-20V. Current when charging sould be 45mA.

Contained in the charger, in series with the output is a 120 ohm 1/2 watt current limiting resistor. Under normal use (including momentary short circuit test) this part should not fail.

If you receive a charger with no output, the unit may be opened by fracturing the glued seam by a sharp moderate hammer blow. Place the charger on its side ofon a hard, flat surface. A layer of cloth at top and bottom will protect the case from marring. Strike the seam first on one side, and then the other. The case should open in two pieces.

Replace the 120 ohm 1/2 W resistor with a 1 W resistor. After replacing and before closing the unit, perform voltage and current checks. A spot of glue or cement at each corner will reseal the charger.



19-07-1998 Speaker Mic for TR-2400
Author: Trio-Kenwood Communication, inc.

The SMC-25 Speaker Microphone may be adapted for use with the TR-2400 by performing the following:

Parts Required:

Qty  Part No.       Description
1    E30-1628-08    SMC-24 Cable Assembly
1    J42-0429-08    SMC-25 Bushing

Procedure:

1. Remove the three chrome and one black Phillips head screws from the microphone case.
2. Seperate the case falfs and remove the PTT switch, the microphone and the speaker assembly.
3. Carefully pry the brass clamp from the SMC-24 cable assembly, and remove the hard rubber bushing.
4. Slide the SMC-25 bushing (J42-0429-08) onto the cable and replace the brass clamp.
5. Remove the SMC-25 cable assembly from the speaker, PTT switch and the microphone. Leave the small resistor (Parallel cap on some models) connected to the mic element for now. Also save the small black and the small brown wire from the SM-25 Cable.
6. Solder the white wire from the SMC-24 cable to one side of the resistor on the mic element and the small brown wire to the mic element at the other side of the resistor. The resistor and capacitor may now be removed.
7. Assemble the remaining components: Short black wire to center pin of PTT switch, red wire to switch common, Blue wire to one side of the speaker, and the remaining wires to the other side of the speaker (1 short brown, one long brown, and one short black.
8. Replace the back cover, and lapel clip, to complete the procedure.

Note: This change may be performed at the owners option and may not be performed in warranty.

In some cases, users may report RF interference, or motor-boating, when using a tone encoder in their TR-2400. A secondary complaint of excessive tone level may also be encountered.

1. For RFI, bypass the B+ terminal to ground with a 100 uf cap.
2. For excessive tone input to the TR-2400, install a 100 K ohm resistor between the encoder and the TR-2400 Tone input terminal.

For complaints of a tone burst type noise, or simply a noise, at initial key down, suspect either a broken losse component, or incorrect valued component on the RX TX unit.

On the RX TX unit, Q16 emitter, check C82, a 33 uf tantalum cap for broken connection.

If you find a 22 uf cap at C82 replace it with a 33 uf cap.



19-07-1998 TR-2400 Display or Keyboard trouble
Author: Trio-Kenwood Communication, inc.

Display

An intermittent or blank digit may be caused by either a broken lead, or intermittently shorting lead on the PLL unit.

On the PLL unit, look in the area of Q12, the touchtone generator. Between Q12 and the board edge locate the D1-D4 lines. Inspect this area for either an open (Broken) lead, or shorted (pinched) lead. Repair as necessary, and check lead dress before reassembly.

Keyboard

An intermittent or inoperative keyboard row or column may be caused by a torn or pinched lead, or a cracked diode.

Again, in the area of Q12, inspect the "T" and "Y" lines for shorts or open connections, and inspect diodes D19-D26 for physical breakage.

For any of the above complaints, suspect a broken loose component in the RX IF or audio output circuit on the RX TX unit. Simply pull up on the leads and resolder.

Adjacent to Q9, the audio output IC, find C49, a 1uf cap. If broken loose from the board, audio output may be down, while current consumption may be up from the normal 30mA to about 100mA due to the audio output amp oscillating.

Adjacent to L10, the discriminator, locate C33, a .033uf cap. If this component is broken loose, audio output may be up approximately 6 dB with excessive high frequency audio response.

Complaints of scratch audio, noise when flexing the antenna, or noisy audio when handling the unit during transmit may be remedied by tightening the Printed Circuit Board screws.

To disassemble the unit remove the back cover and battery compartment screws. INspec t the VCO shield solder points along the edge and bottom of the PLL board. Resolder if you find a broken solder bond.

Flex the metal frame several times to reseat the board, and retighten the board mounting screws. Be certain the flat metal spring has good tension when installed between the RX TX unit a fram (below the PTT switch).



18-03-2000 TR-2400 Optional charge input protection
Author: Trio-Kenwood Communication, inc.

Some users may request addition of a series diode to the Charge Jack to prevent inadvertent shorting of the battery pack if a voltmeter probe, headphone jack, or other conductor accidentally shorts across the external Charge Jack.
This can be used only for the standard wall changer. The optional fast chargers require battery voltage be available at the charge jack as feedback to the changer regulator.

Add a S1 diode in series with the battery changer line, at the Charger Jack. Observe battery polarity, as shown. Charging current will drop approximately 2 mA.

Note:

1. Si diode must be rated at least 200 mA.
2. Install carefully-don't short the YELLOW B+ lead when reassembling.

For intermittent or no offset, suspect as intermittent abort between the metal body of the REV NOR SW and an adjustment jumper on the PCB, or intermittent contact between the volume control metal body and the PLL PCB.

1. Disassemble the radio and inspect the board to the right of the REV/NOR SW. Using a small flat blade screwdriver or similar tool, gently pry the short metal jumper and the metal body switch tab apart. This should clear the offset trouble. (Fig.1)
   
2. Run a strip of cloth tape (nul vinyl tape) approximately ½ inch wide, across the top edge of the Display unit directly under the volume control. This will prevent the control using from intermittently touching the PCB and causing loss of offset functions. In similar manner, add insulation as shown at "B" and "C". (Fig.2)
   
3. When reassembling, make certain the PLL unit does not inadvertently ground the power switch tab. (Fig.3)
   

For apparent unlock, or either RX or TX failure, suspect not PLL unlock, but low RX or TX XTAL activity. Adding or replacing circuit components and returning the oscillator will cure the problem.

For NO RX

Suspect low XTAL activity for X3 on the RX unit. At Q1, add 7-12pF Base to Emitter. At Q5 replace L5, 22uH with a 15uH with choke, L40-1501-05. Adjust TC1 for 42.6 MHz in RX.

For NO TX

Suspect low XTAL activity for X2. At Q4, add 7-12pF Base to Emitter. Replace L15, 22uH with a 15uH choke. L40-1501-05. Adjust TC2 for exact 146MHz transmit frequency. At the base Q4, also check L2 for intermittent shorting against the Display unit mounting screw.



19-03-2000 TR-2400 pulse noise
Author: Trio-Kenwood Communication, inc.

For elimination of pulse type noise, either in receiver, include by the LCD oscillator, or in transmit, inducted by stray RF in the H.T., install additional chokes and a capacitor as detailed.

Disassembly:

1. Disconnect the battery pack and remove from the unit.
2. Remove the 4 case screws, plus two battery pack compartment screws.
3. Seperate the front and rear halves of the radio. Do not tear wires!
4. Unscrew two screws and two threaded retainers holding the PLL unit X50-1640-10. Slide the unit down to clear the three push switches from the top panel.
5. Seperate the PLL and RX/TX unit. Remove the fish paper insulation from between the two boards.

TX RF noise:

1. On the RX/TX unit, locate the battery ground (BLACK) lead soldered to the right edge of the PCB. Desolder this line and install a choke with ferrite bead L33-0632-05. Resolder along the bottom edge of the board, as shown.
2. Also on the RX/TX unit, locate the YELLOW lead attached to the foil aide of the charge jack J1. Install a .001uF capacitor across J1 to ground as shown.

TX or RX LCD pulse noise:

1. On the display unit X54-1480-10 locate the YELLOW lead marked B+. Resolder this lead and install a 1uH choke L40-1032-03 in series. Lead dress MUST be as shown for physical clearance.
2. Also on the Display unit, adjacent to the B+ lead, desolder the GREEN E (earth) lead and the BLACK E lead, and wire as shown to another 1uH choke, L40-1021-03. Again, observe physical parts placement for clearance.
3. For reassemble, reverse step 5 through 1. If components where installed as specified, there will be no clearance problems.

Some units may exhibit excessive background noise (up to several hundred Hertz deviation). This may be reduced or eliminated by installing an additional shield between the Display and PLL units.

This changes applies only to units between serial numbers 011xxxx and 101xxxx. Radios before this group (with a momentary REV switch) will not show improvement by addition of this shield. Refer to Service Bulletin #815 for this early group.

Units appearing with serial numbers after 101xxxx will have this shield factory installed.

Parts supplied:

N09-0627-05  Pan head screw    3 pcs.
F10-1627-05  Shield w/lead     1 pcs.

1. Remove 4 rear case screws, and 2 screws from inside the battery compartment.
2. Spperate front case body. DON'T tear leads.
3. Remove 2 small and three large screws from the bottom edge of the Display unit. Save the two small screws.
4. Installing the three pan head screws in place of the round head screws.
5. Install the shield foam towards the Display. Lift the protective plastic only enough to secure the shield with the two small screws. Cover the screw heads with the plastic film.
6. Secure the shield ground under the small Philips screw located between the BUSY/OPEN and S TONE switches.
7. When reassembling, the wiring harness must be positioned to the right of crystal X2 (44.1666MHz) or the case will not close correctly, and wires will be pinched.
8. Close the case and reinstall 6 screws.

Installation time for this shield is approximately ½ hour.