Modifications for the Kenwood TR-2400
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TR-2400
Volume Control Replacement |
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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, solder 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 path 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.
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TR-2400
Battery Charger Failure |
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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.
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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:
- Remove the three chrome and
one black Phillips head screws from the microphone
case.
- Seperate the case falfs and
remove the PTT switch, the microphone and the speaker
assembly.
- Carefully pry the brass clamp
from the SMC-24 cable assembly, and remove the hard
rubber bushing.
- Slide the SMC-25 bushing
(J42-0429-08) onto the cable and replace the brass
clamp.
- 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.
- 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.
- 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.
- 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.
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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.
- For RFI, bypass the B+
terminal to ground with a 100 uf cap.
- For excessive tone input to
the TR-2400, install a 100 K ohm resistor between the
encoder and the TR-2400 Tone input terminal.
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TR-2400
Unwanted Noise: Tone or burst at TX |
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For complaints of a tone burst
type noise, or simply a noise, at initial key down,
suspect either a broken loses 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.
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TR-2400
Display or Keyboard trouble |
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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.
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TR-2400
RX low, Intermittent, or distorted |
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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.
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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 frame
(below the PTT switch).
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TR-2400
Optional charge input protection |
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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:
- Si diode must be rated at
least 200 mA.
- Install carefully-don't short
the YELLOW B+ lead when reassembling.
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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.
- 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)
- Run a strip of cloth tape (nul
vinyl tape) approximately ˝ 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)
- When reassembling, make
certain the PLL unit does not inadvertently ground the
power switch tab. (Fig.3)
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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.
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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:
- Disconnect the battery pack
and remove from the unit.
- Remove the 4 case screws, plus
two battery pack compartment screws.
- Seperate the front and rear
halves of the radio. Do not tear wires!
- 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.
- Seperate the PLL and RX/TX
unit. Remove the fish paper insulation from between
the two boards.
TX RF noise:
- 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.
- 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:
- 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.
- 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.
- For reassemble, reverse step 5
through 1. If components where installed as specified,
there will be no clearance problems.
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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.
- Remove 4 rear case screws, and
2 screws from inside the battery compartment.
- Spperate front case body.
DON'T tear leads.
- Remove 2 small and three large
screws from the bottom edge of the Display unit. Save
the two small screws.
- Installing the three pan head
screws in place of the round head screws.
- 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.
- Secure the shield ground under
the small Philips screw located between the BUSY/OPEN
and S TONE switches.
- 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.
- Close the case and reinstall 6
screws.
Installation time for this shield
is approximately ˝ hour.
This
modification are sent to KB2LJJ by packet system
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Remember it is Illegal to transmit out of band. This Modification is for
Informational purposes ONLY.
Doing such modifications on your radio may void any warranty and damage your equipment.
All mods found on this database are offered to me by other amateur radio hams or captured by Packet system.
KB2LJJ take no responsibility or liability for any damage done resulting from any modification.
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