A

B

C

Cobra 148-DX (early)

Adjustments:
AM/FM S METER VR1
SSB/CW S METER VR2
SSB SQUELCH VR3
AM SQUELCH VR4
FM DEVIATION VR5
TX FREQ VR6
CARRIER BALLANCE VR7
RF METER VR8
DRIVER BIAS VR11
FINAL BIAS VR12
ALC VR12
AM POWER VR13
AMC VR14

Cobra 25 GTL/LTD/CLASSIC
SAMS PHOTOS: 207
AM LIMITER: D-9
POWER TWEAKS:
1. Change R76 (3.3k) to a 1k (located near mike socket)
2. Change R43 (10 Ohm) to a 2.7 Ohm.
3. Change R108 (1 Ohm) to a .47 Ohm.
4. Replace stock final with a 2SC1969 transistor.
5. Re-tune coils L10,L9,L8 for maximum forward power.
MODULATOR
PARTS NEEDED: 1- 220uF (16 to 25 volt) electrolytic capacitor.
1- 100 to 200 Ohm resistor. (1/4 to 1/2 watt)

ASSEMBLY:
1. Make sure your radio is peaked out.
2. Unsolder JP6 near final.
3. In JP6 holes, solder the 220uF capacitor. (negative side of cap. faces final)
4. On the solder side of the board, solder the resistor across the 220uF capacitor.
You can use different resistor values to get the desired dead-key.

VARIABLE POWER:
1. Find the two wires that are attached to the RF gain control, follow them to the PC board and UNSOLDER them.
2. Solder in a jumper wire from where you removed the wires on the board. This will restore receive.
3. Place the two wires from the RF gain control in your mod kit by soldering one wire to each of the 220uF capacitors leads.

REPAIR TIPS:
25 GTL:
1. Channel display reads all 7's or 8's: Leaky/shorted C104(470uF 10v). Replace with a 16v or 25v.
2. NO TX: Check for shorted 33uF(10v) capacitor across C87.
3. OVERMOD: Check D19,TR14,VR5
25 LTD
1. OVERMOD: Check D9
2. LED goes out and NO TX when keyed up: Check C118
25 LTD Classic:
1. Burned R89(15 Ohm 1/2 watt): Replace with a 1 watt.
2. OVERMOD: Check for missing or cut D9, missaligned VR5.

Cobra 29 GTL/LTD/CLASSIC
POWER TWEAK #1:
1. Change R58(10 Ohm) to a 2.7 Ohm.
2. Change R123(1 ohm) to a .47 Ohm.
3. Re-tune L14,L13,L12 for maximum forward power.
POWER TWEAK #2
1. Remove final and replace with a 2SC1969 transistor.
2. Remove R123 and replace with a jumper.
3. Replace C58 with a 180pF capacitor.
4. Re-tune coils.
CAUTION!!! I do not know if both of these power mods can be done at the same time!!!

SAMS PHOTOS: 217
AM LIMITER: D-11
MODULATOR AND VARIABLE POWER
ASSEMBLY:
The instructions are the same as the Cobra 25 above,EXCEPT the following:
1. Unsolder JP36 instead of JP6.

REPAIR TIPS:
29 GTL:
1. "Motorboating": Locate C242(.001)on pin 5 of TA7222 audio ic and move to pin 4 of ic.
2. Weak mic gain: Some raios have a 2SC372 mic amp. Replace with a 2SC945.
3. Receive on adjacent channel: Bad solder joint to C131 (next to 10.240 crystal).
29 LTD:
1. OVERMOD: Check D11
2. PLL dead, no TX or RX: Shorted C112
3. No TX/RX with Channel LED lit on RX and then goes out when keyed: Bad /shorted C119.
29 LTD Classic:
1. OVERMOD: Check D11. Missaligned VR4.
2. Internittent audio/modulation: Bad solder joints on pins 1&2 or 2&3 of audio ic.
3. TUNE UP TIPS: L11 is the TVI trap. DO NOT adjust!!! Stretching L12 gets moe output. L14 peak is about a turn or two up from factory original setting.

Cobra 148 GTL
POWER TWEAKS:
1. Remove TR24
2. Change R126 (10k) to a 2.2k
3. Change R124 (10k) to a 4.7k
4. Re-tune L37 and L38 for maximum AM forward power.
SAMS PHOTOS: 249
MODULATION: Cut R131
AM POWER: VR10
SSB POWER: VR11

CHANNEL TWEAKS:
I have found that the easiest way to do this without hacking your radio with a lot of switches is to install the EXPO 100 kit "L" expander kit.
This is an excellent kit and installs quickly with very little tools. This way you don't have to fumble around trying to remember which switch goes where, etc...

CLARIFIER:
1. Cut one side of R44 and D52. Remove R174 and solder a jumper wire in its place.
2. Follow the RED WIRE from the clarifier control to where it connects to the PC board and cut it loose.
3. Solder this RED WIRE to the circuit board ground.
NOTE: Some radios have a YELLOW WIRE instead of the RED WIRE.
4. Follow the ORANGE WIRE from the clarifier control to where it connects to the PC board and UNSOLDER it.
5. Resolder this ORANGE WIRE to pin 3 of the MB3756 regulator.
With any luck, you should slide about 5Kz down and 1Kz up.

COBRA 140,142 GTL , PRESIDENT P-400, UNIDEN WASHINGTON-(8719 PLL)

MODULATION: Remove R104 or TR32
AM POWER: VR6
SSB POWER: VR7
"RX" METER: VR1
"TX" METER: VR10
SQUELCH: VR2
TX FREQ.: VR3
CARRIER BAL: VR5
DRIVER BIAS: VR8
FINAL BIAS: VR9
MOD. METER: VR12

POWER TWEAK
1. Remove TR32
2. Replace R99 (10k) with a 2.2k
3. Replace R94 (10k( with a 2.2k
4. Re-tune coils L36,L37 for maximum forward AM power.

CLARIFIER:
1. Remove R187
2. Remove D36
3. Jumper D35
4. Follow the RED WIRE from the clarifier control to the PC board and UNSOLDER it.
5. RESOLDER this RED WIRE to pin 3 of regulator IC MB3756.
6. Follow the ORANGE WIRE from the clarifier control to the PC board and UNSOLDER it.
7. RESOLDER this ORANGE WIRE to the PC board ground.
NOTE: The Orange and Red wires may need to be reversed in some radios for this to work right.
8. Re-align center slot by adjusting CT3.
If all went well and you didn't smoke your radio, you should slide about 1 Kc up and 4 Kc down.

NEED MORE SLIDE??: Install a 5.6uH choke on the banded end (grounded end) of the varactor diode D37 or replace D37 with a super diode.

CHANNEL TWEAKS:

EASY TWEAK: Install EXPO 100 kit "B".
FOR THE DRILL HOLES ALL OVER MY RADIO LOVERS...:
1. Replace 11.1125 crystal with a 11.3258 crystal.
2. Isolate the ground pin 10 of the MB8719 PLL by cutting the PC trace.
3. At this point, turn your radio on and check to varify that all channels are locked in and working. If it is not, adjust these in the following order:
a. CT3 for USB.
b. L20 for LSB.
c. L19 for AM.
4. Install a SPST switch between pins 11 and 12 of the MB8719 PLL
5. Install a SPST switch across the cut you made to isolate pin 10.
6. Check all connections for shorts.
7. Check to make sure everything is working before you drill holes for the switches!

ROAD MAP:

SW1 / SW2 DOWN: NORMAL 1-40
SW1 UP / SW2 DOWN: (ch.15-27) 26.815 to 26.955
SW1 UP / SW2 UP:
1= 27.605 6= 27.505 11= 27.565 20= 27.525
2= 27.455 7= 27.515 12= 27.585 23= 27.575
3= 27.465 8= 27.535 13= 27.595
4= 27.485 9= 27.545 14= 27.605
5= 27.495 10= 27.555 16= 27.475
SW1 DOWN / SW2 UP: (ch. 1-40) 27.605 to 28.045

COBRA 2000 GTL
MODULATION: VR12 or Cut R131
AM POWER: VR10
SSB POWER: VR11
AM SIGNAL METER: VR1
SSB SIGNAL METER: VR2
SQUELCH: VR3
CARRIER BALANCE: VR4
TX FREQ.: VR5
TX METER: VR6
MODULATION METER: VR7
FINAL BIAS(50 Ma): VR8
DRIVER BIAS(25 Ma): VR9
POWER TWEAK:
1. Remove TR24
2. Replace R126 (10k) with a 2.2k
3. Replace R124 (10k) with a 4.7k
Re-tune coils L37,L38 for maximum forward power.

REPAIR TIPS:

Frequency counter eratic:
1. Find D528 (5.7v 1/2W zener) located in the freq. counter module.
2. Replace it with an NTE-136A 1 watt zener.

Transmit on SSB, but not on AM:
1. Find the regulator TR41 (2sc1419) and remove it.
2. Replace with a GE-66(10 amp) or an NTE-152 (7 amp)

Channel display glows dim after radio is shut down, freq. counter may be unstable
1. Find Fet-501 and Fet-502 located in freq. counter module and replace them.
Older models use: 2SK19GR
Newer models use: 2SK192A

CLARIFIER:
1. Remove R44 and D52.
2. Remove R174 and put a jumper in its place.
3. Follow the YELLOW wire from the clarifier control to where it connects to the PCboard and UNSOLDER it.
4. Solder this YELLOW wire to the PC board ground.
5. Follow the RED wire from the clarifier control to where it connects to the PC board and UNSOLDER it.
6. Solder this RED wire to pin #3 of MB3756 regulator.
7. Find the BROWN wire on the clarifier control UNSOLDER it, and tape it out of the way.

No smoke? Then you must have about 1Kc slide up and 5Kc down!

COLT RADIOS

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