Hello, anyone know where I can find schematics to a Midland 79-290?
Thanks
CB Schematics?
-
cavemanmoron
- Donor
- Posts: 245
- Joined: Dec 25 2006, 17:45
- Real Name: Lee
- Contact:
-
316
- Wordwide & Qualified
- Posts: 1,462
- Joined: Jan 01 2007, 20:43
- Handle: 316
- Real Name: Skylar
- Antenna: Wilson 5K
- Radio: RCI 2950 and IC-7000
- Contact:
try this:
--------------------------------------------------------------------------------
STEP 1 Remove top and bottom cover.
STEP 2. Prepare a small gauge jumper wire Tin both ends.
STEP 3. Remove the 1K ohm chip resistor on the radio front panel (it is R306 see pic below for a diagram)
STEP 4. At the removed resistor location, solder the prepared jumper to the pcb pad nearest the center of the radio.
STEP 5. Solder a 1K ohm 1/8 watt lead resistor to the other end of the jumper (a 1/4 Watt will be OK).
STEP 6. Solder the free end of the resistor to the emitter lead (lead nearest the rear of the radio) of Q61 (which is the main voltage regulator).
STEP 7. Turn the radio over so the bottom of the pcb is facing up and the front is closest to you.
STEP 8. Locate chip resistor R63 (a 1 KOhm) and remove
Explaination:
The 8V RX only supply is removed from the clarifier by removing R306, the jumper that is attached to the pad supplies the clarifier with a constant 8V, this allows the clarifer to work in TX as well as RX, the 1K 1/8th watt resistor is installed to protect the power supply.
R63 is removed to......
(As you can see there is some text missing from above, it may be because some people can not find R63 and it may be due to a slight design change, if you can help with this let me know)
--------------------------------------------------------------------------------
Clarifier Modification Version 2
--------------------------------------------------------------------------------
This mod was posted on a foum I am a moderator on:
REMOVE: R306, R105, D27&27A
JUMPER: R305, D27A
R306 is 1Kohm & is located on front PCB, R305 is 6.8Kohm and is located on front PCB, R105 is on the Main PCB bottom, D27/27A is a three legged Diode located on the Main PCB bottom.
Prepare a 6" jumper wire and attach a 1/8 watt 10Kohm resistor to it (insulate the connection).
Connect one end to emitter of Q61 (leg nearest rear of unit).
Connect the other end to the solder pad nearest the center of the radio that was left vacant by the removal of R306.
Tune AM, LSB, USB with T14, 15, 16 to same location on clarifier.
Center clarifier by tuning can that is nearest front Main PCB left corner next to the crystal.
This transformer has different numbers in different production runs as do T14-16.
Once clarifier is centered it should slide 10KCs but may drop out on one end or the other so be careful!
The unit I modded put out a solid 25 watts PEP SSB and I did not do the NPC mod because it was not going to be used on AM very much.
BTW, you can increase the mic gain by changing the value of R138 to 150Ohms instead of 270Ohms, play with this value because too much gain will cause oscillation.
Good luck with all of this.
Take your time to study the schematic and the radio until you have identified all the components in the clarifier circuit before you begin the mod.
These radios are all slightly different depending upon time of their production run.
--------------------------------------------------------------------------------
240 Channels
--------------------------------------------------------------------------------
Press and hold "DW" and "9" then turn radio on. Select bands by using the "CH99" button. To set for 28Mhz to 29.7 Mhz press and hold "LCR" and "MIC" then turn radio on. To switch back to 40 channel mode repeat process.
--------------------------------------------------------------------------------
Modulation boost
--------------------------------------------------------------------------------
One Chip resistor R138 controls mic gain, decreasing the value of the resisitor increases the gain. Its best to use 270 Ohms, but the value can be as low as 150 Ohms.
CAUTION!!
If too much gain is used oscillation may occur.
--------------------------------------------------------------------------------
Various Mods
--------------------------------------------------------------------------------
These mods were posted on a forum I am a moderator on:
To disable the power limiter remove Q33.
NPC mod: Connect a 1N4001 diode/100ohm resistor in series.
The diode cathode(banded end) goes to the collector (center leg) of Q75.
The other end goes to the junction of R228 & R243.
Modulation limiter can be defeated by the removal of chip resistor R148.
Optional: Use VR10 to set the driver bias to 50ma.
Check that the final bias is at least 100ma.
Remember there are 2 finals. You will have to use a schematic to locate components.
--------------------------------------------------------------------------------
STEP 1 Remove top and bottom cover.
STEP 2. Prepare a small gauge jumper wire Tin both ends.
STEP 3. Remove the 1K ohm chip resistor on the radio front panel (it is R306 see pic below for a diagram)
STEP 4. At the removed resistor location, solder the prepared jumper to the pcb pad nearest the center of the radio.
STEP 5. Solder a 1K ohm 1/8 watt lead resistor to the other end of the jumper (a 1/4 Watt will be OK).
STEP 6. Solder the free end of the resistor to the emitter lead (lead nearest the rear of the radio) of Q61 (which is the main voltage regulator).
STEP 7. Turn the radio over so the bottom of the pcb is facing up and the front is closest to you.
STEP 8. Locate chip resistor R63 (a 1 KOhm) and remove
Explaination:
The 8V RX only supply is removed from the clarifier by removing R306, the jumper that is attached to the pad supplies the clarifier with a constant 8V, this allows the clarifer to work in TX as well as RX, the 1K 1/8th watt resistor is installed to protect the power supply.
R63 is removed to......
(As you can see there is some text missing from above, it may be because some people can not find R63 and it may be due to a slight design change, if you can help with this let me know)
--------------------------------------------------------------------------------
Clarifier Modification Version 2
--------------------------------------------------------------------------------
This mod was posted on a foum I am a moderator on:
REMOVE: R306, R105, D27&27A
JUMPER: R305, D27A
R306 is 1Kohm & is located on front PCB, R305 is 6.8Kohm and is located on front PCB, R105 is on the Main PCB bottom, D27/27A is a three legged Diode located on the Main PCB bottom.
Prepare a 6" jumper wire and attach a 1/8 watt 10Kohm resistor to it (insulate the connection).
Connect one end to emitter of Q61 (leg nearest rear of unit).
Connect the other end to the solder pad nearest the center of the radio that was left vacant by the removal of R306.
Tune AM, LSB, USB with T14, 15, 16 to same location on clarifier.
Center clarifier by tuning can that is nearest front Main PCB left corner next to the crystal.
This transformer has different numbers in different production runs as do T14-16.
Once clarifier is centered it should slide 10KCs but may drop out on one end or the other so be careful!
The unit I modded put out a solid 25 watts PEP SSB and I did not do the NPC mod because it was not going to be used on AM very much.
BTW, you can increase the mic gain by changing the value of R138 to 150Ohms instead of 270Ohms, play with this value because too much gain will cause oscillation.
Good luck with all of this.
Take your time to study the schematic and the radio until you have identified all the components in the clarifier circuit before you begin the mod.
These radios are all slightly different depending upon time of their production run.
--------------------------------------------------------------------------------
240 Channels
--------------------------------------------------------------------------------
Press and hold "DW" and "9" then turn radio on. Select bands by using the "CH99" button. To set for 28Mhz to 29.7 Mhz press and hold "LCR" and "MIC" then turn radio on. To switch back to 40 channel mode repeat process.
--------------------------------------------------------------------------------
Modulation boost
--------------------------------------------------------------------------------
One Chip resistor R138 controls mic gain, decreasing the value of the resisitor increases the gain. Its best to use 270 Ohms, but the value can be as low as 150 Ohms.
CAUTION!!
If too much gain is used oscillation may occur.
--------------------------------------------------------------------------------
Various Mods
--------------------------------------------------------------------------------
These mods were posted on a forum I am a moderator on:
To disable the power limiter remove Q33.
NPC mod: Connect a 1N4001 diode/100ohm resistor in series.
The diode cathode(banded end) goes to the collector (center leg) of Q75.
The other end goes to the junction of R228 & R243.
Modulation limiter can be defeated by the removal of chip resistor R148.
Optional: Use VR10 to set the driver bias to 50ma.
Check that the final bias is at least 100ma.
Remember there are 2 finals. You will have to use a schematic to locate components.
