[Technical question] Colt 480 needs repair
 

Hello,

I bought an old Colt 480 to use in my car (40 channels, AM/SSB,
Circuit Board PTBM048A0X, pll-02A, 2sc1969 final) but it doesn't work.
Here are the symptoms:

1. When I turn on the radio, it seems to change frequency during a
couple of second before it stabilize.

2. The red led light up on transmit but there is no power on the
built-in meter nor on my external meter. I can not hear myself in a
receiver when keying in a dummy load.

3. When I turn the channel selector, the channel numbers change, BUT
the radio stay always on the same frequency.

4. The clarifier doesn't work.

5. The only thing I tried is to change slightly the position of the
VCO core. I can receive other frequencies by turning the core.

6. The frequency seems to be unstable when receiving.

A visual inspection inside show no sign of abuse, repair, mod or
damage. All wires seems well connected.

Do you have an idea of what I do?


Eric Merlen

Take all the covers off the radio and locate the screws
that hold the PCB to the metal chassis frame. Remove
the screws and carefully clean the PCB where the
printed circuit foil around the screwhead outline
forms the GROUND RETURN PATH for the radio.
There may be returns on both sides of the PCB.
Clean with a Q-tip dipped in alcohol. Dry for 10 minutes.
If necessary, re-tin with solder such contacts if so
equipped/treated. (this technique also works for
Astron DC power supplies which are "acting up")

The problem is corrosion forms between the PCB
foil traces and screw head, and sometimes also
between the PCB and the metal chassis frame.
Cleaning and re-tightening them fixes many a
problem, especially if the radio has been in a car
for awhile and subjected to road vibrations, heat,
cold, cigarette smoke etc....

Kenny


"Eric Merlen" wrote in message
om...
Hello,

I bought an old Colt 480 to use in my car (40 channels, AM/SSB,
Circuit Board PTBM048A0X, pll-02A, 2sc1969 final) but it doesn't work.
Here are the symptoms:

1. When I turn on the radio, it seems to change frequency during a
couple of second before it stabilize.

2. The red led light up on transmit but there is no power on the
built-in meter nor on my external meter. I can not hear myself in a
receiver when keying in a dummy load.

3. When I turn the channel selector, the channel numbers change, BUT
the radio stay always on the same frequency.

4. The clarifier doesn't work.

5. The only thing I tried is to change slightly the position of the
VCO core. I can receive other frequencies by turning the core.

6. The frequency seems to be unstable when receiving.

A visual inspection inside show no sign of abuse, repair, mod or
damage. All wires seems well connected.

Do you have an idea of what I do?


Eric Merlen

In ,
(Eric Merlen) wrote:

Hello,

I bought an old Colt 480 to use in my car (40 channels, AM/SSB,
Circuit Board PTBM048A0X, pll-02A, 2sc1969 final) but it doesn't work.
Here are the symptoms:

1. When I turn on the radio, it seems to change frequency during a
couple of second before it stabilize.

2. The red led light up on transmit but there is no power on the
built-in meter nor on my external meter. I can not hear myself in a
receiver when keying in a dummy load.

3. When I turn the channel selector, the channel numbers change, BUT
the radio stay always on the same frequency.

4. The clarifier doesn't work.

5. The only thing I tried is to change slightly the position of the
VCO core. I can receive other frequencies by turning the core.

6. The frequency seems to be unstable when receiving.

A visual inspection inside show no sign of abuse, repair, mod or
damage. All wires seems well connected.

Problems 1, 3, 5 and 6 indicate a PLL problem. Problem 4 could be a seperate
issue, but is likely related to the PLL fault. The cause could be any number of
possibilities, but it sounds like the radio was tweaked by someone that didn't
know what they were doing, and turned the VCO control voltage out of capture
range of the PLL.

Problem 2 could be anything.

Do you have an idea of what I do?

Take it to a qualified tech.






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