Cobra 2000 gtl problem

[pikey]

I just unpacked my cobra 2000. It has been in storage for about 5 years. It worked great when I put it away. Now I have no receive on AM. I do have it on USB and LSB. Does anyone know what this issue could be? Is it something that I with a little electronics background could fix? Where would I get parts? Some info on the radio...It has mods. Extra channels using the ANL and NB switches. The tone knob is now a dial a watt. I am attempting to sell the unit and the D104 silver eagle mic. I just want to make sure it works well before I do. Thanks.

[TheCBDoctor]

Hi Pikey,

I specialize in the Cobra 2000 GTL. I have provided a link, just click on the photo for more info. The worst thing you can do to any radio is not use it. Since, the SSB and AM go through two different circuits on receive, I would bet the 455 KHz ceramic filter is shot. I can provide more info by Sunday.

I must go now, but stay in contact, and I will talk you through some trouble shooting techniques.



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Respectfully,

[pikey]

Cool, thanks alot

[pikey]

If it is the filter, are they easy to find? I searched a little bit and found some with 5 pin and 3 pin connections. Is this something that would just snap in or is there soldering involved?

[Black Lightning]

If it is the filter, are they easy to find? I searched a little bit and found some with 5 pin and 3 pin connections. Is this something that would just snap in or is there soldering involved?

Soldering is involved, and you will want the one with 5 pins.

[pikey]

Will a CQ 33-455D 6 ELEMENT CERAMIC FILTER 455KHZ 5 PIN work?

[pikey]

Doc, What are some of the troubleshooting things I can start? Thanks

[silverstreak]

I can bet its one of the 10volt caps went south,when these start to go bad one section of the radio starts to act up,and then another section.I have done at least 20 of these radios for locals.Replace caps with same value but at least go with 16V caps.Here is a list of caps with some upgrades to improve the radio.
C10-.22
C18-1000 (stock value is 330uF. this value is increased to eliminate mic squeal)
C23-.47
C24-4.7
C25-.47
C29-.47
C33-1
C62-1
C67-1
C72-33
C73-22
C74-47
C80-2.2
C81-2.2
C84-1000
C90-.47
C92-4.7
C95-47
C99-2.2
C100-22
C101-.1
C103-10
C104-.47
C108-.47
C109-10 (a 4.7uF cap to replace this cap. it will speed up the AMC response time)
C133-10
C134-10
C135-.47
C144-1
C153-47
C172-3300 (stock value is 1000uF. increasing this value helps the whole radio operate better)
C173-10
C174-1
C175-470
C176-47
C179-22
C180-4.7
C181-10
C186-220
C190-.47
C191-1
C214-47
C217-10
C218-1
C230-.47
C231-.47
C232-2.2
C302-10

[TheCBDoctor]

Hi pikey,

If your SSB receive is fine, but the AM is not, then the problem is in the 455 KHz second IF circuit. I always start at the 455 KHz Ceramic filter. Since, you have found where the filter is I would replace that first. Any type of 455 filter will work but the 2000 uses a dual 5 pin ceramic filter. I take them out of scrap radios. There are plenty to be found.

If the problem is still there after the filter is replaced, then check for a bad capacitor in the AM 2nd IF circuit. If the SSB is fine, then problem must be after the 1st IF (7.8 MHz) and before the audio detector.

Respectfully,