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Cobra 2000 cannot get to evenly sync transmit and receive frequency

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Jonsue

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Feb 19, 2020
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It is the first time I have posted ever so here it goes.

I picked up a used Cobra 2000.... Or very abused Cobra 2000

It had been modified extra channels etc via a screwdriver junky.. Poorly soldered wiring so i recapped pulled out the bad wires to get it back to semi stock put in the veractor diodes that were pulled soldered in the missing diodes and resistors that were cut.

No sound... replaced the audio amplifier still no sound which traced the RF back to the initial AF transistor and found a shorted diode.... many hours and hours later tracing and checking.

It began to come back to life.... Am, SSB good modulation 4-7 watt AM 12-18 watt ssb. Sound was back and loud

The frequency on transmit and receive were off by 1khz so I tuned the pots as close as I could get to each other.

on 22 Am it is 27.250 on transmit and receive on 22 is 27.261 I cannot seem to get any closer as it just moves the receive on tune or the transmit on tune.

VR5 kicks it up 1khz so it is tuned down as far as it will go.

I am using an HP frequency counter external and the internal counter/clock is the same off by .011 to .013 ish.....

any help would be appreciated.
 

gary123

Member
Joined
Sep 11, 2002
Messages
1,670
Check the voltage to the varactor/clarifier circuit on TX and RX. Most often the cause is different voltages between TX and RX.
EG 5.0v RX and 4.8v TX causing the difference in frequencies.
Also SSB warble (FMing) is caused by minor voltage variations to the varactor/clarifier circuit. A scope shows that very nicely.
 

RBMTS

Active Member
Joined
Apr 28, 2002
Messages
1,095
Due to the age of the 2000, the capacitors have probably gone bad. I had a 2000 several years ago and it drifted horribly due to the bad capacitors. There are some YouTube videos about this problem and how to replace them. There is also capacitor replacement kits available through various sites. I never did this and gave the thing away as parts eventually.

Something for you to consider to solving your problem.
 

Jonsue

Newbie
Joined
Feb 19, 2020
Messages
2
Thank you, will check voltage and clarifier.... all electro-caps have been replaced.
 

jassing

Member
Premium Subscriber
Joined
Jan 31, 2012
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282
Location
Shelton, WA
I would toss it and buy an unmolested radio. A cheap unmolested radio is better than an expensive molested radio.
 
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