Cobra 2000 GTL

[mafatone]

I pulled out my Cobra 2000 GTL after 12 years and noticed that when keyed up the meter lights go dim.The radio has a dial-a-watt tone control mod.I see that the AM regulator has been replaced with a NTE 152 7 amp.Would it be the power supply,shorted driver/final or capicitor? I don't want to stress the radio out.Any advice would be appreciated.Thank You from a 38 year fellow CBer.............

[Circuit Breaker]

I'm thinking some components have started to fail...more than likely some electrolytic capacitors.

[mafatone]

Thanks for the reply Circut Breaker.I have noticed that the radio does not transmit in the 13.8v DC mode.I think this is due to the TONE control wattage mod.If I remember,VR10 is replaced with the tone control,then the 8.13 volts was replaced with 13.6 volts from one of the legs on the first IC chip on the right hand side heat sink.I'm thinking this chip may be weak being that it was the source of power.I'm going to try to replace the wire that supplies the voltage from the chip to the tone control as it is very very thin and may not handle the current.If that is not the problem then i'm going to try to put it back to the factory VR10 AM carrier control.I am looking foward to getting back into this great hobbie again.Any advice would be appreciated by anyone.Thanks Guys......Frank

[TheCBDoctor]

Hi mafatone

If you have a regulated DC power supply I would try that and see if the lights dim. If the lights don't dim then the supply has issues. If the lights still dim using a DC supply, then the power supply in the radio is fine.

If you have an AM power modification, then I would suggest restoring the radio back to original. There is no benefit to varying the AM carrier. How does the radio work on Sideband?

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Respectfully,

[mafatone]

Am carrier only. No SSB, no audio on AM,no audio on recieve,does not transmit at all with DC power applied.Lights dim upon AM carrier with the AC.I would like to fix it but if not then i will Ebay it. I have a HR2600 i could use.The 2000GTL has the best recieve of any radio that i ever had.That's why I would like to repair it.What does an average repair go for today?

[Badlander61]

There is a guy who specializes in the Cobra 2000 GTL repairs, he advertises on ebay and his handle is the CB Doctor. just log onto ebay and put in Cobra 2000 GTL and his ad will come up. good luck.

[Black Lightning]

There is a guy who specializes in the Cobra 2000 GTL repairs, he advertises on ebay and his handle is the CB Doctor. just log onto ebay and put in Cobra 2000 GTL and his ad will come up. good luck.

He posted above, two posts above yours.

As for the dimming issue, it is likely a capacitor on the regulator board on the power supply. It's an electrolytic cap. It's a 10uF, 25 volt cap, C134. It's in the middle of the regulator board. When this goes south, on AM the lights will dim, and on SSB the lights will dim more and the radio will warble.

[TheCBDoctor]

Am carrier only. No SSB, no audio on AM,no audio on recieve,does not transmit at all with DC power applied.Lights dim upon AM carrier with the AC.I would like to fix it but if not then i will Ebay it. I have a HR2600 i could use.The 2000GTL has the best recieve of any radio that i ever had.That's why I would like to repair it.What does an average repair go for today?

Hi Mafatone,

You have a bad audio chip if you have no audio receive and no AM transmit modulation. The fact that the audio chip is not used on sideband throws a monkey wrench into that diagnosis. That is a strange one. If you had sideband Transmit, then it is definitely the audio chip TA-7222.

It may have more than one issue. Have you tried seeing if the radio works with an external power supply? If it does, then the AC power supply is N/G. It still may have a bad audio chip. Measure pin 9 on the audio chip and see if the voltage is half of the supply voltage (13.8 volts). If it is Zero or 13 volts then the audio chip is bad. You should read about 6 volts.

There is J-Fet in the power supply, if it is bad, then power supply will not regulate and you will see the symptoms you describe.

Respectfully,

[redlght]

Instead of a new thread i will post here since it applies. I have a 2k that dims channel display and tx light on ssb tx modulation not on am tx it has been all recapped and does it on ac or dc power, Any ideas?

-- Monday, 08 February 2016, 10:17 AM --

I also noticed that there is no audio limiter working and i can;t see why not nothing looks removed that i can tell.

-- Monday, 08 February 2016, 16:13 PM --

TR24 a 945 had a 711 in it that fixed thew limiter problem

[hilldwler420]

C134 on the power supply circuit board. 10μf 25v cap.

[redlght]

C134 on the power supply circuit board. 10μf 25v cap.

All caps were changed before and an NTE 152 installed still does it on ssb

[redlght]

Just to follow up on this issue:
If you have a 2k that dims on tx modulation and you tried every thing then this is for you.
Check voltage drop at the bridge rectifier + and - if you see very little drop or with in spec.
Go to the power switch check the voltage drop chances are you will see your big voltage drop there on the ground side (since corba 2000 gtl uses a switched ground to turn off the main board).
I have found the on off switch in these radios losses good contact and causes the dimming light symptoms.

[jessejamesdallas]

Just to follow up on this issue:
If you have a 2k that dims on tx modulation and you tried every thing then this is for you.
Check voltage drop at the bridge rectifier + and - if you see very little drop or with in spec.
Go to the power switch check the voltage drop chances are you will see your big voltage drop there on the ground side (since corba 2000 gtl uses a switched ground to turn off the main board).
I have found the on off switch in these radios losses good contact and causes the dimming light symptoms.

Good to know...If mine ever starts doing that, I hope I can remember where I read this!