• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Barnyard 2000 GTL recommendations...

Hawkeye351

Well-Known Member
Jun 27, 2021
463
330
73
56
Hi All,
I truly enjoy all the useful info on here. I'm NC Hawkeye, 351 AM, 592 SSB, KM4VAZ Ham. I recently acquired several radios from a broken down, collapsed barn. The roof was caved in and the floor was collapsed. The radios I got from there were laying in a pile in the dirt, but dry and hasn't been used in years.

1 Cobra 2000 GTL
1 Teaberry Stalker XV
1 Teaberry T Command

I chose to start on the 2000 GTL first.
Cobra 2000 details:

1. Receive low but does receive.
2. Transmit fine at 2.5 watt key swing to around 14 watts peak on AM and up to 16 watts on ssb.
3. Signal/rf meter stuck in receive, but works on xmit.
4. Controls and switches need cleaning.
5. Meter lights dim slightly on xmit, am and ssb same on AC, but dim dramatically on DC power with a substantial power drop.
6. Clarifier strapped, course tune must be all the way right and fine tune dead at 12 o'clock.
7. Amc and alc removed.
8. Channel kit installed at Tone Control position (expo kit).
9. Constant hash sound (sounds like a fan on an amp) coming from speakers when volume is turned all the way down.
10. Frequency counter shows 92.0002, but clock and alarm works fine.
11. Anytime I touch the base of the mic im using (Turner +3B) then the frequency on ssb shifts.
12. No mods to the audio or mic circuit.
13. Original pll (MB8734), regulator, audio IC, bridge rectifier, driver (1306) and final (2166).

Need to do first:

1. Replace all caps (already ordered them).
2. Replace filter cap on power supply side on bottom, and cap on power supply board.
3. Remove heat shield and apply new compound on bottom of shield and corresponding parts (driver, final, audio IC, regulator and rectifier).
4. Replace AMC and ALC components.
5. Adjust 3 transformers to align clarifier up to 12 o'clock on both fine and course tune.
6. Clean switches and controls.
7. Remove any old glue (not much in it).
8. Realign IF and RF stages.
9. Replace meter (already ordered).
10. Apply any upgrades for performance.

My questions are:

Why does the radio xmit better on AC power rather than DC power, lights dim bad and low xmit power on DC?

What causes the constant hash noise (like a fan running) through the speakers with the volume turned all the way down?

Why does ssb frequency shift when I touch the base of the mic I'm using on it?

Why are the lights dimming slightly when transmitting on AC power?

Everyone says the radio is loud with the Turner +3B mic. Great reports on audio sound and swing. But I would like some of y'alls best audio/mic circuit mods that are proven to improve the sensitivity and clarity of the xmitted audio. Hifi is welcome if it's proven as a benefit not only for AM but also for SSB. I will not be hooking any eq's or the likes to this radio, no direct inject or volting of the final.

Can anyone answer the above questions, and give recommendations for circuit improvements on this radio? Not looking to hack it up, just fix it and improve it.

Thanks in advance.
Goldfinger
Kid viscous
Patzerozero
Etc...are all welcome to chime in please.
 
  • Like
Reactions: Shadetree Mechanic

Hash noise is most likely coming from the 9 or 10 failed electrolytic capacitors inside the clock/counter module. If the sound changes when the digits change, or when switching from clock to counter, that confirms it. The chips in that module draw huge but very brief surges of current when they change from one digital state to the other. Those small caps provide that short burst of current to one or two chips each, and filter the noise it would cause.

There is a tiny 10uf electrolytic cap C302 square in the middle of the voltage-regulator board, bolted to the heat sink alongside the bridge rectifier. This capacitor can cause dimming when it fails. And if replacing it has no effect, you didn't waste a lot finding out. The replacement's voltage rating should be at least 25 Volts. We use a 50-Volt just because it's the lowest we stock.

Never have figured out why that little part screws up the power supply's regulation so much.

73
 
Can someone explain these:

Why does the radio dim more dramatically and drop more in wattage on external DC supply?

Why does the frequency shift on ssb when my hand touches the base of the Turner desk mic (+3B) I'm using?

Why do I have that loud hash noise (like a fan running) when the volume is turned all the way down?

Why does the S/RF meter work just fine on transmit but stays stuck at 30db on receive? If the meter was bad, then wouldn't it also stick on transmit?
 
The lights' dimming is worse on the external supply? This is the reverse of what you would blame on the radio's internal supply. Makes it sound as if the wire in your DC-power cord is too thin, maybe? Or the external supply is not so stout on current output?

Frequency shift when you touch the mike? Now that's a wacky one. Don't remember seeing that. Have you listened to this radio transmitting sideband when you do this?

If it jumps that far off frequency, you'll hear that in the monitor radio, for sure. And if your transmit signal is still clarified and understandable when touching or letting go of the mike, it's not your frequency that's changing. It's the counter's behavior that's changing.

A pegged S-meter could be a bad trimpot on the receive meter. VR1 sets the sensitivity of the meter in AM receive. VR2 is for sideband. If it only pegs out on AM but not SSB, this is the place to check first.

Oh, and receiver noise you can hear with the volume at zero is coming through the audio circuits' power supply, and NOT through the volume control. This is what filter capacitors scattered around the radio's various circuits are there for. They keep out noises generated by other parts of the radio by filtering the power separately for each sensitive circuit.



73
 
Last edited:
  • Like
Reactions: Hawkeye351
So basically most of the problems are more than likely due to caps? Kinda figured that.

And as far as the dimming getting worse on DC and not on AC, and the output power dropping dramatically on DC and not on AC, yes it does, a lot worse. The power supply is the one I use on all my radios, 13.8v - 16v @ 35amp. I always run it at 14.1v. No other radio does this on this power supply. The cord is the same cord I use on other radios, never had this issue with any other radio, just this one.
 
Did you get to CB Tricks yet, might want to - wanted to fill you in on something many don't use often - so that when they do, they don't understand the "why" it doesn't do as expected.

It deals with what you are doing - using the EXTERNAL supply.

upload_2021-7-29_19-51-2.png
The external jack is the problem - older units have a "switch" by the EXT. Power, the jack that allows the internal power supply to bypass and short straight across - when others want to use the external power supply - the plug when it isn't used often enough, the DC/AC switch will develop a "memory" or "dirt" that affects the ability of the switch to disconnect the mains and switch over to external so both supplies aren't fighting each other.

The plug should be ok, but schematically - it is due to that switch and the age - due to that built in bypass switch feature - that adds a level of resistance that drops current thru the plug - which heats it up and can make the radio act weird.

upload_2021-7-29_19-53-56.png

So the switch - can be completely bypassed - the internal supply can be unsoldered from the AC/DC switch and route the power thru the DC power direct - but jumper the switch - you can keep it in there, but the AC side - the one from the Internal supply - needs to be bypassed.

The switch is supposed to do that, but age caught up to it. So you can suffer thru the efforts of replacement or just direct wire the DC side to take over that AC side.

You might also want to VERIFY that the Clock FREQ Counter and Alarms work off of DC - there is a "keep alive" wire used for the Clock - so you know.
 
Last edited:
As far as the voltage drop when powered from an external power supply, I've seen one case where someone hooked up the polarity backwards blew up the two stock chokes on the DC socket and replace them with ones that were way too small and current.
 
  • Like
Reactions: Hawkeye351

dxChat
Help Users
  • No one is chatting at the moment.
  • dxBot:
    Tucker442 has left the room.
  • @ BJ radionut:
    LIVE 10:00 AM EST :cool:
  • @ Charles Edwards:
    I'm looking for factory settings 1 through 59 for a AT 5555 n2 or AT500 M2 I only wrote down half the values feel like a idiot I need help will be appreciated