Cobra GTL 2000 Power up Issue

[AJAY0618]

please measure all 8 DC voltages starting at pin 1 (rear) and list the voltages you get on each pin. they should not fluctuate.
LC

8. 6.48v
7. 6.50v
6. 6.49v
5. 5.09v
4. 7.50v
3. 5.06v
2. 5.09v
1. 6.45v

Voltage from fuse = 13.58v

Also, I now see one more led on the clock after 12:00 0<= this flashes?

Didn;t see that ever but it has been plugged in for a while.

 

[loosecannon]

your voltage regulator is most likely shot.

just to make somewhat sure you don't have a new one fail immediately, unsolder pin 2 of the voltage regulator and move it off of the trace gently.

then turn the radio on, and measure the TRACE that goes to pin 2, not the pin you just unsoldered.

this trace is the 13.8 volt input to the regulator and you should read the same voltage on this now empty trace that you did at the fuse.

if you do, you can be pretty certain that your voltage regulator has blown and you need to replace it.

you can get one here:

MB3756 VOLTAGE REGULATOR

MB3756 VOLTAGE REGULATOR

stores.goldeneagleradios.com

hope this helps!
LC

 

[AJAY0618]

your voltage regulator is most likely shot.

just to make somewhat sure you don't have a new one fail immediately, unsolder pin 2 of the voltage regulator and move it off of the trace gently.

then turn the radio on, and measure the TRACE that goes to pin 2, not the pin you just unsoldered.

this trace is the 13.8 volt input to the regulator and you should read the same voltage on this now empty trace that you did at the fuse.

if you do, you can be pretty certain that your voltage regulator has blown and you need to replace it.

you can get one here:

MB3756 VOLTAGE REGULATOR

MB3756 VOLTAGE REGULATOR

stores.goldeneagleradios.com

hope this helps!
LC

Does this regulator tie into the small bard adjacent to bridge rectifier? That board reads low as well.

 

[1iwilly]

this is what it looks like when looking from the front of the radio on the right side bolted to the aluminum rail second pic where the arrow from the mouse is pointing

 

[AJAY0618]

this is what it looks like when looking from the front of the radio on the right side bolted to the aluminum rail second pic where the arrow from the mouse is pointing

Thanks! Yeah this is what I read the voltages off if

 

[loosecannon]

Does this regulator tie into the small bard adjacent to bridge rectifier? That board reads low as well.

if you are measuring 13.5 volts at the fuse then the power supply board is fine.
LC

 

[AJAY0618]

your voltage regulator is most likely shot.

just to make somewhat sure you don't have a new one fail immediately, unsolder pin 2 of the voltage regulator and move it off of the trace gently.

then turn the radio on, and measure the TRACE that goes to pin 2, not the pin you just unsoldered.

this trace is the 13.8 volt input to the regulator and you should read the same voltage on this now empty trace that you did at the fuse.

if you do, you can be pretty certain that your voltage regulator has blown and you need to replace it.

you can get one here:

MB3756 VOLTAGE REGULATOR

MB3756 VOLTAGE REGULATOR

stores.goldeneagleradios.com

hope this helps!
LC

LC,

Unsoldered pin 2 and checked the trace against ground which gives 4.5v! Checked pin 2 from that regulator against ground and am getting 8.00V. What gives? Pin 2 based on the tech sheet would be toward the front correct? It would seem I am not getting 13.5v at the trace.

Note this LC from a few responses ago:

So I have narrowed it down to the board adjacent to the rectifier. 19v coming from the main 4700uf cap to this board with 19v. The C1419 transistor only reads 4.5v as does the mylar capacitor next to it.

If I am only getting 4.5v from the power supply board so something would seem to be amok with this board or a component on it.

 

[AJAY0618]

I changed the 1000uf 25v and 1000uf 10v caps as well.

 

[1iwilly]

i have my 2k open been I'm still working on the freq counter issue, here are what I have for voltages on the board by the transformer and the regulator these are my reading your reading from the big cap is about correct my other 2k shows close to 19 v too hope this help let me know if you need other reading

 

[loosecannon]

the voltages you are measuring at the power supply are correct.
that big cap is before the voltage regulator transistor that sets the voltage at the 13.5 volts you are seeing at the fuse.

the power supply is good.

pin 2 of the MB3756 voltage regulator is the second pin from the rear of the radio.

pin 1 is the rear-most pin, then 2 is next to that, just in front of it.

resolder the pin you undid (pin 7 most likely) and try the test again on pin 2.

if you get 13.5 volts on that trace then it's time to order a new MB3756.
LC

 

[AJAY0618]

the voltages you are measuring at the power supply are correct.
that big cap is before the voltage regulator transistor that sets the voltage at the 13.5 volts you are seeing at the fuse.

the power supply is good.

pin 2 of the MB3756 voltage regulator is the second pin from the rear of the radio.

pin 1 is the rear-most pin, then 2 is next to that, just in front of it.

resolder the pin you undid (pin 7 most likely) and try the test again on pin 2.

if you get 13.5 volts on that trace then it's time to order a new MB3756.
LC

I had the correct the first time pin 2 towards the back which gave 4 5v to ground. Unsoldering the other pin while resoldering 2 gives 0.00v to ground. I had it right the first time so why is the voltage low?

 

[loosecannon]

" Pin 2 based on the tech sheet would be toward the front correct? It would seem I am not getting 13.5v at the trace."

this was the statement that led me to believe you might have unsoldered the wrong pin.

so, if you're only getting 4.5 volts at the trace that goes to pin 2 of the voltage reg then there is something on that trace dragging the voltage down.

this could be a bad component or even a worn out power switch because the ground for the main pc board runs through that switch.
LC

 

[AJAY0618]

" Pin 2 based on the tech sheet would be toward the front correct? It would seem I am not getting 13.5v at the trace."

this was the statement that led me to believe you might have unsoldered the wrong pin.

so, if you're only getting 4.5 volts at the trace that goes to pin 2 of the voltage reg then there is something on that trace dragging the voltage down.

this could be a bad component or even a worn out power switch because the ground for the main pc board runs through that switch.
LC

LC,

Yes, I agree. Now I changed the 10uf 25v cap on the power board and still no change. You know I am beginning to wonder that the switch may be the issue. I can't wrap my head around opening a circuit from ground instead of from hot. This is very weird. The power board has the name low voltage as the main board so there must be some connection.

 

[loosecannon]

you can test the switch by jumpering past it.

be sure to unplug the unit and then switch the power switch on and off to discharge the filter caps, then with the unit still unplugged use your meter to find two contacts on that switch that are disconnected with the switch off and connected with the switch on.
solder a jumper across those two pads.
now plug the radio in and it should be on regardless of the position of the switch.

if you now have 13.5 volts on the pin 2 trace, you can resolder it and you might be good to go.
LC


PS-i just read your last sentence again, and it is indeed possible to read 13.5 volts at the fuse but not make it past the AC/DC switch itself.

I honestly wish it had occurred to me earlier. you can check DC voltages at that switch itself and may just find 13.5 on one side and 4.5 on the other.

you can also switch that switch back and forth a whole bunch of times and/or use some contact cleaner to see if that makes the problem go away.

I have seen these switches get bumped inward and just come apart.
LC

 

[AJAY0618]

you can test the switch by jumpering past it.

be sure to unplug the unit and then switch the power switch on and off to discharge the filter caps, then with the unit still unplugged use your meter to find two contacts on that switch that are disconnected with the switch off and connected with the switch on.
solder a jumper across those two pads.
now plug the radio in and it should be on regardless of the position of the switch.

if you now have 13.5 volts on the pin 2 trace, you can resolder it and you might be good to go.
LC


PS-i just read your last sentence again, and it is indeed possible to read 13.5 volts at the fuse but not make it past the AC/DC switch itself.

I honestly wish it had occurred to me earlier. you can check DC voltages at that switch itself and may just find 13.5 on one side and 4.5 on the other.

you can also switch that switch back and forth a whole bunch of times and/or use some contact cleaner to see if that makes the problem go away.

I have seen these switches get bumped inward and just come apart.
LC

LC,

I decided to first test continuity on the switch terminals before attempting the solder junction.


BK WHT RED

#1 | | #2


#3 __ __ #4


#5 | | #6



Here is what I got when I tested continuity.

Terminals ON OFF
4-6 1 0.00

2-4 0.037 0.063

3-5 1 0.00

1-3 0.00 1



So in the OFF position there is still continuity from pin 2 to 4 on the red side which I assume is hot but keep me honest. Then in the ON position there is not full continuity! Your thoughts?

I am questioning this switch now more than ever based off these readings.