Recently acquired a cobra 2000 gtl has output only on ssb but none on am any help would be appreciated
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Cobra 2000 gtl issue
- Thread starter kaos513
- Start date
If you're lucky, the problem lies with TR41. Factory type is 2SC1419. It's bolted to the heat sink at the right-rear corner of the main circuit board. If you have about 13 Volts DC on the metal tab of TR41, and nothing on the metal tab of either driver or final transistor, TR41 is probably the culprit. We have been using a part with a higher current rating than stock, mostly because the price difference is too small to sweat. A long list of possible subs is out there, but we use TIP41, with any suffix letter, A, B, or C.
Back in the day, we'd send people to RatShack for the TIP3055 transistor that they stocked for decades. Now it's fleabay.
73
Back in the day, we'd send people to RatShack for the TIP3055 transistor that they stocked for decades. Now it's fleabay.
73
On sideband has right readings during tx on am during tx is where will not give me the right measurements.same go for the finals & drivers
Here's why I ask...
Cobra 2000 and the Cobra 148 are very similar - even in function.
IF the AM Regulator seems ok - why don't you get power?
Requires the AM Regulator to even have something to turn on with.
So TR41 can show good.
So can TR42...
So Switch to AM mode - if no voltage...turn off the power on the radio.
Locate Collector Leg of TR38 - or use TP8 WIRE (not post)...attach one lead of DVM here.
Locate MB3756 Pin 2 - or the Radio Power Switch.
Switch MODE to SSB - USB and LSB - to test should show SHORT (nearly 0 ohms) using other Test lead of DVM sent to 1X.
Now, switch radio to AM mode - Test the same way, only in X10 setting...
Does it show 200 to 230 ohms? (May need to reverse leads to help offset polarity of caps along the line)
If so - remove test leads - replace TP8 back to post.
Restore power to radio and locate VR10 - make sure VR10 is sending out an adjustable voltage to the UNBANDED side of D63 - if none to very low voltage - locate C173 10uF 16V - replace and try again.
Power restored?
(... I'll wait here for you to catch up... )
Cobra 2000 and the Cobra 148 are very similar - even in function.
IF the AM Regulator seems ok - why don't you get power?
Requires the AM Regulator to even have something to turn on with.
So TR41 can show good.
So can TR42...
So Switch to AM mode - if no voltage...turn off the power on the radio.
Locate Collector Leg of TR38 - or use TP8 WIRE (not post)...attach one lead of DVM here.
Locate MB3756 Pin 2 - or the Radio Power Switch.
Switch MODE to SSB - USB and LSB - to test should show SHORT (nearly 0 ohms) using other Test lead of DVM sent to 1X.
Now, switch radio to AM mode - Test the same way, only in X10 setting...
Does it show 200 to 230 ohms? (May need to reverse leads to help offset polarity of caps along the line)
If so - remove test leads - replace TP8 back to post.
Restore power to radio and locate VR10 - make sure VR10 is sending out an adjustable voltage to the UNBANDED side of D63 - if none to very low voltage - locate C173 10uF 16V - replace and try again.
Power restored?
(... I'll wait here for you to catch up... )
Damn Handy Andy, thats specific instructions right there. Im absolutely confident he will get it fixed with your help.