148 GLT LSB quit working

[Michigan Muskrat]

1994 Malaysia made 148 GLT was working fine, but switched from AM to LSB, and the channel light dimmed, then completely went out over about 4 seconds. Now no sound or channel light on LSB, no tx on my meter, the meter is still lit however. AM and USB work fine, good sound, good tx, channel light is lit. Could someone give me a general area on the circuit board where to start? I'm not sure if it is a diode, cap, etc. It's only affecting the LSB. Thanks to you all.

 

[Robb]

Think I would start by checking D32 and D40 first. Then check your mode switch next. Look for shorts in the diodes. You might also check TR-31; doubtful.

http://www.cbtricks.com/radios/cobra/148gtl/graphics/cobra_148gtl_sch_redraw.pdf

 

[Michigan Muskrat]

OK Robb, I will check D32, D40, mode switch first and let you know. Thanks for the fast response.

 

[sonoma]

you should have 8 volts coming into the mode switch then going out to the main board.

 

[Michigan Muskrat]

you should have 8 volts coming into the mode switch then going out to the main board.

Thanks Sonoma. I will check that. I appreciate the help.

 

[sonoma]

if the diodes are good that Robb told you about. look at the schematic and look for the mode switch and trace the drawing to each part leaving the mode switch and check each one. there is a lot of parts that could be bad causing this. all you have to do is check the trace leaving the switch for LSB. Robb gave you the 1st ones to look at that normally cause this. if one is shorted you may not have 8 volts at the switch depending on what went bad. I had a pc122 a cap shorted out in the USB mode and just had to trace it by looking at the parts and lift one leg to get the voltage to show up.

 

[Michigan Muskrat]

I will get the schematic and do as you suggest and will also look at Robb's suggestions and see what I come up with. Thanks, this forum really helps a person, especially a guy like me, who really doesn't dabble in electronics too much.

 

[mechanic]

Good info here to be found! Since the Cobra is getting on in years you may want to think about doing a re-cap of the whole radio. Very much worth the effort!

mechanic

 

[Michigan Muskrat]

Your right Mechanic, new caps throughout would be a good thing in an older radio. Good suggestion.