Cobra 29LTD cold dead

[dss56]

I have a cobra 29LTD lights up bright dim works Green receive Led and red Led work when mic is keyed.

Radio has no receive no transmit and I tried next to a radio to transmit dead cold and i tried to transmit a radio and to see if i had any receive cold dead.
No voltage on any pll pins at all. So somewhere 5 volts is gone. Cant seem to get a good schematic for this radio with a voltage chart.
I can hear a bit of a click when mic is keyed in the speaker and meter shows nothing.
Anyone ever have one dead but all lights work.
I checked the regulator on the side of radio and seem to be ok.

Any help appreciated

 

[doffo]

May not be the case for yours, but most of my PC66 and PC68 radios had cold solder joints just before the PLL chip area. Maybe poke around with a plastic piece around the board underneath in various areas and see if it will come to life again and hear static. Turn up your rf gain, hook up yer mic, Hook up an antenna or wire in the back and do some probing.

Just an idea, but if it still dont come back, it may be something more. Hope you get it fixed.

 

[dss56]

Thanks for the reply

Already looked and probed for cold solder joints. Just have to get a good schematic and trace back to the voltage thats suppose to be at the pll, im sure that is why no transmit/recv.

thanks

 

[NZ8N]

Check the voltage at JP1 next to the PLL and C153, this is part of the voltage rail for the PLL and VCO IC's.
Pin 11 (bottom right corner) and 16 are listed as VCC for the PLL.

If it is Zero, pull and check C112 (red circle). D19 (5.1v Zener) could also be shorted.

https://cbtricks.org/radios/cobra/29ltd_29ltd_st_29wx_st/graphics/cobra_29_ltd_classic_sch.pdf

 

[nomadradio]

My money is on D19. No need to pull it. Tends to fail as a short, so checking for a short to ground where R98 and R124 come together would reveal if it's shorted.

73

 

[NZ8N]

If you are going to pull D19, make sure to swap it with another 5.1v Zener before turning it back on, if you just cut D19, that will unleash 13v into the PLL. It needs to be voltage regulated.

 

[Amperex]

Many older 29 LTD with side mic connector are failing. Buy front mic connector 29 LTD 2010 or newer year. About $35 on eBay.

 

[dss56]

Update on the 29LTD
removed D19 checked out ok
Removed C112 and Bingo it was shorted replaced and radio working.

Again thanks to all for the info posted on what to check out.

 

[doffo]

Update on the 29LTD
removed D19 checked out ok
Removed C112 and Bingo it was shorted replaced and radio working.

Again thanks to all for the info posted on what to check out.

Awesome you fixed it. Information like this is great to have. Why Forums will reign king for information. Forums have been around much longer than Facebook so there is still a ton of good information.