Brand New Cobra 29 LTD Classic No TX or RX

[Crossbow]

Had a brand new Cobra 29 Classic that was only two weeks old died.
There was no TX or RX not even a nudge on the meter showing any kind of life!
Light did change from green to red when keyed.
Went through the whole radio tracing down the problem and everything was checking out good up to L22 which would not adjust at all. Had Handy Andy follow along with me to make sure I was not missing something.
After we had pulled our hair out trying to figure this one out I pulled L22 out and took it apart to find a wire was broke inside. You can see it sticking up on the right top corner. Thanks Andy for all the help buddy!

 

[Crossbow]

Andy when you chime in on this can you let everyone know what we found about the new PLL chip and how they power the channel LED's on these new radios?

 

[sunbulls]

I’m curious. Did you reattach the wire or replace it with another can? When a replacement wasn’t handy I repaired a few in desperation, but my success rate wasn’t very high.

 

[Handy Andy]

Hi folks...

(Added more details...)

Yeah, that was me helping. But I also wanted to warn others out there that the older NEC or UPD 2816 PLL chip used in the Cobra - you know, the ones that said Cobra 29 LTD? Well, they've been replaced with a 24 pin PLL with two "dummy legs" as Pin 12 and Pin 13...

KEPC-1106



Wait...it' gets better.

They use an encoder now....


That's the one, in the bottom left of the pic. The Orange wire from Main PCB and the Orange wire from main 8V Regulator (TR22) - goes here. The Orange wire to the main PCB from the encoder shows 5 V - which is where D19 and a buffer resistor of 56 ohms comes into play, but note the 56 ohm resistor and the D19 - this orange wire bypasses it...



Later thru the dialog Crossbow found out L22 went bad...that is the photo above. Replacing L22 took care of the problem - but the LOCATION of the L22 part is where I have a question or two...



What caused the failure? The can uses a tuning cap to make it resonate and by what is in the photo - the wire is just "loose" like it was nicked - and perhaps in assembly at the plant during insertion - but all is speculation.

So, with these new 29 units, there are several changes - a 22 pin PLL using a 24 pin pinout. - here's a copy of the TSB they sent to Crossbow...

...

Well, that is the best I can make of a summary of this repair - good job Crossbow for persevering thru the ordeal and sticking with it until you got it working again.

Enlarged PLL and Encoder section...foil side...


WOW...stuff we have to look forward to folks...



The schematic to help Crossbow, this was sent by their corporate HQ people - which upon reflection - were jerks, and not very cooperative - note the missing encoder and updated 24 pin changes not expressed...even the board number in the upper left corner - is wrong.



So apparently the Left hand does not know what the Right hand is doing...

Cobra is not following through on their work and changes in their production - so current models are not properly disclosed nor are they properly assembled - L22 - I'd have to rate the whole experience an EPIC fail on Cobras part but I Laud and congratulate @Crossbow for his efforts on finding a solution.

Thank you for letting me work with you...

:+> Andy <+:

 

[TheRealPorkchop]

Andy what program do you use to make your pics?

 

[Handy Andy]

Windows Paint...

 

[TheRealPorkchop]

We don’t have that...

 

[Crossbow]

I’m curious. Did you reattach the wire or replace it with another can? When a replacement wasn’t handy I repaired a few in desperation, but my success rate wasn’t very high.

I pulled one out of an old junk parts radio I had laying around.

 

[Crossbow]

Awesome job done Andy!
The wire was tucked down in the slot and I could not get the camera to focus on it so I lifted it up so you could see it.
There was a small chunk of plastic that was broke off laying in that grove. It looks like when they put the case on over the coil they chip the plastic and shoved the can over it pinching the wire to make it break.
My question is how did this thing work for a couple weeks? Mystery we will never know I guess.
Thanks again for going along this trip of the unknown to figure it out. One we will never forget! Thanks for showing everyone the changes they have made on these new radio's and I can not agree more on the left hand not knowing what the right hand is doing!!

 

[kaos513]

Must had been a cold solder joint and when you moved the radio around it moved around.

 

[Rwb]

Handy andy amazes me.he knows a radio and digs till its right. A TRUE RADIO TECH.
Id love to meet andy in person .he is a great person

 

[Crossbow]

Must had been a cold solder joint and when you moved the radio around it moved around.

I grant you this was not a cold solder joint.

 

[Crossbow]

Handy andy amazes me.he knows a radio and digs till its right. A TRUE RADIO TECH.
Id love to meet andy in person .he is a great person

Yes Sir Andy is awesome is all I can say. Very happy he is here to help us!

 

[Handy Andy]

Aw, come on guys!

I do this so I can learn. You are out there in the trenches, Winnebago's, and strip malls - in conditions reeking of diesel fuel, car exhaust, drafty cold or exceptionally hot office spaces, mean customers (and other techs scouting out your place) and who knows what else...

You guys get all the fun, I have to watch over an 86 year old that can't remember the last place she put her teeth...

​

MOM! You left them by the Kitchen Sink again!

 

[Rwb]

Aw, come on guys!

I do this so I can learn. You are out there in the trenches, Winnebago's, and strip malls - in conditions reeking of diesel fuel, car exhaust, drafty cold or exceptionally hot office spaces, mean customers (and other techs scouting out your place) and who knows what else...

You guys get all the fun, I have to watch over an 86 year old that can't remember the last place she put her teeth...

​

MOM! You left them by the Kitchen Sink again!

i feel for you andy,i cared for my uncle,wife n i had fits with him.i truck local n id be home nites n her days.he had alzhiemers bad.
Its hard but has to be done