Cobra 89 XLR, low modulation.

[Robb]

PA works okay, ferrite in L16 is noticeably cracked as is the primary in the double can by TR2 (unmarked)
Would the cracked ferrites cause this, i don't think so but I've never encountered a busted ferrite until I got inside this radio.

You're gonna have some real fun with that. This is why only nylon tools are prescribed to use, Use any metal tool at any time on these cans - and you are royally screwed. Probably will have to take each coil off of the board and take the screw out from the underside of the coil. Chances are it is broken off so much ferrite that it will be unusable.

 

[LeapFrog]

You're gonna have some real fun with that. This is why only nylon tools are prescribed to use, Use any metal tool at any time on these cans - and you are royally screwed. Probably will have to take each coil off of the board and take the screw out from the underside of the coil. Chances are it is broken off so much ferrite that it will be unusable.

Thanks, tell this to the 'tech' who butchered the core before I ever opened the radio...
I have now swapped that can (single one) out, problem persists still. Looking at audio section now.

 

[ExitThirteen]

If the ferrite cores in the cans have been damaged, it's most likely going to need a full TX chain alignment done for the modulation to come up. The previous person that was in there may have gotten golden screwdriver happy and played with all the silver cans in the TX chain. I'd see about doing a TX alignment and see if that brings up your modulated output any. Good luck.


~Cheers~

 

[LeapFrog]

I think it's almost there, I just need a picture of the underside of ic2 upc5h2h where the traces are buggered, im going to buy 29 xlr to compare if i absolutely have to.

After this radio i'm seeking medical attention, I lack the focus required to study schematics and compare to the board. (cognative issues) Maybe I need more coffee lol.

 

[Robb]

I hear ya all right. Fixing someone else's hacks. Couldn't agree more. I think you have learned quick, you have a 'not gonna quit' attitude, and you have fixed things. Better than the opposite; right?

You could use the schematic to get those traces straightened out if you really wanted to . . .

 

[LeapFrog]

I hear ya all right. Fixing someone else's hacks. Couldn't agree more. I think you have learned quick, you have a 'no gonna quit' attitude, and you have fixed things. Better than the opposite; right?

You could use the schematic to get those traces straightened out if you really wanted to . . .

Robb you just gave me the confidence I need to push trough it!
I will work out the traces from the schematic, I can do it. I just have to believe in myself, and be patient!

 

[LeapFrog]

If only you guys could see the point to point soldering, no copperfoil on the board it was a blank canvas.

I noticed the mic gain and volume and RF gain do nothing for the audio level PA and receive does work but the audio is not as loud as it should be

i notice a hum in all modes when running off of the internal power supply

 

[222DBFL]

Keep at it LeapFrog. You've come this far, as long as the issues you have that remain are resolvable, then hey why not learn to push through it and fix it!! Best way to truly learn something IMO. You won't forget that radio I'll bet, for a long time!! Be it good, bad, or indifferent!!
At any rate. Keep up the hard work and patience. It will pay off later on down the road!!
Hope you get it all resolved and again, keep at it!!
73 and God Bless

 

[LeapFrog]

Keep at it LeapFrog. You've come this far, as long as the issues you have that remain are resolvable, then hey why not learn to push through it and fix it!! Best way to truly learn something IMO. You won't forget that radio I'll bet, for a long time!! Be it good, bad, or indifferent!!
At any rate. Keep up the hard work and patience. It will pay off later on down the road!!
Hope you get it all resolved and again, keep at it!!
73 and God Bless

This radio has kept me up all night, suffice to say at the 8 am roll call I will be heard (on this radio)!

I by passed the mic pre-amp and behold the radio will modulate the carrier, with a little yelling I can see upwards of 90% modulation, in a few hours I will be running this radio with a power mic and my own power supply. Just for a little listen and a radio check lol!

Then after I rest I will find the boogered component!
Thanks for all the support 222, Exit, LC, Robb, CK, 399, you guys all rock and I hope you have an awesome day 73!

 

[LeapFrog]

If only you guys could see the point to point soldering, no copperfoil on the board it was a blank canvas.

I noticed the mic gain and volume and RF gain do nothing for the audio level PA and receive does work but the audio is not as loud as it should be

i notice a hum in all modes when running off of the internal power supply

I love old hardware, something failed in the power supply, the radio was running at 24v d.c., i only noticed after a tried to tx a carrier, when I saw it was over ten watts my jaw dropped, with the radio running at 13 volts no hum noise is noticed and all the controls work as they should. Carrier is back around 3-4 watts

I'm glad nothing fried running at 24volts (short time anyway) as far as I can tell it's all okay still.
Going to work on the pre-amp so I can modulate properly with a stock microphone.

 

[222DBFL]

Get er done man!! Knew you could do it!!

 

[Robb]

What did you do about L16?

 

[LeapFrog]

What did you do about L16?

I removed it and installed a spare inductor from a parts radio (not the same exact one but uH close enough untill I find a parts 89 XLR)

 

[LeapFrog]

After the re-cap, I LOST IT "shot-gun replaced" tr11,tr12, tr13,tr14,tr15,tr16 radio now modulates fine! When I have more time I will determine what the failed part was.
Thanks Guys