My Cobra 29 LX issue... assistance needed please.

[DakAttack]

Hello everyone, this is my first post. I have lurked forums for the past few weeks getting information here and there. But i haven't been able to find an answer to this besides something like a line filter. But its not really about just general noise picked up from the truck, theres very little to begin with. I have a few Cobra 29 lx's. One is stock, the one i'm working on WAS stock, and then i'm repairing another. This is a new hobby i've picked up so bear with me. Please, I'm just looking for advice. Not your opinions on whether or not i should be trying to mod my radio. Its fun to me and its already done. So...

I bought the radio in stock form and worked fine. I installed an IRF 529 mosfet kit and Hi-Fi receive kit. I installed the Hi-Fi kit first and it subdued the regular noise pretty well, but it seemed as though it had quieted everything a little more. I wasnt able to bring my cal meter up to where it needed to be either.

Then, I then installed the mosfet kit and it amplified everything to where when nobody was talking I would have to turn the volume down a LOT. But if i did that I could not hear anyone hardly. And if I turn it up, the amplified noise would completely drown out a weak signal, and most anyone talking I could barely hear. I can hear people but still the noise is way too loud. The best way to explain it I guess would be that I can hear people, but the noise overpowers 90% of them.

I've also just recently installed the schottky diode kit to try fix this but it hasn't helped.

What I've done
Mosfet Upgrade;
IRF520
R56 --> diode kit (1n914+470ohm resistor) diode towards front
C53 --> 3.3k resistor
C61 --> removed
C62 --> 100pf across it
R55 --> Removed and installed 22pf
C71 --> Removed and installed 82UF cap (polarity is correct)
C42 --> Removed and replaced with 2200UF cap (polarity is correct)
C59 --> 68pf installed on reverse side (had to increase power)

HiFi
C33 --> .1uF mylar
C40 --> .1uF mylar
C48 --> 1000uf electrolytic (polarity correct)
C39 --> 22uf electrolytic (polarity correct)

C37 --> .1uf mylar
C43 --> empty when i got my radio
C68 --> .33uf tantalum ( + towards right side of radio on component side)
C69 --> .1uf Mylar
C125 --> .001uF mylar


My question is would anyone know what I should look at to remedy this? I may just undo everything I've done and put it back to stock. But for now I will begin with removing the Hi-Fi kit.

Thanks and I look forward to hearing from y'all!

 

[sonoma]

personally I do not like the receive mods due to it just bringing in all the hash noise. you might try aligning the L cans for the receive and see if you can tone it down. just like a amp with the preamp for the receive when you turn it on if you have a 1 s unit noise level it just amplify's it to a 6 or 9 s unit on your receive, the only RX mods I like is the diode and trans install for the 1st RX area.
the mosfet out put mod is fine and the diodes for the receive is fine. I just do not like the high RX mods.
maybe some one else will jump in on this.

 

[DakAttack]

Thanks for your reply Sonoma. I actually did revert the receive mod back to the stock layout last night after I posted. I just got home so I’ll go test it out here in a few.

 

[DakAttack]

Ok, so I just got back inside a few minutes ago. With the MOSFET in, Schottky kit in, and the HiFi tx/rx mods removed... the amplified noise has definitely gone away. I adjusted the L pots a little here and there to get the clearest audio without quieting them and I feel pretty satisfied so far.

On a side note it appears that my radio has the 29 LBT board in an LX chassis. And I don’t know if people can hear me, the cal is only half way on ch 40 but I can max it out on ch 1. It may just be that they don’t give me a chance to talk, they just key up as soon as the other lets off. But so far the receive and sound quality is great.

The only downside is that I have LED headlight bulbs and causes pretty loud static when they’re on no matter what radio I use.