Sidebar Sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
  • Click here to find out how to win free radios from Retevis!

Cobra 89xlr static

S

Smack32

Member
Aug 26, 2023
47
10
18
64
I have an 89xlr I picked up cheap.. It's getting lots of static on recieve transmit and on the pa.. Recapped the radio no change.. I have 4 watt output stable 13.8 v dc off the power supply.. Same results with a 25 amp exteenal supply.. Staticie has no change in volume no mater where the volume or mic gain is set.. Do get a little audio between the static..
Any clues as to where to look
 

The audio power amp chip is the long-discontinued uPC1156H chip. If you have replaced all the electrolytic caps connected to that chip, you don't have many other things to blame. One quick test is to take the tip of a small screwdriver, or a probe tip and short pin 4 to pin 5. These are the differential inputs. If you still have noise with these two pins connected together, the chip is almost certainly the culprit.

And if this makes the noise go away, maybe there's trouble in the squelch circuit that feeds into this chip.

73
 
  • Like
Reactions: Cable Guy and Smack32
nomadradio said:
The audio power amp chip is the long-discontinued uPC1156H chip. If you have replaced all the electrolytic caps connected to that chip, you don't have many other things to blame. One quick test is to take the tip of a small screwdriver, or a probe tip and short pin 4 to pin 5. These are the differential inputs. If you still have noise with these two pins connected together, the chip is almost certainly the culprit.

And if this makes the noise go away, maybe there's trouble in the squelch circuit that feeds into this chip.

73
Click to expand...
Ok try that.. Wold.it still cause this in.PA mode..
 
nomadradio said:
The audio power amp chip is the long-discontinued uPC1156H chip. If you have replaced all the electrolytic caps connected to that chip, you don't have many other things to blame. One quick test is to take the tip of a small screwdriver, or a probe tip and short pin 4 to pin 5. These are the differential inputs. If you still have noise with these two pins connected together, the chip is almost certainly the culprit.

And if this makes the noise go away, maybe there's trouble in the squelch circuit that feeds into this chip.

73
Click to expand...
I have a couple ta7222ap chips that are the replacement for the 1156.. I'll try what you said tomorrow .. Thank you
 
Smack 32 -
Do you have any LED lights in the room where the CB is?? When I set up my base a while back, I had a LOT of static in my receive. When I turned off the LED lights the static stopped. Maybe the problem.

-399
 
unit_399 said:
Smack 32 -
Do you have any LED lights in the room where the CB is?? When I set up my base a while back, I had a LOT of static in my receive. When I turned off the LED lights the static stopped. Maybe the problem.

-399
Click to expand...
This is on my workbench where I do all my stuff this is the only radio that does it .. Low output audio on transmit . The static is at full volume .. No controlling it with any controls .. Mic gain volume squelch pa.. Any other radio is fine.. Definitely just this radio
. I'll test the chip as was suggested .. I think that's the issue . If so I have a replacement .. Hopefully that the issue ..
Thank You for the suggestion .. Oh I have solar panels .. That can also interfere .on some bands I was told.. So far 5 years down the road no problems
 
Is the static erratic, crackly static maybe with pops or steady white noise static? Is the trace side of the board clean or still some flux left over from soldering?
 
Cable Guy said:
Is the static erratic, crackly static maybe with pops or steady white noise static? Is the trace side of the board clean or still some flux left over from soldering?
Click to expand...
Hi. It's clean.. First thing I did was clean both sides b4 recapping .. Resoldered alot that looked poorly /cold soldered.. Tried shorting out pins 4 n 5 on the audio ship.. Some noise stopped . Ordered 3 new chips from great Britain .. As I have 3 89 xlr radios only one wuth the static.. .. Like hetrodin but no control over it in any mode. Cb PA TX Rx nothing when I pull out the mic.. Tried 4 different mics same issue
 
If clean, no solder blobs, reversed or missed caps then id follow up with what nomad said above. It could be a faulty chip, but you still get some static with pins 4+5 shorted, I'd replace the chip.
 
  • Like
Reactions: Smack32
Cable Guy said:
If clean, no solder blobs, reversed or missed caps then id follow up with what nomad said above. It could be a faulty chip, but you still get some static with pins 4+5 shorted, I'd replace the chip.
Click to expand...
That's the pint I'm at now.. Orderd the chips hope to.see them soon..
Thank.you all for your help
Greatly appreciated
 

dxChat
Help Users
  • No one is chatting at the moment.


      Top Bottom
      Back