in scan mode it stops receiving after short while

[rareco]

hi folks,

an older handheld uniden 3500xlt ( should be fairly close to an 396 ) gives me a headache.

when turned on i can manually select channels and reception is fine. verified on continous atis broadcast.

when in scan mode everything looks normal ( display shows scanning through systems and groups ) but it refuses receiving after 20 seconds more or less.

when scanning is stopped it will not receive on manually selected channel ( atis ) either.

you have to turn it off then on to regain receiving.

with the volume knob you can move thru the programmed group manually.

i am able to recreate the problem this way. meaning, if i go thru the group manually it will lose its receiving function.

it does depend on how fast i switch from channel to channel though.

when you do this manually with an open squelch there is a definite difference in the white noise before and after.

also, when you monitor a selected channel for a longer period ( 5 minutes ) it will also lose its reception function.

any suggestions ?

tim

 

[Whiskey3JMC]

Hi & welcome to the RR forums! Can you provide some info on what you are trying to monitor? Conventional channels? Trunked radio systems? Both? Providing database links would help greatly too

 

[rareco]

thanks whiskey. i am monitoring vhf airband only. it is a technical issue as i can replicate it manually ( other scanner works fine ). thats why i posted it here in the tech thread. in what section of the forum would you recommend putting this to get a broader audience.

 

[Ubbe]

If the white noise change then you are not receiving the signal from the antenna any more. It's just the IF noise. It might be the PLL or VCO that are the problem and Uniden never displays if the PLL isn't locked, that some other scanners do.

Best bet are to take the cover off and then use freeze spray on different parts of the circuit board when the noise indicates that it has gone into it's fail mode and listen if the noise are restored. Then go into smaller parts on that area of the circuit board. It's probably nothing you can do without a microscope and components to replace the faulty one. Only thing to try, if you can pinpoint a faulty area, are to resolder as much as possible.

/Ubbe

 

[tvengr]

If a component failure is temperature related, hitting it with the freeze spray will cause the scanner to begin functioning again. You can speed up the troubleshooting by using a hair drier to heat up the scanner to cause failure again.

 

[rareco]

thanks for the inputs. i will hint at it when i talk to a repair guy.
by the way the u.s. equivalent is the br330