BCD436HP/BCD536HP: BCD436HP UHF RX signal weak, VHF still good, problem follows scanner...

[radioman2008]

I have a 436HP and recently noticed that in UHF, signals that are normally strong are weak, but VHF signals are still good and at levels i would normally see. Ive swapped antennas and connector adaptors and other 436HP scanners on the antennas and connector adaptors, and the problem follows this one scanner.
one specific 462 frequency is full scale with my other unidens, on antennas and with this 436hp, it is not even one bar signal strength, very scratchy. just using this one freq as an example, ive tested it with other local repeater reception.
it also happens on the UHF (450-460) Trunked systems, DMR and LTR, same story, should be full strength, but is only no scale to maybe 1 scale.

the Connector center looks ok, (I would think if i had a bad scanner antenna connector it would be degrading everything)
I took apart and reflowed the antenna solder joints, (no change)

has anyone else noticed this weak on one band but not on another? easy fix?

 

[gary123]

I have seen such circumstances. Without a schematic I am absing this on past service experiance. It might be that the UHF RF amp has been damaged. This could have happened from being real close to a UHF transmitter while listening to a UHF signal. The scanners have some protection to prevent such situations but the can occur.

The repair is to send it in for service. Provide the information you have above and the service people should be able to go right to the issue.

 

[Ubbe]

I haven's seen separate amplification circuits for different bands in a scanner. It's usually a group of passive band pass filters and after that are a common amplifier for all bands. The components used are of medioker performance and needs the band pass filters to reduce the signal levels from other bands. Filters will attenuate a couple of dB's and that's why preamplifiers can help to improve the signal as well as provide a lower system noise level.

If the 800MHz band are even worse then it could be a quick solder job around the circuit board where the antenna connector are soldered. But if only the 400MHz band are affected then it is a component failure and needs to be sent in to Uniden. Almost all of those components in the band pass filter are covered in epoxy.

/Ubbe

 

[ChrisABQ]

Wouldn't this be the same old battery compartment shielding issues that have been reported for years? Poor reception on UHF, foil on the battery compartment door was the cheap but effective fix.

 

[gary123]

I doubt it. The issue started suddenly according to the members description. Ubbe is correct its a component failure of some type. It could be just a cold solder joint but as stated epoxy covers the components.

Without tearing a unit apart and voiding the warranty I suspect Uniden is switching in and out various band pass filters depending on the freq being received the output of those filters is passed to the RF amp. Since the VHF band is good Ubbe is dead on with the issue being in the UHF bandpass filtering. Either way its beyond the average users resources to fix.

 

[radioman2008]

sent the unit in to Uniden and got it back, they replaced D25, Q2, Q3

 

[jtwalker]

sent the unit in to Uniden and got it back, they replaced D25, Q2, Q3

You got that sent, fixed and returned from Uniden in less than three weeks? This is the topic we want to hear about!

 

[radioman2008]

You got that sent, fixed and returned from Uniden in less than three weeks? This is the topic we want to hear about!

they got it the 26th and shipped the 29th. the never updated the repair status page

 

[JoeBearcat]

I will pass along the lack of updates.

 

[JoeBearcat]

The service manager reports that they are caught up on repairs but have bugs with the reporting on the new system. That is why the updates are not seen yet.

 

[radioman2008]

The service manager reports that they are caught up on repairs but have bugs with the reporting on the new system. That is why the updates are not seen yet.

unfortunately I have to send it back in, there is a problem with it not switching to battery when power is removed.
when usb power is removed, it crashes and the discovery mode session is lost. my other 436hp scanners will automatically switch to battery and stay running.
I reported this in the repair request, but perhaps i wasn't stating it with enough detail.

thank you for the update.