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Knackered my UBC125XLT! - repair info required

Posted: 07 Jan 2021, 17:54
by JLow75
I have a Uniden UBC125XLT that has lost it receive - I believe I know why & what happened, I did not know these can be easily damaged by RF in close proximity (even with the unit switched off) I transmitted on a 5W UHF walkie talkie with the Uniden in very close proximity without thinking, now it's stone deaf on all bands.

I have managed to find a small amount of info on the internet that states there has been damaged caused to a particular IC, but without more information i.e. what component(s) require replacing i'm stuffed. The only information I could find was from users who sent theirs off for repair & had them returned back to working order.

Firstly, has anyone else had this happen? - RF damage to a UBC125XLT scanner rendering it stone deaf? if so what was your course of action?

If I could find out what components have been damaged & I could get replacements I can replace them myself, failing that I would be willing to send it off for repair - so if anyone could recommend somewhere I could send it? (I am based in the Midlands)

As these are still £120+ to replace I don't want to bin it (yet)

Thanks in advance

Re: Knackered my UBC125XLT! - repair info required

Posted: 07 Jan 2021, 18:22
by ch25
I would start from downloading service manual, than asking myself: am I capable of diagnosing and fixing it? Can I read schematics? Do I have DMM?
Link valid 30 days: https://www.swisstransfer.com/d/00ace00 ... 478f84dff3
Is it deaf on all bands?
Chris

Re: Knackered my UBC125XLT! - repair info required

Posted: 07 Jan 2021, 23:02
by f4phixeruk
Just a quick one before you take the back off. The attenuation isnt switched on is it ?? Mays seem a silly question, but speaking from experience [Done it myself in error - then panicked as the scanner has gone deaf] This is now the first thing I check.

Re: Knackered my UBC125XLT! - repair info required

Posted: 08 Jan 2021, 09:27
by JLow75
ch25 wrote: 07 Jan 2021, 18:22 I would start from downloading service manual, than asking myself: am I capable of diagnosing and fixing it? Can I read schematics? Do I have DMM?
Link valid 30 days: https://www.swisstransfer.com/d/00ace00 ... 478f84dff3
Is it deaf on all bands?
Chris
Hi thanks for the service manual!, looks like a assembly manual, but the schematics & component list/designators are there that is the main thing that is great, I will still need some more info/advice where to start though. Yes deaf on all bands

I don't believe there is any attenuator settings on this scanner? - anyway it packed up without me touching anything at all. I performed a factory reset & then re-loaded my codeplug, in case it was a settings issue but it made no difference.

The scanner is already completely stripped - right down to bare PCB's, I wanted to see if there was anything visually obvious, but as I expected nothing.

Yes I'm ok with schematics - I'm a 25 year time served electronics/electrical technician & a 30 year radio enthusiast (although no experience with scanners)

Yes we have all the test equipment at work - DMM's / Scopes / Signal Generators etc, also all the tools & equipment to remove & replace surface mount components.

Re: Knackered my UBC125XLT! - repair info required

Posted: 08 Jan 2021, 10:33
by ch25
1. Is there any voltage on TP1?
2. Is VCC_R present?
I suspect Q1 might be fried, but could be also AGC issue. Can you hear anything when transmitting close to scanner?

Re: Knackered my UBC125XLT! - repair info required

Posted: 08 Jan 2021, 12:37
by JLow75
Thanks, yes will do those checks.

Yes it still receives with the transmitter right next to the scanner & with audio - but signal very weak

I've printed the schematics out in A3 which always helps a lot!

Re: Knackered my UBC125XLT! - repair info required

Posted: 08 Jan 2021, 14:23
by JLow75
The VCC Reference seems ok = 3.28v
There doesn't appear to be anything on Test point 1 ? - PCB is covered in conformal coating so will make sure I've scraped it off properly & check again. This will be Monday now as I can only do it at work where I have all the kit here.

Another pain is the two PCB's are piggy-backed by a header & you can't access the test points on the receiver board when it's powered up via the main board

God send we have a good illuminated magnifier here!

Re: Knackered my UBC125XLT! - repair info required

Posted: 08 Jan 2021, 14:56
by ch25
TP1 is antenna output, measure here.
For piggy-backed PCB's I usually make a cable to connect them while disassembled.
Chris

Re: Knackered my UBC125XLT! - repair info required

Posted: 08 Jan 2021, 15:21
by JLow75
No definitely nothing on the Antenna output, with reference to chassis/ground.

Many thanks for your help on this, problem I'm not a service engineer in the true sense of the word, I'm a wide range electronics & electrical build/installation/repair technician - and when it comes to fault finding to component level, my experience is limited, especially with
modern radio equipment, never worked on a scanner!. Obviously I can use all the kit & can follow a test procedure no problem, but without such a procedure I'm stuffed

Re: Knackered my UBC125XLT! - repair info required

Posted: 08 Jan 2021, 15:42
by ch25
Sorry, I need glasses. Measurement correct, there should be no voltage on antenna socket.
use signal generator, touch collector of Q1 and check if any signal will be received.
Safe way would be via small capacitor inline to separate DC.