BCT15X Deaf above 30mhz

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cbreads

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Ive seen multiple older (closed) posts about this particular scanner suffering from a front end overload/de-sense issue, and apparently ive been "had" on this one...Purchased cheap enough but it does in fact have the BCT15X deafness above the 10/11 meter bands.

Nothing- not weather, fire, police, even local key ups of an HT elicits ANY audio out of this thing above 30 mhz

But CB/10 meter work fine...

Ive seen posts at some point of people having similar issues with this scanner, and they send it in and its repaired within a few weeks.

Can someone advise what their invoice showed what part(s) was replaced to make the unit work again? unless i fix it myself, i dont believe spending another 100 bucks repairing an analog only scanner is even worthwhile...

TIA
 

cbreads

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Im sure its happened. I am also sure ive never done that. Its been on its own antenna day one... Ive seen quite a few postings on the deaf BCT15X but all are closed threads. hoping someone has an answer.
 

Ubbe

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It probably depends of which filter are in use when and if a huge signal comes from the antenna when somebody very close transmits.
There are several band specific filters that gets activated by switching diods. If a switching diod are conducting the RF signal goes thru it and if the signal are big enough it will blow that diod. The other diods that are not conducting for the other band filters can probably cope with the voltage as they are usually specified for something like 50v-100v.

If all frequency bands suffer from almost no sensitivity then the first transistor after the filters are probably blown. Or the transmission where so long that the scanner scanned thru all frequency bands during that time.

/Ubbe
 

kruser

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It probably depends of which filter are in use
/Ubbe
Ubbe,

I've never really paid any attention before as I've not had a blown front end in any newer Uniden but my question would be, how much of the band switching components and RF amp transistors are encased by black epoxy making repairs very hard if not impossible?

I'm talking about the epoxy the FCC made them add in ECPA Rev. 2 so end users could not alter the band switching stages in order to receive the old AMPS analog cell phone band via images.

I've managed to pop the entire blobs of epoxy off the boards in older Radio Shack models like the Pro-93 and 95 so I could replace users blown 1st stage RF amp transistors. I was always lucky that doing this did not also lift other components off the board but it never did.

I've never really paid any attention to how well Uniden protects these stages in their scanners. Can repairs be made by removing the epoxy somehow or did Uniden leave the RF amp transistors outside of the epoxy coating so they can be replaced?

I could see a service manual being very valuable in this case for those that may need to try and get under an area of epoxy for a repair.
I know Uniden must be able to do it as you see repair notes showing Q1 and Q2 replaced which are usually the first two RF amps in the front end.
So did Uniden leave the RF amp transistors accessible and not under epoxy or does Uniden have a way of removing the epoxy for repairs?
 

Ubbe

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The cellular monitor thing modifications where done by forcing the 700-900MHz band filter being in use while the scanner where actually monitoring a frequency in a different band, which had no frequencies blocked, and the mixing products made it possible to listen to 700-800Mhz from a "mirror" frequency.

So I guess it's only the diodes and filter components that needs to be "tamper proofed" and not the following amplifier and mixer transistors.
But the actual control of the switching diodes are done from an expander ic-circuit or the processor itself so it can just as easily be modified at another place and not necessarily at the actual filter and it's switching diodes. So it's probably only to show to FCC that they have done what is required by them. But all cellular nowadays are encrypted and digitial anyway so it shouldn't be needed to block any frequencies from being monitored and save the manufacturer from extra work and hazzle and also makes repairs harder to do, as blown front ends are probably one of the more common faults in a scanner.

/Ubbe
 

kruser

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So I guess it's only the diodes and filter components that needs to be "tamper proofed" and not the following amplifier and mixer transistors.
/Ubbe

Several of the models I worked on with blown RF transistors had epoxy that probably spilled over when it was applied to the band switching components. They should have used a thicker epoxy mix that did not run to other components when applied and also probably less of the epoxy so it stayed contained over just the band switching components to satisfy the FCC.
Some of the radios needed epoxy over several areas of the PCB as the band switching power traces were accessible a fair distance away from the actual band switch transistors. That usually made for a real mess if repair was needed. One could not even troubleshoot the circuits as everything was covered in epoxy so you could not even attach a meter probe.
 

cbreads

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It probably depends of which filter are in use when and if a huge signal comes from the antenna when somebody very close transmits.
There are several band specific filters that gets activated by switching diods. If a switching diod are conducting the RF signal goes thru it and if the signal are big enough it will blow that diod. The other diods that are not conducting for the other band filters can probably cope with the voltage as they are usually specified for something like 50v-100v.

If all frequency bands suffer from almost no sensitivity then the first transistor after the filters are probably blown. Or the transmission where so long that the scanner scanned thru all frequency bands during that time.

/Ubbe
appreciate the reply. Cant find a service manual so its going into storage until another one pops up cheap.
 
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