Bearcat BC855XLT Looses it's Memory Occasionally

Hi,

My Bearcat BC855XLT looses it's memory once in a great
while. Note: I am a service technician.

I did NOT find (Google search) a schematic for this scanner.

This scanner has a "unique capacitor type memory back-up".

I would like to modify this scanner and use a battery back-up because
it is a HASSLE to reprogram the 50 channels.

Does anyone know where I can find (willing to buy it) schematic?

Or.....

Does anyone know where I can find the modification I want to make
to maintain memory?

Thank You in advance, John

 

[Fred McKenzie]

In article <93707e9n1eca880srascnr59t56g1krnnr@4ax.com>,
jaugustine@verizon.net wrote:

Hi,

My Bearcat BC855XLT looses it's memory once in a great
while. Note: I am a service technician.

I did NOT find (Google search) a schematic for this scanner.

This scanner has a "unique capacitor type memory back-up".

I would like to modify this scanner and use a battery back-up because
it is a HASSLE to reprogram the 50 channels.

Does anyone know where I can find (willing to buy it) schematic?

Or.....

Does anyone know where I can find the modification I want to make
to maintain memory?

John-

I have a Radio Shack HTX-10 transceiver with that problem. When
disconnected from any power source, memory contents were maintained by
the charge on a 220 Microfarad capacitor. Over a month, memory contents
were lost due to leakage.

I installed a 3.6 Volt Lithium battery, isolated by a 1N4004 diode,
across the capacitor. This approach may work for you if the operating
memory voltage is higher than 3.6 Volts.

Last time I checked, memory contents were still good after ten years!

Fred

 

[Lucifer]

On Fri, 22 Feb 2019 11:08:32 -0500, jaugustine@verizon.net wrote:

Hi,

My Bearcat BC855XLT looses it's memory once in a great
while. Note: I am a service technician.

Have you tried bending the pins to stop the memory
becoming loose?

I did NOT find (Google search) a schematic for this scanner.

This scanner has a "unique capacitor type memory back-up".

I would like to modify this scanner and use a battery back-up because
it is a HASSLE to reprogram the 50 channels.

Does anyone know where I can find (willing to buy it) schematic?

Or.....

Does anyone know where I can find the modification I want to make
to maintain memory?

Thank You in advance, John

 

[Allodoxaphobia]

On Sat, 23 Feb 2019 08:28:43 +1100, Lucifer wrote:

On Fri, 22 Feb 2019 11:08:32 -0500, jaugustine@verizon.net wrote:

Hi,

My Bearcat BC855XLT looses it's memory once in a great
while. Note: I am a service technician.

Have you tried bending the pins to stop the memory
becoming loose?

https://theoatmeal.com/static/misspelling.html

 

<SNIP>

John-

I have a Radio Shack HTX-10 transceiver with that problem. When
disconnected from any power source, memory contents were maintained by
the charge on a 220 Microfarad capacitor. Over a month, memory contents
were lost due to leakage.

I installed a 3.6 Volt Lithium battery, isolated by a 1N4004 diode,
across the capacitor. This approach may work for you if the operating
memory voltage is higher than 3.6 Volts.

Last time I checked, memory contents were still good after ten years!

Fred

Hi Fred and others,

I forgot to mention that I was unable to identify the "unique capacitor"
by visual examination of the circuit board. I do not see any "out of the
ordinary" capacitors.

John

 

[Jeff Liebermann]

On Fri, 22 Feb 2019 11:08:32 -0500, jaugustine@verizon.net wrote:

My Bearcat BC855XLT looses it's memory once in a great
while. Note: I am a service technician.

How long is a great while? There's a low leakage electrolytic
capacitor that will hold a charge to keep the memory alive for about 3
days maximum according to the user manual.

> I did NOT find (Google search) a schematic for this scanner.

Same here. Some user manuals, but no service manuals.

> This scanner has a "unique capacitor type memory back-up".

It's a low leakage type, probably one of these:
<https://www.mouser.com/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/Aluminum-Electrolytic-Capacitors-Radial-Leaded/_/N-75hqw?P=1z0wrk5&Keyword=Nichicon+Low+Leakage+Aluminum+Electrolytic+Capacitors&FS=True>

I would like to modify this scanner and use a battery back-up because
it is a HASSLE to reprogram the 50 channels.

You'll probably need to find the capacitor in question and measure the
operating voltage. Try turning OFF the scanner and measure the
voltage across all the likely culprits (large value electrolytics).
Anything with voltage when it's off is a possibility. You might also
check the minimum voltage needed to keep the memory alive. Then, add
a battery with a reverse protection diode to prevent the radio from
charging the battery.

Does anyone know where I can find (willing to buy it) schematic?
Or.....
Does anyone know where I can find the modification I want to make
to maintain memory?

Sorry, but it's the best I can do.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Chuck]

On Sat, 23 Feb 2019 15:21:49 -0500, jaugustine@verizon.net wrote:

SNIP
John-

I have a Radio Shack HTX-10 transceiver with that problem. When
disconnected from any power source, memory contents were maintained by
the charge on a 220 Microfarad capacitor. Over a month, memory contents
were lost due to leakage.

I installed a 3.6 Volt Lithium battery, isolated by a 1N4004 diode,
across the capacitor. This approach may work for you if the operating
memory voltage is higher than 3.6 Volts.

Last time I checked, memory contents were still good after ten years!

Fred

Hi Fred and others,

I forgot to mention that I was unable to identify the "unique capacitor"
by visual examination of the circuit board. I do not see any "out of the
ordinary" capacitors.

John
They are usually .47F to 1F and are normally short and squat.

 

[Ken Layton]

On Saturday, February 23, 2019 at 12:52:57 PM UTC-8, Jeff Liebermann wrote:

On Fri, 22 Feb 2019 11:08:32 -0500, jaugustine@verizon.net wrote:

My Bearcat BC855XLT looses it's memory once in a great
while. Note: I am a service technician.

How long is a great while? There's a low leakage electrolytic
capacitor that will hold a charge to keep the memory alive for about 3
days maximum according to the user manual.

I did NOT find (Google search) a schematic for this scanner.

Same here. Some user manuals, but no service manuals.

This scanner has a "unique capacitor type memory back-up".

It's a low leakage type, probably one of these:
https://www.mouser.com/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/Aluminum-Electrolytic-Capacitors-Radial-Leaded/_/N-75hqw?P=1z0wrk5&Keyword=Nichicon+Low+Leakage+Aluminum+Electrolytic+Capacitors&FS=True

I would like to modify this scanner and use a battery back-up because
it is a HASSLE to reprogram the 50 channels.

You'll probably need to find the capacitor in question and measure the
operating voltage. Try turning OFF the scanner and measure the
voltage across all the likely culprits (large value electrolytics).
Anything with voltage when it's off is a possibility. You might also
check the minimum voltage needed to keep the memory alive. Then, add
a battery with a reverse protection diode to prevent the radio from
charging the battery.

Does anyone know where I can find (willing to buy it) schematic?
Or.....
Does anyone know where I can find the modification I want to make
to maintain memory?

Sorry, but it's the best I can do.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

To follow up on this problem, I sent John copies of the schematics from the BC855XLT service manual I have. Hopefully, he will be able to fix his problem with the channel memory. As a side note, my late mom had this same model scanner and it exhibited the same problems as John is having. So it would appear this problem was happening to other BC855XLT scanners too.