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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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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 |
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On Sat, 23 Feb 2019 08:28:43 +1100, Lucifer wrote:
On Fri, 22 Feb 2019 11:08:32 -0500, 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 |
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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 |
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On Saturday, February 23, 2019 at 12:52:57 PM UTC-8, Jeff Liebermann wrote:
On Fri, 22 Feb 2019 11:08:32 -0500, 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+Alumi num+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 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. |
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