Power Stability Issues with Uniden Bearcat BC-70XLT Scanner

[TeeJayZee]

Click the link to view pictures and specifications of this vintage radio: RigPix Database - Bearcat/Uniden - BC-70XLT

I wanted to share this information since there doesn’t seem to be any mention of this issue when attempting to use the radio without the battery connected.

Background:
The Uniden Bearcat BC-70XLT scanner exhibits a peculiar behavior when operated solely on AC power without the battery pack. When the battery is removed and the scanner is plugged in with the AC adapter (12V), increasing the volume results in a loud, stuttering noise and potential loss of programmed frequencies.

Key Points:
1. Power Supply Stability:
- The AC adapter provides a steady 12V output under load, but the scanner's performance becomes erratic when the battery is removed.

2. Battery as a Stabilizer:
- The battery seems to play a crucial role in stabilizing the power supply, acting as a buffer to smooth out any minor fluctuations or noise from the AC adapter.

3. Charging Behavior:
- Interestingly, the battery charges only when the scanner is turned off, indicating that the charging circuit is designed to function without the interference of the radio's operation.

4. User Experience:
- Users with similar scanners have reported that keeping the battery connected while using the AC adapter ensures stable operation and prevents the erratic behavior observed when the battery is removed.

Conclusion:
For optimal performance and to avoid issues with volume control and loss of programmed frequencies, it is recommended to keep the battery connected to the Uniden Bearcat BC-70XLT scanner while using the AC adapter. Regularly checking and maintaining the battery's health will help ensure consistent and reliable operation.

I hope this information is useful to someone.

 

[dmfalk]

Volume levels can add drain to voltage consumption, which seems to be what you're experiencing. Sounds like possible capacitor failure.

 

[MTS2000des]

One must also consider this is an almost 40 year old radio. ASSuming all components are original, things like electrolytic capacitors, especially in the power supply section, may be way out of tolerance, shorted, leaky (electrically and even physically) or open causing erratic operation.
If one is going to use vintage equipment as a daily driver, might be prudent to go through it and replace discrete components such as those caps.

 

[TeeJayZee]

Thanks for the input, everyone—I really appreciate the information.

The radio works perfectly with just the battery connected, with or without the AC adapter connected. It only does this erratic behavior when the battery is disconnected or dead.

Ever since I got this radio in the late '80s, I've always kept the battery inside and used the AC adapter whenever I wanted to conserve battery power or charge it overnight when depleted.

It wasn’t until the battery started failing—I've replaced it twice over its lifetime—that I began noticing the glitch. In a way, it serves as a sign that the battery needs recharging or replacing.

So you guys don't think the battery helps stabilize the radio when only connected to the AC adapter?

 

[MTS2000des]

So you guys don't think the battery helps stabilize the radio when only connected to the AC adapter?

I haven't studied the schematic, if there even is one out there for the unit, but it's possible. The battery itself acts as a capacitor if the power supply is designed that way. If it gets soft, then yes, just like a bad electrolytic going leaky, same result. (Still a good idea to replace caps or at least check them for ESR in a rig that old).

 

[TeeJayZee]

Given the age of the radio, I agree that it would be prudent to check the capacitors for ESR and consider replacing them if necessary.

Thanks again for your input.