Re: #v5 #power issue #v5 #power

Dale Parfitt

Hi Tim,

It is a simple procedure to measure the output of the regulator and see whether it is nominal  or not. A 7805CV is rated as max input (from memory) of around 25V.  Let us know what you find.


Dale W4OP


From: [] On Behalf Of wt1im@...
Sent: Wednesday, June 24, 2020 2:51 PM
Subject: [BITX20] #v5 #power issue


Another mystery!

I power my uBitx v5 with a LiFePo 3.5Ah battery from Bioenno. It's a new battery but a little while back, the radio stopped powering up. Long story short, the battery was found to have a bad BMS (battery mgt system). The only symptom that I might have needed to pay more attention to before the radio failed was that the battery put out a little more than the 13.8v that nominal 12v systems typically do. My VOM is analog but it looked to be between 14 and 15v. 

With the LiFePo out of commission, I thought, no problem, I have lots of 12v sources. 

NONE of them would power up the radio. All verified good power sources that work fine on other things, test well, etc.

Meanwhile, the fellow ham who diagnosed the BMS issue charged my LiFePo by bypassing its BMS and using an external one. 

With the LiFePo back, it, and *only* it, will power the radio. But not for long, due to the BMS issues (I'm going to get a new BMS)--it cuts the voltage to zero. I can "reset" it by momentarily connecting it to a charger. Not a viable solution, just part of the troubleshooting chain. 

I do notice that the LiFePo shows 12v now--not the higher voltage it was showing before all of this happened.

My best guess is that the voltage regulator in the uBitx is bad, and will only power the rig with a very narrow range of voltages. The LiFePo is the only DC source I have handy that delivers less than 13.8v. 

I have read that the uBitx "wants" 12v or less. But the symptoms of running it with a bit more seem to be things like distorted RX audio. I haven't seen anyone say that 13.8v actually kills the radio. 

My best guess is that the 7805cv voltage regulator is bad It's not fully dead since I can get the rig to turn on with (only) the LiFePo, but perhaps it's gravely injured. Maybe the 14-15v that the LiFePo originally delivered fried it? Is my best next step to replace the regulator and see what happens? 

And--if 13.8+v really did kill this regulator, does it make sense to swap it with another part that can accept slightly higher voltages? I really am hoping I don't have to do deeper hacking on the power supply system to drop the voltage below 13.8 since that is such a universal DC voltage. A swap-in regulator replacement would be ideal. 

Thanks in advance!


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