KB UP31 battery discharging - UK Vintage Radio Repair and Restoration Discussion Forum

crackle · 30th Oct 2018, 5:39 pm

I went to try my KB UP31 yesterday to find that it would not work.

It turned out that one battery was more or less completely flat at 2v. I had not tried the radio for a good few months but found it surprising as the Ever Ready silver batteries I had left in the radio, although a good few years old now were all bought at the same time.

I measured the current from the battery clip with a fresh battery and found approximately 0.6mA of current flowing whilst the radio was switched off.
Dodgy electrolytics I thought, but when I checked the circuit the on/off switch apparently disconnects the batteries from all the circuit.

I checked with the meter on resistance and found approximately 15k between the faulty battery clip terminals.

I removed the chassis and examined the wiring, my first thought were maybe the speaker chassis was shorting on the printed circuit, but that was not the case.

It seemed that there was a fault in the switch block. I didn't really fancy removing it from the radio and dismantling it so I did a few more tests to see if there was any one of the 2 sets of contact terminals for that battery which was faulty, maybe I could isolate it and just rely on the single set of contacts.

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Anyway tests showed that with the bridging wire removed from the terminal marked with a yellow blob the problem was not present. But strangely when I tested the terminals for shorts there were none. So I soldered the bridge wire back and all seemed OK.

It seems a bit of a mystery, I wonder what the cause was?

Mike

G6Tanuki · 30th Oct 2018, 5:44 pm

The switch looks a bit 'slimy' - have you been dosing it with any kind of switch-cleaner or contact lubricant?

Unsoldering/resoldering the bridging wire from the switch tag could have put enough heat into the switch to evaporate any conductive deposits.

Refugee · 30th Oct 2018, 5:45 pm

Perhaps there is a dead spider in the switch that has now dried out from the heat of the soldering iron.
There have been a lot of spiders about this year and hibernating space is at a premium for them.

crackle · 30th Oct 2018, 6:27 pm

Hi, Yes it got a good squirt of Super 10 after the problem was found.

Mike

30th Oct 2018, 5:39 pm	#1
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	KB UP31 battery discharging I went to try my KB UP31 yesterday to find that it would not work. It turned out that one battery was more or less completely flat at 2v. I had not tried the radio for a good few months but found it surprising as the Ever Ready silver batteries I had left in the radio, although a good few years old now were all bought at the same time. I measured the current from the battery clip with a fresh battery and found approximately 0.6mA of current flowing whilst the radio was switched off. Dodgy electrolytics I thought, but when I checked the circuit the on/off switch apparently disconnects the batteries from all the circuit. I checked with the meter on resistance and found approximately 15k between the faulty battery clip terminals. I removed the chassis and examined the wiring, my first thought were maybe the speaker chassis was shorting on the printed circuit, but that was not the case. It seemed that there was a fault in the switch block. I didn't really fancy removing it from the radio and dismantling it so I did a few more tests to see if there was any one of the 2 sets of contact terminals for that battery which was faulty, maybe I could isolate it and just rely on the single set of contacts. Anyway tests showed that with the bridging wire removed from the terminal marked with a yellow blob the problem was not present. But strangely when I tested the terminals for shorts there were none. So I soldered the bridge wire back and all seemed OK. It seems a bit of a mystery, I wonder what the cause was? Mike

30th Oct 2018, 5:44 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	Re: KB UP31 battery discharging The switch looks a bit 'slimy' - have you been dosing it with any kind of switch-cleaner or contact lubricant? Unsoldering/resoldering the bridging wire from the switch tag could have put enough heat into the switch to evaporate any conductive deposits.

30th Oct 2018, 5:45 pm	#3
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: KB UP31 battery discharging Perhaps there is a dead spider in the switch that has now dried out from the heat of the soldering iron. There have been a lot of spiders about this year and hibernating space is at a premium for them.

30th Oct 2018, 6:27 pm	#4
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: KB UP31 battery discharging Hi, Yes it got a good squirt of Super 10 after the problem was found. Mike