Farnell E30/2 Current Problem - UK Vintage Radio Repair and Restoration Discussion Forum

JamieEC · 26th Apr 2014, 4:55 pm

Hello

I have had this power supply for a while now and recently it's developed a problem where the output current seems to be limited to about 50mA, but as far as I am aware there is no current limiting on this PSU so I am not sure where the issue lies. I have looked at the board and cannot see any obvious faults (Caps blown etc.).

Any help appriciated
Thanks

WME_bill · 26th Apr 2014, 6:43 pm

Farnell E30/2. While there is no variable current limit, there is overload protection. I will scan the circuit etc and post it. Poor old capacitors get blamed for everything, but it sounds rather as though a resistor has gone high. The voltage across R16 -1ohm in the emitter of Tr6, the 2N3055 driver of Tr7, is measured by the chain R9-220, VR3-500, R10 5.6k with R11 5.6k in parallel for the 15v range. When the voltage at the base of Tr4 reaches 0.7v, then it limits. Try tweaking the variable present VR3. This may be enough to allow you to trace the trouble before I post the circuit. wme_bill

JamieEC · 26th Apr 2014, 6:59 pm

Thanks for the quick reply
I do have a diagram and have found the area of the diagram you are referancing.
I will try tweaking VR3 now

JamieEC · 26th Apr 2014, 8:30 pm

Thanks again
Adjusting this pot made a difference, but i can still only draw .4A on the 2A 15V range

JamieEC · 27th Apr 2014, 12:59 pm

I have found R17 is open, whereas it should be 1 ohm
Will try and replace it asap, dont have any that low at the minute

Thanks

Refugee · 28th Apr 2014, 2:51 pm

Last time I had that problem it was a loose nut on the back of the output terminals. The output was coming through the voltage sense feedback resistor and gave the same symptom and if you load it too much while the fault is there you may also blow the feedback resistor or transistor.

26th Apr 2014, 4:55 pm	#1
JamieEC Tetrode Join Date: Apr 2011 Location: Cheshire Posts: 79	Farnell E30/2 Current Problem Hello I have had this power supply for a while now and recently it's developed a problem where the output current seems to be limited to about 50mA, but as far as I am aware there is no current limiting on this PSU so I am not sure where the issue lies. I have looked at the board and cannot see any obvious faults (Caps blown etc.). Any help appriciated Thanks

26th Apr 2014, 6:43 pm	#2
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Farnell E30/2 Current Problem Farnell E30/2. While there is no variable current limit, there is overload protection. I will scan the circuit etc and post it. Poor old capacitors get blamed for everything, but it sounds rather as though a resistor has gone high. The voltage across R16 -1ohm in the emitter of Tr6, the 2N3055 driver of Tr7, is measured by the chain R9-220, VR3-500, R10 5.6k with R11 5.6k in parallel for the 15v range. When the voltage at the base of Tr4 reaches 0.7v, then it limits. Try tweaking the variable present VR3. This may be enough to allow you to trace the trouble before I post the circuit. wme_bill

26th Apr 2014, 6:59 pm	#3
JamieEC Tetrode Join Date: Apr 2011 Location: Cheshire Posts: 79	Re: Farnell E30/2 Current Problem Thanks for the quick reply I do have a diagram and have found the area of the diagram you are referancing. I will try tweaking VR3 now

26th Apr 2014, 8:30 pm	#4
JamieEC Tetrode Join Date: Apr 2011 Location: Cheshire Posts: 79	Re: Farnell E30/2 Current Problem Thanks again Adjusting this pot made a difference, but i can still only draw .4A on the 2A 15V range

27th Apr 2014, 12:59 pm	#5
JamieEC Tetrode Join Date: Apr 2011 Location: Cheshire Posts: 79	Re: Farnell E30/2 Current Problem I have found R17 is open, whereas it should be 1 ohm Will try and replace it asap, dont have any that low at the minute Thanks

28th Apr 2014, 2:51 pm	#6
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Farnell E30/2 Current Problem Last time I had that problem it was a loose nut on the back of the output terminals. The output was coming through the voltage sense feedback resistor and gave the same symptom and if you load it too much while the fault is there you may also blow the feedback resistor or transistor.