Derek Marpole Posted July 31, 2020 Share Posted July 31, 2020 I have dragged my old flight box out of (34 year) retirement and although the MFA Power Box fuel pump and starter supply is fine the plug sockets are showing 12volts. Would this problem be repairable or should I invest in a new power box. If the latter is the case, any suggestions for a replacement would be appreciated. Thanks Quote Link to comment Share on other sites More sharing options...
wingcoax Posted July 31, 2020 Share Posted July 31, 2020 Not sure what the layout is inside, but i suspect a resistor has gone down. That would drop the 12v to 2v for the plug. If you have a multimeter check against what is on the resistor/s. Steve. Quote Link to comment Share on other sites More sharing options...
Derek Marpole Posted July 31, 2020 Author Share Posted July 31, 2020 Thanks Steve, I’ll dismantle it over the weekend and see what I can find. Quote Link to comment Share on other sites More sharing options...
Dickw Posted July 31, 2020 Share Posted July 31, 2020 If the volts are dropped by a resistor then a voltmeter would show 12v until a load was placed on the socket. It is the load that caused the volt drop (Vdrop=IR). Try it with a glowplug or a small torch/car bulb connected. Dick Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted July 31, 2020 Share Posted July 31, 2020 I agree with Dick....it's so simple internally it's unlikely to be faulty, you just need to put a load across the plug output to get it to regulate the voltage. Quote Link to comment Share on other sites More sharing options...
Derek Marpole Posted July 31, 2020 Author Share Posted July 31, 2020 Thanks all. The reason for the post was the result of trying a plug which immediately zapped when when connected. I’m not an electrical expert but will try to check the resistors tomorrow. It would appear that the glowplug was not sufficient load to drop the voltage. Derek Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted August 1, 2020 Share Posted August 1, 2020 When you get into the back of the panel Derek, just scan along and feel the hard wires are actually soldered down. It is very easy for this kind of hard wiring to spring apart due to age and stress. I hope the simplest scenario presents itself, as these early units were assembled by putting stiff wire across to components taking the shortest route, and pinned down with solder Edited By Denis Watkins on 01/08/2020 08:41:57 Quote Link to comment Share on other sites More sharing options...
Gary Binnie Posted August 1, 2020 Share Posted August 1, 2020 Is this the panel with an integral fuel pump and white line border around the front panel and a yellow capped selector knob? I had one the same, it had a 'plug' and 'hi-amp plug' position, using the wrong setting could blow a plug and also fail to start an engine with a hi amp plug! Can't remember why I stopped using it, think the fuel pump gummed up. I fly mostly gliders but recently finished an Xtra Wot, my cobbled together flight box was not up to the job so I gave it a birthday. New power panel, JP, under £20 with variable plug current, adjust to get the right colour glow. It needs a separate fuel pump (which I was using already). Second battery, the old gel cell was not good enough to turn a 120 engine over, the battery is from a motorcycle in storage. The new battery only powers the starter. Volt meter for the motorcycle battery, mainly to make sure I don't kill it using it to power a field lipo charger. 12V cigarette lighter socket, Jeti transmitters have an optional 12V charger accessory. I'm planning to make a pure charging station using a new car battery that my daughter bought and then decided to scrap the car. I charge a lot of small lipos for F5J practise and competitions. Cheers Gary Quote Link to comment Share on other sites More sharing options...
Former Member Posted August 1, 2020 Share Posted August 1, 2020 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Former Member Posted August 1, 2020 Share Posted August 1, 2020 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted August 1, 2020 Share Posted August 1, 2020 Some of the older designs used a dropper resistor without the clever electronics. Most of the ones with adjustable glow power seem to be, as you say, switching circuits. Quote Link to comment Share on other sites More sharing options...
gangster Posted August 1, 2020 Share Posted August 1, 2020 If it’s the old mFA with the rotary switch is is a simple beast. Nice panel though using dropper resistors. I would expect to see 12 volts on the plug socket without a load. Maybe test with something like a sidelight bulb if you do not wish to risk a plug. They are nice no nonsense panels Edited By gangster on 01/08/2020 16:01:19 Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted August 1, 2020 Share Posted August 1, 2020 From my old flight box in the shed You can see the ballast resistors and the makeshift Hardwiring Quote Link to comment Share on other sites More sharing options...
Derek Marpole Posted August 2, 2020 Author Share Posted August 2, 2020 Thanks to everyone who contributed to this post. I found some new plugs and used the’Plug’ setting and all was well. I probably had it on the High-Amp setting when I tried the first plug. I tried to attach a photo but couldn’t get the post to see my photo albums. One to resolve on a wet day!! Kind regards, Derek Quote Link to comment Share on other sites More sharing options...
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