AC/DC power supply

[sparkync]

Hi, I'm new here and may be a little over my head in this subject I'm asking. I have been an electrician for 40 years, but haven't done much in electronics. I have an ac/dc converter that I want to repair if possible, and am wondering if someone might guide me a little through the troubleshooting of it. It is actually a converter for a cooler that plugs into a regular 120 volt outlet and changes it to 12 volt dc for the cooler. It is rated at 1.2 amps. I am not getting any voltage out of it when plugged in. Could someone help me with where to start?
Thanks for any help you can give me.

 

[davenn]

hi sparky
welcome to the forums

ok are there any fuses in the PSU ? either on the AC or DC side ?
I am assuming you have opened it up and had a look inside ?

its possible that the transformer has a thermal fuse hidden under the paper/plastic wrapping thats over the windings. pretty common these days.
check for continuity of the primary winding with you meter on Ohms range. not sure what you would get on a 120V transformer ( Im in a 240V country) but you should get at least a few 10's of Ohms.
A 240AC to 16VAC that I just tested here has 125 Ohms for the primary winding

try that for a start and report back we can go from there

cheers
Dave

 

[sparkync]

Thanks for the quick reply. There don't seem to be any fuses on the board at all.
I can't determine which is the primary winding solder joints on the circuit board.
thanks again...
By the way, the board I'm working on is a "Data Electronics Device Inc." Model # 1674 Output 12VDC 5A, input 1.2 amps/144 VA
It is an "Igloo Kool mate Converter" Date Code 9/91
Hope this helps identify what I'm working on...
Thanks again..

 

[duke37]

The transformer primary will be the two connections that go into the wall. You do not need to dismantle anything to check the primary.

If it is a switch mode power supply it will be weigh very little and be open circuit on the primary except for when the meter is first connected which will show a short deflection.

 

[sparkync]

I am not getting anything on the plug where it plugs into the wall. I'm using a fluke multimeter. Thanks again.

 

[Resqueline]

At 5A output I doubt it uses an old-fashioned iron transformer (heavy), I'd expect it's a light-weight electronic "solid-state" supply. Post a pic' of its guts please.
The first thing to do is to listen carefully if it makes any sounds at all. If it klicks there's a diode shorted. No sound could mean a bad capacitor or resistor.
There is a fuse, but it might not be in the shape you're used to, and if it's blown there's a good reason for it (shorted rectifier bridge or transistor).

 

[daddles]

If the code means it was manufactured in 1991, it's over 20 years old. I'd scrap the thing and buy a new wall wart (I'm assuming that's what it is). You can get a 12 V 1.5 A wall wart from Radio Shack for about $15 IIRC. Make sure to save any needed connector from the old one.

 

[sparkync]

Thanks for all the replies. I called my local Radio Shack and they don't carry one with 5 amp. output. I did find one online for around $25.00 + tax. I may go that route if I can't solve it soon. I'll try the other test when I get a chance. Thanks again...

 

[daddles]

Sorry sparkync, I thought I saw 12 V 1.5 A -- not the 5 A you in fact wrote. Instead of a wall wart, there are inexpensive switching power supplies that might work. There are lots of places that sell such things; here's one. Also here and here.

 

[sparkync]

Thanks for all the replies. I just went ahead and ordered the one from Radio Shack. According to most of the reviews, it works well with a cooler. All I'll have to do is splice the correct end for the cooler onto the converter. Thanks again...