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Old 29th August 2014, 08:37 PM   #1
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Default Dual Voltage power supply ??

I've got an issue with a dual voltage power supply. I have a full wave bridge with 4 diodes fed by 2 12vac secondaries with a center tap. at each output from the bridge I have (or should have) negative 12v and positive 12v referenced to the center tap ground. I have 2 capacitors on each leg coming off the bridge and instead of getting 12v outputs they are out of balance with say +13.5vdc and -9.65vdc. Where should I be looking to get the balanced voltage out that the circuit requires. The circuit works sort of .... its a led light bank on a citation16/19. Could this cause of the imbalance be due to a possible cold solder joint to ground somewhere in the circuit??

I've been working on trying to get this circuit to work properly for a few days and I'm missing something ...

Voltage from the secondaries is the same measured at the input to the 12v circuit, tested diodes all measure the same, tested capacitors both the same uF (new replaced), with no load the measurements are different and with load the measurements are still different (same as without load).

Any help would be appreciated.

Cheers,
Bob
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Old 29th August 2014, 08:58 PM   #2
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I got it - pulled a leg on each diode to double check and after re-soldering them to the board I've got balanced voltage!! Light board still not working properly tho.... more cold solder joints probable......I couldn't tell even under VERY close look I couldn't see the bad solder joint, I was looking I swear!

Cheers,
Bob
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Old 29th August 2014, 09:25 PM   #3
rayma is online now rayma  United States
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Quote:
Originally Posted by bobrown14 View Post
I got it - pulled a leg on each diode to double check and after re-soldering them to the board I've got balanced voltage!! Light board still not working properly tho.... more cold solder joints probable......I couldn't tell even under VERY close look I couldn't see the bad solder joint, I was looking I swear!

Cheers,
Bob
Try getting some eutectic solder, 63/37 tin/lead. It's hard to go wrong with this type.
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Old 30th August 2014, 12:16 AM   #4
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Originally Posted by rayma View Post
Try getting some eutectic solder, 63/37 tin/lead. It's hard to go wrong with this type.
I use Cardas Quad Silver Eutectic Solder - get it cheap of epay, I love it.

Been touching up all the solder joints on the LED board. Still have an issue. One of my ICs on the problem side is putting out negative voltage at the output when I want to see positive voltage - so I've got some more trouble learning to do with the LM741 ic. I've most likely got another cold solder joint I've yet to find. I did find a bad 1N914 diode thats on the output side of this chip... I'm going to have to figure out how to trouble shoot/test the ic. Lots of parts to test ....

Cheers,
Bob
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Old 30th August 2014, 12:40 AM   #5
rayma is online now rayma  United States
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Quote:
Originally Posted by bobrown14 View Post
I use Cardas Quad Silver Eutectic Solder - get it cheap of epay, I love it.

Been touching up all the solder joints on the LED board. Still have an issue. One of my ICs on the problem side is putting out negative voltage at the output when I want to see positive voltage - so I've got some more trouble learning to do with the LM741 ic. I've most likely got another cold solder joint I've yet to find.
Them you must have a soldering tip that's not hot enough, or corroded, or dirty. Before each connection, wipe the tip on a wet sponge,
and it should look shiny and clean. Hold the tip on the junction of the lead and pcb, and flow solder into the joint without touching the solder
directly to the tip. The metal should be hot enough to melt the solder by itself.
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Old 31st August 2014, 12:45 PM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by bobrown14 View Post
I use Cardas Quad Silver Eutectic Solder - get it cheap of epay,..............
Cheap and Ebay makes me think "fake" !
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Old 31st August 2014, 01:56 PM   #7
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Cheap and Ebay makes me think "fake" !
Nope - I've been using this type of solder for years .... it's excellent.

linky

25g Solder Cardas Quad Silver Eutectic Solder Authorized Cardas Dealer | eBay

Cheers,
Bob
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Old 31st August 2014, 05:21 PM   #8
AndrewT is offline AndrewT  Scotland
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$11.75 is not cheap.
That's $235 for a 500gm reel.

And then he adds on $10 for postage !
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Old 31st August 2014, 07:35 PM   #9
Elvee is offline Elvee  Belgium
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Originally Posted by AndrewT View Post
$11.75 is not cheap.
That's $235 for a 500gm reel.

And then he adds on $10 for postage !
Dreams and phantasies rarely come that cheap....
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Old 1st September 2014, 01:39 AM   #10
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$11.75 is not cheap.
That's $235 for a 500gm reel.

And then he adds on $10 for postage !
Wow.. seriously? I bought 4 sets or 100g and it was free shipping there.
Good quality silver solder is getting more and more $$. I used to use the WBT German stuff that is like 2x the money or more @ $165/250gm roll, so I'm actually slumming it with this stuff. Thought I'd give it a try before buying a bunch. I like the WBT probably best but this is not too bad pretty close actually so for the price hard to beat unless I get a roll.

Cheers,
Bob
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