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Old 10-04-2015, 12:04 AM   #21
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Join Date: Oct 2015
City & State: Dallas, Texas
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Default Re: General PSU Discussion and FAQ contributions

Hello all, this is my first post here, so please be kind
I have a couple of power SMPS power supplies, that are doing some wired stuff:
one of them, the Vcc (pin 7) of the UC3842, is fluctuating, it does seem to get to 16V, since I do see the square pulse on pin 6, but it is fluctuating between 13v and 10v!!
I have replaced the power IC, all caps and made sure all the resistors associated with this device are good. I use the light bulb to check the parts, since If I power it with the fuse in place, the rectifiers get very hot and short out...
The second one, is, I am getting about 70v after the start up resistor!! I back tracked it,
on a good board I have about 105v DC on the output of the bridge rectifier , but reading 155v DC on the non-working unit...if I lift the +dc output pin from the PCB, then it drops to 95v, put it back, the DC output voltage goes up to 155v dc.
If I am not providing enough information, please excuse me, but will be more than happy to expand on what I have posted here. your help is greatly appreciated.
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