Low +5v advice

[bones]

Hi, before I just source and replace all the components in this circuit, can anyone logic out the most likely problem device.
This circuit when functioning correctly pumps out 5.67v, at the moment I am getting 4.9v at the regulators output pin. The regulator has the same input voltage as a good circuit producing the 5.67v. Any educated guesses ?

 

[Georgian2]

Did you measure 4.9V loaded or unloaded?

 

[bones]

It was without load, I have several of these power supplies to compare against, this unit came from a machine that was resetting whereas the PSUs with the 5.67v do not reset the machine. Just grabbed a regulator off of a good psu and that is only giving 4.9v ? So not the regulator I'd say.

 

[Georgian2]

Most likly the bigger capacitor on the regulator output. It is good to change them all. That 1000uF on the input can make trouble as well.

 

[bones]

That is electrolytic so a good call, will swap that next, must nip out for some cow juice for tea lol

 

[bones]

Bugger not the electrolytic, can only be one of the other 3 caps, never had that sort go before.

 

[John Bennett]

Which pins are you measuring between for the output?
The regulator absolute output maximum voltage is 5.25V

 

[Georgian2]

Are the other ceramic? Weird that there is no bigger cap on the output

 

[John Bennett]

Yeah I wondered that, 200nF is tiny

 

[bones]

Middle pin is 0v, left input, right output, original regulator was a tl780-05 but thought that was just a 1.5amp too.

 

[bones]

Oh caps are yellow boxes

 

[bones]

Ok stopping now, changed everything except the bridge and no change. If the regulator is 5.25v max then best I check the working units again. Confused as the bridge is putting the same voltage into the input of the regulator as the others. There are other voltages on the pcb but the only connection between them is the 0v line ugh

 

[gunblade]

that circuit looks to be reliant on the ac input level?

 

[bones]

It comes from a transformer at 8.11v hits the pcb bridge and comes out at 9.69v the off to the regulator. Seriously considering that the diagram doesn't match the pcb as the unregulated 5v is coming from the unregulated 12v circuit on the pcb so best I go to bed lol