[sdiy] P.S. troubleshooting help

[Scott Gravenhorst]

I would start with a dummy load on both + and - sides of the supply and
see if you can replicate the failure outside of the synth cabinet. 
Power resistors calculated to draw a certain amount of current, perhaps
something in the range of 15 ohms for 1 ampere 60 ohms for 0.25 A. 
Remember to consider power dissipation and provide for that.  Really
sucks not to have the schematic.  Do you know how much current the
synth draws?  Are you possibly causing it to shut down due to
overcurrent?  The part number - does that suggest 3 amperes per rail? 
Is it possible to trace out the schematic by looking at the PCB?

"Scott" <Scott at scottwick.com> wrote:
>Can someone help me troubleshoot my power one hcc-15-3-A? I took 
>it out of my synth cabinet last night to test it. It tested fine. 
>(checked for ac ripple w/ the scope, checked to see if it was 
>loosing power when my AC power drops, etc.. was all fine) I put 
>it back in my synth today.. doesn't work. Take it out and test 
>it. I get 15 volts on the + and .66 volts on the - side. 
>
>The pins of the main power transistor on the + side read 15 
>volts. On the negative side the pins read 23! (I'm guessing it 
>should read -15) Then Im not sure what happens to the signal, 
>because almost everywhere else I test on the - side of the pcb, I 
>read .66 volts. 
>
>I did try replacing the regulator IC (lm723n) (swapped sides, put 
>negative on pos, pos on neg) and the positive side still works 
>fine, so that isn't it. (If you aren't familiar w/ them, they 
>aren't positive and negative regulators.. they are the exact same 
>chip) 
>
>So, having never tried to fix a power supply, and not having the 
>schematics for this thing... im not sure where to go from here. 
>
>let me know if anyone has any ideas. Hopefully that .66 v on the 
>negative side will give someone more informed than me, a clue as 
>to what is going on. I also tested the transformer, and it is 
>outputting exactly what it should on every 2ndary. 
>
>thanks a lot!
>
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-- ScottG
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-- Scott Gravenhorst
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