[sdiy] P.S. troubleshooting help

[Scott Gravenhorst]

music.maker at gte.net wrote:
>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. 

Oh - I missed this - so out of the synth is shows .66V on the - side?  Is that with
or without a load?  Some power supplies need some kind of load...

>>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
>________________________________________________________________________
>-- Scott Gravenhorst
>-- FPGA MIDI Synthesizer Information: home1.gte.net/res0658s/FPGA_synth/
>-- FatMan: home1.gte.net/res0658s/fatman/
>-- NonFatMan: home1.gte.net/res0658s/electronics/
>-- When the going gets tough, the tough use the command line.
>
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-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- FPGA MIDI Synthesizer Information: home1.gte.net/res0658s/FPGA_synth/
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- When the going gets tough, the tough use the command line.