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[sdiy] System 100 101 power supply issues

[sdiy] System 100 101 power supply issues

2026-02-17 by Todd Sines

Finally, getting around to getting this thing fixed.

#1: power supply. No +/-15V voltage.

Recapped the entire supply, no voltage.

Then I tried to replace the Roland 022-86C (100-120V) transformer with a Triad Magnetics toroidal transformer that delivers +/-15V, still nothing. Wondering if anyone else here has done work on one and what the typical points of failure were my were, perhaps the L723DC / LM723CN?? Or the 2SD-324 voltage regulators? Nothing is burnt out, and I’ve definitely got the winding correct.

Got any other ideas? Thanks,


Todd


Re: [sdiy] System 100 101 power supply issues

2026-02-17 by Oren Leavitt

With the power off, did you do visual inspection and continuity check on 
connections and PCBs?
Cracked PCB traces or loose solder joints are common problems in vintage 
gear.

With power on, is there:
Mains AC at the transformer primary?
Low voltage AC at the transformer secondary?
Unregulated DC across the main filter capacitors?
Regulated DC after the regulator?
Is it reaching the output connection?
Is there excessive current draw even though no output?
Is something triggering the 723's overload protection?
etc ...
Show quoted textHide quoted text
On 2/17/26 3:02 PM, Todd Sines via Synth-diy wrote:
> Finally, getting around to getting this thing fixed.
> 
> #1: power supply. No +/-15V voltage.
> 
> Recapped the entire supply, no voltage.
> 
> Then I tried to replace the Roland 022-86C (100-120V) transformer with a 
> Triad Magnetics toroidal transformer that delivers +/-15V, still 
> nothing. Wondering if anyone else here has done work on one and what the 
> typical points of failure were my were, perhaps the L723DC / LM723CN?? 
> Or the 2SD-324 voltage regulators? Nothing is burnt out, and I’ve 
> definitely got the winding correct.
> 
> Got any other ideas? Thanks,
> 
> 
> Todd
> 
>

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