[sdiy] Polysix Repair - Panel/Ground Electrified!?

[rsdio at audiobanshee.com]

First things first:

Have you confirmed the polarity and voltage of the power coming from the wall? I recently helped someone diagnose noise in the background of their computer screens, which turned out to be that their apartment was wired with Hot and Neutral reversed on most of the outlets. They had to hire an electrician to correct everything, and then the problems went away.

There are also systems that put 60VAC on Hot and inverted 60VAC on Neutral, with only the Ground at 0V. Those balanced power systems are incredibly rare, though, and probably only installed by people who need it specifically for their audio equipment because some electronics would not function with this kind of power.


Just to review - and you may already know this - the Ground lug on a three-prong power cord is not supposed to connect to the transformer. It's designed only to connect to a metal case for the purpose of ground fault protection. Ideally, the Neutral wire should not be connected to the Ground lug (only your breaker box should connect them, not your electronics equipment!). Only Neutral and Hot should connect to the transformer. Center-tap transformers make this confusing, so I'll stop here.


I'll have to look at the Polysix schematics if your problem isn't at the wall.

Brian Willoughby


On Jul 19, 2017, at 7:49 PM, Ian Michael Ferguson <ifergu1 at gmail.com> wrote:
> I am working on a Polysix with a very bad case of battery leak damage.
> I did my best to restore it with the Old Crow method and put the board back in and hooked everything up. Lots of work!
> 
> Upon test power-up it immediately makes a synth noise, but does not respond properly to keyboard input. The rate LEDs blink, and the preset 1 is active, volume control works, pitch wheel works, etc.
> Upon switching to manual mode, however, nothing happens at all.
> 
> While prodding around I then noticed the panel and all grounds were electrified (because they shocked me)! Unplugging the transformer assembly from the second power PCB (with the large capacitors - filter PCB?) and thus presumably from the synth boards, and powering on still electrifies ground, so it must be earlier up the chain? The only thing I see touching ground on the first power PCB/transformer is a ground lug.
> 
> Does anyone have any suggestions and/or stupid things to check?

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