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

[Tom Wiltshire]

The 74LS08’s sound quite likely, but the tracks to/from them are also very likely. Mine had corrosion on the tracks that wasn’t enough to break the track, but was enough to prevent signals getting through. Testing for continuity along as many tracks as you can stand is an excellent start. I had to patch some of them with fine wire. It’s sometimes possible to work out which tracks are the likely candidates by looking to see what functions are working and what aren’t and where those lines are driven from, but since most of the panel os controlled via those bus lines, that’s the bit that usually causes the chaos. Since the bus is shared, even one of them going down can take out many functions.

HTH,
Tom

------------------
Tom Wiltshire
Electric Druid
------------------

> On 25 Jul 2017, at 03:39, Ian Michael Ferguson <ifergu1 at gmail.com> wrote:
> 
> Appreciate the follow-ups.
> 
> I checked all three voltages at the test points, and they were all very close to spec. +15, -15, and +5, so no worries there.
> 
> So I've discovered you can make limited synth sounds in Manual mode, but it's not quite right. All controls don't do what you'd expect, if anything.
> All sound also stops if Resonance is much past 8 o'clock on the knob. Probably a bad pot(?) Once I happened to turn that knob full counter-clockwise I started getting sound.
> Switching to preset modes still gets stuck in a drone sound though that might be because there's no data there from losing the battery(?)
> 
> I'm thinking I'll replace the two SN74LS08N chips that were in the battery damaged area, but otherwise looked OK, just in case, since they are readily available and I've already socketed them.
> Going to check on that Resonance pot and maybe look into reloading the factory presets...
> 
> 
> When it was "shocking" me it was a dull, unpleasant, shock, sort of like licking a used 9V battery.
> You could hold your finger on it, but you wouldn't want to, to be sure. Certainly not full mains voltage.
> The chassis has not been charged in this way in the last several days of me turning it on, and I've not been able to reproduce it.
> So I'm not confident it will never come back, but I will have to get an RCD to do those tests.
> 
> -Ian
> 
> On Mon, Jul 24, 2017 at 2:01 PM, ASSI <Stromeko at nexgo.de> wrote:
> On Thursday, July 20, 2017 4:49:44 AM CEST Ian Michael Ferguson wrote:
> > While prodding around I then noticed the panel and all grounds were
> > electrified (because they shocked me)!
> 
> When you say you got shocked, what exactly does that mean?  You say you've
> tried different places so I'm guessing that it wasn't a very hard shock that
> made you throw everything away.  But please do no further experiments without
> using an RCD (30mA trip point or less)!  Make sure you are isolated from
> earth, put one hand in your pocket and keep it there.  Then (using your other
> hand), measure the voltage of the chassis against some known-good earth
> potential and then measure it again across some not-too-small resistance
> (~33kOhm) you put between chassis and earth (while the power is
> disconnected!).  Chances are that there is a leaky input filter (look for Y-
> or X-capacitors) or improperly connected electrostatic shield in the
> transformer.  Otherwise you're probably having an isolation fail in the
> transformer (which will most likely trip the RCD when you connect the resistor
> to earth), which you'd need to replace immediately in that case.
> 
> 
> Regards,
> Achim.
> --
> +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
> 
> Wavetables for the Waldorf Blofeld:
> http://Synth.Stromeko.net/Downloads.html#BlofeldUserWavetables
> 
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