On Tue, 2010-12-28 at 03:46 +0000, n8 wrote:
> Hi Mike,
>
> Even the Korg Poly 800 OEM adapter gives out 12 volts...
>
> Looking at the adapter, its shows it as 9V neg center 700mA 15W @ input. But when I measure the voltage it gives out 12V! But this works fine with my other Korg Poly 800. So I doubt its the power supply adapter. As long as the polarity is correct (which even if its not the D2 diode will protect the circuit from wrong polarity).
> Its not the supply (though I agree seems rather high for a 9V).
>
> One odd thing is the other wall wart supply I have, with the correct voltage and polarity, it started to heat up very hot!
> Did not start a fire thank god but it too is rated at 9V, 500mA and gives out 13V!
That should ∗not∗ overheat when driving the Poly 800, unless there's
some horrible fault.
> Whats the deal with 9V giving out ~12-13V?!
9∗sqrt(2) = 12.7V - you're reading peak not RMS voltage ;-) Under load
it will sag a bit.
> I swapped out the D2 diode (not sure it was bad, my diode checker is kaput! LOL)
And you were careful to put D2 the "wrong way", with the cathode to
positive?
> Found an electronics shop that has Q1, Q3 and Q16 gonna swap those out and remeasure voltages.
>
> Right Now I am getting around 3.7 volts across EC on Q1...10V across D4 and .4V at pin 6!
I'm not sure what you mean by "pin 6". 3.7V across Q1 emitter/collector
sounds about right. You should see roughly 9-10V across C4 and whatever
your supply voltage is across C1. If you've got 10V across D4 that
sounds about right. Q1 may be faulty.
Leave Q2 and Q16 alone - if it works off batteries there's ∗nothing∗
wrong with the 5V supply. Don't touch it until you get the 9V regulator
working.
Gordon MM0YEQ