Okay, time to dive into this overly-complicated 5V regulator
circuit. Yes, it's a very good candidate for just unsoldering most of it and
replacing it with a 7805, but somehow that just seems like cheating....
1) It's important to note that we are dealing with two
different "ground" levels here. The ground from the wall wart supply is on the
collector of Q1, while the ground from the batteries (also the ground for the 5V
output) is on the emitter of Q1. If you can run it with batteries but not from
an A/C adapter, there is a good chance that Q1 is not switching on to allow
current through it. It's the negative return path for the power supply
current.
2) The only thing between 6-11A and 6-10A is the power
switch on the volume knob, so they should both be 12 or 13 volts when the power
is switched on, using the negative terminal of the A/C adapter or collector of
Q1 as a ground reference. You should get 12 volts all the way over to the
emitter of Q3. On the collector of Q3 (also on 6-6A) is where the +5V should be,
using the collector of Q1 or 6-7A as the ground reference.
3) The thing that switches Q1 on is the 12 volts which needs
to get through D4 to the base of Q1. D4 is a 10 volt zener, so if you don't get
at least 10 volts across it, it will be starved and Q1 will never switch on. If
you've got 10 volts across the zener, and 13 volts from 6-10A to the collector
of Q1, then it should turn on and you will only have about 1 volt across
collector to emitter of Q1 (collector is the negative side). If you've got more
like 13 volts from collector to emitter of Q1, then Q1 didn't turn on and
is most likely bad.
4) If you don't have 13V on 6-10A then you probably forgot to
turn the synth on.
5) Q18 is part of the -5V supply and it does get faily warm.
The unregulated 13V is used to drive Q17 and Q18 which form an oscillator to
convert it back into AC. This AC signal is stepped down through the transformer
into a full-wave bridge rectifier (D8,9,10,11), then to a zener diode D7. If you
have -5V at 6-8A, then Q18 is probably okay. If not, maybe Q18 is switched
permanently on, or shorted inside. If you have an
oscilloscope, try checking across the transformer to see if the AC
signal is there. If not, try the AC range of your voltmeter across
it.
Get some more voltage
readings and we'll see where to go from there. If you've got a diode checker on
you meter, take a look at D2 and make sure it looks good (Turn synth OFF first).
Or just use the ohm-meter setting and make sure it's almost nothing in one
direction and really high in the other (with the power switched off of
course).
Don
Backshall
From: korgpolyex@yahoogroups.com
[mailto:korgpolyex@yahoogroups.com] On Behalf Of backshall1
(dsl)
Sent: Monday, December 27, 2010 9:44 AM
To: korgpolyex@yahoogroups.com
Subject: RE: [korgpolyex] Re: korg poly 800 power problem
Sent: Monday, December 27, 2010 9:44 AM
To: korgpolyex@yahoogroups.com
Subject: RE: [korgpolyex] Re: korg poly 800 power problem
I think what Mike means here is that if you had
batteries installed, and wired the A/C adapter directly to the same circuit, the
higher voltage would feed back into the batteries, like an unregulated charger,
and you can definitely cause a fire trying to charge non-rechargeable
batteries.
From: korgpolyex@yahoogroups.com
[mailto:korgpolyex@yahoogroups.com] On Behalf Of
zoinky420
Sent: Monday, December 27, 2010 1:04 AM
To: korgpolyex@yahoogroups.com
Subject: [korgpolyex] Re: korg poly 800 power problem
Sent: Monday, December 27, 2010 1:04 AM
To: korgpolyex@yahoogroups.com
Subject: [korgpolyex] Re: korg poly 800 power problem
--- In korgpolyex@yahoogroups.com,
Michael Hawkins <korgpolyex800@...> wrote:
>wiring a jack to the battery terminals if done incorrectly could
> To be frank,
> causea battery explosion or fire.
>Well a wall-wart is a more stable power source than batteries. What do you mean by 'incorrectly'?