Korg Poly800/EX800 Users

Hello everyone;

I'm making another attempt to revive some of the carcasses that I have
accumulated over the years. Some of this is venturing into almost bizarre
territory (more about this in another post); I've also come across
something that looks like a factory mod that I have never seen before.

Anyway, this one looks like a comparatively easy to fix problem; but before
I jump in and start replacing parts I would like to ask for some advice.

This particular machine is a pretty straight Mk1. At first it wouldn't boot
at all; and since the signals around IC29 did not look coherent I replaced
it. This  brought the machine back to life; and basically everything seems
to work ok (except one key in the keyboard; but that can wait).
When I turn the Poly off and turn it on again it usually does not work (but
sometimes it does). This can be traced back to the power supply section.

There are several scenarios:

1. Switching on after a longer time usually works right away. All voltages
are there. Q1 has normal temperature.
2a. Turning off the Poly and turning it back on shortly afterwards usually
isn't working. All voltages except +5V are there; instead of +5V I'm
getting a voltage between 2.5V and 4V (which clearly isn't enough for the
processor RESET). Q1 is getting very hot, almost too hot to touch.
2b. Turning off the Poly and turning it back on sometimes also results in a
completely missing +5V rail (all other voltages are still there). In this
scenario Q1 stays cold.

Now before I replace Q1: Could there be another problem? It almost looks
like a thermal problem to me; however I'm a bit irritated simce it doesn't
seem to manifest itself while using the Poly - only when "restarting" it.

Any ideas?

Thanks,

Malte

hello Malte,
 I too have the same problem on my poly 800.
 If I turn off and power back does not start.
 you have solved? 

    Il Domenica 17 Gennaio 2016 21:39, "Malte Rogacki gacki@... [korgpolyex]" <korgpolyex@yahoogroups.com> ha scritto:
 

     Hello everyone;

I'm making another attempt to revive some of the carcasses that I have
accumulated over the years. Some of this is venturing into almost bizarre
territory (more about this in another post); I've also come across
something that looks like a factory mod that I have never seen before.

Anyway, this one looks like a comparatively easy to fix problem; but before
I jump in and start replacing parts I would like to ask for some advice.

This particular machine is a pretty straight Mk1. At first it wouldn't boot
at all; and since the signals around IC29 did not look coherent I replaced
it. This brought the machine back to life; and basically everything seems
to work ok (except one key in the keyboard; but that can wait).
When I turn the Poly off and turn it on again it usually does not work (but
sometimes it does). This can be traced back to the power supply section.

There are several scenarios:

1. Switching on after a longer time usually works right away. All voltages
are there. Q1 has normal temperature.
2a. Turning off the Poly and turning it back on shortly afterwards usually
isn't working. All voltages except +5V are there; instead of +5V I'm
getting a voltage between 2.5V and 4V (which clearly isn't enough for the
processor RESET). Q1 is getting very hot, almost too hot to touch.
2b. Turning off the Poly and turning it back on sometimes also results in a
completely missing +5V rail (all other voltages are still there). In this
scenario Q1 stays cold.

Now before I replace Q1: Could there be another problem? It almost looks
like a thermal problem to me; however I'm a bit irritated simce it doesn't
seem to manifest itself while using the Poly - only when "restarting" it.

Any ideas?

Thanks,

Malte