Korg DW8000, Mono/Poly, MS-20...

> Take CN03, take green as Ground. Output Voltages are on the middle brown
> Connector=-4.9 Volts, on the Right brown one 4.9 Volts.
>
> Next: Take CN2A. Yellow is ground. I´ll start from the left brwon
> connector. 4.9 Volts, 4.9 Volts, -6.8 volts, 4.9 Volts, 11.8 Volts

hey remember me?
well, i've finally gotten around to doing some work on the dw8000. i've
replaced the caps on the voltage converter board except for the large
ones, which i will replace as soon as i get them. the local electronic
supply didn't have them in stock.
i measured the voltages across cn2a and cn3a and this is what i found:
cn3a
-4.9v
965mv

cn2a
-4.9v
4.99v
-6.9v
560mv
12.9v

so the big differences are obviously the mv values and the first -4.9v
value for cn2a(unless that was a typo on your end). i triple checked all
the measurements, so i know they're right.
what does this mean? is the power supply hooped? if so, what is a
suitable replacement?

when i first fired up the keyboard after replacing the caps, there was
the distortion, like before, only it seemed to sound muddier than
before. i can't be sure on that because it's been a few months since i
last messed with it. the distortion was present without touching any
keys and upon pressing the keys it increased in volume and muddiness. it
didn't matter which key was pressed, it was the same note of mud. after
less than a minute, the distortion then faded to nothing. now there is
no sound whatsoever, not even hiss with the volume right up. there is
only a fairly loud and short pop/buzz when powering up. if i turn it off
for a few seconds then back on, there is a quieter and more normal
sounding pop. i have to leave it off for several minutes and then turn
it on to hear the loud pop/buzz.
the battery tests fine and patch changes can be retained in memory.

when replacing large caps how do you deal with the adhesive that is used
to keep them in place? cut around them with an exacto? what is the
adhesive? i'll need to get some.

asking for guidance, once again,
merci,
shayne



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--- In DW8000@yahoogroups.com, Shayne Cafferata <scafferata@s...> wrote:

> when replacing large caps how do you deal with the adhesive that is used
> to keep them in place? cut around them with an exacto? what is the
> adhesive? i'll need to get some.

It's generally just some sort of liquid glue that hardens over time into something very
brittle. You should be able to just carefully chip it away with a small Xacto or even jeweler
screwdriver, just be careful. There's really no need to replace the glue, it just holds
components to the board before flow soldering during mechanized assembly. You'll be
doing your replacement by hand, so you just stick the leads through the holes and spread
them a bit to hold them for soldering.

I'm really impressed that you are component-level rebuilding your DW8K power supply,
but if it starts getting too expensive, pick up a "parts" DW8K, something with physically
damaged keys or cracked case or something, and scavenge the power supply.

-Mark

--- In DW8000@yahoogroups.com, Shayne Cafferata <scafferata@s...> wrote:

  

> when replacing large caps how do you deal with the adhesive that is used 
> to keep them in place? cut around them with an exacto? what is the 
> adhesive? i'll need to get some.
    

It's generally just some sort of liquid glue that hardens over time into something very 
brittle.  You should be able to just carefully chip it away with a small Xacto or even jeweler 
screwdriver, just be careful.  There's really no need to replace the glue, it just holds 
components to the board before flow soldering during mechanized assembly.  You'll be 
doing your replacement by hand, so you just stick the leads through the holes and spread 
them a bit to hold them for soldering.

I'm really impressed that you are component-level rebuilding your DW8K power supply, 
but if it starts getting too expensive, pick up a "parts" DW8K, something with physically 
damaged keys or cracked case or something, and scavenge the power supply.

-Mark

well, the really impressive thing is how people are so willing to help out and share their knowledge. all i'm really doing is following instructions. however, i had been feeling kind of impressed with myself - up until a couple hours ago. i was desoldering one of the voltage converters and i ended up lifting the copper pads, all three of them. shit! i'm using a push-pump desolderer and it is just not doing it for me. someone recommended desoldering braid. is there a specific kind that works well?
i've tried some stuff from radio shack and i thought it sucked.
is there a cure for what i've done? or is it time to start looking for another pwr supply board?

shayne

--- In DW8000@yahoogroups.com, Shayne Cafferata <scafferata@s...> wrote:

> i was desoldering one of the voltage
> converters and i ended up lifting the copper pads, all three of them.
> shit! i'm using a push-pump desolderer and it is just not doing it for
> me. someone recommended desoldering braid. is there a specific kind that
> works well?
> i've tried some stuff from radio shack and i thought it sucked.
> is there a cure for what i've done? or is it time to start looking for
> another pwr supply board?

Lifting copper pads from the voltage regulator isn't the end of the world. Here's my
advice, coming from a long background in electronics repair:

Push pump desolder tools are very useful to get rid of the excess solder on contacts, but
it's really just a first step. You should then do detail desoldering using a soldering iron
and copper desoldering braid. Any brand should do as long as the copper is shiny, rather
than oxidized. If you are not getting good results with Radio Shack desoldering braid,
(which is generally quite good, although more expensive when you go through quantities
of the stuff) also purchase a tube of electronics soldering flux, which Radio Shack also
sells. Wipe desoldering flux on the copper desoldering braid before using it, and you'll be
amazed at how the stuff just sucks up solder.

For your detached voltage regulator pads, (presuming they are completely broken,
detached from everything) you'd generally accomplish a repair like this: Find the circuit
trace that the pad was connected to, and carefully scrape away the (usually) green coating
with an Xacto knife to reveal fresh copper. Apply a dab of fresh solder to it with a
soldering iron. Get some reasonably sized wire, preferably solid, and solder one end to
the solder dab, wrap the other end around the pin of the regulator that it goes to, and hit
it with solder. You can use rubber insulated wire if you need to bridge some length.

Alternatively, follow the trace that the pad was connected to until it hits another
component connected to the same trace. Use an iron to lift that component's pin a bit,
and then use a new piece of rubber-insulated wire to tack-solder one end to that
component, then wrap the other end around the regulator's pin and hit it with solder. For
long wire runs, if you want to be really neat and tidy, you can tack a couple dabs of
silicone sealant or hot glue every couple inches along the wire's length to keep it in place
on the board.

Note that if it's a wide trace you're repairing this way, you should use a reasonably thick
wire. Power supply circuit traces are often wide to accomodate large currents, and you
don't want to be splice-repairing it with ultra-thin wire, which will act as a fuse!

-Mark

Lifting copper pads from the voltage regulator isn't the end of the
world. Here's my

> advice, coming from a long background in electronics repair:
>

right on! thanks, mark. i did a little research and found a lifted pad
repair document, but it involves gluing copper inserts into the
original holes. too anal for me, i think i'll go with your advice. i
picked up the regulators i need, some braid, and solder flux. ready to
give it a go. here's hoping this will do it. i am so dying to play
with that arpeggiator. i haven't had one since my first synth - a
polysix - nearly 20 years ago.

shayne

success!
yeah! uh huh! oh yeah!
a BIG thank you to stephen rinass, mark(bugsiwabbit), and dave vanhorn!
never would've happened without your guidance.
i love these sounds. a little reminiscent of the poly 800, but with more
pizzaz, like extra large meat lover's.
some patches are kinda noisy, but i'm assuming that's a characteristic.
when i turn it on, it gives a skronky sort of buzz for about 1 second.
as soon as it defaults to a patch everything's quiet. is that normal?
now i have to make room in my tiny studio. after this addition the space
will be maxed out for sure. but i am NOT complaining! nuh uh...
thanks guys!
shayne





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