Korg Poly800/EX800 Users

Hi!

I just got myself another broken Poly-800. (The first one I got is now beyond repair. As I was 
offered a second one. I thought: Two minus makes a plus..). But now, after picking the new 
one appart. It seems like the -5V circuit is broken. I've replaced Q18. But the only reading i 
get is +0.9V where it should be -5V.

Could it be that small transformer that's busted? (KD-4? xD-4? It's hard to read the name on 
the schematics. And it says T1 on the circuitboard). The output of it is +0.45V (Measured at 
leg 1 of D10), I asume it shoudl be -2.50V instead?

Any ideas on how to replace it?

The long way, I guess, is to replace the entire circuit with a AC-DC converter that takes 9VAC 
in and with a 7805 and a 7905 regulates it.. But it seems like to much trouble right now.. Or?

Thanks!

//Jon

Unless you can see real physical damage to the coil, I doubt that the
coil would be the problem. Coils are generally very reliable unless
they are physically damaged by a direct impact, a sharp instrument
damages the windings or corrosion from battery or water.

I'm not certain of the voltages but I would check the capacitors first
- especially electrolytic's. Of all of the electronic components, they
age the fastest.

Mike.

--- In korgpolyex@yahoogroups.com, "Jon" <shonokij@...> wrote:
>
> Hi!
> 
> I just got myself another broken Poly-800. (The first one I got is
now beyond repair. As I was 
> offered a second one. I thought: Two minus makes a plus..). But now,
after picking the new 
> one appart. It seems like the -5V circuit is broken. I've replaced
Q18. But the only reading i 
> get is +0.9V where it should be -5V.
> 
> Could it be that small transformer that's busted? (KD-4? xD-4? It's
hard to read the name on 
> the schematics. And it says T1 on the circuitboard). The output of
it is +0.45V (Measured at 
> leg 1 of D10), I asume it shoudl be -2.50V instead?
> 
> Any ideas on how to replace it?
> 
> The long way, I guess, is to replace the entire circuit with a AC-DC
converter that takes 9VAC 
> in and with a 7805 and a 7905 regulates it.. But it seems like to
much trouble right now.. Or?

> 
> Thanks!
> 
> //Jon
>

Hi Marcus,

I thought that since the +5V part was working perfectly I'd leave them out.. But i figure it 
wouldn't hurt to change them anyway.

Thanks for the quick reply!

Cheers!
//Jon

--- In korgpolyex@yahoogroups.com, Marcus Wilson <JB@...> wrote:

>
> Hi  Jon
> 
> in my earlier email, I suggest to replace Q1 and Q3 also
> 
> ensure they are the right way around, and see if that helps
> 
> I also gave part numbers for those
> 
> best regards,
> 
> Marcus Wilson
> 
> On 13/01/2008, at 8:19 PM, Jon wrote:
> 
> > Hi!
> >
> > I just got myself another broken Poly-800. (The first one I got is  
> > now beyond repair. As I was
> > offered a second one. I thought: Two minus makes a plus..). But  
> > now, after picking the new
> > one appart. It seems like the -5V circuit is broken. I've replaced  
> > Q18. But the only reading i
> > get is +0.9V where it should be -5V.
> >
> > Could it be that small transformer that's busted? (KD-4? xD-4? It's  
> > hard to read the name on
> > the schematics. And it says T1 on the circuitboard). The output of  
> > it is +0.45V (Measured at
> > leg 1 of D10), I asume it shoudl be -2.50V instead?
> >
> > Any ideas on how to replace it?
> >
> > The long way, I guess, is to replace the entire circuit with a AC- 
> > DC converter that takes 9VAC
> > in and with a 7805 and a 7905 regulates it.. But it seems like to  
> > much trouble right now.. Or?
> >
> > Thanks!
> >
> > //Jon
> >
> >
> >
>

Hi Mike,

I can't see any damage to the coil. And as Marcus states in the email below; it's probably 
Q1 and Q3 that's the source of the problem.

But as you say, it could be a good idea to check the capacitors aswell..

Thanks!

//Jon

--- In korgpolyex@yahoogroups.com, "patrioticduo" <patrioticduo@...> wrote:

>
> Unless you can see real physical damage to the coil, I doubt that the
> coil would be the problem. Coils are generally very reliable unless
> they are physically damaged by a direct impact, a sharp instrument
> damages the windings or corrosion from battery or water.
> 
> I'm not certain of the voltages but I would check the capacitors first
> - especially electrolytic's. Of all of the electronic components, they
> age the fastest.
> 
> Mike.
> 
> --- In korgpolyex@yahoogroups.com, "Jon" <shonokij@> wrote:
> >
> > Hi!
> > 
> > I just got myself another broken Poly-800. (The first one I got is
> now beyond repair. As I was 
> > offered a second one. I thought: Two minus makes a plus..). But now,
> after picking the new 
> > one appart. It seems like the -5V circuit is broken. I've replaced
> Q18. But the only reading i 
> > get is +0.9V where it should be -5V.
> > 
> > Could it be that small transformer that's busted? (KD-4? xD-4? It's
> hard to read the name on 
> > the schematics. And it says T1 on the circuitboard). The output of
> it is +0.45V (Measured at 
> > leg 1 of D10), I asume it shoudl be -2.50V instead?
> > 
> > Any ideas on how to replace it?
> > 
> > The long way, I guess, is to replace the entire circuit with a AC-DC
> converter that takes 9VAC 
> > in and with a 7805 and a 7905 regulates it.. But it seems like to
> much trouble right now.. Or?
> > 
> > Thanks!
> > 
> > //Jon
> >
>