--- On Wed, 8/11/10, Steve Carter <synth@...> wrote:

From: Steve Carter <synth@...>
Subject: Re: [korg_mono-poly] Re: Burnt Resistor and possibly Faulty SSM2044
To: korg_mono-poly@yahoogroups.com
Date: Wednesday, August 11, 2010, 8:31 AM

 

Dan - forget the DC rating of the original switch suppression cap and fit an X1 cap in its place.  Here is what I used:  

http://cpc.farnell. com/vishay- bc-components/ bfc233810333/ capacitor- class-x1- 0-033uf-440v/ dp/CA06014

It's OK to completely isolate the PSU for testing although I wouldn't remove the additional soldered ground connections unless you're removing the board.  I would just unplug the connectors on the left hand side and measure the voltages on the appropriate pins.  If all is well, I would plug everything back and isolate the EG/VCF board by unplugging the power connector to it.  Switch on and check that your fuses stay intact and your DC voltages are OK.  If so, this confirms that your short or partial short is on the EG/VCF board.  If that board is bringing down the supply rails and blowing the fuses, it could be any of the ICs at fault or even one of the small innocent looking decoupling capacitors. 

Rather than replace the 2044, I would remove the board and carefully desolder the 2044 . Now plug all the connectors back into the board and support it on something non metallic whilst switching on again. If the fuses remain intact then it looks like you've got a toasted 2044.  I'm still puzzled about VR19 being fried and as this is the offset adjustment for the 2044, irrespective of how the pot got fried, it could have taken the 2044 down. If it wasn't for this I would have suspect the 2044 last of all as nowadays we're seeing a lot of the old logic series ICs and early op amps biting the dust for no underlying reason. My instinct would point me to one of the 4007 ICs on the EGs or one of the 4558 op amps.

Steve

On 11 Aug 2010, at 01:03, biggiemoog wrote:

 

Hey Steve,

Thanks for the quick reply. The tuning semi-fixed resistor is what fried, its black, it smoked, im pretty sure its done. Thats fine, ive got a replacement.

As for the capacitors, ill leave them alone and see what voltage is coming from the powersupply. Is it ok to disconnect the grounds attached to the powersupply (1 goes to the Osc board and 1 goes to the volume control pot) and then test the voltage on the PSU

Its hard to find an X1 Capacitor for the mains input board, i can get X2 Capacitors but the voltage is 2.5kv not 4kv that the current one is.

If i test the power supply and it reads fine, what would you go for next the SSM2044

Many thanks,

Dan

--- In korg_mono-poly@ yahoogroups. com , Steve Carter <synth@...> wrote:
>
> I would do some logical testing before powering up again. Unplug all the DC output connectors from the power supply and check that the plus and minus 15 volt rails are OK and the +5volt rail also. You don't want to risk blowing other components.
>
> I just can't see VR19 going up in smoke - you're right it's 100K and connected to the SSM2044 via a 470K resistor so if something in the chip went short circuit it wouldn't make the slightest difference to VR19. If there was some liquid spillage on the track of the pot, it may give up the ghost but at 100K across the DC rails it can't pass more than 0.3mA which is not enough to cause a fry-up! It just doesn't make any sense. Are you 100% certain that VR19 is fried I can understand the SSM2044 developing an internal short and blowing the fuses as it sits straight across the rails.
>
> As for the capacitor on the mains input panel - this is a suppression cap to prevent arcing on the mains on/off switch contacts. It's wired straight across the switch and the only trouble it can cause is if it went short circuit it would be as if the on/off switch would be permanently on. If there is a visible crack in it then it would be wise to change it but make sure you use a polyprop X1 type capacitor of no more than 0.047uF (the original is 0.033uF).
>
> Unless you definitely know they're faulty, I would leave C13 and C14 alone - don't worry about the anti-vibration cloggy glue as it's doing no harm.
>
> My guess is that you've an SSM 2044 IC down and changing that along with the fuses will hopefully bring the MP back to life.
>
> Good luck!!
>
> Steve
>
> On 10 Aug 2010, at 14:08, biggiemoog wrote:
>
> > Worked out it was glue but im gonna replace them anyway. The capacitor on the small board that connects the transformer to the ac adapter is also cracked and ive taken it off and im replacing it.
> >
> > hopefully it works after this !
> >
> > --- In korg_mono-poly@ yahoogroups. com , "biggiemoog" <daniel.eden@> wrote:
> > >
> > > Ok - on further inspection, i have found C14/C13 Capacitors on the Power board are actually fused together, its very apparent, i cant slot even a piece of paper in between them.
> > >
> > > Can this be my issue
> > >
> > >
> > >
> > > --- In korg_mono-poly@ yahoogroups. com , "biggiemoog" <daniel.eden@> wrote:
> > > >
> > > > About a month ago my Mp4 died half way through playing an arp in poly mode. It completely shut off, didnt make a bang and wouldnt turn back on. I opened her up the other day and found that the 2x 250v 1A fuses on the power supply had blown. To test if i could get it back on i replaced these with 3.15A just for a second to turn it on, it did come on but then i fried VR19 Semi-fixed Resistor (104J), it was quite apparent, smoke only came from the filter board and when i dismantled it you can see quite easy that its burnt out. Prob not the best of idea to put a 3.15A fuse in but im an impatient prick so i paid the price for that. All that aside, im trying the following ;
> > > >
> > > > Replace the burnt resistor (im 99% sure its a 100KOhm, i checked the service manual and according to the VR18, the resistor right next to VR19, on the schematics, it says "100K").
> > > >
> > > > Replace the fuses with 1A 250V, i have these but i think that they will blow again straight away.
> > > >
> > > > Replace SSM2044 on the filter board, i have come to this conclusion (correct me if im wrong) that there is an issue with the the filter chip, possibly faulty, that is causing the short along the trace to the semi-fixed resistor.
> > > >
> > > > I would also like to say thanks alot for having me on board here, im stoked to be able to post my drama's with people of like minded nature. I hope there is someone that can point me the right way.
> > > >
> > > > My Mp4 is Japanese but i use a step up transformer to have it run here in Australia. My last question before i finish the post is, is it possible to have a Australian PSU put into the MP4 to eliminate the Step up transformer
> > > >
> > > > Many thanks
> > > >
> > > > Daniel
> > > >
> > >
> >
> >
>