Hi Chase

if there is digital noise in the audio, then the problem is typically
wrong or missing grounding.

You may check the power rails with an oscilloscope, whether the digital
noise signal is on the powerrails.
If not: I would use an audio probe (like a multimeter probe, but
connected to an audio amp; ground connected separately) and go through
the complete signal path starting from the VCOs until the output socket.
This should allow to narrow down the cause.

Florian


BTW: Swaping the 8049 doesn't help anything - and also it would have to
be a 8049 for a monopoly. This is a CPU, with embeded PROM. The PROM
content is written once at the factory; a 8049 from a Roland SH-101 is
something completely different from the one in the Korg MonoPoly. So you
need a chip which was produced especially for the related synth.



plus_321 wrote:

> Okay, I did the tests that you suggested and I think they came out okay. I didn't get the exact voltage range that you specified.
>
> I got 25.37 VAC on the fuses and 33.78 VDC on the diodes, but the measurements were consistent so I think it's fine.
>
> I replaced the blown fuse and it's been running fine for a few hours now. Still, I can't help but wonder why the fuse went out.
>
> I have another issue that's bothering me that, I believe, has been around since I got this mono/poly. It has a constant noise coming through the outputs that almost sounds like data noise. I can't seem to upload things now or I would put up a sample.
>
> A while ago, I found through experiementing that if I remove connector CN23 from board 356, then the noise will go away. I remember figuring out that this went to the arpeggiator. I also tested the connector pin to pin from the cable and discovered that the second pin from the left is what creates the noise when connected. I looked through the service manual and found that this pin is for 2OCT arp mode. I pulled it out of the connector, but the arp won't run without it.
>
> A while ago I remember thinking that it was the 8049c since the arp deals with that so I ordered a replacement. Well I just tried to swap the chips and the issue remains so it isn't that. I really need the arp on this guy, because that is part of what makes it unique, but it is hard to deal with noise anymore.. Does this sound like maybe something you've seen or any suggestions on where to look
>
> I replaced nearly all electrolytic capacitors, voltage regulators, and op amps in this machine so I don't really have any idea what it could be. However, I will not go to a tech. I took this very machine to a tech to fix this problem and the result of that was 3 months away from my keyboard and 200 dollars from my bank account. I can not afford such extravagant fees.
>
> I will appreciate any suggestions. Otherwise, thank you for your time.
>
> Chase
>
> --- In korg_mono-poly@yahoogroups.com , Florian Anwander <fanwander@...> wrote:
>
>>Hello Chase
>>
>>first my usual disclaimer:
>>THIS MAIL DESCRIBS AN ACTION THAT REQUIRES TO OPEN THE CASE OF THE
>>MONOPOLY. THIS SHOULD ONLY BE DONE BY PEOPLE, WHO KNOW HOW TO HANDLE THE
>>DANGEROUS VOLTAGES INSIDE OF THE SYNTH PROPERLY WITHOUT ENDANGERING THE
>>LIFE OF OTHERS OR THEMSELVES!!! IF YOU DON'T HAVE THE REQUIRED
>>EXPERIENCE - KEEP YOUR HANDS OFF!!! DOING THE WRONG THINGS INSIDE AN
>>ELECTRICAL INSTRUMENT MAY KILL YOU OR PEOPLE, THAT RELY ON YOUR WORK. I
>>WARNED YOU. I REJECT ALL LIABILITY FOR ALL CONSEQUENCES OF THE FOLLOWING
>>INSTRUCTIONS!
>>
>>
>>>So even if I replace this fuse and it seems perfectly fine, wouldn't a
>>>fuse blowing be indicative of a problem There wasn't really a power
>>>surge as far as I could tell and I think this fuse is only a few years old.
>>
>>It might(!) be indicative for a problem - especially because the
>>transformer was that hot.
>>
>>I recommend the following procedure:
>>* Switch of the synth, and remove the powercable from the power outlet
>>in the wall.
>>* open up the synth
>>* take a thick and stabile sheet of paper and cover all parts at the
>>bottom and rear side of the synth right side of the transformer with it
>>(powerswitch, main fuse pcb, transformer-connections)
>>* Do NOT switch on the synth until you replaced the fuse.
>>* Remove both fuses on the powersupply pcb - still do not switch on the
>>synth.
>>* Disconnect all cables from the powersupply pcb with exception of the
>>cable coming from the transformer.
>>* Prepare a digital voltmeter, which can read DC and AC up to 50 volts.
>>* Connect the minus measuring cable to the wire coming out of the right
>>side of C14 (the largest capacitor on the right side of the power supply
>>pcb)
>>* Set the voltmeter to AC
>>* Plug in the power cable to the power outlet in the wall
>>* Switch the synth on
>>* Measure the voltage at the frontside contact of the fuse sockets => it
>>should read about 15 to 20 Volts, but both contacts should read the same
>>voltage
>>* Switch of the synth
>>* Insert good fuses to the sockets
>>* Set the voltmeter to DC and be prepared to measure immediately after
>>switching on the synth
>>* Switch on the synth
>>* Measure the voltage at the most rear contacts of diodes D2/D3 and
>>D4/D5. It should read somthing around 20 to 25 Volts DC; again I can not
>>tell now exactly what voltage, but it should be the same on both
>>measuring points.
>>
>>If any of these measurements fails or if the fuse blows again, then get
>>the synth to a technician, who knows to handle this.
>>
>>If the mesaurements before read ok, then:
>>* Measure the voltages at CN33. They should read from left to right:
>>+15V, -15V, +5V, 0V. The pins for -15 and +15 may read a little bit
>>different values like 14.98 or 15.02, but it should NOT be like -15.01
>>and 17.5; if this is the case, then switch off the synth and bring it to
>>a tech.
>>If both read a similar but wrong value like +13 and -13, then try to
>>adjust the voltage with the trim potentiometer VR3. VR3 affects both
>>voltages.
>>If +5V reads a slightly other value (like +5.02) it is ok. If it reads a
>>very different value (like 9.02), then switch off the synth and bring it
>>to a tech.
>>
>>
>>Florian
>>
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