Korg Delta... aka The Repair From Hell!!

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Re: Korg Delta... aka The Repair From Hell!!

Postby mjrippe » Sun Jan 26, 2014 5:16 am

Thanks for the detailed reply! First of all, C5 plays correctly with no noises, not silent, all other C notes have the crackle/pop. Capacitor C68 is ceramic and will be the next thing I replace.

Again, the new TOG has clean output. I have replaced the 4013 (IC5), but pin 13 still shows the noisy waveform - it looks like jitter on the square wave, not voltage spikes. When the noise happens it is as though the low parts of the square go high but with ripple, if you know what I mean. Perhaps a video clip would help?

The whole C5 vs C1-4 is a bit confusing. Again, pin 14 on IC3 is a clean square wave. It is pin 40 on IC1 as well as pin 13 on IC5 that show the problem. The other half of the 4013 (IC5) is working fine, octave switching is flawless. Since the C5 note is clean, is it possible the problem is coming from the S10430?
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Re: Korg Delta... aka The Repair From Hell!!

Postby nathanscribe » Sun Jan 26, 2014 12:45 pm

mjrippe wrote:Thanks for the detailed reply! First of all, C5 plays correctly with no noises, not silent, all other C notes have the crackle/pop.


OK, ignore pretty much everything I said! :lol:

Capacitor C68 is ceramic and will be the next thing I replace.


Can't hurt.

Again, the new TOG has clean output. I have replaced the 4013 (IC5), but pin 13 still shows the noisy waveform - it looks like jitter on the square wave, not voltage spikes. When the noise happens it is as though the low parts of the square go high but with ripple, if you know what I mean. Perhaps a video clip would help?


Have you checked the PCB tracks around that second half of the 4013, and between it's output and the 10430? Pics of that noise would be good.

The whole C5 vs C1-4 is a bit confusing. Again, pin 14 on IC3 is a clean square wave. It is pin 40 on IC1 as well as pin 13 on IC5 that show the problem. The other half of the 4013 (IC5) is working fine, octave switching is flawless. Since the C5 note is clean, is it possible the problem is coming from the S10430?


Pin 13 on IC3 is an envelope input. If you hear the note C5 play with no problems, I would forget about that and concentrate on the lower C1-C4.
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Re: Korg Delta... aka The Repair From Hell!!

Postby Steve Jones » Sun Jan 26, 2014 6:45 pm

Not sure if I missed something in this conversation but it sounds like IC 1 is faulty.
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Re: Korg Delta... aka The Repair From Hell!!

Postby mjrippe » Mon Jan 27, 2014 1:03 am

Steve Jones wrote:Not sure if I missed something in this conversation but it sounds like IC 1 is faulty.


That is indeed my fear. Just thought I'd replace all the 10 cent parts before yanking the 50 dollar one ;)
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Re: Korg Delta... aka The Repair From Hell!!

Postby nathanscribe » Mon Jan 27, 2014 2:09 am

True fact.
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Re: Korg Delta... aka The Repair From Hell!!

Postby mjrippe » Thu Jan 30, 2014 4:53 am

As expected, the ceramic cap made no difference. Ordering a replacement S10430.
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Re: Korg Delta... aka The Repair From Hell!!

Postby gibsonripper » Mon Mar 17, 2014 8:57 pm

Just like many of you (I like Rhino's response especially), I, too, can attest to many years invested in repairing vintage music gear. 23 to be exact. Yet, I *still* chase my tail on many problems with all sorts of analog synths. It is most certainly not an exaggeration to say that we as technicians, open a can of worms and in that can is another can of worms. Often times, troubleshooting is 80-90% of the time you spend repairing an old synth while the remainder is the actual implementation for repair and calibration adjustment, etc. We could all write a book on synth repair, combine those books into an encyclopedia of vintage synth repair and still not have a near complete story for which one could consistently and successfully repair old analog synths.

I have to warn my customers that there may be a 2nd, 3rd and possibly 4th estimate. And those can be a wild jump from one to the other.

If I had to count the number of hours that were lost to unbilled repair time (I like to call this "partially paid education"), it would amount to more time than I would want to admit or acknowledge.

And hence, this is why guys like me have semi-retired--whereas we have our "day jobs", doing something completely unrelated, yet pays consistently, and then the occasional/part-time work repairing vintage gear in order to either a) make supplementary income and/or b) because we are masochists​ with a undying love for vintage synths, no matter how many late nights we spent deep into these repairs, sacrificing our increasingly scarce free time for our friends, spouses, or family.
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Re: Korg Delta... aka The Repair From Hell!!

Postby sam » Mon Mar 17, 2014 9:25 pm

Hmm ...I really understand these issues...I have a monooly that fails (short circuit) after 7 seconds, I know the fault is on the osc/ filter board but i can't find the problem.

I have spent weeks on this and the last time it blew something on the psu ...I am still brooding over this and one day i will be daft enough to try again..Maybe look for those caps..?
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Re: Korg Delta... aka The Repair From Hell!!

Postby sneakthief » Tue Mar 18, 2014 1:23 pm

What gibsonripper said... x1000!

This is what I have in my synth-repair hospital right now:

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Re: Korg Delta... aka The Repair From Hell!!

Postby nathanscribe » Tue Mar 18, 2014 4:18 pm

I feel your pain... good luck.
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Re: Korg Delta... aka The Repair From Hell!!

Postby sam » Tue Mar 18, 2014 8:17 pm

Just fixed a very battered omni....Feel free to ask any questions..
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Prophet vs. Pro-one. Wasp.EMS VCS3
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Re: Korg Delta... aka The Repair From Hell!!

Postby sneakthief » Wed Mar 19, 2014 6:44 pm

= EDIT =

Arp Omni tangent continued here:

viewtopic.php?f=5&t=74897
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