ARP Omni burnt resistor

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lukasmayfloor
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ARP Omni burnt resistor

Post by lukasmayfloor » Tue Sep 17, 2019 3:07 pm

hey i'm new here and have never repaired a synth, but i have a decent enough grasp of how electronics work. i recently acquired an ARP Omni with a cut off power cable which i replaced. I turned it on and heard that it was working to some degree, but before i could test all the functions i noticed smoke coming from the far right side up from the keys. I turned it off, opened it up and had a look (and smell) around and pretty quickly found the source. One of the resistors on the release circuit had burned through and was melting the casing off the capacitor directly next to it. Replacing this resistor seems like and easy enough fix that i could do myself, but i'm not quite sure where to find its specs. Its too black to read the markings and i'm having trouble deciphering the manual. Here's a photo. Also i'm not sure if the capacitor also needs to be replaced, or if i can just re-wrap the casing. Thanks for any help!
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Ashe37
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Re: ARP Omni burnt resistor

Post by Ashe37 » Tue Sep 17, 2019 3:54 pm

yow that resistor is crispy

anyway, my actual contribution is: yes, replace the cap. I'd check every cap in it and do mass replacements if you feel up to it.

lukasmayfloor
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Re: ARP Omni burnt resistor

Post by lukasmayfloor » Tue Sep 17, 2019 4:19 pm

Thanks for the reply! How would i go about finding the exact value of this resistor? Can't quite seem to figure it out based on the manual. I guess i could go through all the other resistors on that board and deduce which one it has to be based on the parts list?
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Screen Shot 2019-09-17 at 17.18.08.png
Screen Shot 2019-09-17 at 17.16.54.png

lukasmayfloor
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Re: ARP Omni burnt resistor

Post by lukasmayfloor » Tue Sep 17, 2019 4:23 pm

sorry that parts list photo is incorrect, here is the correct list
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Screen Shot 2019-09-17 at 17.21.24.png

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Yekuku
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Re: ARP Omni burnt resistor

Post by Yekuku » Fri Sep 20, 2019 7:48 am

Hi Lukas,
unfortunately the list that you have provided does not help.
The burned resistor should be R44 = 100 Ohm, but I am not quite sure because all the service manuals that i could find were unreadable at this section.
Also , resistors do not burn by themselves , there is sth else triggering this fault.
my wild guess is that the tantalum cap C18 ( blue cap) is shorted. you should replace both C17 & C18.
good luck !
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