OB-Xa Tracking Issue

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Jacob Hunt
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OB-Xa Tracking Issue

Post by Jacob Hunt » Thu Feb 14, 2013 6:00 am

I recently acquired a broke down OB-Xa, and have been bringing it back from the dead. After a power supply rebuild and replacing a few dead parts it has been mostly working. The lower voice cards were not working, but their respective LEDs were lighting up properly. I found it to be the CEM3360 VCA chip on the lower mother board that was not functioning. I ordered a replacement and put it in today. After tuning up the voices on the bottom, I was quite thrilled with the fantastic sound of my now 7 voice OB-Xa. But my excitement fell as I realized another problem that wasn't obvious before: filter tracking on the bottom boards doesn't work at all. The top boards respond to it fine, but the bottom just won't do it.

Does anybody have a solution as to why only the bottom boards don't respond? The other problems with the OB-Xa I think I can deal with, but this has me stumped. Could it be one of the 4051be ICs on the lower control board? It seems one of them is messing up the functions of my pots (one of them on the pot board of course), and I read that the RCA brand chips are sometimes poor quality. Any help would be greatly appreciated.

radek tymecki
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Re: OB-Xa Tracking Issue

Post by radek tymecki » Sat Feb 16, 2013 6:18 pm

yep. coud be 4xxx ic's problem. had same with my friend's ob-xa

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Jacob Hunt
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Posts: 76
Joined: Wed Mar 09, 2011 10:54 pm
Gear: An old Polymoog that's on it's way.
Location: The Backwoods of Georgia...

Re: OB-Xa Tracking Issue

Post by Jacob Hunt » Sun Feb 17, 2013 5:31 pm

Thanks, I'll definitely have to look into replacing those now!

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