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Prophet 600 Meltdown
Old 19th December 2019
  #1
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Thisiscobras's Avatar
Prophet 600 Meltdown

I've been trying to fix what was a very small issue on my beloved Prophet 600 for the past month. Simply 1 Oscillator was out of tune. Everything else worked flawlessly. I was methodically replacing parts and testing after each. All was well as I was slowly tracking down the exact problem. That was until last night when I got the bright idea to use my multimeter to try and check/compare IC chip voltages between a good voice and the one I was having a problem with. I checked the direct voice IC chips 4016 (quad analog) and 4053 (multiplexer) for 2 voices as well as 2 small op amp chips in the S/H section. I grounded the negative probe on the metal chassis and used the positive to check the legs of the ICs. Apparently I'm an idiot for doing this and/or I accidentally caught 2 legs at once and hopefully just shorted a chip only. All was well minus the 1 Oscillator prior to this and now when I power on immediately I hear a loud screeching/white noise followed by what sounds like an Orbital CD played backwards and not in a good way. Keys respond as does the membrane panel and display. No matter what I do there is just noise in the background and all sorts of digital vomit. I'm really hoping I simply just fried one of the chips I tested and that's it. I'm in the process of putting together an order to replace the 6 total chips I touched. I'm really hoping just to get a little peace of mind in the meantime that this is likely all I did and that whatever happened didn't spread down the line to other places.

*To summarize, when an IC logic chip shorts does the damage spread or remain isolated to the chip?
Old 4 weeks ago
  #2
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acreil's Avatar
 

Quote:
Originally Posted by Thisiscobras View Post
All was well minus the 1 Oscillator prior to this and now when I power on immediately I hear a loud screeching/white noise followed by what sounds like an Orbital CD played backwards and not in a good way.
You're going to describe it like that and not post a recording?

Quote:
*To summarize, when an IC logic chip shorts does the damage spread or remain isolated to the chip?
Check the ICs that are connected to those pins. Once when troubleshooting a Wersi EX20 (the problem turned out to be a faulty IC socket), I briefly shorted two pins on the DAC that generates the amplitude control voltages, and it didn't work properly after that (completely unresponsive, display flashing random characters). It turned out that one of the pins I shorted was +15V, and it killed one of the output port pins on the 6809 slave CPU.
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