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Power supply slightly out of range. Is it a big deal?
Old 16th January 2020
  #1
Gear Head
 

Power supply slightly out of range. Is it a big deal?

I'm diagnosing a Korg sdd1000, and the reading on the 5v pin coming off the power board is slightly out of range from the spec. It is 4.5v, and the spec allows for 0.25v deviation. Is that a big deal?

I kinda doubt that is the main problem, but the audio is getting very distorted before reaching the digital board, and the distortion isn't exactly stable or constant, so it might be underpowered chips.

There are plenty of other candidates as far as issues, so I'm curious if I should address the power before moving on.

...and I'm guessing a recap on the power board is the right place to start?
Old 17th January 2020
  #2
Lives for gear
 
Radardoug's Avatar
 

Logic will still work half a volt down, but it could be a symptom of problems in the supply. If the supply is switchmode, then you probably should recap it.
Old 17th January 2020
  #3
Gear Head
 

Thanks. I'll probably recap it eventually.

I replaced a chip and a cap, which mostly got rid of the distortion, and a decent signal is reaching the digital board now. I hope swapping the ram will get things back and running, but I'm afraid I might have fried the SAR digital converter. The different pins sounded really cool when it was working, so I got a little carried away poking at it. Now I don't hear anything, and the only available replacement is a Soviet era clone from some fellow in Siberia.
Old 18th January 2020
  #4
Gear Head
 
S_mask's Avatar
 

Check for more failed chips and fix that supply, if it's meant to be 5.0. Civilian TTL logic wants, as you say, +/- 0.25 around 5.00 V. Military TTL logic has a broader tolerance. The 5400 series can take +/- 0.5 V. CMOS logic (e.g., 74C00) can operate with only 3V. Best to check the logic type and datasheets to be sure.

[Best wishes, KV]
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