Geoff Posted May 2 Report Share Posted May 2 Any suggestions on how to diagnose a slightly low voltage condition on my main bus? Mine is making 27 volts when 28.5 are called for in a healthy system. Quote Link to comment Share on other sites More sharing options...
M20TN_Driver Posted May 2 Report Share Posted May 2 I think i have a similar issue. Diodes in the alternator are being looked at. Supposedly a bad alternator causes the slightly low voltage. Quote Link to comment Share on other sites More sharing options...
dkkim73 Posted May 3 Report Share Posted May 3 Or the voltage regulator. I took this as a good opportunity to learn a bit about the system... the "M20TN SERVICE & MAINTENANCE MANUAL " (MAN180.pdf) has a pretty good description of theory and also has troubleshooting and service instructions, including voltage adjust. The voltage regulator ("APAC" in that reference) is actually fairly full-featured. That said, if something's changed, you would presumably want to thoroughly check everything before just empirically adjusting the voltage. Perhaps a more experienced person (esp. A&P) can weigh in here on whether these things drift on their own. HTH, D Quote Link to comment Share on other sites More sharing options...
LANCECASPER Posted May 3 Report Share Posted May 3 On 5/1/2024 at 10:40 PM, Geoff said: Any suggestions on how to diagnose a slightly low voltage condition on my main bus? Mine is making 27 volts when 28.5 are called for in a healthy system. First thing I would check would be the logs to see if and when the coupler (or alternator) has ever been changed. You don't want that coming apart. Quote Link to comment Share on other sites More sharing options...
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