Macintosh Classic analog board repair

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  • Опубликовано: 21 июн 2024
  • Changed all low ESR capacitors (Nichicon PL (W) series)
    All of them leaked underneath. With except of one 1 uF /50 V
    Measured ESR of the leaked ones. Between 30 and 50 mΩ
    Replaced with Panasonic FR / Nichicon / Ruycon. Between 17 and 30 mΩ
    After restating the screen wobbled horizontally. Can be seen at both ends.
    Read in forums about the primary power supply 1N4148 rectifying diodes (for opto and TDA IC),
    The diodes did not show any reverse current deviations. Measured at DC 100 V about 27 nA
    The optocoupler (Philips CNY17-3) showed decrease in transfer Id/Ic functions. Between 40 and 30 % depending on diode current.
    Which impacted power supply dynamic feedback characteristics.
    The two rectifying capacitors (optocoupler and TDA / 1 uF/47uF) showed signs of leakage.
    Replaced optcoupler, capacitors and diodes 1N4148 and the screen stopped wobbling. Main suspect is the optocoupler.
    Music by Quincas Moreira

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