576/Repairs: Difference between revisions

576/Repairs (view source)

39 bytes added , 31 July 2019

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 ==Symptom: Low 5V Rail voltage + High current draw on 5V (approx. 425 mA)==
 Replaced C759 (11,000 uF 15V).
-It was shorted, showed high ESR (8 Ohms) and 8,000 uF capacitance.
+C759 was leaky and showed high ESR (8 Ohms), also low capacitance @  8,000 uF.
 Filter cap replacement raised the 5V rail voltage but did not fix the issue.
 Voltage should be 5.0.
-Test readings showed 3.7V before and 3.9V after.
+Test readings showed 3.7V before and 3.9-4.0V after.
 Did not check current draw after, however, it is most assuredly higher than normal and still loading the supply beyond capacity.
 Continued troubleshooting, located high ESR (486 ohms) C789 5V Filter Cap replaced.
-V rail came up to 4.2V.
+V rail came up to 4.2- 4.3V.
 Disconnected Step Generator 5V @ “Q” terminal.
 V Rail came up to 5.04V, therefore shorted cap on Step Generator board.
 Located  high ESR (426 Ohm) C294 5V filter cap where 5V rail enters board.
-Lifted one end off the board, reconnected “Q” and 5V rail stayed at 5.04V.
+Lifted one end of the cap off the board, reconnected “Q” and 5V rail remained at 5.04V.
 Removed Unit Right Side Frame rail, replaced  C294 on Step Generator board.
 V is repaired.