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576/Repairs: Difference between revisions
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→Symptom: Low 5V Rail voltage + High current draw on 5V (approx. 425 mA)
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==Symptom: Low 5V Rail voltage + High current draw on 5V (approx. 425 mA)== | ==Symptom: Low 5V Rail voltage + High current draw on 5V (approx. 425 mA)== | ||
Replaced C759 | Replaced C759 (11,000 uF 15V). | ||
Filter | It was shorted, showed high ESR (8 Ohms) and 8,000 uF capacitance. | ||
Voltage should be 5.0. | Filter cap replacement raised the 5V rail voltage but did not fix the issue. | ||
Did not check | Voltage should be 5.0. | ||
Test readings showed 3.7V before and 3.9V 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. | Continued troubleshooting, located high ESR (486 ohms) C789 5V Filter Cap replaced. | ||
5 V rail came up to 4.2V. | 5 V rail came up to 4.2V. | ||
Disconnected Step Generator 5V @ “Q” terminal. | Disconnected Step Generator 5V @ “Q” terminal. | ||
5V Rail came up to 5.04V, therefore shorted cap on Step Generator board. | 5V Rail came up to 5.04V, therefore shorted cap on Step Generator board. | ||
Located high ESR (426 Ohm) C294 5V | 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 off the board, reconnected “Q” and 5V rail stayed at 5.04V. | ||
Removed Unit Right Side Frame rail, replaced C294 on Step Generator board. | Removed Unit Right Side Frame rail, replaced C294 on Step Generator board. | ||
5V is repaired. | 5V is repaired. | ||
==Symptom: Display trace Running off right side of CRT, cannot center== | ==Symptom: Display trace Running off right side of CRT, cannot center== | ||