77
edits
576/Repairs: Difference between revisions
→Defects found without any noted symptoms
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Lost +12.5 and therefore +225 as well. Also affected were 5V and 4.5V which were both about half the required voltage. | Lost +12.5 and therefore +225 as well. Also affected were 5V and 4.5V which were both about half the required voltage. | ||
==Defects found without any noted symptoms== | ==Defects found without any noted symptoms. . . Could these be part or all of the cause for failures previously noted?== | ||
==NOTE: Just because I did not see "symptoms" does not mean that they were not there, just that I was not experienced enough to find any such symptoms.== | |||
Found D507-D708 9V Zener VR TC shorted (continuity both directions) on both Step Gen and Display Board. | Found D507-D708 9V Zener VR TC shorted (continuity both directions) on both Step Gen and Display Board. | ||
Tek's recommended replacement is a [[1N936]], available at [https://www.mouser.com Mouser Electronics]. | Tek's recommended replacement is a [[1N936]], available at [https://www.mouser.com Mouser Electronics]. | ||
D507 was replaced with a TC Diode, D708 was replaced with a standard 9V ZENER (not TC, did not have the proper part on hand), | |||
RESULT: -75V drifts badly as the machine is turned on and heats up (High @ -73.5V when turned on and drifting slowly to -75.05V when warmed up.). | |||
NOTE: All electrolytic caps which were previously replaced, (except for one cap) tested as high ESR to the point | Found shorted D83 - 1N4152 not aware of symptoms related to this defect. | ||
Undoubtedly loading they power supply and not filtering much at all. | |||
Replaced all remaining electrolytics that could be found on the Right side. | Replaced D708 with proper 9V TC ZENER, -75V Supply is now rock solid @-75.015V, no "drift" as the machine heats up. | ||
NOTE: All electrolytic caps which were previously replaced, (except for one cap) tested as either high ESR or to the point or being shorts to ground. | |||
Undoubtedly loading they power supply and not filtering much at all. | |||
Replaced all remaining electrolytics that could be found on the Right side and Power supply Filter caps. | |||
Voltages in all supplies became cleaner and most of the voltages increased as well. | Voltages in all supplies became cleaner and most of the voltages increased as well. | ||
Power supply is now well within the normal operating range. | Power supply is now well within the normal operating range. | ||
Type 576 electrolytic caps should be your primary suspect when repairing or adjusting these machines. | Type 576 electrolytic caps should be your primary suspect when repairing or adjusting these machines. | ||