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--- indigo2_impact_psu [2026/02/28 23:06] – Added photo captions. iliketech
+++ indigo2_impact_psu [2026/02/28 23:09] (current) – Fixed wording. iliketech
@@ Line 135: / Line 135: @@
 After replacing these components (and clearing an accidental solder bridge) along with all electrolytic capacitors in the supply (the large FA series capacitors were the only ones obviously defective, but all should be replaced), the supply would power up and all rails were within appropriate specification when jumpered to power up and plugged in. However, the supply did not seem to start if shut down and reconnected. It was at this point much time was wasted determining that this was expected behavior, as the computer likely drives the power control input with a push-pull output.
-It was also determined that the supply can be forced to power up by removing the yellow wire closest to the red wire from the control cable. This disables the power-down circuitry, causing the primary side to start switching. This results in the supply running with no over-voltage protection. Before the mag-amp circuitry was rebuilt, this resulted in approximately 22 V being present on the 12 V rail. This resulted in the failure of a diode in another portion of the control circuitry. It is not recommended to operate the supply in this manner, especially not connected to anything other than dummy loads. This over-voltage protection is likely why the supply would attempt but fail to start before repair. It is likely that the rail voltages began to rise before the 12 V rail would trip the over-voltage protection of the UC2903, and the supply would shut down.
+It was also determined that the supply can be forced to power up by removing the yellow wire closest to the red wire from the control cable. This disables the power-down circuitry, causing the primary side to start switching. This results in the supply running with no protection of any kind. Before the mag-amp circuitry was rebuilt, this resulted in approximately 22 V being present on the 12 V rail. This resulted in the failure of a diode in another portion of the control circuitry. It is not recommended to operate the supply in this manner, especially not connected to anything other than dummy loads. This over-voltage protection is likely why the supply would attempt but fail to start before repair. It is likely that the rail voltages began to rise before the 12 V rail would trip the over-voltage protection of the UC2903, and the supply would shut down.
 It should also be noted that this power supply is difficult to rework, especially around the section with the primary low-voltage filters. This section of the board has several large power planes, and the four-layer board requires a lot of heat to clear the holes from the capacitors. This problem is exacerbated by corrosion of the solder joints. Multiple pads were damaged during the repair process. Avoid repeated rework if possible.