Asking for +5v, -5v output SMPS repair

[galaga1982]

Hello?
I would like to ask about the 80W, AC 110V input, DC+5V, -5V output SMPS (shindengen CY05010) fault repair.

symptoms of a breakdown

1. There is no output of +5V voltage. -5V output available and voltage control is possible. If the voltage control volume is raised, the power LED is turned off, resulting in a voltage drop to -1.8V, and if the volume is reduced, it will not recover to its original voltage. (Is it a normal function?) It will be restored only when the power is completely turned off and on.

2. It is thought that the output is achieved only when the RC (REMOTE CONTROL) terminal is SHORT, but when SHORT is made, the power LED is turned off and all voltage outputs are not possible.

3. The voltage at the output end (+5V, -5V) is SHORT state from the beginning. In order to find out the cause, I tried to separate the capacitor, diode, FET, etc., but it is still SHORT state, and finally, when I separate the 8 ohm cement resistance connected between +5V and -5V, SHORT state disappears. (This is cement resistance that was constructed during the initial design, so this can't be a problem, right?)

Attached is the picture, please give me your opinion. I thought it was a simple defect, but it's not easy.

Thank you.

[dobsonr741]

The drawing on the box does not support the idea it’s a dual rail supply. Did it work as a dual rail supply before?

[galaga1982]

I'm not sure the exact meaning of the term dual rail supply, but the +5v, -5v outputs seem to work independently.
Anyway, I think the short state of +5v, -5v output terminal is abnormal.

[Jwillis]

I'm not sure the exact meaning of the term dual rail supply, but the +5v, -5v outputs seem to work independently.
Anyway, I think the short state of +5v, -5v output terminal is abnormal.

Dual rail means that theirs a positive rail and a negative rail in which both voltages are relative to a common ground. +5V to GND (0V) to -5V for example. If and what is used as common ground depends on the circuit. It is possible that it uses the Chassis/Earth ground also as the common ground for the 5V rails. Uncertain unless voltage measurements can be taking.  Or its just a weird way of describing a single floating 5V rail.

[fenugrec]

Or its just a weird way of describing a single floating 5V rail.

That is my interpretation, based on the photos - one single floating 5V supply. User has the option of connecting either V+ or V- to GND, if needed. OP : if you are leaving the outputs floating, you must probe between V+ and V- (unclear if that's what you were doing).

The power resistor connected accross the output sounds like a minimum load to keep the supply happy - do not remove unless it's defective.
RC, "remote control", seems like a simple on / off control based on drawing on the box.