POWER SUPPLY REPAIR

Introduction

The power supplies involved for the repair session are Switchmode Power Supply (SMPS), also known as Switching Power Supply and sometimes chopper controlled power supplies.

For the time being, we (Heong and me) have repaired 13 units of power supplies.
Repairs have been done for the following models:

	1. WRP36SX-U 
	2. FHP36SX-U
	3. WRF24SX-U 
	4. WRF30SX-U

Those power supplies are manufactured by ETA USA.

Common Problems

The bad power supplies units are from the Alphasem machine in CBSM production line or from General Store.When repairing the unit, we will always look for a very simple problem which can give profits in terms of saving and time.The units with other problem (not very serious) like hang-up problem are put aside. We will take a look at it later, as they need to be check with multimeter for further error checking such as burnt fuse, open fusable resistor etc.

One of the common problems encountered is intermittent/unstable output. It is suspected due to rough (unsmooth) movement of the fan. Sometimes, noisy sound can be heard when the fan is rotating and also, the fan got stucked while it turns. This problem is very common, and I would say it needs a very simple and straight forward solution. Disassemble the unit and then, the fan is replaced with a brand new fan. The fan model is 80MM 12VDC PAPST 8412N/2GH Fan , brought from Farnell.(Farnell order code #9600019 or #179504). The old fan is NMB Flowmax 3110NL-04W-B59.

With the new fan, the power supply is tested under no-load and full-load condition. We expects it to run steadily without fluctuation. If the output still not stable, *maybe*, the voltage is not regulated properly. Here, it involves the the parts of the circuit, which is voltage regulation circuit. Leave it aside for further checking!

Pre-Caution

1. Always test the faulty unit through the isolation transformer. So, if overvoltage or overcurrent occurs, the transformer will automatically trip the transformer and avoid the error from hitting the power supply and making more damages.

2. When replace the fan, make sure the connection and polarity is correct. Because the colour of wires are not always the same. e.g: Blue-Red-White or Black-Red-White.



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