Hi group,
I am going to share the steps I took to repair a HP6012A 1kW Power Supply.
Before I get into the details, these power supplies are off-line switching supplies. A large portion of the circuit is connected directly to the line. Read and understand all the warnings in the HP Service Manual before attempting repair of these units.
The nature of this circuit, is that if you don't repair everything, it will fail catastrophically again. It is very important to find all the damaged components.
Some interesting details about this power supply can be found in the HP Journal article:
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1981-08.pdfThis power supply can deliver over 1kW for output voltage between 20V and 60V.
This is the load map:
I bought this unit at local store for $56.50 Canadian dollars in very poor condition.
In the center of the unit is a tunnel which houses the two MOSFET switch assemblies and a down programmer. The down programmer is used to discharge the output capacitors if the output voltage is turned down.
This is the top cover of the tunnel:
I removed the two screws which hold the cover to the chassis and pulled out the three boards. There was the largest collection of dust that I have ever seen in a piece of equipment:
I used a vacuum to remove the dust as I dissembled the unit. Here is a picture of the edge connectors:
I am already thinking that this dust build up has caused inadequate cooling and possible failure of the MOSFETs.
Here is a picture of the original MOSFETs. They were made by IR but are marked with a HP part number:
This is a picture of the component side of the board before cleaning:
After cleaning the board I found some traces that had been fused. You can also see that R10 is damaged:
I studied the schematic in the Service Manual, and assumed that the damage to the driver circuit was probably caused by MOSFET failure:
To Be continued...
Regards,
Jay_Diddy_B