I bought a cheap "laboratory" power supply some time ago, one of these: https://www.manson.com.hk/product/ep-603/.
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| Manson EP-603 Power Supply |
It is quite handy, but the ammeter has never worked and I decided to have a look. I can’t find a schematic for this particular model, though I did find some similar
ones. The "BK Lab Power Supply Schematic 1670A_1671A_schem.pdf" seems
identical. You should be able to find this easily online. All major semiconductors match, at least.
Interesting features include:
- The +12V and +5V outputs are isolated from each other and the main output, which is handy and a surprise.
- The regulators are all linear.
- A relay is used to switch taps on the secondary winding for the main output, thereby allowing a modicum of efficiency over the output voltage range.
- If you have to dissemble one of these, there are two hidden screws each side of the fixed output terminals. These may be accessed though holes in the PCB. It is wise to unsolder the meter terminals before removing the PCB.
The ammeter issue was due to bad soldering on the meter terminals. Now it is fine, and the meter calibration is about right. Despite this issue, the supply has not given me any other trouble and I do think it is reasonable value for money.
Internals
I took a few photographs while I had it apart. These may be useful if you come across a similar model. Click on the images for a more detailed view.
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| Front Panel PCB |
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| Front Panel PCB (Reverse) |
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| Heatsink Assembly |
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