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Old 06-19-2020, 07:31 PM   #25
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Default Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

Originally Posted by pc7fan View Post
Yes, it is. Yes, you can put them in series. However unground the outputs.

Another common problem with these power supplies is the P75NF75 linear regulator FET fails D-S. (makes the supply lose regulation and mashes the output at 100% power)

These supplies are alright after you know their quirks...

The way you can cause that FET to fail is...

1. When you short the output when you set the voltage too high, hence dumping the supply's cap into the linear regulator FET, shorting drain-source.

2. Disconnect the load (esp. if an inductive load) while the supply is on. This scenario can cause inductive spiking, can cause the FET to short.

When this happens, the supply popped the output caps once on me. Mine had 2x 63V 330u caps, those vented, installed 1x 330u 100V and 2x 150u 100V. All Rubycon ZLHs. And I've got a few spare FETs.

Try to not do the two scenarios and your supply should do you well.

If this is true what you have here then correct me if I am wrong but this to me is poorly designed switching power supply
9 PC LCD Monitor
6 LCD Flat Screen TV
30 Desk Top Switching Power Supply
10 Battery Charger Switching Power Supply for Power Tool
6 18v Lithium Battery Power Boards for Tool Battery Packs
1 XBox 360 Switching Power Supply and M Board
25 Servo Drives 220/460 3 Phase
6 De-soldering Station Switching Power Supply 1 Power Supply
1 Dell Mother Board
15 Computer Power Supply
1 HP Printer Supply & Control Board * lighting finished it *

These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps
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