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7300 power supply / PSU

NoTrueSpaceman

Active member
I scored a great deal on a 7300/200 that turns out to have an upgraded processor, ATI Rage Pro, and an OrangePC 620. That's the good news.

The bad news is that plugging in the PSU resulted in sparks and smoke shooting out the back! :O

I'd checked the PSU for leaky caps before, and everything thing looked okay. The thing that exploded was a resistor: R4, 1 ohm ceramic, right next to the connector for where the mains plugs into the PCB.

I replaced R4 with another 1 ohm... and that one also spectacularly exploded.

Strangely the fuse in the PSU didn't blow?

I unsoldered the two large 470uF 200v caps and they look great. I tested the bridge rectifier, and .... well it seemed okay too.

Any ideas? I've got a "tested known good guaranteed" replacement PSU coming in the mail, but frankly I'm suspicious.

My Mac IIsi had all the classic bad caps on both the motherboard and the PSU and I've gone a few rounds replacing more and more and now its working great.

But this PSU shows no signs of bad caps... and frankly, an exploding resistor suggests something else to me.

Ideas? Resources? I should note that contrary to everyone on the internet, the 7300 PSU _is different_ than the 7500, 7600, and other PSUs. It's pinout is very obviously different - the large connector has only orange, red, and black wires. The sense and power-on and trickle wires are all on the smaller connector.

Original blown resistor:

IMG_0797.jpeg

New, freshly installed, blown resistor 8-o 8-o 8-o 8-o 8-o 8-o 8-o 8-o

IMG_0798.jpeg

 
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