Scanner PC

Just a standard warning here - this sort of thing is quite dangerous if you don't know what you're doing. Capacitors can store a lot of power, so I don't recommend this sort of project for just anyone.


Now for the power supply portion of the Scanner PC saga. The power supply alone was a small project by itself. A regular ATX PSU case could not be made to fit inside the scanner's casing, so my only option was to remove the circuit board from the metal case. It would need proper insulation from the rest of the components, as well as from the outside world. Plus, the metallic mounts which at one time served to ground portions of the circuit board while it was in the original casing would no longer be available. I used nylon standoffs for everything - the motherboard, the floppy drive, and the power supply.
Finally, in addition to these special needs, it also would need adequate airflow, as the various large regulators and diodes can put out a lot of heat.

There were a few extra things in the power supply that needed to come out - extra connectors, and the 110/220V switch - as there simply wasn't room for lots of wire, or really anything unnecessary.

110V Hardwire
The 110/220V switch was first to go. It could have caused problems dangling loose, and there wasn't much space to make a mounting hole. So I replaced it with a small length of red wire. That little black wire was factory mounted.
Mounted Power Supply
There's the power supply mounted in place at the rear of the scanner.
Mounting Closeup
And a side-view of the mounted board. It used nylon standoffs for all but one of the corners. The remaining corner mounted directly to the scanner's frame


At this point, I stuck everything into the case, put a fan over the power supply, and powered it up to see that it would actually work. The Knoppix CD booted normally; all seemed well. I rebooted then to check the voltages and temps in BIOS. The 3.3V line was down around 3.1V, and the 5V rail was very low. Plus, the little heatsinks on the PSU were really hot. That's what really cheap power supplies do. A stroke of luck though - a case I'd ordered (Antec SLK3700AMB) came with a 350W power supply. As I already had a 430W Antec PSU destined for the system, the 350W PSU became the new candidate for the Scanner PC. It had much better regulation, and more stable rails. But it also presented some problems.

Filter
For one thing, it had a little circuit board right on the power connector, which needed a place to go.
Size Comparison
Here's the two power supplies. The Antec had a lot more wires coming out of it, much bigger capacitors and heatsinks, and just a whole slew of additional components.
Modded Antec Power Supply
And so the modifications began. This power supply received the 110/220V switch replacement as well. But it also got grounding wires installed. I realized that the mounting holes were grounded, and that this was likely important. The yellow wires were all connected and grounded.

The little filter board presented a problem in its original form, as did the big capacitors on the main circuit board - they hit, which prevented the two halves of the scanner casing from closing. So that needed to be changed.

Power Filter Closeup
There's the board, minus the power connector. The gray capacitor was soldered onto the printed side of the board. It had to come off...
Filter Capacitor Switchover
...and go on this side of the board.
Minor Problem
This of course caused a problem then with the power connector.

Problem Solved
A needlenose pliers helped here - I bent the leads to the power connector, and resoldered it onto the board. It no longer interfered with the relocated gray capacitor, and it fit right over the big caps on the main circuitboard.
Sophisticated Insulation
And lastly, it got some insulation. This is a piece of an expired medical card, epoxied in place. The power connector has been removed again - it needed to first be secured to the scanner casing. Then it would be soldered.
Mounted Power Supply With Tied Wires
This is the mounted power supply, with some wire ties to keep the wires out of the way of the fan that would go over this area. Note also the metal plate at the lower right of the picture. It is a slice of a power supply case, put there to mount the on/off switch, as well as keep fingers away from the power supply.


Spliced Power Connector for the Top Part
With the new power supply in place, attempts were made to fit the top and bottom of the main casing together. This exposed one big problem - I'd need a way of connecting the main power plug, on the top half, to the components, which were almost entirely on the bottom half of the case. So, I spliced a power connector onto the power supply and a mating one onto the power plug. This would allow for easy connection while the casing was very nearly fitted together.
The Less-Than-Safe Power Connector for the Bottom Part
There's the other connector. The white wires toward the right were spliced in to reach to the rear on/off switch. These plugs were marked with black so they wouldn't get plugged into the wrong thing, which would have definitely been a very very bad thing.


And with the mention of the fans, Page 3 shall detail the cooling aspects.

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