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> Frankenstein Compaq iPaq
post Jan 23 2014, 02:02 AM
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I started with one of these things (the version 1, not the version 2):
Compaq iPaq Desktop

It was originally bought by the owner of a local restaurant that I'm friends with back in 2001. Its original configuration was a Pentium 3 600/128 MB PC-100 and an 8 GB Seagate hard drive running Windows 2000. He had the thing in service for probably 10 years before it was decommissioned and given to me. I maxed the specs out at the time with a Pentium 3 1000/512 MB PC-133 and a 40 GB drive running Windows XP, then I basically gave it to people in need of a basic computer, but the problem is that it always found its way back to my hands. I recently got it back again (probably two weeks ago now) and since I was tired of getting it re-gifted back to myself, I decided to see what the most powerful thing I could stuff in the thing and have it still work without massively overheating and failing.

Well the first thing I had to work out was the power supply. The original PSU was 90W, which was plenty to run a barebones Pentium 3 workstation, but not much else. And it being a Compaq, the form factor of the PSU was obviously proprietary and nothing would fit it. So I took the PSU out of the case, took it apart and stared at it for a few hours. I then realized that I could probably replace the guts of it with the guts of a more powerful MicroATX PSU, which is what I did (eventually.) In order for the MicroATX PCB to fit into the proprietary Compaq PSU case, I had to do a bunch of cutting on the primary heatsink as seen below:

I had to cut a square chunk off for the power plug on the upper left to fit, and I also had to cut fins into the straight piece of heatsink to unblock the rear vent (since the fan sucks from the back and blows into the case.) I also had to replace the AC power wires with longer ones, since the location of the solder points were different. After a liberal application of electrical tape to prevent shorting and some craft sticks for spacers, the whole thing went back together with a bit of muscle and it worked great.

Now that I had the PSU taken care of, I needed to find a motherboard that would actually fit inside the case. Thankfully Compaq wasn't too retarded and the motherboard mounts were standard MicroATX mounts (probably because the original motherboard was an Intel OEM board.) The problem was that even though the mounts were MicroATX, there wasn't enough room in the case for a regular MicroATX motherboard either width or height wise. I searched through probably 50 motherboards before I found one that would fit, which ended up to be this:
MSI FM2-A55M-E33

It mounted in the case:

You'd figure it would get easier at this point since the PSU and motherboard are out of the way, but Compaq had a few more challenges for me to overcome. The first was that all of the front panel wiring was proprietary (the power button, LED indicators, audio jacks and USB ports.) I had to scour the internet for about a day to find the pinouts for the proprietary audio header and USB headers, then reconfigure the wires inside the connector to be standard. While those were easy to sort out, the power button and LED indicators were on a proprietary ribbon cable and couldn't be easily changed. To solve that problem, I was able to cut an old CD-ROM audio cable in half and solder some pins on the wires to fit in the ribbon connector and convert to an order that would work on the new motherboards front panel header. You can see all of the header work on the left side of the above picture (the long one on the top left is the front panel audio, while the middle under the PCI slot is the USB and the lower is the front panel.)

The next thing I wanted to do is get the internal mini-sub working (bottom right on the above picture.) I could use external speakers, but the mini-sub sounded too good to be wasted just sitting there. The original motherboard had an integrated monaural 5W op-amp (TDA7056B) that drove it. The new motherboard had no such thing and there was no way that it could drive the mini-sub by itself, so I set out to build one on a piece of Radioshack prototype board. I've built a few op-amps in the past so I knew mostly how it would work, but I knew that you can't power an op-amp by a PC power supply without getting bus noise getting injected into the audio stream (ie. if you'd scroll the mouse or hard drive activity, you'd hear buzzing or clicking in the audio output.) After some experimentation, I found that a toroidal inductor with two inputs/outputs that I pulled from a dead computer PSU put between the +12v and GND lines filtered out all of the interference caused by the rest of the computer and proceeded to build the op-amp on a prototype board:

I had the choice to use an LM386 or a TDA7052A, and I ultimately chose the LM386 because it required less parts. The audio input is pulled from a soldered CD-ROM audio cable on the front panel audio PCB on the case and is plugged into the bottom of the prototype board. The two capacitors on either side of the CD-ROM audio cable and resistors going to pin 3 on the LM386 combine the L and R channels into a single channel without backfeeding audio back to the motherboard sound chip and causing problems. Overall the op-amp board works pretty nicely, the only issue that I noticed is that it does filter out the higher ranges, but that doesn't matter much since it's powering a mini-sub. You can see it tucked away on the motherboard picture on the bottom right next to the mini-sub.

The last major issue was the CPU heatsink/fan and the hard drive. Basically in the original design the PSU fan blew across a passive CPU heatsink and the hard drive mount was on top of the motherboard attached to the door. Well this obviously isn't going to work with the new AMD cooler because it has a fan on it, and of course I want the fan to actually work and not be sucking on metal. I basically had to use a small hand band saw and cut 1.5mm steel casing to make a hole for the CPU fan, and in the process removed part of the HDD mount.

I haven't really figured out an elegant solution, other than letting the HDD sit where it is in the picture and having the plastic door hold it in place. A more ideal solution would be to replace the desktop HDD with a laptop HDD or SSD for a smaller footprint. Once the case is closed up, it gets a nice convection current going (the vents are on the top of the case) and everything stays within safe operating temperatures.

The last optional thing was an optical drive. Again being Compaq, the multi-bay on the other side of the case was proprietary and had proprietary cabling. And since this model of computer had a very limited production run, getting parts for it is all but impossible. I had some laptop IDE DVD burners lying around, but that wouldn't do much good since this motherboard is SATA only. After some searching, I found that Startech made a laptop IDE to SATA converter board that fits nicely on the back of the drive itself. I was a bit skeptical whether it would work or not, but I decided to try it and it works like a charm.

It's held in place with craft sticks on the sides and bottom

And here's it powered up and running Windows 7:

Final specs:
Motherboard: MSI FM2-A55M-E33
CPU: AMD A8-6500 @ 3.5 GHz (65W FM2 Socket)
GPU: (Integrated into CPU) HD8570D
RAM: 2x4 GB Crucial Ballistix Sport DDR3-1600 (8 GB)

Total cost of the Frankenstein was around $270
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