HP Elitedesk 800 G3 PSU reverse engineering

[NiHaoMike]

I recently got a refurb Elitedesk 800 G3 for the low price of $60. (The intent was to use it as a host machine for my SQRL Acorn.) It was easy to tell what made those machines so cheap, the GPU built into the CPU is basically garbage (except for its Quick Sync functionality) and the 180W proprietary PSU is too small to run anything but the most basic of GPUs.

The PSU has 2x 4 pin connectors for 12V. The 12V, unlike an ATX PSU, is always on. Then there's a 7 pin connector for control signals.
1, black - ground.
2, violet - POWER METER, gives an analog voltage in proportion to the output current.
3, gray - PSU-ID, 383k to 12V for 180W. This likely is different for different wattages.
4, green - PS-ON. Unlike an ATX PSU, it just tells the PSU to go into full power mode when grounded. The 12V output doesn't change in voltage at all.
5, black - ground.
6, white - FAN TACH, just a passthrough to the internal fan.
7, red - FAN CMD, goes to some 8 pin chip that takes care of fan control.

While I haven't tested it, I assume a resistor to pin 3 and something to provide a fan signal on pin 6 are all that's necessary to replace the PSU with something bigger. If the intent is to install a GPU, a switching circuit will be needed for the GPU 12V to ensure correct power sequencing.

[MathWizard]

So what's that PSU rated for ? Compared to even a cheap 420W PSU I worked on once, that looks more like a 12V charger it's so small and low part count.

But it ran a 65W i7-7700 and whatever else. I'm impressed I think, but it looks pitifully compared to any other modern ATX I've seen.

[NiHaoMike]

A mere 180W, plenty if you stay with the integrated GPU but won't get very far if you want a proper GPU. And that's why those machines are going for Raspberry Pi prices.

If they took ATX PSUs, I would expect they would be a popular option for a budget gaming PC.

[soldar]

I would not have bought that machine but I guess it's too late to change your mind. Buying one of those "compact" machines is almost like buying a laptop when it comes to lack of flexibility for upgrades, etc.

For the same price or little more you could have bought a full size minitower which gives you better PSU, slots, etc.

I have this machine which I have been using for some years now and I am very happy with it because I got it for very good price. You could probably get one for what you paid or little more.

HP Compaq Elite 8300 CMT
CPU: Quad Core Intel Core i5-3570
16 GB DDR3 (4x4GB)
GeForce GT 730
SSD ST500DM002

[NiHaoMike]

I would not have bought that machine but I guess it's too late to change your mind. Buying one of those "compact" machines is almost like buying a laptop when it comes to lack of flexibility for upgrades, etc.

For the same price or little more you could have bought a full size minitower which gives you better PSU, slots, etc.

It's the "standard" variant, not the super tiny "mini". There are 4 expansion slots plus a 4 lane M.2 and a 1 lane M.2. Looking around Ebay, the next level up that made any sense were the Ryzens for about $100 in a mini case, good for a HTPC but not for my intended use as the Acorn is too high to fit in one of those mini cases and there would be nowhere to fit a M.2 SSD and a 4 port NIC at the same time.

[MathWizard]

So do you know how they work or did you want to learn about it by taking it apart ? That's one of the big things that got me way more into EE, was when some scammer sold me a broken computer PSU. And I managed to fix it.