Off-lease 1-liter business PCs (Lenovo ThinkCentre Tiny, Dell OptiPlex Micro, HP EliteDesk and ProDesk Mini) are some of the best-built small computers you can buy used. They were also configured for, and locked down by, a corporate IT department. Most problems buyers run into are not failed hardware but leftovers from that first life: the wrong power brick, a BIOS password nobody wrote down, theft-recovery firmware still switched on, or a drive bay with no bracket. This checklist covers what to confirm from the listing, what to ask the seller, and what to test in the first hour.
1. The power adapter: wattage and plug
These machines run from external notebook-style bricks, and the brick is the part most often swapped or lost. ServeTheHome, which has bought dozens of these units for its Project TinyMiniMicro series, notes that each vendor uses adapters from its own notebook line, so the plug has to match the brand. Dell has also changed connectors over the years; its OptiPlex 5090 Micro specifications list a 4.5 mm x 2.9 mm barrel. Do not assume an adapter from a different generation fits.
Wattage matters as much as the plug. A 35 W "T" processor does not mean a 35 W brick is enough: the adapter also feeds USB ports, drives and, in some builds, a PCIe card. ServeTheHome's own experiences make the point:
- A Dell OptiPlex 7070 Micro with a 65 W adapter showed a firmware warning at boot; with the 90 W adapter Dell specifies for that model, the warning went away.
- An OptiPlex 7060 Micro with a 65 W desktop CPU (Core i5-8500) arrived with a 65 W adapter. That configuration needs the 130 W adapter just to boot, and the listing only said "Dell power supply."
- A Lenovo ThinkCentre M920q throttled on a 65 W adapter, so ServeTheHome recommends the 90 W unit. Lenovo's spec sheet lists 65, 90 and 135 W options for the M920q, and only a 135 W adapter for the ThinkCentre M920x.
- Newer 35 W systems such as the OptiPlex 7080 Micro and EliteDesk 800 G6 Mini peaked just over 60 W in testing, which is why they ship with 90 W adapters.
Ask for a photo of the adapter's label showing wattage and part number, and compare it with the vendor spec sheet for the exact CPU in the unit. A 65 W-CPU variant (no "T" suffix) or a unit with a PCIe card or GPU needs the larger brick its spec sheet lists.
2. BIOS supervisor or admin passwords
A BIOS administrator password (Lenovo calls it the supervisor password) stops you from changing firmware settings: boot order, Secure Boot, TPM, virtualization, and on many models firmware updates. Lenovo's ThinkCentre user guide says that when a supervisor password is set, you are prompted for it each time you enter the BIOS menu, and only the supervisor password can change configuration settings. Dell's BIOS adds options such as Admin Setup Lockout and a switch that blocks UEFI capsule updates from Windows Update and the Linux Vendor Firmware Service.
Do not buy a locked unit expecting to clear the password yourself. Lenovo's user guide tells owners who forget a password to contact a Lenovo-authorized service provider, and says Lenovo cannot remove a forgotten hard disk password or recover the data behind it. Dell's service manuals say the RTC reset (holding the power button with AC connected) restores BIOS defaults but leaves the admin, system and hard drive passwords in place, so the old trick of pulling the coin cell is not a fix on these boards. Ask the seller for a photo of the BIOS security page showing no admin password set, and test entry to the BIOS (F1 on Lenovo, F2 on Dell) as soon as the unit arrives.
3. Absolute (Computrace) and lease locks
Many business PCs carry Absolute Persistence, formerly sold as Computrace, in firmware. Absolute says the module is installed at the factory and stays dormant until an organization installs the Absolute agent. Once activated, the agent is reinstalled automatically if it is removed, and Absolute says this survives reimaging, drive replacement and firmware updates because the enable or disable state is stored in a part of the BIOS that cannot be flashed.
How the BIOS setting reads depends on the vendor and year:
- Dell OptiPlex 5050 Micro: a "Computrace" field with Deactivate (the default), Disable and Activate.
- Dell OptiPlex 5090 Micro: an "Absolute" field with Enable, Disable and Permanently Disable. Enable is the default and only means the module interface is available; it is dormant until an agent activates it.
- Lenovo lists an "Absolute persistence module" among BIOS security features (for example on the ThinkCentre M75q Gen 2), and its user guides describe the Computrace agent embedded in firmware on selected models.
"Permanently disabled" is the reassuring state, since the option is designed as a one-way switch. A factory default or deactivated state is normal on most off-lease units. If the BIOS shows the module as activated, ask the seller to confirm the machine was released from the previous organization's Absolute account; otherwise it may keep reporting to them. While you are in the security menus, also look for leftover asset or ownership tags, disabled USB ports, and Lenovo's Smart USB Protection, which allows only keyboards and mice and blocks USB storage.
4. Intel vPro and AMT
Intel vPro includes Active Management Technology (AMT), out-of-band management that runs on the Management Engine and lets an administrator power-cycle and remotely control a machine below the operating system. It needs three things together: a vPro-eligible CPU (Intel's ARK pages list "Intel vPro Platform" eligibility, as for the Core i5-8500T), a business chipset such as Q370, and the Intel I219-LM network controller. The lower tiers don't have it: the ThinkCentre M710q uses a B250 chipset, the M720q is listed by Lenovo as non-vPro, and the ProDesk 400 G4 Mini and OptiPlex 3070 Micro use chipsets without it.
Even the right parts don't guarantee it. ServeTheHome had an HP ProDesk 600 G4 Mini with a Q370 chipset and a vPro-capable i5-8500T that still did not support vPro; the Intel sticker on the case did not say vPro. Check that sticker and the listing photos.
If a unit has AMT, set it up or switch it off. Intel's documentation says the MEBx setup screen is usually reached with Ctrl+P at boot and that an unprovisioned system uses the default password "admin" until it is changed. Intel advisory INTEL-SA-00075 (CVE-2017-5689, rated critical) covered AMT firmware 6.x through 11.6, which includes the AMT 11.0 Lenovo lists for the 7th-gen ThinkCentre M910q, so install the latest BIOS and ME firmware from the vendor. Dell's newer BIOS restricts MEBx access by default, and Dell notes that an RTC reset un-provisions vPro.
5. RAM: type, slots and real limits
From 6th gen onward, the business minis use two DDR4 SO-DIMM slots. Older 4th-gen units such as the ThinkCentre M93/M93p Tiny take DDR3 SO-DIMMs (16 GB maximum per Lenovo). Many consumer mini PCs solder their memory, so check whether a given box has slots at all. Treat the vendor maximum as the tested floor, not a hard ceiling: Lenovo lists 32 GB for the M720q and M920q and notes the system may support more as memory develops, and ServeTheHome ran 2 x 32 GB (64 GB) in an M920q, an M920x and an OptiPlex 7070 Micro. That works but is outside vendor support. Low-power chips are stricter: Intel lists 16 GB and a single memory channel for the N100.
Look at how the memory is fitted, not just the total. A single module runs in single-channel mode, and 2 x 4 GB means replacing both sticks to upgrade. Memory also runs at the speed the CPU supports: ServeTheHome's DDR4-3200 ran at 2666 with a Core i5-10500T.
6. Storage: M.2 type and length, and the 2.5-inch bay
M.2 slots differ in length and protocol. Dell's M.2 explainer notes that the four digits give width and length (2280 is 22 x 80 mm), that SATA M.2 drives typically use B-keying, and that PCIe x4 NVMe drives use M-keying. Some slots take both: Dell's OptiPlex 5050 Micro shipped with M.2 SATA and PCIe options in the same slot. Lenovo's M720q and M920q spec sheets list only PCIe NVMe M.2 drives (2242 and 2280). Before you reuse a drive, match the type and length to the spec sheet.
The 2.5-inch bay needs its bracket and, on Lenovo and HP, an internal cable. ServeTheHome received an EliteDesk 800 G6 Mini with no 2.5-inch tray or SATA cable, and an EliteDesk 800 G3 Mini whose SSD was held in place only by its connector because the mounting pegs were missing. Ask whether the carrier, cable and M.2 screw are present.
7. Wi-Fi card and antennas
Wi-Fi was an option, so many units have an empty M.2 2230 Wi-Fi slot. The card is easy to add; the antennas are the problem. ServeTheHome found that a Lenovo M710q only has the antenna wiring if it shipped with Wi-Fi, and that a Dell OptiPlex 3050 Micro was not pre-wired, while HP's ProDesk 600 G4 Mini kept its antenna wiring even without a card. If you need wireless, buy a unit that already has it or plan on a USB adapter.
8. Missing drives and "no OS"
Recyclers often have to destroy the original drives. ServeTheHome has seen units with an aftermarket consumer SSD added by the seller and units sold with no Windows license. "No SSD/no OS" listings are fine if you plan to install your own, but budget for a drive and check whether the listing mentions an embedded Windows Pro license, which is stored in the firmware and reactivates automatically.
First-boot checklist
- Enter the BIOS and photograph the main and security pages: CPU, memory, BIOS version, admin password status, Absolute/Computrace state, TPM and Secure Boot.
- Load BIOS defaults, then update the BIOS and ME firmware from the vendor's support site.
- Run Memtest86+ for at least one full pass, especially after adding RAM.
- Check drive health with smartmontools (smartctl) or a similar tool: power-on hours, reallocated sectors, and NVMe percentage used.
- Watch temperatures and fan noise under a sustained CPU load. ServeTheHome found one OptiPlex noticeably quieter after cleaning out dust.
- Confirm the adapter wattage matches the CPU and that every USB port, display output and the network port work.
- Check for physical damage: ServeTheHome received a unit whose front faceplate fell off because a latch was broken. Test everything inside the return window.
For model-by-model differences between the big three, see ThinkCentre vs OptiPlex vs EliteDesk. If Windows 11 matters, check the CPU against Windows 11 support by CPU generation before you buy.
