What is inside a bitcoin miner: hashboards, a control board, a power supply and fans

A bitcoin miner is not one mysterious chip. It is three boards of mining chips, a small computer that runs them, a power supply and a way of getting the heat out. This guide opens one up, part by part, and says what happens to the machine when each one stops working.

A miner is a few boards in a metal case

From the outside a bitcoin miner is a heavy metal box with a power cable, a network port and either fans or water pipes. Inside there are only four kinds of part: boards of chips that do the guessing, a small computer that tells them what to do, a power supply, and something to take the heat away. Knowing which is which makes a spec sheet, a repair quote or a hosting conversation much easier to follow.

The details differ from maker to maker, so this guide follows one family all the way through: MicroBT's Whatsminer M30S. The maker's shop page for the M30S++ gives a 13.5 kg chassis 430 mm long, 155 mm wide and 226 mm tall, a power supply fed by 220 to 240 volts through an IEC C19 cable rated for at least 16 amps, and a working temperature of -5 °C to 35 °C. Our guide to what a miner is explains what the chips are guessing at. This one is about the machine around them.

The hashboards do the guessing, and there are three

A hashboard is a flat circuit board covered in mining chips. Each chip is an ASIC, a chip built to do one thing: make guesses at bitcoin's puzzle as fast as possible. A repair shop's guide, D-Central's page on hashboards that are not detected, gives the count for the M30S: “3 × 105 chips = 315 total”. Three boards, 105 chips on each. On the M30S++ a second D-Central guide says a board carries about 70 chips, and that when one board fails, the other two keep hashing.

Each board forms what that guide calls a chain, and the control board keeps a chip map of what it can see. When a board does not answer, the page says the chain is absent from the chip map, and the miner's hashrate drops to about two-thirds of its nameplate figure. Three equal boards mean each one is a third of the machine's output, which is a useful way to read any fault report.

Everything about a machine's hashrate and efficiency comes from these boards. When a spec sheet gives terahashes per second and joules per terahash, it is describing what the hashboards do and what they draw.

The control board is the small computer in charge

The control board is the miner's brain, a small computer rather than a mining chip. The D-Central guide to the M30S control board describes it running the machine's firmware, offering an interface on the network, and linking by ribbon cables to the power supply, to a small button board and to all three hashboards, with an Ethernet connection out to the world.

That Ethernet cable is how the machine reaches its pool and receives the work the hashboards then guess at. It is also how an owner reads the machine's hashrate and temperatures. The same page gives the failure in one line: “the Whatsminer M30S control board cannot reach or hold a hashing state.” Its symptoms are the machine restarting in a loop, dropped connections and hashboards that never receive work. The chips are fine; nothing is telling them what to do.

The power supply turns the wall socket into what the chips need

A miner draws a lot of power, and the chips cannot use mains electricity directly. A built-in power supply converts it. D-Central's guide to the M30S power supply says a stock M30S pulls about 15.5 amps on a 220 volt circuit, wants at least 205 volts at the inlet, and delivers about 14.2 to 14.8 volts of direct current to the hashboards through a thick copper bar. The control board gets its own small 24 volt supply, and a small adapter plate between the power supply and the hashboards carries both power and sensor signals.

This is why a miner needs a proper circuit rather than a household socket, and why hosting sites quote power in kilowatts. A power supply that fails completely leaves the machine dead: no lights, no fans, no network address. A partly failing one shows up as a machine that starts, runs for two to fifteen minutes and shuts itself down, according to the same page.

The fans, or the water, take the heat away

Nearly every watt the miner draws leaves as heat, and if the heat stays in, the chips fail. In an air-cooled machine, fans pull air across metal fins on the chips and push it out of the back, which is why the shop page above gives a working temperature, 35 °C at the top, and why an air-cooled machine wants a cool hall. In a hydro machine the fans give way to water plates on the chips and a loop to a cooler outside; in an immersion machine the whole unit sits in fluid. Our guide to air, hydro or immersion compares the three.

The cooling is the one part of the machine that changes by type, and it does not change the boards. The same chips and the same efficiency can come in an air, a hydro and an immersion version: the S21 XP is 13.5 J/TH in air and in immersion alike.

When a part fails, you lose that part's share

Read the four parts together and a fault has a size. A hashboard that drops out takes its share of the output: with three boards, about a third, with the other two still mining. A control board or power supply failure stops the whole machine, until the part is swapped.

None of this makes failure a reason to stay out of mining. Every machine develops faults, and what a fault costs depends on who is next to it. Our guide to a failed hashboard as a line item covers the repair side: hosted with us in Argentina, a repair is billed at the cost of the parts and nothing else. We found no failure rates for these parts that we could cite from the sources above, which are repair guides and not surveys, so we make no claim about how often any of them fails.

A failed hashboard costs a third of a three-board machine's output. A failed control board or power supply stops all of it.

What it means for a miner

Before buying a machine, four questions follow from the four parts. How many hashboards does it have, so you know how much one fault costs. Is the power supply built in, and what voltage does it need at your site. What does the maker's warranty cover and for how long: MicroBT's shop page for the M30S++ promises “a one-year warranty period”. And which cooling it uses, because that decides where it can live.

Then keep the coins in view. Bitcoin a machine has already mined is in your wallet, and a part that fails stops the machine for the days it takes to swap it, not the coins already kept. Machines are the roof, not the building, as the roof guide says: parts wear, are replaced, and the operation carries on. A habit worth keeping: whenever someone quotes you a fault or a repair price, ask which of the four parts it is and how much of the machine it takes down.

Sources and further reading

WhatsMiner M30S++ — MicroBT shop, 2026
Whatsminer M30S hashboard not detected — D-Central, 2026
Whatsminer M30S control board failure — D-Central, 2026
Whatsminer M30S internal PSU board failure — D-Central, 2026
Whatsminer M30S++ buck-boost fail — D-Central, 2026

Disclosure

Firsthand Bitcoin sells and hosts mining hardware, including this machine. No manufacturer, distributor or affiliate programme paid for or reviewed this page and we take no commission on the links above. Historical figures are computed from daily bitcoin price and network hashprice, each day valued at its own prices. Nothing here is investment advice.