Buying a used card that has been mining

Is a used mining GPU worth buying?

Often, yes. Used cards that have been mining sell at a discount, and the discount is bigger than the risk. Knowing why also tells you what to check.

The parts that wear are cheap and easy to service: fan bearings, thermal paste and thermal pads. The part everybody worries about is the processor itself. A couple of years at the voltages these cards run does not meaningfully age it.

Why can constant load be kinder than gaming?

This sounds like special pleading, but it is not. Solder joints and thermal interfaces are aged by thermal cycling. That means heating up and cooling down, over and over. Each time, the parts expand and contract at slightly different rates.

A gaming card does that several times a day for years. A mining card left running warms up once and stays there. Steady load is easier on a board than spiky load.

There is a catch: this only holds if the card was kept cool. A card that ran at its thermal limit for a year is a different matter. The checks below are there to find it.

What should I ask the seller?

• How long did it mine, and at what power limit? A card run undervolted for two years is often in better shape than one run at stock for one.
• What temperatures did it run at, for memory as well as core? Memory temperature matters most, and people are least likely to have watched it.
• Were the paste or the pads changed, and when?
• Are the cooler and fans original? Replacement fans are not a red flag. They show somebody maintained the card, but the seller should mention them, not leave you to find them.
• When was it first bought, and is any warranty left? Ask, even though the answer usually does not help, for the reason below.

A seller who answers all five clearly is different from one who says it was barely used. Clear answers are worth paying more for.

Does the warranty still cover it?

Usually you cannot count on it. Two things get in the way, and both are common enough to expect.

First, many manufacturers make the warranty non-transferable. It belongs to the original buyer and ends when the card is sold. Others do transfer it, and a few tie it to the serial number whoever owns the card. So check the rules for the specific brand rather than assuming either way.

Second, several manufacturers state that mining on a consumer card voids the warranty. Whether that holds where you live is a legal question. As a buyer, though, the practical answer is the same.

Price the card as if it has no warranty. If one turns out to exist, treat it as a bonus, not part of the deal.

How do I test a used card?

Work through these steps in order. This order finds problems fastest.

• Look at the card before it goes near a machine. Dust is fine and expected. Browning around the power connector, a bent bracket, a bowed board or a smell are not.
• Spin the fans by hand. Grinding, rattling or resistance means worn bearings. That is cheap to fix, but it should be in the price.
• Run it under sustained load, not for two minutes. Thirty minutes is the minimum and an hour is better. Heat problems appear once everything has warmed through, not at the start.
• Watch memory temperature, not just core temperature. Mining puts its heat into the memory, and dried-out pads show up there first.
• Test the memory for errors under that load. This is the most valuable test for a mined card. Worn memory shows up as errors, not as a dead card, and errors will cost you shares later.
• Check that it holds its clocks, meaning its running speed. A card that quietly slows down after twenty minutes is telling you about its cooling.
• Plug in a display and look at the picture. Outputs go unused for years in a rig, so a dead port is easy to miss.

What does a refresh cost?

Assume the card needs new thermal paste, new thermal pads and possibly new fans, and price it that way. On most cards this takes an afternoon and a small amount of money. It turns a card with an unknown heat history into one you know.

Pads are the part people skip and the part that matters most. They carry heat away from the memory and the voltage regulators, and they dry and harden over time.

Match the pad thickness the card came with rather than guessing. A pad that is too thin conducts nothing. One that is too thick holds the cooler off the chip.

When should I walk away?

• Any browning or melting at the power connector. That is heat where it should not have been, and you cannot see what it did underneath.
• A refusal to let you test it under load, or a sale that has to happen today.
• Memory errors that stay when the card is set to stock clocks.
• A card that will not hold clocks after twenty minutes, when paste and pads cannot explain it.
• A price that is not really a discount. If it is close to a new card of similar performance, the warranty and the unknowns are worth the difference.