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Board repair · fault patterns

Control Board Dead After a Power Surge or Outage

A surge does not have to reach the board to kill it. It only has to use up the part that was protecting it. Protection components are rated for finite energy: the first transient is clamped and the component degrades, and the one after that goes straight through to the supply section and the drivers. That is why a board can die in a storm that did no visible damage to anything else, and why the second board sometimes dies faster than the first.

Book a board inRates and terms

$85

Bench diagnosis

Credited when the repair is approved

$1,200–8,000

Typical replacement

What the OEM board costs new

10–25%

Repair cost

Of the replacement price

1–3 business days

Turnaround

Bench time, plus transit. 90-day warranty.

Before you pull the board

Cheaper things that produce the same symptom

Work through these first. Each one is faster and cheaper to check than a board is to ship, and each one is a real reason a working board arrives on the bench.

  1. Low-voltage fuse and the transformer secondary

    A blown 3 A fuse or an open secondary looks exactly like a dead board from the thermostat side — no display, nothing energising, no response. Measure for 24 V at the board input before condemning the board. This is the single most common reason a working board gets mailed in.

  2. The incoming legs and the disconnect

    One lost leg on a three-phase unit takes control power with it and leaves the board blameless. Surges and outages are frequently the same event as a dropped leg or a tripped breaker, so check the supply before the thing it supplies.

  3. The contactor or valve coil the board was driving

    A shorted coil takes out the driver switching it. If the coil is still shorted, a new board puts a fresh driver across the same fault and fails on the first call for cooling. Measure the coil, not just the board.

  4. Whether anything else on the circuit also died

    If the thermostat, a motor control, and the board all stopped at once, the event was bigger than the board and the board may be the least of it. Worth knowing before you spend on one part.

Then it is the board

What actually implicates it

With the list above cleared, these are the signs that point at the board itself. None of them is proof — that is what the diagnosis is for — but together they are enough to make shipping it worthwhile.

  • Visible damage on the board: a cratered component, a lifted or burnt trace, soot, or a cracked case on the surge-protection part
  • 24 V present at the board input and nothing at all on the outputs
  • It worked until a storm, an outage, or a generator transfer, and has done nothing since
  • A replacement board also failed within days, which means the cause is still connected
  • A faint smell of burnt epoxy on a board that otherwise looks untouched

Failure modes

What is physically wrong, and why

The cause matters as much as the fault — a board replaced into the condition that killed it fails again.

The clamp has already done its job once

An MOV or TVS diode absorbs a transient by conducting, and it is rated for a finite number of joules. It can survive the first event, degrade, and then fail open — protecting nothing — or fail short and take the fuse with it. Either way the board is now unprotected and reads as fine until the next surge.

The 24 V supply section

The rectifier and the filter capacitors sit directly behind the transformer and take the transient first. A punched-through rectifier usually kills the board outright; a stressed capacitor lets it keep working for weeks and then fail in a way that looks like something else entirely.

Relay and contactor drivers

The driver transistors are referenced to the same low-voltage rail and switch inductive loads, so they see the transient from both sides. A shorted driver leaves an output stuck energised, which on a reversing valve or a gas valve is the fault worth finding before it is wired back in.

The microcontroller, through a shared ground

A common-mode transient lifts the whole ground reference rather than coming in on one wire. The processor can be damaged while every component around it measures good, and the symptom is a board that powers up and behaves erratically instead of one that is plainly dead.

Latent damage that has not shown up yet

Semiconductors degrade without failing. A board that survived a strike and is working today has a shorter life than it had last week, which is the real argument for finding out what the event did rather than waiting to find out twice.

Mail-in

Getting the board to the bench

Book it in first. An RMA number comes back the same business day, and the board arrives with the paperwork already attached to it.

Ship to

System Voidz — Repair IntakePO Box 33 (USPS)413 Railroad Ave (UPS, FedEx)Watrous, NM 87753

Use the PO Box for USPS and the street address for UPS or FedEx — a PO Box cannot accept courier deliveries.

Wait for the RMA number before shipping.

Tell us this much on the form

  • Which of the checks above you have already cleared. It is the difference between starting the diagnosis and repeating your work.
  • Photograph the board in place, connectors attached. It is the single most useful thing you can send.
  • The equipment make and model, and the number printed on the board itself.
  • Pack it in an anti-static bag. Bubble wrap alone is not enough.
Book a board in

Questions

Dead after a surge or outage — common questions

Will a repaired board survive the next surge?

No better than a new one would, unless something changed outside the board. A repair restores the protection components to new condition — it does not make them bigger than the OEM fitted.

If the same board has now failed twice in storms, the answer is surge protection ahead of the unit, not a third board. That is cheaper than either.

The replacement board died too. What does that mean?

That the cause is still connected. A new board dropped into a shorted contactor coil, a failed motor winding, or a supply with a lost leg will fail the same way, usually faster, because nothing absorbed the first event for it.

Send the board and say it is the second one. That changes what gets tested first, and it is worth more to the diagnosis than anything else you can tell us.

Insurance is calling it a lightning strike. Does that change anything?

Not for the repair, but it may change what is worth doing. A written diagnosis naming the failed components and the failure mode is normal to supply and is often what a claim needs.

Ask for it when the board is booked in rather than after it ships back, so the board is still on the bench when the report is written.

Equipment

Where this pattern turns up most

The same fault, on the equipment it is most often seen on. Each page covers what that class of board does and what else goes wrong with it.