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Error code reference

Dacor Oven Error Code C78

Light error

Dacor codesDacor oven codes

Light error - display voltage has dropped below 15V.

First step from the service manual

Replace LED board. If LED board replacement did not resolve issue, replace logic board.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What C78 means on a Dacor oven

The C78 error code on a Dacor oven indicates a light system fault caused by the display voltage dropping below the 15V threshold required for proper LED operation. The oven's control system continuously monitors the supply voltage feeding the LED lighting board. When that voltage falls below 15V, the logic board registers the fault and triggers the C78 code. This is a voltage-level fault, not simply a burned-out bulb, meaning the root cause is almost always a component failure rather than a simple lamp replacement.

The LED board itself is the most likely point of failure. A failing or failed LED board can draw excessive current or develop an internal short, which loads down the supply rail and causes the measured voltage to sag below the 15V threshold. In some cases, the LED board may appear visually intact but still be electrically defective. This is why the diagnostic procedure begins with LED board replacement as the primary corrective action.

If replacing the LED board does not clear the C78 code, the fault moves upstream to the logic board. The logic board regulates and supplies the voltage to the LED circuit. A damaged voltage regulator section or faulty output on the logic board can cause persistent undervoltage on the LED supply rail regardless of the condition of the LED board itself. In that scenario, the logic board must be replaced to restore proper voltage and resolve the error.

Source: manufacturer service documentation.

Common causes of C78

  1. 01

    Failed LED Board

    Part replacement

    The LED board is the most common cause of C78. An internally shorted or degraded LED board pulls the supply voltage below the 15V minimum, triggering the fault. Replacing the LED board is the first recommended corrective step.

  2. 02

    Logic Board Voltage Output Failure

    Part replacement

    If the LED board replacement does not resolve the error, the logic board's voltage output circuit is likely at fault. A damaged regulator or failing output stage on the logic board can cause the LED supply rail to remain below 15V.

  3. 03

    Wiring or Connector Issue Between Logic Board and LED Board

    Wiring / connection

    Loose, corroded, or damaged wiring between the logic board and the LED board can cause a voltage drop along the supply path. Inspect connectors and harness continuity before or alongside component replacement.

  4. 04

    Intermittent LED Board Connection

    Wiring / connection

    A partially seated connector at the LED board can cause fluctuating voltage readings that dip below the 15V threshold. Reseating the connector may temporarily resolve the fault but the board typically still requires replacement.

See the test procedure for each cause

Frequently asked questions about C78

What does C78 mean on a Dacor oven?
C78 on a Dacor oven means the voltage supplying the LED lighting board has dropped below 15V. The oven's control system monitors this voltage level and triggers the C78 code when it falls below the required threshold. This fault points to either the LED board or the logic board as the source of the problem.
Can I fix C78 on my Dacor oven myself?
A knowledgeable DIYer can attempt this repair by starting with an LED board replacement, which is the first recommended diagnostic step. If that does not resolve the code, the logic board must also be replaced. Both repairs involve working inside the oven's electrical system, so anyone uncomfortable with appliance electrical work should contact a qualified technician.
Is it safe to use my Dacor oven while it shows error code C78?
C78 is a lighting circuit fault and does not directly affect the oven's heating or cooking functions. However, operating an appliance with a known electrical fault is not recommended without understanding the full scope of the issue. It is best to have the fault diagnosed and repaired before continued regular use.
Will resetting my Dacor oven clear the C78 error code?
A power reset may temporarily clear the C78 code, but the fault will return if the underlying component failure is not repaired. The LED board or logic board must be addressed to permanently resolve the undervoltage condition causing the error.
How much does it cost to repair a Dacor oven showing C78?
Repair costs depend on which component is at fault. LED board replacement parts typically range from around $50 to $150, while a logic board can range from $150 to $400 or more depending on the model. Adding professional labor, total repair costs can range from $150 to $600 or higher depending on the technician and parts required.

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