the clock on my em720cb7 keeps losing time, i set it and it's wrong the next day

Diagnosis

The Black+Decker EM720CB7 utilizes a low-cost quartz crystal oscillator and a series of electrolytic capacitors on the main control board to maintain the timekeeping frequency. When the clock consistently loses minutes over a 24-hour period, it indicates "clock drift." This occurs when the capacitor responsible for filtering the voltage to the timing chip begins to leak or lose its capacitance value, causing the internal pulse count to deviate from real-time. This is not a software glitch but a hardware degradation issue. You can confirm this by observing if the time loss is linear (e.g., it loses exactly 5 minutes every 12 hours) or if the clock resets entirely after a brief power flicker. If the clock remains on but is simply "slow," the timing capacitor is failing. If the clock disappears and returns to 12:00, you are dealing with a failure in the standby power rail or a loose connection at the primary power inlet.

How to Fix It

Since the timing circuit is integrated into the proprietary main control PCB, there is no adjustment screw or software calibration setting to "speed up" the clock. However, you can stabilize the power delivery to the board to minimize drift.

1. Isolate the Power Source: Unplug the microwave from the wall outlet. Do not use a power strip or an extension cord, as the EM720CB7 is sensitive to voltage drops which can exacerbate clock drift. Plug it directly into a grounded 120V AC outlet.
2. Perform a Hard Logic Reset: With the unit unplugged, press and hold the 'Stop/Clear' button for 30 seconds. This drains the remaining charge from the capacitors on the control board, clearing any corrupted volatile memory.
3. Recalibrate the Clock: Plug the unit back in. Press the 'Clock' button, enter the current time using the numeric keypad, and press 'Clock' again to confirm.
4. Sync Test: Set the time exactly to the second using a digital reference. Check the clock again in exactly 12 hours. If it has lost time, the hardware failure is permanent.

If That Didn't Work

• Replace the Main Control Board: The only permanent hardware fix is replacing the entire control PCB. Locate the part number on the white sticker attached to the board (usually found behind the front bezel). Ensure you discharge the high-voltage capacitor before opening the chassis, as these store lethal charges even when unplugged.
• Check for Interference: Ensure the microwave is not positioned directly next to a high-frequency device like a powerful Wi-Fi router or a large subwoofer. Electromagnetic interference (EMI) can occasionally disrupt the low-frequency oscillation of the quartz crystal in budget microwave controllers.
• External Clock Implementation: Because the EM720CB7 is a budget-tier model, the cost of a professional board repair often exceeds the replacement value of the unit. The most practical solution is to ignore the onboard display and utilize a dedicated digital kitchen timer or a smart plug with a built-in timer for scheduling.
• Voltage Stabilizer: If your home experiences frequent "brownouts" or voltage sags, install a small UPS (Uninterruptible Power Supply) or a voltage regulator. This prevents the control board from dipping into a low-voltage state that causes the timer to skip pulses.

Heads Up

• High Voltage Danger: Never open the outer casing of the EM720CB7 unless you are a certified technician. The capacitor inside can hold 2,000V+ even after the unit is unplugged.
• Avoid Power Strips: Microwaves draw significant peak current. Using a power strip can cause voltage fluctuations that lead to "ghost" button presses or clock resets.
• Cleaning the Bezel: If the 'Clock' button feels sticky, do not spray liquid cleaner into the panel. Use a damp microfiber cloth to avoid shorting the tactile switches on the control board.
• Cooking Safety: Note that clock drift does not affect the actual cooking timers or the magnetron's output; your food will still cook for the exact time programmed.