A common and frustrating situation in clock repair is a movement that runs perfectly on the test stand, yet develops problems once it is installed back into the case. This guide walks through a real-world chime power loss issue encountered on a late 19th-century Junghans mantel clock and explains how the root cause was identified and resolved.
After a full teardown, cleaning, pivot polishing, and mainspring replacement, the time, strike, and chime trains all operated correctly on a test stand. The trouble appeared only after the movement was mounted in its case. The time train continued to run normally, and the strike could be triggered manually, but the chime train lacked the power needed to start on its own and would stall under hammer load.
Initial checks focused on common causes. Case level and beat were verified. Mounting screws were confirmed to be snug but not overtightened. Dial and hand clearance were ruled out, and the chime barrel was checked to ensure it was not contacting the case or hardware. None of these steps resolved the issue.
Attention then turned to how the movement was supported in the case. When tested on the stand, the plates were free of external stress. Once mounted, even slight twisting or uneven support could introduce friction significant enough to stop a chime train, which typically requires more power than the time train.
A key diagnostic step was testing the movement while still attached to its seat board, but removed from the case. When the chime failed again in this configuration, it confirmed the problem was not the case itself, but the seat board. Upon closer inspection, the original seat board was found to be warped. This distortion twisted the movement plates just enough to rob the chime train of power.
A new seat board was fabricated from flat plywood, ensuring even support across the movement. Once the movement was remounted and carefully secured, the chime train operated normally in the case, fully resolving the issue.
Frequently Asked Questions
Why would a clock run on the test stand but not in the case?
The test stand supports the movement evenly. Case mounting can introduce stress from warped seat boards, misaligned supports, or overtightened hardware.
Why is the chime train affected more than the time train?
Chime trains require more power due to hammer lift and locking mechanisms, making them more sensitive to added friction.
How can I test whether the seat board is the problem?
Run the movement on the test stand with the seat board still attached. If the problem appears, the seat board is likely causing distortion.
What is the best material for a replacement seat board?
Flat, stable plywood works well and resists warping better than many original softwood boards.
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