Sigma 24-135 Aperture Error: Flex Cable Repair
Overexposed photos and camera freezes with a Sigma 24-135 on Canon? A broken aperture flex cable is the usual cause — and it can be replaced at a fixed price.
Symptoms
- Sigma lens overexposing photos
- Camera freezes or locks up when shooting with the lens
- Aperture error only with this lens attached
- Lens works at full aperture but not stopped down
Overexposed frames and a camera that freezes mid-shoot are the classic signs that a sigma lens aperture error repair is needed: inside the lens, the flex cable that carries the aperture commands has failed. On the Sigma 24-135mm f/2.8-4.5 for Canon this is fully repairable, at a fixed price of €100.
The symptoms
- Shots come out overexposed — occasionally at first, then more and more often.
- The camera locks up completely while shooting with this lens, and only removing and reinserting the battery brings it back.
- Everything works normally with other lenses attached.
That is exactly what happened to a customer with his well-kept Sigma 24-135mm f/2.8-4.5 AF for Canon — a lens that is now quite old and genuinely hard to find on the used market, which makes repairing it especially worthwhile.
What causes it
On every Canon and Canon-mount lens the aperture is regulated electronically: the camera sends open/close commands to the lens through the mount contacts. Inside the lens, a thin ribbon cable — the flex (or flat) cable — carries those commands to the aperture unit. When a lens stops responding correctly to the camera, one of two things has happened: either the communication flex has broken and no longer carries the signal, or the flex is intact but the aperture motor itself has failed.
A failing flex rarely dies all at once. Because the cable flexes with the moving barrel sections, the break usually starts as an intermittent fault — the occasional overexposed frame — and becomes more frequent as the damage spreads. In this case the diagnosis was clear: the communication flex was physically broken in two places.
Can you fix it yourself?
There is no user-accessible fix. You can clean the gold contacts on the mount with a dry cloth and rule out the camera by testing another lens, but a broken internal flex requires full disassembly of the lens and precision soldering work. Flex cables are fragile and routed through moving barrel sections — improvising here usually adds damage rather than removing it. Until the lens is repaired, keep a spare battery handy: pulling and reinserting the battery is the only way to recover the camera when it locks up.
How we repair it
Our technicians completely disassembled the lens, desoldered the old broken flex cable and soldered in a new one. After reassembly, the aperture was tested through its whole range as part of our Sigma repair service.
The result: the Sigma 24-135 works exactly as it did before the failure. It shoots wide open and at every level of aperture closure, with no overexposure and no error reported by the camera. Internal cleaning and the final functional check are included in the fixed price.
Price and turnaround
| Service | Price |
|---|---|
| Aperture flex cable replacement | €100 (fixed) |
| Internal cleaning | Included |
| Final test & calibration | Included |
Typical turnaround is 10 working days, as the repair involves board-level soldering. Return shipping within the EU is a flat €20.
Ship your lens from anywhere in the EU — diagnosis is free and every repair carries a 6-month warranty. See how it works.
Frequently asked questions
Why does my Sigma lens overexpose every shot?
On Canon-mount lenses the aperture is controlled electronically by the camera. If the internal flex cable that carries the aperture commands is broken, the blades never stop down and the image is overexposed.
What is a sigma lens aperture error repair and how is it done?
The lens is fully disassembled, the broken flex cable is desoldered and a new one is soldered in its place. We then verify aperture operation at every f-stop.
How much does it cost to fix a Sigma 24-135 aperture error?
Our fixed price is €100, including internal cleaning and a full functional check.
Could it be the aperture motor instead of the cable?
Yes — when a lens stops responding to aperture commands the fault is either the communication flex or the aperture motor itself. Diagnosis is free, and we confirm the actual cause before repairing.
