Minolta Dynax/Maxxum 7 aperture error analyzed

I bought a Maxxum 7 off eBay, and it had the classic problem where it would beep on powerup, and power off/on would clear the error, but pressing the DoF button would cause another error.

So I googled around and found the messages about gears probably being stripped on the aperture base plate assembly. I couldn't find a repair place that would fix the camera, and it was dead and worth nothing, so hey I decided to sacrifice it so I can understand the problem.

So I disassembled it down to the aperture base plate, and here's what I found:

o There's a tiny motor with a plastic pinion on it.
o The plastic pinion drives a very thin gear near the base of the motor shaft.
o The plastic pinion worked its way up the motor shaft and no longer touches gear

So it looks like it could have been fixed with a little bit of superglue.

If someone can explain to me how to attach a photo here, I'll post one.

Toshi

Hi Toshi,

Having had a long career in the consumer electronics the repair business I can can tell you from experience this type of problem is very common, to all sorts of consumer electronics, not just the aperture base plate. The probable reason for the gear slipping out of position is a hairline crack in the (probably) nylon material, which is press fit onto the motor shaft. Super glue probably won't hold long term though you can try it. What we used to do is remove the gear and use something to hold the crack together tightly and use a fine tipped soldering iron on the ends of the gear. This is tricky and takes some skill because you can't deform the gear teeth nor the motor shaft opening. Sometimes we would clip off a piece of spring the size of the gear and embed it into the ends of the gear with the soldering iron. Off course the super glue is the safest bet, though you have to be careful not to let it run into the motor bearing. I bought an Alpha 7 from KEH in new condition but with the same aperture base plate defect. Once I found out that parts were NLA I returned it. I would say, because the bearing is press fit, and the load on it from the aperture assembly is causing the crack.
Kind regards,
Kelly

Edited by AudioDoc - 13 February 2017 at 14:13

I've not had much success with superglue on Nylon ...

Your best bet maybe to find another cheap camera with something else wrong with it.

stiuskr wrote: If all else fails go see your local jeweler/watchmaker, making gears isn't that hard to do with the right files and material.

Files??? I've made gears before now and normally a lathe is required with considerable expertise.
You might get someone to make you up one by 3-D printing, though. Removing the original, gluing it securely and then laser scanning and printing it should be viable, or else someone has to do a cad drawing. The properties of the material used for the printing may be an issue, though. The materials I've seen used aren't very strong.

The unit isn't repairable anymore as I've had to cut flex cable to reach the aperture base plate assembly. I've taken another look at it, and the pinion doesn't appear damaged in any way - there are no cracks. It's just loose on the motor shaft.

The seller refunded my payment, so I've already purchased another Maxxum 7, and it's already arrived and I shot a dozen shots before work today.

Toshi

How did you Get to gears