Please let me know if this is the wrong place to post this as I'm new here

I've been working on my broken Yashica T4 film camera for a while, trying to find out why it won't autofocus. These have become very expensive lately so I think it's worth the time/effort to try and fix it. I've been able to narrow down my issue by purchasing a second working camera. The photo interrupter that senses the movement of the lens appears to be damaged, as swapping the parts around makes my "good" camera show the same symptoms as my "bad" camera and vice-versa.

There is a repair manual available for this camera, but unfortunately it seems like the part numbers are internal and therefore don't result in any good google searches. Now to my question: How would I go about finding a replacement part for my camera? I have a scope, multimeter, soldering iron etc. so tools are not the issue, I just don't have any clue how to identify my part and also don't know what tolerance my camera's main board has for a slightly different photo interruptor.

Please let me know if you have any ideas or if I should measure/take photos of parts to provide more context. Thanks in advance!

Yashica T4 Repair Manual
Photo of the Lens Assembly, the damaged part in question is located on the right side next to the gears and is soldered to a flex cable.

 

Welcome to AAC.

This is a tough question. It could be a proprietary part, and it is at least going to be an obsolete one. Finding a substitute is probably the least likely solution. I suspect it is particular to Yashica and so repair parts or donor cameras seem the most likely source.

I have two suggestions that really don't answer your question directly. One is to occasionally check your local Goodwill and/or Salvation Army stores. They often get old cameras and they go cheap. The likelihood of them having this particular camera does seem low but not impossible so it might be worth a gamble.

The other is usedphotpro.com. I buy almost all my used gear from them and they are great. Customer service is top notch, I mean really good. I never worry about a purchase from them, even multi-thousand dollar lenses and camera bodies. They have an additional advantage of taking actual photos for the listings you can literally see what you are buying.

That link is to a T3. Unfortunately they don't have a T4 in stock. But they get new inventory regularly and they sell repair/parts cameras so they list them.

I have one more suggestion, though I consider it a long shot. Perhaps you can reuse the housing, or 3D print one, and use equivalent LED and sensor parts in it. You'd have to characterize the two components but I think it could be done. It doesn't sound like an easy road, though.

 

For the total time the IR LED is in use for the sensor, I really doubt the LED or sensor have come to the end of their life. I suspect it is much more likely that there is some debris blocking the light path of the sensor - it could be anything from a flake of skin, hair, or other lint, dust or pollen or sand that managed to collect there over time.
You can try to remove as much of the gear assembly as possible to get in front of the photo-interrupter's light path and visibly check what might be there. As a last resort, you could remove the photointerrupter and we can do some tests.

 

You should be able to get your scope onto the diode, run your lens, and get a good idea if it is performing. That assembly is typical of the mass production in consumer cameras of its time. If that sensor is counting gear teeth, it will be a calculation, determined by the AF, from a parked reference. I would look to see that the lens returns to its ‘parked’ position, via the appropriate sensor. Most problems that I’ve seen with these units is some issue that prevents free travel of the mechanical assembly.

 

Thank you so much for all of your responses! Sorry for responding late, it's quite a lot of work to disassemble this camera and reassemble it as it requires soldering, keeping track of screws, adhesive etc.

For the total time the IR LED is in use for the sensor, I really doubt the LED or sensor have come to the end of their life. I suspect it is much more likely that there is some debris blocking the light path of the sensor

That's was one of my first thoughts as well, but I thought it would be fine since the sensor is optical (not mechanical)... I guess not! I looked at the sensor under a microscope and there was indeed some debris. I cleaned it off carefully and reassembled the camera, thinking it wouldn't work. To my surprise, it seems to be working just fine! I'm running a quick test roll through the camera as we speak and I will report back with results.

I'm very grateful for all of you taking the time to write such well thought out responses.

 

Thank you so much for all of your responses! Sorry for responding late, it's quite a lot of work to disassemble this camera and reassemble it as it requires soldering, keeping track of screws, adhesive etc.



That's was one of my first thoughts as well, but I thought it would be fine since the sensor is optical (not mechanical)... I guess not! I looked at the sensor under a microscope and there was indeed some debris. I cleaned it off carefully and reassembled the camera, thinking it wouldn't work. To my surprise, it seems to be working just fine! I'm running a quick test roll through the camera as we speak and I will report back with results.

I'm very grateful for all of you taking the time to write such well thought out responses.

I'm really happy to hear you got it working - and with a reasonably simple solution. Stick to it. Post a photo when you get some developed.