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06-01-2019, 03:26 PM   #1
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645n not rewinding after 16 frames

Hey all!

First time posting, thanks for having me!

Iíve got a 645n with an assortment of 120 backs and converted 220 backs. Iíve got an issue that I thought only happened with my converted 220 backs, but itís happening with my 120 backs as well. My film on my 645n never winds after frame 16. Iíve got to keep hitting the shutter until frame 23 (or hit the rewind button), then it finally winds, but gives me the flashing ďEĒ at the end of the roll. Anyone know why this is happening?

06-01-2019, 03:45 PM   #2
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Try replacing your batterys
06-01-2019, 05:44 PM - 1 Like   #3
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The 645 (and all medium format cameras that I know of) do not rewind.

The film goes onto the take up reel, and you put the newly emptied reel into the take up position for the next roll.

From what you've described, your camera is working correctly.
06-01-2019, 05:58 PM - 1 Like   #4
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Welcome to the Pentax Forums!

As you already know, the camera does its automatic end-of-roll wind after 16 or 33 actuations depending on whether a 120 or 220 holder is detected. Therein lies your clue. If you have been having this problem with a properly converted 220 holder, you should not have been. The detection mechanism in the camera is probably malfunctioning. You may also be having frame spacing problems.


Steve

P.S. The educated opinion exists that using a 220 holder with 120 film has potential to overwork the film advance motor due to excess pressure plate thickness.


Last edited by stevebrot; 06-01-2019 at 06:12 PM. Reason: completeness
06-01-2019, 06:40 PM   #5
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QuoteOriginally posted by Alex645 Quote
The 645 (and all medium format cameras that I know of) do not rewind.

The film goes onto the take up reel, and you put the newly emptied reel into the take up position for the next roll.

From what you've described, your camera is working correctly.
Nope. It should finish the roll and ďwindĒ after frame 16. Itís not doing that until ďframeĒ 23. Since 120 film is only 16 exposures, I shouldnít be able to click the shutter 7 more times before the roll finishes.
06-01-2019, 06:47 PM   #6
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QuoteOriginally posted by stevebrot Quote
Welcome to the Pentax Forums!

As you already know, the camera does its automatic end-of-roll wind after 16 or 33 actuations depending on whether a 120 or 220 holder is detected. Therein lies your clue. If you have been having this problem with a properly converted 220 holder, you should not have been. The detection mechanism in the camera is probably malfunctioning. You may also be having frame spacing problems.


Steve

P.S. The educated opinion exists that using a 220 holder with 120 film has potential to overwork the film advance motor due to excess pressure plate thickness.
Think it could still be the detection mechanism if itís happening with my 120 backs as well?
06-01-2019, 07:29 PM   #7
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QuoteOriginally posted by Ericjgay Quote
Think it could still be the detection mechanism if it’s happening with my 120 backs as well?
Absolutely. A converted 220 holder/insert is detected the same as a 120 holder/insert such that both give 16 exposures. Below is an image from pentax645.com showing the part of the insert that is used in detection.


From: Convert Pentax 645 645n 645nii 220 film back to 120 film back – Pentax 645

Conversion involves turning that little part end-for-end such that the "finger" points toward the pressure plate. If the "finger" is detected (or not detected depending on how it actually works*), the camera behaves proper for 120 film.

BTW...don't use a slot-blade screw driver as in the video on that site. The screw is JIS cross head and requires the proper JIS screwdriver.


Steve

* I don't have access to a 645N anymore to check how the detection works; I just know that the conversion involves that small part.

Last edited by stevebrot; 06-01-2019 at 07:34 PM.
06-02-2019, 01:32 AM   #8
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QuoteOriginally posted by Ericjgay Quote
Think it could still be the detection mechanism if itís happening with my 120 backs as well?
I see....sorry, I didn't read your original post carefully enough. Yes, I also agree with Steve it's the detection mechanism.

06-02-2019, 04:54 AM   #9
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QuoteOriginally posted by Alex645 Quote
I see....sorry, I didn't read your original post carefully enough. Yes, I also agree with Steve it's the detection mechanism.
Ok cool, looks like there might be a consensus. Iím having trouble finding any info on this piece. Any idea if itís repairable?
06-02-2019, 10:34 AM   #10
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QuoteOriginally posted by Ericjgay Quote
Ok cool, looks like there might be a consensus. Iím having trouble finding any info on this piece. Any idea if itís repairable?
Before sending it off for repairs, I'd suggest "rebooting" the camera by taking the AA batteries out and also the button cell. While the button cell is out, check the voltage as it may be marginal and should be replaced.

Next check the inside of your 645 with the back off that nothing is sticking. Then I would go back to your non-converted 120 back and run a roll thru it, to see if it is still dysfunctional. If it is, then here's a thread of repair options:
Pentax 645N repair - PentaxForums.com

If it does work after the 'reboot', I suspect your converted 220->120 backs is causing the problem.
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