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01-17-2016, 02:19 PM   #1
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Location of MX flash contacts

I've happily just put a film in my MX and now found the X-sync isn't working - it was last year. I've tried both the hot shoe and front port with two different flashes, a Pentax AF280 and an old Cobra. The former works fine on my K2, the latter also and I've been using it on old 1950s/60s cameras with the PC cable, so no problem from the flash end. I've done some googling but not managed to figure out what to remove to find the contacts - there is a suggestion they're under the front where the terminals are. Any thoughts?
Ta

01-17-2016, 03:48 PM   #2
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I get the impression the camera was stored unused for a while? The switch contacts are designed to be self cleaning, so I suspect if you shoot a few frames, with flash or not, any film of corrosion will be cleared off. This wasn't as big of a problem in the old, high trigger voltage flash, days since the HV would readily "punch" through oxidation.
01-17-2016, 04:00 PM   #3
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IIRC, if the pc port isn't working either, the fault is pretty deep in the camera and requires a lot more disassembly than if just the shoe is out.
01-18-2016, 12:43 AM   #4
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If the PC connector doesn't work either, you will need to remove the top, bottom, and the front panel to get to where the flash switch is. Maybe it is dirty and maybe the part needs to be replaced.

01-18-2016, 01:59 AM   #5
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Thanks for the replies. The camera was stored for a few years before I got my hands on it, and it was working fine then (including the flash) but I haven't used it for about a year. I've shot maybe 5 frames so far but also I was testing the shutter speeds a couple of months ago so did quite a few dummy shots then. I don't know about the voltage of the AF280 - I presume it's a bit lower as it can do lots of fancy dedicated stuff? I don't know about the Cobra either come to think of it but it's no spring chicken. Interesting about being self-cleaning. I have a really old Jessops one somewhere, will give that a go, it's from the late 80s I think.

Pentaxus, have you got any further info? I have the service manual but it's a bit esoteric. Does the mirrow box have to come out, or once the front is off can you get tot the switch?
01-18-2016, 12:20 PM   #6
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From my records (my modification to original Pentax diagram)

01-18-2016, 12:26 PM   #7
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Ah, fantastic, many thanks. So do I peel the skin back and take off the plate where the lens mounts? I've been trying to find photos or diagrams, but nothing for the MX, seen some for KX and others.
01-18-2016, 01:49 PM   #8
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It's a long time since I have done one of these and I cannot remember if you have to remove the lens panel or not, anyway the MX skin peels off and refits easily so if you take it off first on the self timer side then you should be able decide from there.

I do remember that the couple of these that I have had trouble with were both problems with the switch on the bottom of the mirror box. Plug a flashgun into the FP socket, if it doesn't fire on that then it's the mirror box switch, if it fires on FP and not on the X socket then it's the X switch that's faulty.

01-21-2016, 03:36 PM   #9
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You're a star Ray but I'm not out of the woods yet. The FP/winder switch is fine, but there is no connection between the front X port and the hot shoe. I need to re-set the meter so will take the top off an investigate. Flash still doesn't fire from the front port. Connections from outers of the PC connectors to ground are fine, from FP inner to FP switch and thus to ground when the mirror is up. Also discovered I have two dodgy PC cables, which explains one badly underexposed shot from a roll film camera recently. Think I am going to have to peel the front back and find the X switch in order to diagnose what's going on but one step at a time. So far looking like the connection between the X port on the front and everything else so will be in there too.
01-23-2016, 09:31 AM   #10
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@Johnny:

I just pulled apart an MX to fix this same problem, so if you haven't done it yet, let me know, and I can attach some pics and instructions on how to get to the switch. The self-cleaning anecdote seems to be apocryphal. It's just a standard leaf switch that is activated by very little pressure. There's no lateral motion or the like that would keep the surfaces clean, even with regular use.
03-10-2016, 02:05 AM   #11
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@dcshooter

Hi! I have that same problem whit my dad's old MX, X-sync dosen't work.
If You can post pics, how to get that fix, i will be grateful

Regards:
Skebat
03-10-2016, 07:56 AM   #12
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This was a while back, so I'll have to see if I can dig out the photos. If I can't find them, I think I have another body with a similar problem. The contacts are accessed by removing the timer switch , the front left leatherette, and the plate underneath. Then you'll see a pressure switch with red leads coming off of it. The contacts tend to get tarnished and have to be cleaned. It's part 0-j621 on the diagram above.
03-14-2016, 08:20 AM   #13
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Mine still has film in it; looks like I'll need to take the top off to get the front bits off, which means removing the rewind crank. When I get around to it I'll post some pics. Have you already checked the FP switch as in Ray's info above? Does Fp sync work? Does the front X port work or is it just the hot shoe?
03-16-2016, 11:01 PM   #14
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Hi,

Fb sync work and both X sync do not works.
03-17-2016, 02:52 AM   #15
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Probably a problem with the X sync switch or its connections, which is on the shutter-button side of the front, that's where I need to get into as well.
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