Questions about the MT24 and inside pictures

I have complained before (though not too recently) that my a99 turns on the MT24 flash when I don't want it to. Specifically any time I turn on the camera, any time the camera comes out of power save, and recently I discovered when the camera switches from video to still mode. The A900 doesn't do this, so something clearly slipped by the A99 (and other SLT) code writers. However maybe they didn't bother since most Sony flashes have an air gap power switch, so no software on signal can get through. the MT 24 is a slightly adapted Minolta design with a push-push electronic power switch on the flash, but no cut off from the camera. But I have said most of this before.

This has finally irritated me enough that I though I'd see if I could hack on a real switch. My first step was to open the case to see if there is room for a panel mount type mini switch to fit through the case. Answer: No. So it will have to be surface mount on the outside.

So next issue: which wire might work? Looking at mhohner F2 seems like a candidate. But when I open the flash I saw that there were 5 wires, not the four that are listed for flash function. The fifth seems to go to a small switch inside the foot that it depressed when it slides into the shoe. (I checked F58 and the multifunction to quicklock adapter ADP-AMA. They have the switch too.)

What is this switch and connection? No one seems to list it in flash contacts. Is it perhaps a "flash on board" switch that tells the camera that a flash is mounted? If so, would a switch in that line function as an air gap power switch for the MT24?

Pictures follow, with a few comments. I put pictures of the mt24 foot first since I just talked about it, then more or less in the order of disassembly.

analytical wrote: So next issue: which wire might work? Looking at mhohner F2 seems like a candidate. But when I open the flash I saw that there were 5 wires, not the four that are listed for flash function. The fifth seems to go to a small switch inside the foot that it depressed when it slides into the shoe. (I checked F58 and the multifunction to quicklock adapter ADP-AMA. They have the switch too.) What is this switch and connection? No one seems to list it in flash contacts. Is it perhaps a "flash on board" switch that tells the camera that a flash is mounted?

Almost. It tells the flash, that it is mounted on the camera, not off-camera. This is important to know for ADI flash metering, because the distance flash-to-subject is only known when it is mounted on the camera (because then it is the same as the distance camera-to-subject).

The camera hot shoe presses the switch, when the flash is mounted. If the flash is used wirelessly, the switch isn't pressed. Also, all off-camera hot shoes feature a small hole, so that the switch isn't pressed when mounted in one of them as well. The exception is the FS-1200, which does not feature the hole as well, but the FS-1200 is - by design - for use on the camera, not an off-camera hotshoe, so no problem here either unless it is misused.

There is no signal wire for the switch, because it is not needed.

The new Multi Interface hotshoe does not feature a switch any more, but the concept continues to be used via pin 21.

More info can be found here:

http://www.mi-fo.de/forum/index.php?showtopic=33060

If so, would a switch in that line function as an air gap power switch for the MT24?

No, but you can cut the F3 signal. The camera will assert "high" on this pin in order to force a "sleeping" flash to wake up. If you cut F3 and insert a switch in there, this can no longer happen for as long as the switch is open.

http://www.mi-fo.de/forum/index.php?showtopic=23553

(Note: Both links do not work at present since we are in maintenance right now. Both their contents should be in Google cache and I hope we will be back online soon as well.)

Greetings,

Matthias

Edited by matthiaspaul - 25 September 2014 at 09:33

analytical wrote: Now to find a surface mount mini switch. Even if I have to press the original on/off switch after closing the real switch, that's much better than what it does now.

Another idea since you mentioned that you found what looks like a DC power jack inside the flash. If you could determine that this is actually an undocumented power connector (the predecessor Minolta MFC-1000 had a DC power in jack for 4.3V), it might contain a switch disconnecting the batteries while a plug is inserted. If so, you could drill a hole and use a dummy plug to disconnect the batteries from the control unit when not needed.

Greetings,

Matthias

Edited by matthiaspaul - 25 September 2014 at 09:34

matthiaspaul wrote: Another idea since you mentioned that you found what looks like a DC power jack inside the flash. If you could determine that this is actually an undocumented power connector (the predecessor Minolta MFC-1000 had a DC power in jack for 4.2V), it might contain a switch disconnecting the batteries while a plug is inserted. If so, you could drill a hole and use a dummy plug to disconnect the batteries from the control unit when not needed.

In pictures, the Minolta 2400 version of this flash appeared to have a DC connector with case opening at this location, so it's suspicious.    

And there is even a circle on the case that appears to line up with the plug. Also here's a closer look at the plug (or more correctly the "receptacle" or "socket". The "plug" is on the cord.) Is this a standard plug size?





Edited by analytical - 25 September 2014 at 15:40

analytical wrote: And isn't the 6V connection more likely to be for a battery pack than an AC adapter? e.g. Mhohner site labels it that way. mt-2400 spec page

I'm not aware of a Minolta or Sony battery pack for the Minolta MFC-1000. However, you can, of course, use an external 6.0V DC battery pack to power the control unit. You can trust the information in Minolta-Forum to be correct - it's all carefully researched and/or tested. ;-)

The Minolta EP-1 and EP-2 have completely different connectors.

The point I was trying to make is that the only external power supply offically available for the MFC-1000 was the AC-10, which is specified for 4.3V output only. Most probably Minolta chosed to use a lower voltage in order to keep the MFC-1000 from overheating.

Greetings,

Matthias

I'm confused by references to mfc-1000. The Minolta predecessor to the Sony HVL-MT24 was the Minolta 2400, which apparently had a battery pack connection. Same mhohner link as before. Also I found a picture on Pete Ganzel web site linked below. Near resolution limit, but the label on the side seems to say DC IN 6V



BTW there is no ring flash socket hiding inside the MT24, nor a pcb that would mount one. The why is likely because Sony didn't carry over the Minolta ring flash, but introduced a new ring light (not a flash).    



Edited by analytical - 25 September 2014 at 18:48