Tamiya M4 105 Sherman

[Rad_Schuhart]

Yup, dismantling the MG can be a bit of pain... What I would do is to grab another led and carefully connect it to the CN3 and then, trigger the machine gun. If it works, you know the problem is in your machine gun´s led. If not, a faulty DMD unit, but this would be the first case I have read of...

[Dayle Frame]

Could the LED be wired the wrong way around? If it was pre wired, it's still possible it was done at the factory, wouldn't be the first time silly mistakes have happened.

Good point......when plugged in, the orange wire is on the right (fore) and the white is to the left (aft). Anyone else with a M4 wanna check this for me?

In the meantime, I’m going to try and see if the DMD is putting a voltage on the two pins. Because of the size of the pins, this is gonna be a real trick.

Dayle

[43rdRecceReg]

One of the reasons Tamiya recommend using the enigmatic 'synthetic rubber cement' for joining the the four components of the MG together, might well be the possibility of having to disassemble them. I used rubber cement on mine. Elmer's, in fact. A whole thread was dedicated to the identity of Tamiya's mysterious 'rubber cement' recently.
I wonder whether resetting the DMD unit might help. Since the MG is trim control dependent, and the DMD unit controls the trims, it might be worth a try.
https://www.tamiyausa.com/articles/1-16 ... p2jFracZR4
LED's are of course, diodes, and in general they don't enjoy being wired the wrong way round. It is possible to plug the connector in the wrong way round, and so that's worth checking.
Good luck anyway

[43rdRecceReg]

Could the LED be wired the wrong way around? If it was pre wired, it's still possible it was done at the factory, wouldn't be the first time silly mistakes have happened.

Good point......when plugged in, the orange wire is on the right (fore) and the white is to the left (aft). Anyone else with a M4 wanna check this for me?

In the meantime, I’m going to try and see if the DMD is putting a voltage on the two pins. Because of the size of the pins, this is gonna be a real trick.

Dayle

That's the orientation on my (working) Tamiya Panther G MG, Dayle. You can assume you have the right connection. Just check that the connector block halfway to the gun is also properly pushed in.

[43rdRecceReg]

For confirmation of the correct wiring, have a look at this schematic for the typical DMD. You'll see that white leads are always on the left (fore), and coloured leads on the right (aft)

Tamiya Wiring to the DMD control unit...

Tamiya Wiring to DMD unit.jpg (81.8 KiB) Viewed 2470 times

[Dayle Frame]

I found a replacement MG LED on eBay and have purchased it ($10). This will allow me to test whether the issue is the DMD, the wiring, the LED....whatever. It’s supposed to arrive next week and we’ll take it from there. If it’s the LED, then I’ll have to disassemble the whole widget. But I’ll cross that bridge when I get to it.

Dayle

[Rad_Schuhart]

10 bucks a led? OMG. For that price you can buy 100! https://www.ebay.com/itm/9V-12V-3mm-5mm ... Sw8w1X7xTt

[Dayle Frame]

A quick update: I tried to measure the voltage on the CN3 pins while the MG was "firing". My VOM registered nothing. Of course, I don’t know if I was actually measuring 0.0VDC or my leads were too big to accurately perform the measurement. I also tried to measure the resistance of the LED. I used braided wire strands and inserted them into the LED’s pin holes. I measured 0 ohms.....I don’t know enough electronics to know if a functioning LED should have a resistance or not. But, again, maybe my measuring technique was faulty.

This is when I decided to buy a replacement MG LED. I found Tamiya part # 7255019 on eBay and purchased it. It’s supposed to arrive next week. At that point, I can check to see if the DMD is putting out the correct signal or if the original LED is at fault.

As to SoaG’s point, my LED is wired the same as 43ReeceReg’s working MG......orange wire on the right. Whether o connect the LED directly to the DMD or route it through the extension, they both behave the same.....noise but no light.

One of my previous jobs was to repair analytical instrumentation for chemistry labs. I learned how to diagnose problems that cropped on really complicated pieces of hardware. This is no different.....just smaller. It might be the board (DMD), the wiring or the LED.....I’ll get to the bottom of this one way or another.

[43rdRecceReg]

A quick update: I tried to measure the voltage on the CN3 pins while the MG was "firing". My VOM registered nothing. Of course, I don’t know if I was actually measuring 0.0VDC or my leads were too big to accurately perform the measurement. I also tried to measure the resistance of the LED. I used braided wire strands and inserted them into the LED’s pin holes. I measured 0 ohms.....I don’t know enough electronics to know if a functioning LED should have a resistance or not. But, again, maybe my measuring technique was faulty.

This is when I decided to buy a replacement MG LED. I found Tamiya part # 7255019 on eBay and purchased it. It’s supposed to arrive next week. At that point, I can check to see if the DMD is putting out the correct signal or if the original LED is at fault.

As to SoaG’s point, my LED is wired the same as 43ReeceReg’s working MG......orange wire on the right. Whether o connect the LED directly to the DMD or route it through the extension, they both behave the same.....noise but no light.

One of my previous jobs was to repair analytical instrumentation for chemistry labs. I learned how to diagnose problems that cropped on really complicated pieces of hardware. This is no different.....just smaller. It might be the board (DMD), the wiring or the LED.....I’ll get to the bottom of this one way or another.

Are you using the Futuba 4YWD 2.6G, Dayle? I had an issue lately with the cannon not firing or recoiling on my Panther. The firing trigger for that is: trim control fully up. and elevation toggle up (polar opposite of the MG method).
I discovered there's a certain speed technique needed on my 4YWD to get the change of mode from elevate to fire, to kick in. After two days of fitful attempts, I was in the same position that you're in, wondering which unit is the culprit. I found that by throwing the trim control forward quickly, the cannon would fire, the flash would illuminate, and the barrel would recoil. Eureka! In other words, the glitch probably lies in my left trim control, and has nothing to do with the tank. To be honest, I think it's very unlikely that Tamiya would wire the MG connector the wrong way round. Their quality control is excellent. At their prices- it should be!
I have configured my TX with all drive controls on the right stick, and all the turret functions (including MG and Cannon) on the left. If a real trim problem crops up, I could shift the functions over..but for now, I'm satisfied the tank itself is fine. I expect yours is too. Just try moving the trim control quickly aft, to see if that helps initiate firing. Perhaps the bottom trim control on that toggle could influence firing. Try experimenting. I did, and it paid off.
Again, there's nothing to lose in resetting the DMD.
With the LED cable removed from the DMD, You can test the LED with the Diode/Continuity tester section of your multimeter. The appropriate readings (good and bad) for your meter should come with its handbook, but should be something like this, but I expect you know all this:
http://en-us.fluke.com/training/trainin ... meter.html
I often use pin to pin coloured breadboard connector cables to connect units like the LED MG to my Multimeter, that way you get a good connection, and don't need three hands.
BUT..do look at transmitter issues first. That solved my problem (potentially much more expensive than your LED one )

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Did you do the dmd setup correctly in the instructions?