Elmod on board fuse

[NigelDerEnglander]

Hi Rob,

The last week or so has been the Nuremberg Rally, err, I mean Toy Fair, so I guess ElMod have been busy in the weeks up to that, during it, and would only have got back last week and would have a backlog of things to catch up on.

Nige

[wibblywobbly]

They just replied, and Thomas is sending me a replacement component together with details on where it goes. Thank goodness!

Rob G

[NigelDerEnglander]

Hi Rob,

Tony (Tiger205) came over last night and we surfed the site and looked over your ElMod problems again. Unfortunately you hadn't supplied enough information for me to understand what was going on as I don't have any ElMod stuff. With Tony's knowledge of the old ElMod kit we had a better idea! As Tony had pointed out to me a week or so back, one of the transistors on the 'top' of the board had a brown stain on it (the big bottom left one near the silver 'tinned' area). This must be the blown transistor - not a fuse.

But why did it blow?

Well, I read your other posting and read this same one again properly! Plus a week or so back, Tony had brought his new metal Tiger hull round.
I then started looking for reasons. Unfortunately there isn't just one!

The big factor for me is the new metal hull. There are lots of exposed metal bits all over now, and I reckon the current is shorting via the hull - before being plastic, it couldn't happen. I would imagine that your motor wires are touching the case of the motor. This is then shorting through the gearbox to the hull, then something else is touching this and creating the circuit loop to short out.

Or, something similar, but it is causing the drive transistor (the little one by its feet of the blown one) to power the now-blown transistor all the time. As this is in an H-bridge circuit, when the other transistor is also on it will create a direct short circuit across the two transistors. The weaker one blows first, and the second one survives.

Or, as above, but the drive transistor has a solder splash or a 'dry joint' that causes the blown one to have blown.

There are lots of reasons really and not easy to diagnose without getting hands-on, and having the test kit to hand. What I would suggest is that once you have the replacement parts from ElMod you test the whole lot 'on the bench' out of the tank to ensure no shorts via the metal hull.

Also you may find that if you install with the motors disconnected (wires taped!) one direction will be okay, but the other will cause the replaced transistor to get hot. You can get 'freezer spray' from Maplins to put a frosting over the circuit, then start it up and see which component melts the ice first.

Sorry, but any more help involves years of electronics experience.....and hands on!

Good luck!

Nige

[wibblywobbly]

The saga has now ended.

I got both boards back from Thomas yesterday. During their absence Thomas established that the Jamara 480 HS BB's will burn out the esc's and should not be fitted. I therefore obtained a pair of Protech 400's as these are very powerful 400 series motors. I have also spoken with David at Darkith and he offered the advice that it may be that the high revving HS BB's pull enough voltage to blow the esc's. The lesson is ...don't fit the HS BB's to the new boards, the Pro version is fine though.

I installed a board and everything was working. Woohoo!

However, when I put the top hull on and started it, I had lost all of my turret functions. As I hadn't touched anything since I tested it, I was perplexed to say the least. I spent most of the day trying both boards, new receiver leads etc, and was convinced that an onboard fuse had blown again.

I removed the 8 pin plug and checked the voltage when the left stick was moved, and found that the Elmod socket was fine?
I checked the wires to the turret motors, and found that they had continuity.
Hmmm?
I then put a multimeter on the solder joints on top of the Heng Long 8 pin plug...no voltage?
I tried every joint..no voltage??
I then removed the turret rotation wires from the 8 pin plug and stuck them in the board sockets..the turret worked?

Somehow, and don't ask me how, the entire HL 8 pin plug had decided to stop passing current.
I then desoldered each wire from where they are originally attached to the pcb on top of the plug, and resoldered them to the top of each pin, a bit fiddly but I managed it.

Plugged it all back together, and hey presto, full turret functionality again.

It was one of those things, a simple link in a chain had broken, and the least likely one at that.

I can recommend the Protech motors, the tank weighs around 14 pounds but scampers around like it was made of polystyrene!

Here endeth the first lesson. I will video it and put it on You Tube soon!

Rob G