Alexland

Hi, I have photos but the forum is restricting my upload to 4KB presumably because the picture at the top of the thread used up 94KB of my 100KB allowance. Yes the disc looked like the one in you photo just much thinner with a pair of lines on one edge (a circle only has one edge...) maybe it was some kind of metal thermistor and moved when opening up the case? I'm not planning on opening it up again and this will be the motor I use with my young kids making it very clear they shouldn't pull more than 3 carriages or 4 wagons at once. ;-) I will leave the 12v light bricks and cables in the 7740 as it's a bit messy and sub optimal converting them to 9v parts. Thanks for the help everyone, Alex

Thanks again both of you, I tried the motor again tonight and under the load of the loco only (lights disconnected) it was working fine but as soon as I added 1 carriage it started going sluggish and stopping again within seconds. I then cut off the tabs on the bottom and opened it up carefully on a table and to my suprise there wasn't a thermistor inbetween the grippers on the motor contacts. The motor had been in perfect cosmetic condition with perfect tabs so I don't see how that is possible unless it was omitted by Lego (or their subcontractor) themselves when it was manufactured? I put it back together and again it was acting slugishly and stopping under small loads. I then took it apart again on the table and removed the wheels, gears and motor (looking for a thermistor that might have fallen inside) and found a small thin metal disc around 0.5cm diameter that didn't appear to be serving any puropose underneath the motor. I removed it and put the unit back together again. Then trying the unit again for the past 20 mins it has been perfect in either direction with 12v lights attached and pulling 1 carriage and 2 wagons at various speeds. So it seems to be fixed but I have no idea why? How could the thermistor be missing? What was the small thin metal disc for? Thanks, Alex

Fab video and great achievement pulling all these vintage sets together - it's not often that reality is better than dreams! I am wondering if your collecting has affected the market price of 12v light bricks!

Thanks Thorsten and Zephyr, So if the 12v lights are wired in parallel they should have no impact on the load on the 9v motor and this fault was probably triggered by pulling too many things with high friction 12v wheels as the 9v motor is less powerful. I have spare 9v wheels so it would probably make sense to swap them out if they put less load on the motors and enable them to last longer. I never run the motors for long probably around 5mins at a time and not at top speed as I don't like them derailing and getting the bricks all scratched up. Would the thermister just cut-off the power completely when the motor is running too hot or would there be the gradual deline in performance that I have seen? It could well be temperature related as the motor can stop, not work for a bit then start up again fine for a while before gradually deterioriating again even when the motor isn't under much load. It's unclear if the thermister is doing it's job and protecting the motor or defective. It wouldn't be a problem if it only happened under excess load. It's been a couple of days since I last ran it so I might have another try tonight keeping the load to 3 wagons with 9v wheels to see how it runs. Maybe the problems I was seeing was because even under light loads it hadnt fully cooled down from the high loads... Thanks again, Alex

Yes there seems to be a good market on ebay for broken or part working motors around 15 GBP. Having watched various videos for things that can be done with broken 9v motors I don't fancy my chances either. I will probably just convert the 7740 to normal 9v cables and lights as although it won't be as good I won't be worried about killing another motor. I'll will still power that 12v signal brick from a 9v connector.

The 9v motor is problematic now. It was showing no problems before connecting up both the 12v lights and putting it under the load of wagons but is now running fast then slowing and stopping etc. That even happens now under light loads with no lights connected. Could it have been the combination of 12v lights and some wagons that caused it to develop a problem? Or maybe it was just weak to start with and has got worse? Thanks Alex.

Thorsten - another motor is fine to pull the wagons and carriages with the 7740 on top but I haven't wanted to connect up my 9v lights connector / 12v light bricks for fear of damaging another motor in the same way. I really wish I had put the motor under the load of wagons before connecting up these light so that I could determine the cause of the problem. The motor is now just problematic under small loads with no lights connected. Andy - your prompt caused me to find the below excellent article however this experieince of possibly damaging a motor (if only I knew if it was already damaged...) has put me off using converter cables and I am tempted to just go to standard 9v cables and light bricks. I guess it would take 3x cables as there isn't enough height to stack the 9v connectors at one end so the stack would need to be in the middle. Might be possible with 2 cables and a long 9v plate.. https://questforbricks.wordpress.com/2013/08/31/12v-lights-vs-pf-lights-vs-tin-foil/

Yes 9v track/motor + a 9v connector on the end of one of the 12v lighting wires (and 12v lighting bricks) coming out the bottom of the 7740 (see top photo). The motor is original unmodified recently acquired 2nd hand and never really tested under the load of pulling carriages/wagons before. Seems to run well in a circle under no load but now even with just the 7740 loco top on it it can become sluggish stop for a bit then start working again. It wasn't like that in the previous few weeks since buying it. So either testing it under load of pulling wagons and/or the lighting configuration and/or bad luck has caused it to develop a problem. I've been watching a few videos on Youtube of people swapping out the motor from a more modern one but there's a bit of me that's tempted to sell it as part-working on ebay (maybe it wasn't working well for the previous owner...) and just buy a brand new unused one and pay the difference however I'd be annoyed if my bespoke lighting setup caused it to burn out again. Maybe I would be better replacing the 2 wires and 2 light bricks with proper 9v parts even if they won't line up tightly against the 12v light prism bricks? Thanks Alex

Hi, Unsure if it's a coincidence but th 9v motor on this 7740 has now started to play up. I was running it with 1 carriage and 4 wagons and it started running very slowly and then eventually stopped with just the lights working. It's now intermittently going slugish (even with just the loco top on and lights disconnected) and sometimes stops but occasionally going fast before slowing and stopping again. It's not the track as I don't have this problem running my other 9v motors. Has the motor failed, is there any way to fix it and could it have been caused by the 12v lights and/or cable conversion? Thank you in advance, Alex

Thanks that's all very reassuring on the lights! After some research I believe a Double Pole Double Polarity (DPDT) switch would reverse the polarity of the 9v DC on the wire to the 12v signal light brick so that it can be remotely switched between green and red. After some more digging do you think Lego 9v part 6551c01 Polarity Switch would do the job? Thanks, Alex

Thanks but not looking to keep the 12v controller or implement automatic stop/start - my ambitions are just to have vintage trains from my childhood running on 9v with a good set of accessories. I found the courage to connect the signal light and it works fine even when the 9v controller is set to max. So I just need to find a nice inline switch to put on a new cable to switch the wires around to switch the colour. It would help if I knew what such a switch was called!

Has anyone tried similar powering a more valuable 12v signal light brick from from a 9v controller? Ideally I would like to put an inline non-lego switch on the end of the cable (not sure the name of the type of switch required?) to flip beteen red and green. I would be gutted if 9v makes it go pop as it's a really nice condition part.

Thanks guys so I'll go with the cheapest nice condition black base and just get find some good looking cable that looks right. Nobody has told me that I am doing anything electrically wrong with the lights so I will just leave it alone and hope they don't go pop. I have my 4.5v 7720 running on 9v too although it looks a bit sad without it's battery box so I am building up some old wagons including the Shell 7813 to keep it busy. Just listed my old 12v track including electrically operated points, crossover, isolating rail, etc in a few ebay listings if anyone in the UK is interested. Alex

Also does anyone know the spec of the 12v wire to buy more new? It's impressive how well it has lasted over 40 years compared the the 9v wire which tends to go flaky.

Hi - first post so please be gentle! I have seen a few discussions here about converting 12v trains to run on 9v motors with metal rails but not the steps required to get it working. I have figured out my 7740 needs a new 6x28 base plate as the 9v power connector jams on the underside of the correct 4093b so have found a spare blue 92339 which works until I can buy a black 4093a or 92339. Does it matter which I buy as the 4093a looks cheaper? Also I have fed the ends of the 12v light wire into a 9v connector and it seems to work well powering the lights on both ends but is there any electrical reason that I shouldn't be doing this? While its a lower voltage is there any risk the current, etc could damage the lights long term? Thanks Alex