Need major help with electronics issues - model electronics question - Page 1
Forum section: electronics / beginners

author: Electronicman40
author_rank: Newbie
timestamp: October 14, 2025, 07:41:48 pm
content: Im currently trying to fix a faulty/damaged? modeltrain Heljan terminal crane that I recently purchased. These cranes are wicked old and long discontinued, basically impossible to find. Unfortunately for me I got a bad one of the bunch as it was claimed to be new.The crane had a few previous issues which I was able to successfully fix but I'm now completely stuck on something that might be more sophisticated than my skills.The one function on the crane that doesn't work is the lowering and raising of the hoist. When I initially took the crane apart I found that one of the gears for the mechanism had cracked and was actually a common issue for the crane. I purchased a similar replacement gear from NSWL and the mechanism runs smoothly by hand but when putting the crane back together it still wouldn't work.The only culprits I believe to be left are the motor and what I believe to be the bridge rectifier that both the motor and container magnet mechanism connect to.I don't believe it's the motor because when I test it outside the crane using a 9v battery it spins perfectly fine. When testing it just hooked up to the crane and without the hoist however, it only spins in one direction. When it does spin it it sometimes is jerky like losing power or even weirder it activates the swivel of the gantry function. The motor for the gantry swivel is not connected to the bridge rectifier or motor in anyway. The only place they meet is at some type of other electrical board where the leads from all the mentioned mechanisms connect.This leads me to believe it might be a failing bridge rectifier (if that's even what it is), or now that I mentioned it, the other board where the connections meet. I have no idea how to test if that's what my issue is or the board itself. I can't get a replacement so is there a way to buy a similar one or make one myself?Any help would be greatly appreciated from the super technical/electrical folks.For photo reference:Red tab: Orange wire connects directly from the other boardBlue tab: where the gray wire from the motor tabconnects to.Black tab: black wire connects directly from the other boardWhite tab: Gray wire connects directly from the other boardThe other black wire from the inside of the gantry connects to the other tab on the motor which comes from that other board.The photo for the other board is the one with the just plugs. The top occupied plug is the hoist and the bottom one is the gantry connection

author: Analog Kid
author_rank: Super Contributor
timestamp: October 15, 2025, 05:38:23 am
content: No brilliant answers for you yet, but one thing:A lot of people here post pics that are waaaaay too big.But yours are too small to really see any detail.Maybe edit your post and re-attach the pics at a larger size?That way we can get a better look at them.I'm guessing that if this is just a rectifier issue, probably won't be that hard to fix.Not rocket surgery.

author: jwet
author_rank: Frequent Contributor
timestamp: October 15, 2025, 02:16:54 pm
content: Your little thumbnails are challenging. The first pic and your description helped me generate the following sketch.The two diodes on the board (the little glass pills) control forward and reverse. AC power comes in and by shorting one of the two diodes you get a posiktive out or a negative out. The long curved connections look to be limit swtiches for forward and reverse that feed the other side of the motor. There may be more to this since I can't see board 2.You can test the diodes using a multimeter with a diode function. They should read about .7v in one direction and open in the other.Good luck. As Analog Kid said, I would suspect one of the diodes. When the gears got messed up, the motor likely stalled, drew a lot of current and blew one those. One is likely still good. Those glass smt packages are kind of odd. You can put a standard diode in the place, just connect to the pads. Use some glue so you don't stress the pads too much.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 15, 2025, 03:24:06 pm
content: Diodes are incredibly cheap. sub $0.10