Well, I accidentally plugged my snail speed controller's neg center power supply into my Rokuhan pos center controller, big mistake! My RC02 let out the magic smoke that makes it work. The chip is a timer, I looked at the chip that burned in my other RC02 and it is labelled NE555 93M. But when I look to Mouser or Digikey I see a lot of variations! Would they all work? How do I know I have the right chip? I would love to be able to fix the controller with a 50 cent part, I'd just like to try. The controller still lights up and only shuts down when the knob is turned to run a train. The burned chip is visible in the bottom left corner of the top CB. The lower CB shows the chip from a good controller.
Last Edit: May 22, 2019 14:02:43 GMT -5 by husafreak
The 555 is a generic timer. The additional identifications denote the operating range, the package type and manufacturing date. These are all specific to each manufacturer. Additionally distributors add codes for the type of shipping method.
What you want is a commercial operating range: 0-70 degree C, 4-16VDC and an 8-SOIC package. The package type comes in 2 widths, it looks like you'll want the 154mil width. But measure the plastic width (pin-to-pin)to make sure. The shipping method you want is cut tape. This will reduce your selection at Mouser down to 4.
Sorry, but no wizardry required,
A couple of additional thoughts:
Since the 555 runs at about 25kHz any speed IC will do.
What you show us really shouldn't have happened. You should probably check the various diodes for proper operation. I think you may find one or more shorted out.
The main problem with Your chip is not its type, but the fact that it seems to be a SMD version. And (un)soldering such chips is much more "kamikaze" than with conventional "DIP" chips : the standard raster is 1/10 " for standard chips, 1/20 " for SMD. I soldered many parts during the last 40 years ... but never SMD versions !
Last Edit: May 22, 2019 16:55:59 GMT -5 by alberich
Thanks everyone. I'll try to repair it. Just for fun. I'll cut away the burnt chip and solder the new one to the old one's legs, maybe if I'm quick enough with a hot iron (my Weller station does 850) it will work. I was surprised that it was not polarity protected with a diode. The manufacturer is so secretive, they probably designed it that way to properly punish anyone foolish enough to try something different (that would be me!).
I would advise that you remove the legs before attaching a new 555. They should be easy to remove with a solder wick. SOICs are notoriously difficult to mount to anything other than a smooth surface.
I haven't analyzed the throttle myself but a couple of thoughts.
Once you remove the 555 the throttle may come back to life. I believe the 555 is being used to generate the constant lighting pulse only.
There a quite a number of diodes on the PCB. One may be a protection diode. I can't tell from the images, but the diode would be connected directly to the wall wart input. If so, it's probably shorted.
Actually, input polarity protection diodes are fairly rare in electronic equipment. Ultimately they become the weakest link in a design as they essentially become either an unreplaceable fuse or a useless short. Manufacturers (including Rokuhan) get around this by specifying only manufacturer approved power sources can be used (usually supplied by the manufacturer).
Today I had some time at home with the replacement IC's from Mouser. I found three to buy. I first cut away the burned IC and powered it up but the controller was dead. I later realized that a wire from the power supply had broken so that may have been the problem. I used a solder sucker to clean up the contacts and installed one of the IC's I bought. The controller worked but in a strange way. First the LED ON/OFF doesn't work anymore but the controller does work. I put 9V directly to the LED but no joy. Probably dumb but I know so little. But the controller interacts strangely with my loco's. The easy to drive engines will move very slowly even with the throttle closed, most of them will run their full range of speeds. One of my easy to drive loco's is a Marklin from the first batch of sealed motors, it also moves even with the throttle closed and then won't accelerate much before shutting down. None of my older 5 pole Marklins will run. they just trip the controller. So just very strange behavior. I unsoldered that IC and replaced it with another one and it was the same. Exactly. So it was fun to try but I think this Rokuhan RC-02 is for the bin! I still have one new IC to try but without going through all of the components to find another fried one I suspect the IC's I got are not correct for this application. Or maybe it has something to do with the LED not working. But thanks for the advice and it was a good try... Unless?
its more than just the 1 IC. As Mark pointed out, the Controller also has the pulses for the Constant lighting. This is what is now likely moving some of the locos. Or, components around the main Speed controller are also bad, creating out-of-spec results.