Need pro's advice on controller

[Anonymous]

I got my controller apart. If you guys think you know what part is bad ,I'm good at soldering. The controller runs at 80% and up speed no slow speed on it. And it started to go slowly. At first I noticed it wouldn't stop it just went slow then got worse where it wouldn't go any slower than 80%.Thanks guys here's a pic

http://www3.sympatico.ca/ryoungis/Pic3.html

[Anonymous]

I am certainly not a pro, and am not certain about what you need to replace, but from the symptoms you describe, the first thing I would look at would be the rheostat, since you are describing being unable to have slow speed control while still having high speed control. It might just be that the rheostat is dirty and some of the contamination is causing the problem. I don't know the cost of replacement rheostats, but it may end up being less expensive just to replace the whole unit than to replace the rheostat (if that is in fact where the problem lies). Good luck!

[Anonymous]

Replacement variable resistors aren't pricey - the crucial part is finding the right type. I'm not sure how to work this out unless it's printed on the resistor. Before powering up the soldering iron though, there's another couple of possible solutions. I noticed in the photo that there's a metal plate next to the resistor - have you checked the solder tabs aren't touching this? Shorts can cause all manner of strange effects. I would also suggest a substance I've seen used on theatre lighting boards. Can't remember the precise name, but it comes in a spraycan and is designed to clean sliders (which are basically a variable resistor that slides rather than turning), we had a lot of problems with imprecise lighting controls in the theatre group I'm with, someone sprayed this stuff into the board, worked the sliders a few times, then left it to dry (power off) for a few hours, it worked much better after that. Think it's known as switch cleaner or something similar, if you go into a decent electronics shop they should be able to help though - both with this and with finding the right type of replacement part if the spray doesn't work. Hope this helps!

[rrinker]

It's going to be tough to find the exact replacement part there, notice the extra tap off the top right of the picture to that capacitor, which I am assuming has something to do with the automatic pulse power that the Tech II provides.
Given the symptoms, it may not even be the potentiometer that's bad - it could be that capacitor hanging off there. Without a schematic diagram it's not easy to figure out what the actual design and reason behind it is, and I doubt MRC will give you one. My thoughts for primary source of failure would be the above mentioned capacitor or the power transistor (three lead device screwed to the heat sink on the left side). The capacitor is easy to replace, Radio Shack might even have the correct value. The transistor might be a little harder to find, or it may not even have any markings on it to go by.
Oh yeah - on the other side of that small circuit board are going to be other components - most likely another smaller transistor, some resistors, and diodes. Resistors rarely fail, and will generally look obviously burned if they have. The transistor on that board could be the failed component as well, f the first stage of what is essentially and amplifier has failed, it would reduce or eliminate control of the final stage.
The slow failure over time though, is fairly symptomatic of a failing electrolytic capacitor. It doesn't look obviously bad in the photo, but of there is anything oozing out of it, that's a sure sign. Depending on how this was stored, it could also be dried out, which would also cause failure.


--Randy

[Anonymous]

Well I got my meter out and the blue and yellow leads form the variable control run from 0dc to 16dc very smoothly as well as the red and yellow. After I unplugged it the blue capacitor discharged very smoohly and looks good in appearance.Any thoughts?Does anybody know any boards that guys are into the electronics?Thanks

[Don Gibson]

YOU are going to need an EXACT replacement, and unless you can fibd a OEM part number, and a parts house that HAS it, Model Rectifier is your best bet.

After replacing it - and you still have the same problem - What then?

Frankly i'd send the unit back to MRC and let them take care of o it.

[mcouvillion]

Hi Frostman,

I've been looking at your throttle and have a couple of questions / comments.
1) Is the bare lead on the capacitor touching the case of the potentiometer? It probably should not, but sure looks like it in the photo. If you have already taken it off for inspection, use your volt-ohm meter to check the resistence between that odd lead on the top of the potentiometer to its case and each of the three leads. Which one has zero resistance? Are all infinity? I don't ever remember seeing a capacitor on the potentiometer in any of the throttles I have disassembled and/or repaired, or in any of the scematics.
2) That capacitor looks fine in the picture. The end would probably be bulged a little if it was bad and it would smell funny and possibly be leaking.
3) I've only needed to replace one potentiometer on a failed throttle, and it is on a Troller that is no longer made (out of business) and I can't match the potentiometer with anything in the Mouser or DigiKey catalogues. I would seriously doubt that the problem is the potentiometer.
4) The most likely candidate is the transister on the heatsink on the left side of the picture. I have had to replace these on several occasions. Mark the transistor with a pencil BEFORE removing any of the wires, indicating which wire goes where. Or, better yet, mark on the case by the nut: top - yellow, board; middle - red, board; bottom, yellow, pot. Use a heat sink on the leads from the transistor (hemostat, alligator clip) when removing the wires. They should just slip off when heated. Check the number on the transistor. There is a book that used to be available at Radio Shack called "Semiconductor Reference Guide" (Catalogue # 276-4012) that you could use to cross-reference the numbers on the transistor to an acceptable substitute at Radio Shack, Mouser, or DigiKey. The transistor should not cost more than a few bucks. The book, if it is still available, should be less than $10.00 (mine was $3.99 years ago). Replace the transistor, using heatsink grease and/or the teflon sleeve, if originally provided, and then reconnect the wires. Remember to use your hemostat/alligator clips on the leads and pre-tin them, then solder the wires back. Button up the controller and then plug it in. Use only your test equipment first. If you "let the smoke out", go get another throttle. If you fixed it, remember what you did and don't be afraid to try to fix something else in the future. For an inexpensive throttle, it is almost not worth the effort to repair it unless you just want the experience of trying to fix it yourself. And that is the right attitude for a modeler who wants to learn from others. Good Luck.

Mark C.

[Anonymous]

The transister is D1192
1K3

I'm going to take it off now

[mcouvillion]

Frostman,

I could not find D1192 or 1K3 in my reference book. My book is from 1989. You could try RS 276-1778, a 3-post adjustable positive regulator rated at 1.5 amps over 1.2 volts to 37 volts. The pinout is the same as the transistor on your throttle and it is well within the voltage you need to control. It should not cost more than a couple of bucks. Give it a try.

Mark C.