It would be interesting to know how it all came out. Since the OP said he only wants to spend $30 on a power pack, I would think he would just go buy an old one at a train show (once we start having those again) or pick one up on ebay and use it til it gives up too. It's kinda like cars, you can buy a used car every couple of years, or buy a new one that will last a long time.
mmagliaro I know this is an old thread, but...
I know this is an old thread, but...
Rich
Alton Junction
The speed control is a 2000 ohm potentiometer. See that device the speed control knob pushes onto that says, "B2K" on the back of it in your photo? It's a linear taper potentiometer (pot). Before you go digging for bad transistors, the phenomenon you describe is that of a bad pot. There is a wiper connected to the center terminal that wipes on a conductive circular trace inside that device. If the trace gets worn, or the springy contact loses contact, you can get behavior exactly like this: nothing for most of the dial, and then full speed at the end. You might also get no speed control whatsoever - just full speed all the time. I say all this because I just cracked open an MRC Tech 7 with the same exact problem.
1. Unsolder the 3 terminals on that pot
2. Connect an ohmmeter across the two outside terminals. It should read about 2000 ohms
3. Connect the meter between the center and one outside terminal and rotate the dial. If should smoothly vary between 0 and 2000. Then connect between the center and the other outside terminal. It should also sweep smoothly between 0 and 2000. The two sweeps will go in opposite directions. On one center/outside combination, it will go 0 --- 2000 as you turn clockwise, and on the other combination, it will go 2000 - 0.
My guess is you will find that it reads "infinite" (millions of ohms), and then something between 0 and 2000, randomly as you turn the dial, or it will read infinite, or 2000, the whole time until you get near the end when it will suddenly jump to near 0.
If that's what you find then just look for a 1/2 watt 2000 ohm linear potentiometer that looks like that one - with a nut mount and a 1/4" shaft. They are cheap parts. You can get them from online electronics places like Mouser, or even eBay.
I was off-line for most of March but I see no recent updates. Your Sanyo 2SD1230 is a Darlington npn transistor and an equivalent is a TIP121 available at $2-3 with free shipping on the net. It should be normally closed. If it's shorted replace it. The Darlington is a common fail point. The pot is probably a 3K ohm pot (3Kohm in the zero position). Easy enough to check. BTW I've never heard of one failing. but there's always a first time.
I see that the 260 has a pulse switch. You didn't say which position your "pulse" switch was in during your testing... if the PS was "off" I think that means you got "filtered" 60 cycle DC and it it was on you got pulsed 60 cycle DC for most of the throttle settings. It is my understanding that MRC cuts out the pulsing action as you advance the throttle to full on (to eliminate excessive heating). So I'd be curious to know whether your observations were the same for both PS settings.
This is a $100 throttle (new) and whatever ($65?) used so it's worth a $5 component replacement. good luck and keep us posted.
Some modern multimeters, even 'discount' ones, have explicit 3-pin transistor test sockets in them. If he has access to Harbor Freight, he should look, especially if he has not yet bought a multimeter.
What has not yet been described, though, is the state of that "12V track cleaner" which he was running on the nominal 20V output. Surely some part of this was burned or melted somehow, perhaps to a dead short, during the operation, and this is a guide to finding what is 'wrong' with the powerpack now.
I'm presuming he has 'cooked' a component in some way that makes it not conduct until it is supplied a breakdown voltage (which would be controlled, correctly, through a working potentiometer) but then essentially 'avalanche' conduct above that voltage. This is certainly something that says 'transistor' more than other components...
You should find on the Internet how to indentify the three terminals on a power trnsistor with an ohm meter. It has been about thirty years since I have worked at the component level. Maybe forty since I repaired one. Time's fune when you are having flies.
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Matthew,
Can you identify the part number on that particular transistor? Can you readily get a replacement (the same manufacturer would be preferable, but might not be possible)? If you can, I'd get a new one in hand and go ahead with the replacement.
In my experience, any component that was suspect for any reason would be replaced even without testing, as long as a replacement part could be secured without great cost or effort. Testing your smelly one could be inconclusive - you don't want to remain in doubt. If you replace it properly (make sure it's facing the same direction as the old one) and you still have the same problem, the issue is elsewhere. It's kinds of a shot-in-the-dark proposition. Woth a try if you have the time, can get the part, and it's not too expensive.
John
UPDATE: I've pintpointed the majority of the smell to transistor Q3 (see previously posted picture for reference). Neither the pot nor power transistor smell and don't appear to have any visible damage. What's the purpose of these other smaller transistors and how do I test a transistor with only a multimeter? Is it possible that it could be a problem with one of these that's leading to all these symptoms?
Matthew Cheng
Come check out my Youtube channel! https://www.youtube.com/channel/UCSlaF4fvDX1brq6YOeODLPw
It has been some years ago but they are rearabble if you understand electronics, components.
Google should help you.
Thanks for the help. I'll be testing the suspected the components as soon as I get the time and will report my findings back here. In the meantime, I'd like to hear more responses from others just so I can get a better understanding of what to do.
Also, I've properly inserted the images this time.
Trainzguy2472The power transistor in this model is a Sanyo 2SD1230 in a TO3PB (though hole) package. Does anyone know where to get these or a close alternative to them, preferably from the U.S.?
2nd hit on a google search a PA company I never heard of. https://www.bdent.com
good luck with this, I would be as lost as you are in fixing it.
Google photos can't be displayed in this forum. There is a sticky post in the general forum on how to post. They have to be hosted on the internet in a place that doesn't require sign in and the link to the post either has to end in a picture format extension, like .jpg or you need a BB(Bulletin Board) link
Henry
COB Potomac & Northern
Shenandoah Valley
It's been a few years but I'm inclined to think that the potentiometer (the round gizzie with the turning shaft) should be easy to check. My notion is that the two outboard tabs that are soldered to the PC board are the opposite ends of the coiled resistance winding inside and the offset tab in the center connects to the wiper arm. If that is the case there are two things you can check if you have an ohmmeter to test resistance. What follows is best done AFTER you have isolated the potentiometer by removing it from the circuit board. This will avoid the possibility of phony resistance readings that could be sensed through the board's circuits.
First, place the two probes of the meter across the two outer tabs. That should measure the total resistance of the winding itself. If it's an old analog meter with a face plate and a needle to read the value, start with a range on your meter set to 10-20K ohms or more and work down (that's to avoid whacking the needle against the fulll range stop if the value of your pot winding is more than the range you've set on your meter - not a big issue for a meter with adigital readout). As previously suggested, look for something around 3000 ohms. You will not get zero if your meter is on the 10K range or so. That would be a dead short which would not produce the results you describe and is a virtual internal impossibility if your pack has ever worked properly. If you get no reading at all, even on the highest range, the winding has opened up altogether. Your results indicate that such a break would be near one end or the other.
Second, attach one probe to the center (wiper) tab, and the other probe to either of the outer tabs. Rotate the shaft clockwise. If I'm guessing correctly, you will get no continuity at all when you turn the pot full range and you are connecting between the center tab and the winding tab to the left. When bridging between the wiper and the right hand winding tab (as the shaft is facing you) you will get nothing on your meter until you've turned the shaft almost fully clockwise. If at that point you suddenly show just a few ohms (say less than 100), you've found the point where the winding has opened up.
If either of these two results show up, your potentiometer (pot) is bad and should be replaced. Frankly, this kind of defect is rather rare but not entirely unknown. And as it's the easiest to check, I'd give it a shot first.
If it is bad, there's likely some figure stamped on the pot's casing that indicates its value. You can probably get a replacement at an electronics parts store - if you can find one nearby these days! Otherwise, you'll have to roll your eyes and fork over for one on-line. If so, I hope you have Amazon Prime and have already coughed up for the postage!
This is just one possible fix. There may be other issues. I'd think if your power transistor was bad (I'm guessing it's the one beside the pot that is screwed to the aluminum housing being used as a heat sink), you'd have gotten no action even with your pot turned up all the way.
Here's the bottom line: you will have to judge just where to draw the line here. As Aristotle (?) once said, "Time is money." All the more so when you don't have the right tools, parts, or sense of adventure at hand. There's more than one reason why MRC doesn't provide schematics for these units - or make them easily accessible.
Good luck!
UPDATE: I've gotten the power pack open, so here's some pictures of the inside. It has a funny smell to it, like something burned up in there (which it probably did), but there's no visible damage to anything in there. Capacitors look fine, transistors look fine, etc. Any ideas on what most likely went wrong? How can I test individual components to see if they are functioning, especially the power transistor or the potentiometer?
As other people have previously stated, it's most likely the power transistor that's broken, even though it doesn't look to be so. The power transistor in this model is a Sanyo 2SD1230 in a TO3PB (though hole) package. Does anyone know where to get these or a close alternative to them, preferably from the U.S.?
I dont know why, but I can't insert my pictures inline with the post (it keeps giving me the broken link symbol), so here are the links:
https://photos.app.goo.gl/XtbkzujrnsHtbMiz7
https://photos.app.goo.gl/rAX7FpcvVVi6u4VaA
MRC doesn't release that info, so you won't find any. Mostly because of liability reasons since they plug directly into the wall so messing with the wrong thing could cause a fire or shock hazard.
But cynical me wonders if they even have schematics for the newer models, seeing as how they don't even know which horn sound you get for each value of the horn CV in their DCC sound decoders....
The main power transistors are going to be the bigger ones, hopefully attached to some metal for heat sinking, and about the only thing you nmight find in the circuit after them before you get to the terminals on the case would be the direction switch and the overload protection.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
From the reading I've done, it seems that there are probably multiple transistors. How do I tell which one is the "power" or "output" transistor as previous replies have stated? I can't seem to find any schematics for this model, or any Tech 4 for that matter.
https://www.onmrrc.org/interesting-links.html
You can fix this supply. See the above link and the attached PDF re MRC throttle repairs. You will need a wrench to open the 4 security screws. The Tech IIs required a #10 security torx...the 9370 required a notched screw driver...I am not familiar with the security screws on the Tech 4s. If all else famils..drill them out.
I would love to hear what you find. I suspect the power transitor has failed. The "rheostat" is clearly visible and probably is a 3000 ohm'er. I doubt that it failed but anything is possible. I have yet to hear that an electrolytic capacitor (the big blue (or black) cylinders) fails. If they did fail they would probably show a rupture on the surface of the cylinder...and they are also easily replacable. A power Tx should cost around $8 (for one) plus shipping and in quantity ($0.75) plus shipping. The Tech IIs, 6200, and 970s had TO220 packaged power transistors.
All you need is a 15W iron, some solder, and some flux...good luck.
OK, interesting... I do believe these are T10 security screws, which I have the right kind of screwdriver head for. My main worry is that they're so far down in their holes (2-3 inches) that I might not be able to get them out even with an extension of some sort. Also, I saw the picture in the other forum. What do transistors and potentiometers look like? I've never seen inside one of these before and that picture doesn't have anything labeled.
If I don't get it to work and have to throw it out, what other power pack should I buy as a replacement? I always thought MRC was a good brand, but now I'm starting to doubt that. I mostly run older Tycos and Athearn BBs that tend to draw a lot of power and I don't want to spend more than $30 on a power pack, be it new or used.
It is unlikely to be the potentiometer, as this is only controlling the low current side of the transistor output. More than likely, the output transistor is fried.
It is possibly repairable, if you cna get inside and find the damaged part and get a part number off it. With no schematics, figuring it all out takes a little electronic skill, and identifying just what part is damaged may also, unless it's obvious (sometimes a device like a power transistor will literally blow a chunk out of itself, that makes it kind of obvious without even testing).
I have one but not handy to look at, I don't think they are 'just' torx screws, they may be security torx - but you can easily get interchangeable bit screwdriver sets that have those sort of bits.
As I recall from a previous discussion on repair of a different model is that the screws holding the case together are Torx head. There are no public schematics AFAIK.
This problem was similar to yours,no resolution
Different problem, but some pics of inside the case.
It sounds like the winding of the speed control potentiometer burned out. There is a wire winding between two terminals and a sliding contactor that move across the winding as you turn the speed control knob. You are getting no output until the contactor reaches the maximum speed position
The potentiometer can be replaced if you can get inside the case and find the proper resistance value for it.
Mark Vinski
Hi all,
About 1-2 years ago I bought a brand new MRC Tech 4 260 power pack (yes it's an old model, but it was never used according to the seller) at a train show. It's worked great...until now. Here's the description of what exactly happened, if that helps.
I was using my newly purchased Kadee 236 powered wheel cleaner on a Power Torque Tyco engine. The instructions for this cleaner call for using a 12V power pack, but my lowest output power packs are all 16V or higher and hard to finely control, so I used my MRC power pack (20V).
I ran the locomotive at about 1/3 power for about 2 minutes before the problem occured. This locomotive has always had a tendency of producing a funny smell, so it didn't appear that anything was amiss. Suddenly, the motor started slowing down until it finally stopped. Initially I thought I had burned out the motor (it didn't).
When I tried to run the same locomotive on my test track, it did nothing until the last half centimeter or so of the power pack's dial, when it suddenly shot off the end of the track. The same happened to another Tyco engine I had. I later checked the output voltage on a multimeter and noticed the issue. When I turn up the power, there is no output until the last half centimeter on the dial (approaching full power) where it suddenly jumps to ~10V and then ~20V. As far as I know, the "overload" light did not go on, or if it did, it was so brief I missed it. I'm hoping this was some sort of overheating safeguard, though the power pack didn't feel hot afterwards.
Please let me know what I can do to try to repair the MRC 260 power pack before I have to throw it away. Even if components need replacing or I might need special tools to fix it, please tell me anything that could make it work again.