MRC power packs, dead?

[PJPickard]

Hi,

I have two old power packs:
Tech 3 #9000
Railpower 1300

Both of these don't have any current on the terminals. They both worked years ago and have just been stored(indoors) Is there anything I can check on them? I don't see where either has a fuse(on the outside anyway, I haven't opened them up)

Thanks,
Paul

[eja]

Me too !

[signalmaintainer]

Hi,

I have two old power packs:
Tech 3 #9000
Railpower 1300

Both of these don't have any current on the terminals. They both worked years ago and have just been stored(indoors) Is there anything I can check on them? I don't see where either has a fuse(on the outside anyway, I haven't opened them up)

Thanks,
Paul

You'd have to open the up and start chasing DC voltage with a DVM. Start with the output from the bridge rectifier first. If you have nothing there, there's your answer. My other guess is that either a voltage regulator or filter capacitor(s) have failed.

[mmagliaro]

#1 and #2 things that fail on a lot of MRC packs are either
a) The speed control pot
b) Main output transistor.

The following are general guidelines that apply to a lot of MRC packs.  I've fixed a smattering of them over the years, but never a 9000, so I don't know what's inside there.  I think that one uses a switching power supply and PWM output, so it might have different things to check, but since you say the whole thing is "dead"... it's probably something pretty basic.

You'll have to open the case (probably means drilling out the "security" screws they use to hold it together.
Then check for voltage on the two outside legs of the speed pot.  If they are both dead, then go look at the power supply section (the transformer output, and voltage on diodes or a  bridge rectifier and larg-ish electrolytic cap that will probably be near there.)

If you see reasonable voltage on the pot outer legs (one should be zero and the other anywhere from 16-20 DC or something like that).  Check that the voltage on the center lead (the wiper) goes up and down smoothly as you
turn the dial.  If it doesn't, that's your boy.  replace the pot.

If the pot is okay, check the voltage at the base of the main output transistor.  It will be a larger 3-terminal device screwed to a metal plate somewhere.  If voltage to one lead of that thing goes up and down the the speed control, but it doesn't do that on either of the other leads, then that thing is probably blown.


The 1300 is a really basic unit, so the above items definitely apply to it.  Like I said, I have not happened to get my hands on a 9000 to take it apart, so if you get in there, take some photos.

[peteski]

Nobody mentioned checking the AC accessory terminals.  If there is a voltage, then the transformer os ok, and the problem is in the DC part of the throttle (what Max described).

I owned a 1300 in the past but don't remember if there was internal fuse on the 120VAC side.  The low voltage side has a thermal breaker (which is also supposed to light up the red light when tripped).

[signalmaintainer]

Nobody mentioned checking the AC accessory terminals.  If there is a voltage, then the transformer os ok, and the problem is in the DC part of the throttle (what Max described).

It's a good point, but transformers rarely go bad. Start at the bridge rectifier first. If you get good DC, move forward until you lose DC. If not, go back to the transformer side of the bridge rectifer and check for AC. But the problem is most likely after the bridge rectifier.

[peteski]

It's a good point, but transformers rarely go bad. Start at the bridge rectifier first. If you get good DC, move forward until you lose DC. If not, go back to the transformer side of the bridge rectifer and check for AC. But the problem is most likely after the bridge rectifier.

My point specifically was that testing AC ACC. terminals can be done *WITHOUT* even opening the case.  To me that makes sense when it comes to the troubleshooting sequence.  If there is no AC, there will be no DC. Rigth?

[signalmaintainer]

My point specifically was that testing AC ACC. terminals can be done *WITHOUT* even opening the case.  To me that makes sense when it comes to the troubleshooting sequence.  If there is no AC, there will be no DC. Rigth?

Sure, but you still have to open the case to make repairs. Just open it at the start and do the troubleshooting properly. All you're suggesting amounts to saying, "The patient isn't exhaling." It doesn't answer "Why?" It could be just due to a bad solder joint inside.

We can argue this all day long. Back to you.

[Point353]

You'll have to open the case (probably means drilling out the "security" screws they use to hold it together.

The Klein 32510 set includes the security bit needed to open the case.
https://www.kleintools.com/catalog/screwdriver-sets/magnetic-screwdriver-32-tamperproof-bits
I bought one at Home Depot.  Amazon has it, too.

[peteski]

Sure, but you still have to open the case to make repairs. Just open it at the start and do the troubleshooting properly. All you're suggesting amounts to saying, "The patient isn't exhaling." It doesn't answer "Why?" It could be just due to a bad solder joint inside.

We can argue this all day long. Back to you.

Whatever . . .
You win!!

[Doug G.]

Before opening the packs, I would check the AC at the terminals and if there, give the packs a good whack. The circuit breaker contacts could have just oxidized over the time being stored. If that doesn't do anything, then open and start checking voltages.

Doug

[signalmaintainer]

Before opening the packs, I would check the AC at the terminals and if there, give the packs a good whack. The circuit breaker contacts could have just oxidized over the time being stored. If that doesn't do anything, then open and start checking voltages.

Doug

Yes, few things in life a good whack can't fix.

[mmagliaro]

The 1300 doesn't use a mechanical circuit breaker.  It uses a "Polyswitch" auto-reset thermal device.  Jarring it will have no effect on it.  I would tend to doubt that the 9000, being a much later model, uses a thermal breaker either.

The reason I like drilling out the security screws is that I replace them with regular screws when I reassemble the case.  I'm sure the packs aren't under warranty anymore, and they certainly aren't once you've opened them and started tinkering around.  So to my mind, if I have to open it anyway, I just get rid of those weird screws and make future servicing of the pack easier.

[Doug G.]

On some of my several Tech II/IIIs, I used an old drill bit that fit into the Torx heads and that snapped off the security pin so a regular Torx could be, and was, used in the future. After I got a driver meant for the security screws, I didn't do that anymore.

Doug

[peteski]

On some of my several Tech II/IIIs, I used an old drill bit that fit into the Torx heads and that snapped off the security pin so a regular Torx could be, and was, used in the future. After I got a driver meant for the security screws, I didn't do that anymore.

Doug

I bought a large set of security bits from Harbor Freight. Not expensive. They likely still have them available.  They fit any standard power screwdriver (hex socket), and the only possible problem would be if they are not long enough to reach  the screw in deeper holes in the housing.  I also have some small flat blade screwdrivers which can fit in the security screw, and engage couple  of the Torx lobes while to the side of the center pin.