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Thread: Diagnosing MRC Sound & Power 7000

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    Default Diagnosing MRC Sound & Power 7000

    Ok so I finally bought an MRC 7000 Sound & Power controller so that my kids can control locomotive whistles. Anyway, it was mentioned that it "does not produce the correct voltage" so I guess I am an optimist / like a challenge.

    It seems to progress through the voltage range when the controller is adjusted but it maxes out at 6.5 volts or so on the N/Ho scale setting and 9.7 volts or so on the G scale setting. I am fine with using the G-scale setting and 9+ volts is probably enough given the older locos w/ high top speeds that I give the kids. However, there also seems to be a small inconsistency in voltage -- i.e., voltage varies across a .25 or so range when the controller is static -- happens at maximum as well as intermittent voltages. I have not hooked it up to track yet to see if this is a problem with running locomotives (i.e., it might be reasonable although not perfect for the kids layout). Break and momentum seem to work ok (i.e., slows down the voltage progression towards the maximum -- or towards zero with break) but seems to keep it from reaching the maximum -- maybe dropping the maximum by .5 to 1 volts. I have not hooked up a speaker yet to see how the audio is working (I guess I should do that before I mess with it too much).

    One last thing -- the overload light is on (not sure if that should be on to show protection or if it is on when the fuse blows). In a few pictures online it looks like the light should be off when the power is on so maybe the fuse is blown -- I assume it should not put out voltage then. Maybe someone bypassed the fuse?

    Anyway, I would like to try to fix this unit and I have no idea how to diagnose a transformer. Any idea what might drop the max voltage and create that inconsistency in voltage? Is it worth it to try to diagnose and fix it or should I just replace the innards w/ newer technology?

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    Just reading the documentation -- http://www.modelrectifier.com/v/vspf...20AA333%20.pdf

    Supposed to put out 15 volts in Ho/N and 20 volts in G. I guess there is a short or the fuse or light is bad or something since the light should only be on if there is a short (it was on from the moment that I turned the device on). I will need to open it up and check the fuse first I guess. I cannot find a wiring diagram yet...

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    Ok - here are the insides and pretty sure that is a broken (exploded?) thermal circuit breaker / fuse...(is that what it is?)

    20161114_151930.jpg 20161114_152143.jpg

    It looks a bit like this: http://www.ebay.com/itm/1-Amp-Glass-...-/150584358081 (I think - hard to find good pictures of this old technology).

    Any idea what I can replace that with?

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    without seeing a schematic could you just solder a lead to both ends, crimp female spade connectors, and use a 1A auto fuse? Looks like its been really hot at one time or another, which might explain why your transformer is underperforming.


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    Thanks @magalyto - Yes I was wondering if I could replace with a self-resetting fuse of some type - I have some PTC fuses so could put a 1 or 2 amp PTC fuse. I am concerned that I am still getting power with the fuse so damaged (although it may still be making a connection albeit a poor one).

    Still looking for a schematic and might email MRC to see if there are any engineers w/ enough tenure to know about these units.

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    A fuse or breaker would stop the current completely.

    It is a bit of solid state electronics, most likely a form of transistor, voltage regulator or simple IC.

    If it is a common piece, you might be able to convince MRC to let you know what the replacement part is. If it a proprietary part, they might want to replace it themselves.

    While the power pack may be an old model, the technology is still being used today. The only thing special about that unit is the sound. The rest of it is the same as other models.
    Use what you know about the world to model…
    Learn from modeling what you don't know about the real world.



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    I emailed MRC to see what they say but it is interesting to think that there might be the same technology in other old MRC controllers (i.e., I could salvage one for parts). At least MRC is local to me here in NJ so I could stop by one day to pick-up or drop off this quite heavy transformer.

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    No response from MRC since Monday -- anyone know how long it usually takes them to respond?

    I asked for a link to schematics as well as insights into where I could buy a replacement for that broken fuse/circuit breaker (or other types of fuses I could use in its place).

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