# USA Trains SD 70 MAC main circuit board



## Keoky (Aug 17, 2016)

Hi everyone!
I have a little problem with my main circuit board for the USA trains SD 70 MAC. As you can see on the picture, two diodes of the light part burned. The rest of the board is okay. As long as I’m turning of the lights the train works fine. Instead of buying a new circuit board at USA Trains I want to try to fix it myself. My question is: *Does anybody know what specification that diode has?* I could not find the correct color code on the internet. It looks like one blue line!? Maybe somebody can help?

Thanks
Keoky


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## DonR (Oct 18, 2012)

Is that Vienna, Austria or Vienna, Illinois, USA?

I know nothing about that circuit board. However,
before replacing the diodes you should first
determine what caused them to burn out. It's
not that common. There may have been a wire
that shorted to ground or touched some metal
part that is grounded. Since the loco operates with
the lights turned off, that seems to indicate a
short in the light wiring.

What type of lights are on the loco, incandescent or LED?

Once you find what caused the issue, you could take
the board to an electronics parts store and should
be able to find replacements. The amperage capability
is the most important spec for a diode.

Don


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## Keoky (Aug 17, 2016)

It's Austria 

The burnout was caused by a broken cable. I already fixed that. The problem is, here in Vienna there is no small part shop where you can ask somebody and they help. Only big stores where you have to give the exact id number and they order it for you. No service here in Austria


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## mopac (Feb 24, 2011)

Try contacting USA Trains for diode specs. I bet they will help.


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## DonR (Oct 18, 2012)

What a shame. Here in the US some of us are blessed
to have Radio Shack stores that sell diodes, transistors,
and various other electronic parts. 

There is not that much to a diode. It is merely a
material that passes current in one direction
only. Yours are likely used
on that board to control head and back up lights
when track polarity changes.

I have a bag of diodes which I suspect would
replace your burned out ones if you can cut those
out and solder the new ones in.

They are dirt cheap and I would be glad to
send you some if there is not a problem mailing
them to you. They are so light they could go
first class mail.

Don


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## Keoky (Aug 17, 2016)

Thanks mopac for the tipp. I finally got the specs from usatrains :thumbsup:


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## Keoky (Aug 17, 2016)

Thanks DonR for your offer. Since I know now the specs of the diodes, I can buy it here. They also only cost some cents here, but you have to know what you need.


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