Lionel motherboard 691MBO00B0 different than original

Jimmy,

Here's an annotated photo of the motherboard (courtesy @Rod Stewart):

(See: Updated Revised Version of Lionel Motherboard Connections PDF Available | Rod Stewart)

In this photo I see the capacitor near J1, and it looks like the P1 space is occupied.

You can either send your new, incorrect motherboard back and request a new one, or transfer the potentiometer (P1) and capacitor from the old one to the new.

Two points:

1. If you elect to transfer the parts make sure you install them both in the same exact orientation on the board from which they came; for the capacitor -- polarity is important.
2. If either of these is currently bad, and is the root cause for your decision to install a new board, the new board you have, after moving over the two components, will also not work correctly.

Good luck.

Mike

Thanks Mike The attachment really helps. It looks exactly like what the new one I have except for the capacitor. I'm thinking to remove the capacitor from the old board and solder it to the new board however
I'm not sure if the capacitor is good, I do not see any burn marks or swelling. I'm not sure how to test a capacitor. I do know it 50v I'm not sure of the mfd and to make sure it doesn't have any charge left in it. Do you have any suggestions?

Just use a new cap, they're dirt cheap!

@JimmyT posted:

Thanks Mike The attachment really helps. It looks exactly like what the new one I have except for the capacitor. I'm thinking to remove the capacitor from the old board and solder it to the new board however
I'm not sure if the capacitor is good, I do not see any burn marks or swelling. I'm not sure how to test a capacitor. I do know it 50v I'm not sure of the mfd and to make sure it doesn't have any charge left in it. Do you have any suggestions?

As @gunrunnerjohn said it's must simpler to just replace it, assuming you know the value.

You'll have to look at the capacitor closely to find its capacitance value because none of the available online documentation shows it clearly enough for us to read.

For instance, here's a photo from lionelsupport.com:

The problem with this picture is that the capacitor is on the back side, so we can't see it here in order to determine the value.

Because it's physically a fairly small part, I'm thinking it has to be between 0.47 and 4.7 microfarad, especially since you've indicated that its working voltage is 50 VDC.  If I had to guess I'd say it's 1.0 microfarad.

From where it's placed, and the fact that it's electrolytic cap, it's most likely filtering out noise of some sort.  Therefore taking a guess, as long as you're reasonably close, won't hurt anything permanently.  I'd go with 1.0 uF and see if you have any side effects like annoying low-level buzzing or distortion from the speaker when the sounds play, or inability to select sounds.  If you do see one of these then increase the value to the next highest.

Mike

The Cap is a non-polarized 1uf 50V cap placed across the power input.

I have two of those boards in my parts box, one has the cap and one doesn't.  I suspect it was added after design to address some issue, though I'm not sure how effective it is soldered across the track power, and it'll screw up DCS operation if you run MTH stuff.

FWIW, you should be fine without the cap.

Thanks   Mike & gunrunnerjohn for your response. The capacitor is a uf 1  I had to order a assortment  to get what I needed. But I'll try the board without it. 

Remember, the capacitor is a 1uf non-polarized, not a normal polarized electrolytic!