Skip to main content

I have a PS1 bottom board (and top board) that were in an MTH Premier 20-2138-1 Baldwin AS-616 chassis (minus body shell) I won in a Cabin Fever auction a couple of months ago. When I powered it up I saw the "magic smoke" come out from the end of the board after a couple of tries to get the thing moving out of the "start-up/reset" phase.

Bit the bullet and bought a new PS1 top and bottom board (and sound chip) from MTH (yeh, they still have them), and this fixed the problem....the chassis is now up and running, and everything is working as it should.

Question: It appears the large capacitor on the end of the "dead" bottom board has gone to the great capacitor graveyard in the sky, as I can see a "burn-out" hole on the side of it....source of the magic smoke??


I went to our major (only one) electronic store (Jaycar) and showed the assistant the board, and the stuffed capacitor, and this is what he gave me as a replacement. Will it be OK to use this capacitor in an effort to get this board up and running again, as the replacement doesn't exactly match the numbers of the one on the board???


Thank you in advance to our esteem electronic wizards.

Peter.....,Buco Australia.


Images (4)
  • DSC03024
  • DSC03025
  • DSC03028
  • DSC03032
Original Post

Replies sorted oldest to newest

First off, tha capacitor is part of the electrocoupler firing circuit and is not needed for anything else.

Step 1 is simply cut the leads of the original capacitor to make it open circuit.

Test the board, If the board works fine without the capacitor and since many people never use o even read the manual to go through the sequence of firing the couplers, you could just leave that part out. In fact, on some boards used in units without electrocouplers, there is a line on that circuit board and they just cut that entire section off.

You can replace the capacitor and then attempt to fire an electrocoupler if you truly want to fix it for full function. But I would test first to see if the diode had failed.

From the looks of it, this may have been a built in or dented defect in the capacitor and just burned through the side of the can. That said, again, in theory, that condition of the capacitor in full short internally, put huge short circuit current through the charging circuit of the capacitor and may have killed it. If you feed the new cap with AC instead of DC (because of a failed diode) that could get ugly.

Last edited by Vernon Barry

Thanks for the reply GGG.

Yeh......I have replaced the cap with the new one, but have not tested the board to see if it is working.

You are probably right in that the original problem may have been with the top board.

I was not able to get this top board or bottom board for that matter to work in my "test mule" PS1 Rail King C.S.X . SD60M Diesel (30-2116-1).

I tried each board individually with the matching good board in this loco.....problem bottom board with good CSX top board, and then good CSX bottom board with problem top board. That is the way I was able to determine that both boards were bad and to be relegated to the "junk box".

Question: The older/original QSI reverse boards - Proto-DCRU's (I have a number of these older boards I use to transplant into conversions when I remove the broken AC armature motors in my Swiss Buco loco's, and replace them with modern Maxon DC can motors) can be bench tested to see if the reverse relays are working properly.

Can I bench test the PS1 bottom board on its own (no top board attached) to determine if the bottom board will run a DC motor, and change its direction by applying on-off-on power??

Thanks again has been a steep learning curve for this old AC armature and field coil magnet model train nut.

Peter.....Buco Australia.

Add Reply

This forum is sponsored by MTH Electric Trains
OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653
Link copied to your clipboard.