Reply to "NY MTA R-21 30-2198-1 Pop sound, then smoke!"

I had this happen to the 5 volt (9 volt battery) PS2. The trick is to get the problem solved before it blows the board. Before you turn on any old ps 2 5volt  change the electrolytic capacitor. I believe it's 220uf @ 35 volts  and 105 degrees. It's on the edge of the board, it might show swelling on the top. It is documented on this forum if you do a search. It's a little tricky to change, and don't try to separate the boards like I did the first time. That did it in for sure!. I changed all my early ps 2 engines' capacitor and so far so good. Hope this helps, Vic