It turns out that the regulators were the problem on my old, non-working boards, but not on the new boards I received from Lionel; I have since learned that those boards are actually all fine. Here's what happened.
The first board that I replaced the regulator on was the original board that came from the factory on the powered A unit of my 6-34513 WP F7 ABA set. When I tested it on the powered A unit it worked perfectly! FEELIN' GREAT!!
Then I replaced the regulator on my second defective board and tested it in my WP powered F7 unit and I got the old symptom of the resistor heating but the fan not running. FEELIN' -- not so great! I then replaced the regulator on my third defective board and again the resistor heated but the fan didn't run. And as noted in my above posts, none of the 3 boards I received from Lionel ran the fan in my F7. So I tested all 6 boards in the Conrail LionMaster SD80 from my 6-31772 set and got the same results: only the original board from my powered F7 ran the fan. Now I'm not feelin' good at all!
So I started testing around with my multi-meter on the 3 boards on which I replaced the regulators, looking for resistance or continuity. After quite a bit of time I finally came up with the answer. The power plugs in my F7 and SD 80 that connect to the PCB look like this:
But the board that it plugs into looks like this:
The 2 wires on the plug connect to "GND" and "HTR" on the board, but nothing connects to "3RD" on the board. GND is internally connected through the board to "FAN -". I found out that the problem was that the regulator circuit for "FAN +" draws its power from "3RD," which has nothing connected to it. That's why the resistor heats but the fan doesn't run. I realized this when I saw, under a magnifying glass, that the first board I fixed, which came from the factory on my F7, had the HTR and 3RD circuits connected via a solder bridge, shown in this picture:
I tested this theory by holding a jumper wire across 3RD and HTR on all the other boards, including the ones I received from Lionel, and all of them started the fan with the jumper wire. So I concluded that the "solution" to my problem was either to solder a small jumper wire from 3RD to HTR, or scrape off the cover of the copper foil connected to 3RD just below the HTR connection and "build" a solder bridge between the 2 points like on the original F7 board. I decided to build a bridge. Here's a photo of the exposed copper foil from 3RD:
And here's a photo of a completed solder bridge:
EASY PEASY!!
Finally, I also have a 6-28307 Legacy FM Trainmaster that uses the same smoke unit. I removed the shell and found that the power plug that connects to the smoke unit looks like this:
It has it's own "bridge" between 3RD and HTR so it runs the boards as received from Lionel. And the 2 boards I replaced the regulator on that didn't have the solder bridge came from this unit. I remember replacing it in the past.
Unfortunately, the bottom line is Lionel has sold multiple diesel engines that use the same smoke unit board, but the replacement board it sells won't work in all of them. But now we know what to look for.
Good Luck! John
