I have a few Legacy diesels from 2006 to 2010 (e.g., 6-34513, 28307, 31772) that all use a 620-8265-200  6-Volt regulated fan driven smoke unit.  That smoke unit uses a 691-FSMR-E00 PCB.  Both parts are available from Lionel's Parts Department.  Last year a couple of my smoke units stopped running the fan although they all continue to heat the resistor.  So in November I ordered from Lionel 1 complete smoke unit and 2 PCBs.  When I received them they all had the same problem: they heat the resistor but fail to run the fan, just like my "defective" boards do.  When I tested the fan motor on the new 620-8265-200 smoke unit with a known good board in one of my diesels it worked fine, so I suspected something was wrong with all 3 PCBs.  I am testing all these boards on 34513 and 31772 engines that have correctly operating smoke units.  I emailed Lionel all the facts and asked if there was something I might try to check the fan circuit on the PCBs.  After several weeks of no reply Lionel finally gave me an RA and I returned the boards and smoke unit just before Christmas.  After a month of waiting I finally got them back last week.  The paperwork from the Lionel tech says the 2 PCBs tested "good," and the test of the new smoke unit showed a "bad fan motor" which he "replaced."  This is the exact opposite of what I tested.  The fan motor on the new smoke unit I returned to Lionel operated perfectly fine,  just not with the board mounted to that smoke unit.  So it was no surprise that none of the items returned from Lionel run the fan!

Does anyone know a magic trick to get the fan motor running with these 691-FSMR-E00 PCBs?  I now have 6 of these boards that all heat the resistor but don't run the fan.  Any help greatly appreciated.

Thanks.  John

Original Post

First off, I'm pretty sure this board has a 5V regulator.  All that's on the board is a simple 5V power source for the smoke fan, it should be very easy to diagnose what is happening.

First step is to see if the board is capable of generating 5V without the smoke motor plugged in.  Next, I'd be checking the motor to see if it's drawing excessive current.  One common issue is the smoke motor draws more than 30-40 milliamps, and the little TO-92 package 5V regulator can't supply the current and shuts down.

From what you describe, I am having difficulty with the idea that all these boards are really bad.

GRJ, thanks for your analysis.  I agree with you that 1) this is not rocket science (there is only 1 external two wire connection to the PCB), and 2) it's hard to believe all the boards are bad.  However, I am testing all the boards with the powered units from my  6-34513 and 31772  sets.  Both have working smoke units.  When I plug the new (just returned) smoke unit into those engines they don't run the fan, either the one that originally came on the new unit in November or the one the tech just replaced.  If nothing else the returned smoke unit with the new motor should work when I plug that smoke unit into either engine, but it doesn't.  Also, when I plug any fan motor into either of those 2 working smoke units it always runs.  So what's up with that?  I have to go out for awhile but will test these boards for the +5v when I return.   Thanks again.  John

Well, the regulator has thermal shutdown, but frequently they seem to die a permanent death.  I think the real thing that should happen here is a bit more analysis as to what is failing.  Obviously, that requires some basic test equipment and the smoke units to do the analysis.

Gunrunner, once again your help proves invaluable!  I tested the fan output of the PCBs on 2 of my engines that currently have their shells off and have properly operating 620-8265-200 smoke units.  Both are putting out 5 volts DC.  Then I test the 3 boards I just received from Lionel and all 3 are putting out 0 volts!  So it seems that the TO-92 package 5V regulator (whatever that is) is bad on each board.  Would you agree?  If so, is there any fix other than a replacement board?  Thanks again.  John

Just replace the regulator, they're a bog standard LM340L or the LM78L05, either one will drop right in.  Of course, I'd check the capacitor and diode to make sure they're OK.  The small cap on the top is probably a non-factor, I don't think you'll kill a ceramic cap.

  Ordered them, they are due by the end of the week.  The diodes and caps all checked out.  Don't know if I'll be able to do the fine soldering required to remove the old regulators.  I just use a 25 or 40 watt iron and bulb syringe.  Haven't done this kind of work in a long time.  Any tips?

Yes, make it easy on yourself.  Grab the regulator body with a pair of needle-nose pliers and bend it back and forth to break the leads right at the body.  Then clip onto each lead, one-at-a-time with forceps and heat the joint to gently pull each wire out.  Trying to suck the solder out for all of them and release the part is far harder.  Since we have no illusions of saving the part, no reason to try to remove it intact.  Once you have the parts out, you can clean the holes by my simple "bang" method.  Heat the solder-filled hole to melt the solder and then quickly rap the board face down on the bench.  This will clean all the solder out and you're ready to solder the new part in.

GRJ, I completely echo Hancock52's thank you.  Great Tip!  And thanks again for ALL your help with this thorny issue.

My regulators are due Saturday so hopefully  by Monday I will update this thread with with a report of successful results.  John

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:



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


Photos (6)

Add Reply

Likes (1)
OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653