PS 2 5V locomotive headlight voltage sag when smoke turned on

Be sure heater and fan are isolated from ground.

Unplug fan and test again.  If motor is drawing high current, it can cause these problems.

Check solder connections at 10 pin socket in loco.  A bad ground connection can have a higher voltage drop when the smoke is turned on.

if flicker is a problem and it uses MUX boards, there are fixes for that will be addressed later (more involved).

I thought I read somewhere that this was a known problem with the original 5v boards. I think there were some component modifications and maybe some circuit mods to fix it.

Dealt with this issue on this very engine. Most likely a MUX board, the fan is a shot in the dark and I do hope it's that simple. MTH has a whole technical excerpt that illustrates a 2 to 4 step process for fixing this that may include modifications to the MUX board and/or the PS2 board.

There is a known issue with PS/2 steam with the 5V board and mux boards, there's a fairly involved four step procedure for correcting it.  Sometimes it just requires a fairly simple fix, other times you end up modifying surface mount components on the boards.

FWIW, I've had several engines that just the first step resolved the issue.  However, I've also had to do the whole shooting match at times to fix it.

Here's the procedure for fixing it.

PS2 Steam Light Flickering With Smoke.pdf

I can't take credit for the repair document, that was from MTH. I'll just take credit for getting out the word.   It should solve the problem, I've done a few of these, and for the ones that I had to do all the steps, it did finally resolve it.  Before the Digikey order, try just doing step #1, that fixed it for several of them.

I finally was able to implement step 1 of the fix (the rewiring) and it took care of the issue. Thanks for the great help on this.

I was delayed because in the process of changing the wiring, I broke the pins off the 3 terminal voltage regulator in the socket and had to order a replacement. I am proceeding with the same fix on another loco of the same vintage that has a similar problem.

Regards,

Walter

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