MTH Proto smoke problem

That sounds like an electronic failure on the board.  There is a regulator that switches around the 12V threshold to change the configuration of the smoke resistors for the higher voltage.

Here's the schematic of the smoke board.  The Q1 and Q2 transistors bypass R1 for low voltages, so I'd check and see if R1, one of the smoke resistors, is bad.

<click to expand graphic>

PS1 style (AKA proto-smoke) uses 2 resistors, and the electronics switch them to series at higher voltage- so my educated guess is, you burned out the second resistor.

https://ogrforum.com/...0#149239177121526100

@stan2004 posted:

The PS1 smoke units I've seen discussed most often on OGR is as below schematic.  As GRJ says there is a rather curious heater regulator circuit.

https://www.mthpartsandsales.com

Specifically listed on this page https://www.mthpartsandsales.c...ts/240?type=products

You can get just the resistors and repair your unit, or buy a complete unit.

Thank you guys so much I’m not really good with the electronic stuff. It was so easy with the post war engines, now u have to have a phd lol

@finbar posted:

Thank you guys so much I’m not really good with the electronic stuff. It was so easy with the post war engines, now u have to have a phd lol

The resistors perform the same basic function as your favorite postwar, ….if you can diagnose & repair a postwar smoke unit with a bad resistor ( remember, your old postwar wire round smoke element is a resistor ) you can diagnose this smoke unit,….

Pat

Stan is it the orange one that needs to be replaced or are there some other ones

You’re overthinking this, …..the resistor the fellas are referring to live inside the bowl I’ve circled,…….the actual resistor that makes the smoke …..you can see the solder pads on top. You can read the resistance without taking anything apart yet, and diagnose the issue,….

Pat

Thank you Harmony I was under the impression that they were just calling heating elements and I have a few in my repair kit

@finbar posted:

Stan is it the orange one that needs to be replaced or are there some other ones

Who's Stan?

@finbar posted:

Thank you Harmony I was under the impression that they were just calling heating elements and I have a few in my repair kit

Make SURE the resistor you're putting in is a 16 ohm resistor, or things may go from bad to worse!

Interesting fault.  I imagine the second element failed open.    Remove 4 screws and remove top.  You probably have a broken element.  When low voltage one element is shorted across to provide 16 ohm resistance.  You have smoke, so that first element is good.  When voltage goes up above 13-14ish the transistor turns off and the second element is no longer shorted across.  Now resistance is 32ohms to correlate with higher voltage.  2 elements in series.  If that second element is open, you no longer have a path for current thru either element as the transistor is off and no path to DC ground since one element is broken.   G

Probably only have to remove two screws, that smoke unit appear to be the split bowl.