# MTH DCS Scale speed question



## L0stS0ul (Feb 6, 2015)

I have 2 PS2 engines that I run on my 2 track layout. I recently purchased the full DCS system and I'm loving it. One thing that caught my eye is that the 2 engines don't agree on speed. If I set both engines to scale 10 mph my crescent limited engine is significantly faster. It looks like as I set them faster the difference gets worse. At the 35mph speed I have to set my PRR 2-8-0 to almost 45 before they are going the same speed. 

Is this common? I was expecting them to be closer in speed than this. If this is not correct is there a way to fix it so they are closer in speed? I'm not sure which one is right.

The engines are:

MTH 30-4137-1 Pennsylvania 2-8-0
MTH 30-1554-1 Southern 4-6-2 Imperial P47

I just got a new ps2 engine that I have not tested in the same way. I'll do that tonight.


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## gunrunnerjohn (Nov 10, 2010)

You can adjust the speed, but it takes a bit of work. The speed is controlled by the motor flywheel tach strip. For a given speed setting, if you have more stripes (within reason), the locomotive will go slower, less stripes, it'll go faster.

I have a file of a variety of tach tape images that span a fairly wide range of speeds if you need them.

Of note is the scale speed will frequently vary for non-MTH stuff or PS/1 upgrades as they may not have the same gear ratio as the sound file used.


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## L0stS0ul (Feb 6, 2015)

OK, that is interesting. Both of these have always been ps2 engines and never upgraded. The crescent was not new though so I guess it's possible it has had it's sound file changed. I might try re-loading the sound file from MTH's website. It sounds right when compared to the clip on the site but I'm no expert in that. I'm surprised these would be off this much if this is how they came from the factory though. I guess I have something new to tinker with


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## L0stS0ul (Feb 6, 2015)

There is definitely something going on with the Crescent limited. My brand new ps2 engine is dead on with the other engine when it comes to speed. Now to learn how to replace sound files. This should be fun


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## gunrunnerjohn (Nov 10, 2010)

Well, the first thing I'd do is take a look at the tach and tach strip on the flywheel before you screw around with sound files. The classic problem here is the tach reader is mis-positioned or the tach strip is dirty or damaged. If the tach isn't seeing all the stripes, the engine will go faster as it expects 24 stripes for each flywheel rev. It computes the scale speed from that input and the gear ratio of the locomotive.


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## Lehigh74 (Sep 25, 2015)

I had a similar problem with a Decapod (30-1176-1). It is an early PS2 and has a tape tach strip (not painted like later PS2) engines. The tach strip was faded and falling off. I replaced it which solved the problem. Your pacific shows up as 2010 production, so the tach strip is probably painted on the flywheel (not a tape strip), but I wouldn’t be surprised if it’s dirty/damaged as GRJ suggested. I’m interested to hear how this turns out.


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## gunrunnerjohn (Nov 10, 2010)

If the tach reader is dying or has slipped in the holder, it can have the same effect as a damaged flywheel.

FWIW, the tach reader spacing should be about the thickness of a dime from the flywheel. If it's significantly closer or farther away, it can cause misreads and the symptoms you see.


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## L0stS0ul (Feb 6, 2015)

thanks for all of the info. I will take it apart and check all of these things out and see what's up.


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## L0stS0ul (Feb 6, 2015)

I took the engine apart tonight and checked everything over. The tach strip is painted on and it is clean and undamaged. I did wipe it down but I saw no difference before and after. I also checked the distance between the reader and the motor and it does look to be about the thickness of a dime. I don't see any way to adjust it but I did make sure it is pushed all the way down. I think it was up a bit.

I put the engine back together and I see no difference. With the 2-8-0 set at a scale 30mph and the crescent set at 30 as well they are drastically different. The crescent is lapping the 2-8-0. I have to bring the 2-8-0 up to over 40 before they are close to the same speed.

I did notice something else interesting with the crescent. When set to 1 or 2 mph it does not move along smoothly. It moves a bit, comes to a stop, then jerks forward very consistently. I have to get it up near 5-6 mph before it smooths out. That doesn't seem right to me as both of my other PS2 engines, while not completely smooth, do not surge and stop at low speeds.


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## gunrunnerjohn (Nov 10, 2010)

Actually, the low speed surging is not that abnormal. While most PS2/3 engines will run pretty well at 2-3 MPH, the actual MTH specification is 5 scale MPH and more for smooth running. I have one that is rough as a cob below 4-5 MPH, nature of the beast.

For the speed issue, I think my next step would be to replace the encoder, that's the top suspect if the tach stripes are not damaged or dirty.


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## L0stS0ul (Feb 6, 2015)

What part is the encoder? I'm not finding much online and there is no parts list for this engine on MTH's site.

Thanks


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## gunrunnerjohn (Nov 10, 2010)

Here's the common parts.

Tach Reader board (no spacer)	AG-0000033	for Mabuchi motor w/ 30mm flywheel
Tach Reader board (1.5 mm spacer)	AG-0000047	for Mabuchi motor w/ 27mm flywheel
Tach Reader board (2.2 mm spacer)	AG-0000041	for Pr Steam with 30 mm flywheel
Optical sensor component	AG-0000078	Omron part EE-SY124


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## L0stS0ul (Feb 6, 2015)

Thanks John. I have a locosound engine that I can pull one of those from if it is the same. I'll check it out tonight. I'm not as worried about a locosound engine not being right speed as I am the PS2 engine.  Crossing fingers I can test that out.


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## gunrunnerjohn (Nov 10, 2010)

There's a different part number for Locosound, so I'm not entirely sure they're exactly the same. I think some of them are, look closely before using it.

I can get them if you end up needing one.


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## L0stS0ul (Feb 6, 2015)

Thanks John. I might have to take you up on that. The number on the board is 8007-20. My locosound engine was 8008-20. So close yet so far. The flywheel diameter is quite a bit larger on the locosound engine so no dice. 

It does look like someone has replaced the board before. Either that or it was someones really bad day at the factory when it was built. The locosound engine is a very clean solder job with the wires poking thru the board. The crescent has the wires not going thru the board at all and just soldered to the top. I'm tempted to resolder these thru the board and see if that makes a difference. 

That will have to wait for another night though.


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## gunrunnerjohn (Nov 10, 2010)

The flywheel diameter has nothing to do with the sensor, the same sensor element is used on all of the PS/2 and Locosound stuff. The difference in the sensor board is the spacer behind the sensor and some have a couple extra parts, most just have the sensor.

If the sensor is working at all, the soldering job probably isn't affecting the actual operation, though you are right that it sounds like a hack job. When I replace a sensor, I suck out the solder and try to make them look like the factory job, or at least close.


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## L0stS0ul (Feb 6, 2015)

The locosound board is almost twice as thick as the crescent and it has a resistor on it as well. No way it can fit unfortunately. Will try cleaning up the connections and retest. If that doesn't work I'll have to figure out and order a new one.


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## gunrunnerjohn (Nov 10, 2010)

Is the existing board one without any spacer behind the sensor on the board?


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## L0stS0ul (Feb 6, 2015)

Here are some pictures of the thing. I'm not sure. I've not had a chance to touch it yet other than pull it apart.


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## gunrunnerjohn (Nov 10, 2010)

The connections look fine to me, it should work as far as the wiring. Note that you could have a board issue, but the tach sensor is usually the first suspect if the stripes are good and the spacing is correct.

That's the AG-0000033 part, I have those in stock.


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## L0stS0ul (Feb 6, 2015)

Thanks John. I'll play with this a little bit more. I want to put the original sound file back on the engine. I'm really not sure if it's the right one. Do you have to do the sound files through the serial port or can you use the USB on the new ones? 

If cleaning up the solder connections a bit and the sound file doesn't fix it up I'll shoot you a PM for the new board. I don't think I'd go any farther than that since it does run.


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## gunrunnerjohn (Nov 10, 2010)

I use the USB, it works the same as the serial port.

Since it does run fairly consistently, I'm having trouble with the sensor or the board being bad. If the speed was varying, I'd be thinking sensor issues.

I have an idea, why not try a different tach tape with more stripes and see if it slows it down to the proper speed. You can calculate how many stripes you need. The stock wheel or tape has 24 stripes, if the locomotive was 20% fast, you'd want 20% more stripes. That would be 4.8, so I'd make a tape with five ore stripes and see if it was close.

I have a set of files with the whole range of custom tach tapes, I'll attach them here. There's also a file that explains the procedure for making custom tach tapes. I print these on full page shipping label stock.

These might give you inspiration, and if you don't like the result, you just peel the tape off and go back to the painted flywheel.


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## L0stS0ul (Feb 6, 2015)

Thanks John, If reloading the sound file doesn't fix it I'll give the tape a try. I just find it strange that they would ship an engine with the wrong setup on the flywheel. I now have 4 PS2 engines and my 3 others are all the same speed. Seems like a pretty big mistake since everything else is very consistent. 

Thanks for the calculation as well. I can do that calculation to see if the strips are correct or not.


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## Lehigh74 (Sep 25, 2015)

I wonder if someone changed the flywheel and/or motor at some point. In one photo, it looks like the flywheel paint is chipped near the armature shaft and the solder joints to the motor don't look like factory.


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## L0stS0ul (Feb 6, 2015)

Once I can do the calculations from John's post above it should indicate if the flywheel is correct or not. I believe this engine has a worm gear so no easy way to change that out to different gearing. 

Looking over the rest of the engine it's clear the solder work on the entire engine is sloppy. Pretty shocked from an imperial engine. My rugged rails PS2 engine as well as my LocoSound engine are much much cleaner. Must have been a really bad day for someone.


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## gunrunnerjohn (Nov 10, 2010)

Hard to say why it's off, but it's not the first time I've heard about an apparently "factory stock" PS/2 locomotive having scale speeds that were incorrect.


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## L0stS0ul (Feb 6, 2015)

I think the engine had a different sound file installed. I just pulled the one off that was on the engine and it clocked in at 2mb on disk. The one I downloaded from MTH's website is just under 1mb. I should know in about a half hour or so if this resolves the issue. It is promising.


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## L0stS0ul (Feb 6, 2015)

well that was not it. With one of my known good engines going 40 SMPH and the Crescent set to 40 SMPH it's flying around the track. I have to set it back to 30 SMPH before it's close to the other one. One thing I did notice is that the engine seems to be surging faster as it comes out of the tunnel on my layout. Not sure if that could be a clue to something or not but it goes in slower and comes out much faster then slows down in the turns.

I guess the next step is to try a different tach tape. Now to figure out which one to start with.

I do hear a difference in the sound. The horn is much louder now. Almost twice as loud and I had it set to 100% on the last setup.


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## gunrunnerjohn (Nov 10, 2010)

If it's changing speed at a constant speed setting, I'd be looking for other causes, that sounds like the tach is missing some stripes at times.


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## L0stS0ul (Feb 6, 2015)

I think I might have destroyed this thing. It was running like I said, a little off, and I tried to create a new tach tape. It ended up being exactly the same as the one that was already on it as I applied it. the .087 one in your list. Turned out to be 24 stripes all the way around. I tried to run it with the top off and it was like the strip was not being seen. The engine took off at 1 smph. I tried to stop it with switching directions and all sounds shut down but the smoke unit was still running. 

I pulled the printed tach tape off and put it back exactly like it was and it's doing the same thing. I took a video. I have no clue now. It's just not working.






Any ideas? Maybe the control piece was in the process of dying and just finally kicked it


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## gunrunnerjohn (Nov 10, 2010)

Well, that's a symptom of it not seeing the tach at all. Obviously, the simple failure would be the tach reader or perhaps a broken wire on the reader. Hopefully, it's not the board...


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## L0stS0ul (Feb 6, 2015)

OK, I'll start with the wires and see if I find anything. I guess the next step after that would be to replace the sensor.


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## L0stS0ul (Feb 6, 2015)

Tonight I took the engine side apart and looked really close at each of the wire connections. I resoldered all 3 leads on the tach reader. They all look nice and clean from both sides now and the wires are thru the board as they are on my other engines. 

Testing the engine proved no different though. Note that the wires to the shell lights and the smoke unit are all unhooked. I'm not sure if that makes a difference or not in what I am seeing. 

I put the engine on the track, powered up to 1 smph, and the engine shot off just like in the video. I hit the direction button and the engine stopped. Put the speed to 1 smph and it came back around to me just as fast as before. Hit the direction button to stop it, it stopped, and then nothing. When I press a button on the controller it says "check track" so it's not seeing the engine anymore. 

Could this be a strange battery issue maybe? If I completely shut my system down and restart it the engine comes back until I move it around again and then I get the check track again.

One thing is for certain. I can work on the engine side but I can not touch the tender side. That is a mess of wires and there is no way I can fix that side.


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## L0stS0ul (Feb 6, 2015)

I checked the battery and it's sitting at 2.7v so I don't think the battery is the problem. It's the green ni-mh 7.4 700mAh battery. I have a spare ni-cd 2.4 700mAh battery but no way it will fit in the mount. I don't think it would matter anyway.

It does seem that the tach reader has completely died. Redoing the solder joints didn't do a thing. I think the next step is to replace it and then hope that it's not something else.


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## gunrunnerjohn (Nov 10, 2010)

Well, that's a classic sign of a track reader failure. If the wires end-to-end are good, the first and cheapest thing to try is the actual tach reader.


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## L0stS0ul (Feb 6, 2015)

Some closeups of the tach board


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## L0stS0ul (Feb 6, 2015)

Thanks GunrunnerJohn. I got the new tach reader yesterday and installed it a few minutes ago. I still need to do some cleanup of my work but the tach reader has resolved the issues completely. The engine now runs at the exact same speed as the other engines. It must have been dying for some time.


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## gunrunnerjohn (Nov 10, 2010)

That's good to know, glad it was a simple (and cheap) solution.  Those do go bad, and I've never really figured out why, it's a simple solid-state component.


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## L0stS0ul (Feb 6, 2015)

I think there is something else wrong. I've run the engine about 3 hours since the fix and it was all working fine until yesterday. The same symptoms have come back. At high speeds the engine is no longer accurate and when stopping it is reducing speed way to fast. There must be an issue with power or something going to the tach reader.

The only thing I can think of from looking at the wiring is that the strange ground wire could be causing an issue. It's the one attached to the board hooked into the shell. That ground wire is soldered into the same spot to the tether connector the blue wire to the tach reader is. 









Either way I'm guessing this tach reader is dying the same way as the old one. It's just not quite dead yet but getting there. :dunno:


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## gunrunnerjohn (Nov 10, 2010)

The ground wire is just a DC ground wire, it's in many locomotives with the mux board. That's the proper connection point for it. Note that that wire must NEVER come in contact with the frame or shell, that will kill a lot of stuff.

At this point, I'd measure the voltage between that round wire and the other two tach wires, what do you see?


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## L0stS0ul (Feb 6, 2015)

With the engine sitting on the track switched on but in neutral I see

3.86 - 3.90 v DC on the orange wire
0.00 - 0.03 v DC on the gray wire. 

Both are fluctuating a bit within that range. The top sensor looks to be getting voltage. The bottom one is getting nothing.


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## gunrunnerjohn (Nov 10, 2010)

That seems totally wrong. From the blue wire on the tach to the gray wire, I see 1.2V on the DC scale, those are the two outside wires. From the blue to the orange wire I see a varying voltage as I turn the flywheel slowly. 3.9 volts across the sensor would indeed be cooking it, that's the PS/2 board I would suspect.


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## L0stS0ul (Feb 6, 2015)

sounds like this is a dead engine then. That really sucks


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## gunrunnerjohn (Nov 10, 2010)

Well, it can be revived, the processor board is likely defective from the sound, but it's hard to tell.


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## L0stS0ul (Feb 6, 2015)

Right now it seems like just the tach reader is busted. I might be able to still run it conventionally without speed control. That's what I'll try to do next. I purchased the engine for $200 shipped to the house and I've already got $20 - $30 into it to fix it. Not sure it's worth finding a new board.


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## gunrunnerjohn (Nov 10, 2010)

It's a nice engine, but it's obviously your call as to spending money to fix it.


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## L0stS0ul (Feb 6, 2015)

I tried running it conventionally but it's acting extremely strange and the chuffs and smoking are all off because of the sensor. Don't think that will work. It was definitely a quick death and it's a risk I knew buying it used. Still pretty depressing. From what I understand it's really hard to find the ps2 boards and when you do they are very expensive.

I just finished fixing up the Crescent Limited passenger cars for it too lol.


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## gunrunnerjohn (Nov 10, 2010)

I still have PS/2 boards, but as you say, they're not cheap. It sure sounds like the processor board has taken a dive and is cooking the sensor.


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## L0stS0ul (Feb 6, 2015)

Are all PS2 3v boards the same? I'm looking around to see if I can find an engine or trolley or something for cheap that I could cannibalize. If I can find something for under $100 shipped I might try to fix this thing.


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## gunrunnerjohn (Nov 10, 2010)

There are a couple of variations, but what you have would work with any of the versions. There is a FLASH board with added capability, and also a 1gb and 2gb board.


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## L0stS0ul (Feb 6, 2015)

Thanks for the info John. That's good to know if it comes to it. I found a PS2 trolley from 2009 for $75 I might try to bid on. 

In the mean time I thought I would tear this thing apart and make sure there is nothing wrong with the wires or anything. Maybe there is something wrong.

The orange wire looks like it is connected to the power board. I think that's what the top board is. I tested for continuity to trace the leads. 








The gray wire has continuity to the little board off on the right side. This is the first spot it goes to from the tether









The blue ground wire to the tach reader has no continuity to any wires in the tender. The large blue wire does have continuity everywhere I see a blue wire connected in the tender. The small blue wire coming off the tether is connected to the connector that goes to the board in the engine shell. The blue wire for the tach reader is connected right next to the one that goes to the tether. I'm not sure how I was getting a reading without the board in the shell connected. Based off this I think the engine should not function properly without the shell connected as the tach reader is not grounded.


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## gunrunnerjohn (Nov 10, 2010)

The "final" destination of the tach reader is the 7-pin connector. It's on the power board. If I were trying to fix this, I'd first replace the power board and then the processor board. With the mux board that locomotive has, the tach output goes to the tether, but the P5V and DC ground return goes to the mux board.


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## gunrunnerjohn (Nov 10, 2010)

Thinking about this particular locomotive, I might look at the mux board in the engine first, it's cheaper. 

It's much easier if you have the parts and test set to chase this kind of thing down.


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## L0stS0ul (Feb 6, 2015)

hmm, I'm seeing only the blue wire going to the mux board. The orange and gray wires go right to the tether. 

Could I have damaged the engine by running it without the mux board connected? Would the mux board be AG-0000059 - Mux Board for Engine PS2.0

I clearly don't have the tools to really diagnose this and I really don't trust any of the shops around here


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## gunrunnerjohn (Nov 10, 2010)

That's probably a 1-channel mux, I was looking at the 2-channel mux drawing. The two that go to the tether go to the 7-pin plug on the power board.


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## L0stS0ul (Feb 6, 2015)

I was looking at this a little more tonight. A few things stuck out to me:

1. All of the lights connected to the mux board in the engine are non-functional. That's the marker lights and the firebox. I had not noticed that before. The headlight and tail light still function as do all of the sounds and control other than speed control from the tach reader. If the main boards were fried I would think more would be wrong?

2. I connected the mux board and tested the voltage on the tach reader. Now I see 5v on the gray wire and 0v on the orange wire. It looks like the ground being connected did make some kind of difference

3. I now have 0 speed control. The new tach board is completely fried like the last one. No sign of chuffing from the sound system either as would be expected. 

4. It looks like whoever owned this last also painted the driver wheels black. From MTH pictures in the catalog it looks like they are supposed to be silver. I can see globs of black paint on the wheels and I have been able to chip it off a bit. Not sure if this could also cause some issues but it clearly was something new I had not seen.

I do know that the ground to the capacitor on the mux board was disconnected for some time. I fixed that a while back. Now that I know all of the lights are out connected to the mux board maybe it is the source of the issue. It is shooting in the dark a bit since I have no way to test the boards separately. It would be nice if I could fix this engine for $40 with a new mux board and tach but I'm afraid to put out the money at this point. This engine has long since become a money sink.


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## gunrunnerjohn (Nov 10, 2010)

Sadly, you typically need spare parts to swap out, maybe there's a local person that would be able to sort it out? I wonder if the previous owner also did some creative rewiring?


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## L0stS0ul (Feb 6, 2015)

I've had bad experiences with the local shops and I don't really trust them to do any work anymore. Plus they all charge a lot of $$ just to look at the engine. I think for the time being this engine will go on the shelf. Maybe I'll do something with it at a later time. It is very pretty that is for sure. 

Thanks for all of the help John.


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