0-8-0 out of control

Could be bad harness, bad tach reader or wiring to tach reader, or bad speed control chip on processor board.

I would check tach reader after ensuring no pinched wires or bad harness connection.  G

Also make sure flywheek hasn't loosened on motor shaft, and check gap between tach reader & flywheel.

Both great answers, Check to make sure the tach strip is in tack, also reseat the tach reader in it's bracket and reseat the tach's plug.

If that still has not addressed the situation it may very well be a bad tach reader, but one other thing you might want to try just before replacing the tach is reloading the sound file. I had a dash 8 that did the same thing and reloading the sound file which also contains the programming for the unit, did fix the situation. 

One more possibility, Make sure the Tether is plugged in solidly, a loose (or bad) tether can drop the signal from the tack to the PS2 board and it's launch time.

check the gap between the tach reader and the flywheel.  No sure what the exact spec is, but 1/16th" to 3/32" should be close.  The larger the gap the worse.

MTH- why not make an adjustable bracket for the tach reader board?  Something simple like a jackscrew and lock nut arrangment would allow very precise adjustments.

What Russell said

devbull:  getting the precise gap isn't that critical and not that often a problem, to justify the added cost.  The gap range can be found in the PS2 upgrade kit manual.

Over the years I've installed maybe 8 or 9 upgrade kits.  A couple of times I've had to place shims behind the tach reader board to close the gap.  I think using a screwdriver on an adjustable mount would be better than trying to unsolder the reader and then add or remove shims behind it as MTH instructs.

Additional cost?  I dunno, maybe 10 cents or so.  We're talking the cost of one 2mm or 4mm screw & a couple of nuts. That's a lot less than a new tach reader if the installer makes a mistake.    

Currently MTH has several different tach boards available.  An adjustable bracket might just allow them to reduce their parts inventory to a single standard board.  That's a potential cost savings.

Getting back to the orginal discussion,  I saw same run-away symptoms that Larvic describes in his post.  Shimming the tach reader towards the flywheel resolved the problem for me.

I agree it was a terrible job to unsolder, shim, & resolder a tach board.  I did it once, and then found out that MTH offers several tach readers identical except with different shimming, so I bought a variety for stock and used what was appropriate. 

When you're removing a chip, the easy way is to simply clip the leads of the old chip, then you can desolder the leads one at a time and remove them.  Obviously, if you're trying to save the chip, it's different.

I've yet to come across a through-hole chip that I can't cut the leads.  I realize you are going to have to unsolder and clean the holes, but it's a lot easier as a rule to do them one at a time than try to do them wholesale.  It becomes even more difficult the larger the chips become.

Obviously, there are many ways to skin the cat, I was just presenting what I have found to be the easiest method if you're not trying to save the part.  Clearly, you should use whatever works for you.

GGG..you using a 30X stereo microscope to change the audio chip?

I think I need to clarify my previous post just a bit.  I have gone through the process of desoldering the tach reader board, installing shims, and resoldering the board.  I've also screwed up two boards doing that.  It is tedious work.

Recently I tried another approach that worked just as well for closing the gap between the reader and the flywheel.  I simply insert a small plastic wedge between the plastic tack reader mount and the motor itself to close the gap to where I want it.  Add a drop of cement to hold the wedge and it's done.

Hope this helps.

I don't know the maginification.  It is a lighted magnifying work light.

Just need to be careful with the pads, some of them can come up easily.  G

I don't understand how this works, could you post a picture? I don't see how you can move the tach reader bracket.  G

He's simply tilting the board so that the pickup is closer to the wheel.

My hat's off to you as that takes a mighty steady hand as just changing the motor diode is small enough work for me. 

I still need to know how, that is impossible with the tach brackets I have seen.  The fit of the tach reader board into the bracket pocket is extremely tight.  There is no room for shimming.  Additionally the bracket that straps around the can motor isn't moveable closer.

The only way I did it was cutting the tach board shorter and gluing it to a donor board that went into the tach bracket.  This was for a pittman with an extremely small flywheel since it was a older PS-1.  Even with the tach sensor mounted all the way out it was too far from the flywheel.  G

GGG - Gunrunnerjohn has it correct, the board sits in the pocket as normal. The wedge or shim goes in between the bottom of the tach board mount and the motor body. 

Insert a small flat screwdriver between the motor and the bottom of the mount. Carefully pry up the bottom of the reader bracket and insert a thin piece of plastic under it.  Moving the mount bottom away from the motor causes the reader head to move towards the flywheel.

It usually doesn't take much of a shim, maybe 0.010" to 0.015" thick.

Ok,  Now I understand how you are doing it.  Interesting technique.  No ill effects from angling the tach reader?  I always try to keep them flush.   G

Sorry  to respond so late.... been outa town.  No ill effects from tilting the board.

I thought your board on board technnique was interesting also.

This is what I like best about the forum.  Different viewpoints, different solutions to the same issues, lot's of great ideas and tips in general.  Seems I have learned something from everyone.