Tach Reader in 5 Volt PS2

Cheryl,

What is the "issue"?

Speed control, continuity presents from board to reader, but engine has no speed control or chuff.  It also will run slowly upon start up without advancing thumbwheel.  We have tried 4 or 5 different readers.  No joy.  Board tests fully functional on fixture.  Not sure why an inline 10k resistor is present on tach wire from connector to tender harness.

I would say some one added the resistor to control the chuff in neutral issue on early 5 volt boards.

That was a mod to correct chuff.  Many 5V engines and even later 3V RTR harness had that resistor.  That is not the issue.

Replace tach reader or tape if wires and board good.  G

As Noted above, we have gone through 3-5 readers, all new, and tested continuity on wire harness, all good.  The board runs perfectly in test fixture, will not control speed in engine.  Truely baffled here.

Have you tried a different sound file?

Gregg,

Did continuity testing of the 3 wires to the tach reader go all the way from the board's 7-pin power connector to the contacts on the tach reader board?

Did you additionally confirm no shorts between adjacent wires?  In other words you tested continuity from A-A, B-B, C-C.  But did you also confirm NO shorts between A-B, B-C, C-A.

I don't have that test fixture or service notes that MTH apparently provides to Authorized Techs but what I'd do next is measure the voltages at both ends.   IIRC, one contact is a fixed reference voltage.  Then measure this relative to the LED transmit voltage which should be stable at just over 1V DC.  Then measure the sensor receive DC voltage which should wiggle up and down by 1/2V (or so) as you manually rotate the flywheel.  

If not tach reader, tach tape not readable or, wire problem, bad wire in tether.  As stated you must check continuity from tach reader joint, to pin on board with tender connected to engine.  G