Megasquirt Support Forum (MSEXTRA)

Good Evening All, I recently assembled a new JimStim 1.5 and conducted all the assembly testing successfully.

Now when hooked up to my MS2 Extra V2.2 board, the RPM flashes to a ridiculous value (like 50,000 RPM) and the drops to zero and won't come back unless I back the Fine RPM pot completely CCW. I've attached a datalog and current msq with me cycleing either the fine or course RPM pots.

I have the primary tach jumpered for square wave and as well as the 12v pullup. I also have the WBO O2 jumpered. I have an EDIS setup, so have all of the DIP switches set to off.

The strange thing is that when I connect my old MegaStim everything seems to work fine, except that I cannot get the MegaStim RPM to go to zero (lowest is 157 RPM).

Any thoughts?

I will clarify that my MegaStim has been that way for many years, so the not be able to get zero RPM on that isn't a new fault.

You can get to zero on mine. Are you sure the pots etc are the correct ones?

DaveEFI wrote:You can get to zero on mine. Are you sure the pots etc are the correct ones?

Hi Dave, definitely the correct ones, but it was built 11-12 years ago. The pots may have broken down. I do have spares that I can fit, but I don't think that explains why my JimStim is erratic?

I'll replace the pot on the MegaStim and see if it changes anything?

Woz

How steady should the RPM be when on a MegaStim or JimStim? Should they be rock solid once set of fluctuate by a few RPM?

In certain positions you will get some RPM jitter.

James

jsmcortina wrote:In certain positions you will get some RPM jitter.

James

Thanks James.

I haven't done anything to my MegaStim, but thought I'd do the tach signal test again on my JimStim. This time it failed? I pulled the CPU and all pins have voltage as expected apart from pins 15 and 16 which both show -1.6v (negative 1.6)? I must have a short somewhere?

I've done a bit more trouble shooting and I'm getting the following voltages on my JimStim with the CPU removed and not connected to MS.

JP12 - (19 Pin)

Pin 1 - FP: 1.5v
Pin 3 - INJ1: 1.6v
Pin 4 - INJ2: 1.6v
Pin 6 - FIDL: 1.6v

From the schematic, I would have thought these pins should be at zero?

Advice appreciated, even if it is to say I'm a buffoon and doing something stupid!

The voltage for these pins is meaningless when the MS is not connected because they won't be connected to anything. I don't know where your meter probes are when you take the measurements but either your meter is measuring some spurious voltage or you have a fault on your board somewhere.

Also note that all these pins go through a LED and the voltage you see is close to the voltage dropout of a LED. I don't know how that would be possible with any logical measurement location or with any simple board fault but that is likely significant.

Jean

Thanks for the reply Jean. Measurements were taken with 12v (1A) power source through the power jack and my Multimeter negative probe at the negative terminal of the two position terminal block. I also got similar readings if my negative probe was at the 3 Pin ground posts.

That is very strange. Check the voltage across the 4 LEDs corresponding to the same 4 pins and across R1-R4 (by across, I mean one probe on each side of the LED/resistor). Also check if you see anything on the 5V pins (without the MS, there should not be any voltage because that is powered from the MS Vref).

Jean

racingmini_mtl wrote:That is very strange. Check the voltage across the 4 LEDs corresponding to the same 4 pins and across R1-R4 (by across, I mean one probe on each side of the LED/resistor). Also check if you see anything on the 5V pins (without the MS, there should not be any voltage because that is powered from the MS Vref).

Jean

Jean, I get zero voltage drop over resistors R1-R4, but get a voltage drop of 1.6v across the LEDs (FP, INJ1, INJ2, and FIDL). That is with pos probe on one side and neg probe on the other side of the LED/Resistors.

What about the 5V pins?

racingmini_mtl wrote:What about the 5V pins?

Sorry Jean, 5v pins show zero volts.

I can't see how you're getting those readings without some major multiple board failures which seems quite unlikely. Can you take good resolution pictures of both sides of the board and post them?

Well that's alarming! Here's the pictures. I'll also double check all my readings.

I don't see anything obviously wrong except that some solder joints don't look too good (blobs instead of nice concave profile). But that would definitely not explain what you're seeing. I can't think of what else to do. You would need to get the board to someone who can test it thoroughly with the board in hand because that's not something that can be done remotely (at least not by me). I wish I could be more helpful.

Jean

Jean, not a problem. Thanks for your help thus far. Very much appreciated.

While I'm not an electrical genius, I'd like to think I could pick up the obvious things? I do have someone I can take it to, so maybe it's time to admit defeat! The strange thing is it passed the bench test for both LEDs and Tach Signal? It was only when I connected to MS that it spit the chips!?

Thanks again.

Ok, everything now fixed. I had an Elec Tech take a look with his microscope and a couple of the DIP switch pins were suspect on the soldering. They were soldered properly and the CPU pad pin voltages checked. I still had negative 1.6v, but was told this could be a phantom voltage?

So I did the tach test and it passed! Through it on my MS2 and it now works fine? I don't fully understand it, but I'm taking the result!

Thanks to all that helped.