Blown MS1 processor? Many test results inside.

[Broke4speed]

So, in my haste to make a harness to flash new firmware to my ms1 processor, I put 12v into pin 26 instead of 28. A trace immediately popped, but that's fixed. I've checked as many things as I can, both from the assembly guide, and this:

To check for a short in the Megasquirt PCB, power up the Megasquirt on a Stimulator or on the car and check the following points for voltage with a multimeter.

You should find the same voltage as the battery voltage on the following points: the small hole to the right of the larger three holes marked X11, X12, and X13, the top (non-banded) end of D20, the left leg of U5, and the left (banded) end of D12.

You should have 5 volts at the following points: the right (non-banded) end of D12, the right leg of U5, and pins 1, 20, and 31 of the CPU.

All tests (and I mean all, even the stim tests(bought pre-made)) check out properly WITH THE PROCESSOR OUT. The loopback test works great on the cable, and on the bare socket (powered up, jumped pins 12-13), but the minute I install the processor...I get no power coming out of U5, or anywhere else that uses VCC/VREF power. There IS battery power (from stim) on pin 1 of U5 though, and all places that read straight from the stim get proper batt power. I even checked for power at the MAX232 chip, and with the main processor out, pin 16 gets VCC. The minute that processor goes back in...dead as a doornail.

With the processor out, all voltages read properly from the pots on the stim (but no LEDs go on), but again...the minute I install that processor...nothing.

So, I'm thinking I blew up the processor. Would that be a safe bet? It was working great after I built it, but I just HAD to reflash...sigh.

[Broke4speed]

Also, for a minute (literally 60 seconds), I ran the stim off a 12v/500milliamp wall plug/adapter...and my TS batt gauge registered 17.5v. I quickly shut it all down, but it was running for a minute before I noticed. I think this may have done some damage to the processor, and then my flub with pin 26 and 12v probably finished it off.

I'm just looking for a second opinion before I order a replacement.

[billr]

The 5V is OK with the processor out, but goes down (to what V?) when the chip is back in? Yeah, that sure sounds like the MS1 is bad. I think applying 17.5VDC through the Stim wouldn't hurt, but if there was AC ripple on that, with a peak well-beyond 17.5V, then who knows?

[racingmini_mtl]

There probably wasn't 17.5V. If the CPU failure was pulling down the 5V supply to a lower voltage, that would make it look like 12V was higher since the CPU uses 5V as its ADC reference. With around 3.4V supply (instead of 5V), a 12V supply would register as about 17.5V and you would that on your TS gauge.

So the failure had probably already happened when you saw the wrong voltage. But regardless, the lower voltage with the CPU in place does point to a failed CPU which will need to be replaced.

Jean

[Broke4speed]

When the processor is in, I get 0v from the 5v side of U5. I stumbled on that tonight, after about an hour of testing everything against the schematics after work.

[Broke4speed]

There probably wasn't 17.5V. If the CPU failure was pulling down the 5V supply to a lower voltage, that would make it look like 12V was higher since the CPU uses 5V as its ADC reference. With around 3.4V supply (instead of 5V), a 12V supply would register as about 17.5V and you would that on your TS gauge.

So the failure had probably already happened when you saw the wrong voltage. But regardless, the lower voltage with the CPU in place does point to a failed CPU which will need to be replaced.

Jean

I'm glad it may not have been 17.5v, because everything was working GREAT for that minute, haha. I'll order a new processor, and triple check my work from now on.

I was pretty stoked with myself too, this being the first MS I've built from the ground up. I wanted a learning experience I guess ;).

Thanks Jean!