V3 PCB Weirdness (Excessive current draw, raised "pimples")

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Myrrhstang
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V3 PCB Weirdness (Excessive current draw, raised "pimples")

Post by Myrrhstang »

(Admin: please file this under "Tales of Woe", the opposite of "Megasquirt Success Stories" :mrgreen: )

I screwed up. Big time.

Without boring you with the details of exactly how I managed to do it, I accidentally put +12V from a gel-cell onto the IAC stepper pins of my brand-new V3 PCB/MS3 daughtercard Megasquirt while bench-testing it.

There was an immediate BANG! as the stepper motor chip on the MS3 daughtercard blew up. Copious quantities of magic smoke escaped from the enclosure, illuminated by the light of a small fire within. :shock:

Immediately cut the power, and the fire went out. But the damage was done -- once I dared reconnect the power, I could not get TS to connect to the Megasquirt. The +5V regulator (U5) was running WAY too hot, and voltage checks at the processor socket showed 0.7 V where it should've been a full +5.

Something was obviously shorted to ground, but what? The only part that seemed to be getting hot was U5. Desoldered D19 -- no effect. Hmmm... After a thorough visual inspection, I noticed several small raised bumps on the board that I didn't remember being there before.

Could a short have developed between the +5V and ground planes? Sure enough, when I drilled one of the "pimples" out using an X-Acto knife, the current draw dropped, and voltages at several points rose back up. I now have SOME communication between the CPU and Tuner Studio, so perhaps there is some hope for me after all.

Has anyone else ever seen anything like this?
5.0L 1965 Mustang coupe, V3 PCB/MS1, EDIS 8 (planned)
"Faux-SVO" Turbo 2.3L Foxbody Mustang Convertible, V3 PCB/MS3, EDIS 4 (in progress)
5.0L 1971 Ford Maverick, V2.2 PCB/MS2, MSD 5 ignition
Matt Cramer
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Re: V3 PCB Weirdness (Excessive current draw, raised "pimple

Post by Matt Cramer »

Usually this just smokes the stepper driver - but the "pimples" on the board suggest it may be something worse this time.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
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Re: V3 PCB Weirdness (Excessive current draw, raised "pimple

Post by jsmcortina »

Sounds like some traces or power planes in the board got damaged. Sorry to say, but the best solution is a new PCB.

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Myrrhstang
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Re: V3 PCB Weirdness (Excessive current draw, raised "pimple

Post by Myrrhstang »

I came to the same conclusion, so I have a whole new V3/MS1 kit on order from DIYautotune. I don't relish trying to desolder/unstuff the bad board... At all!

From the DIYautotune website, it looks as though the PCB cannot be purchased alone, but is bundled with the processor and MAP sensor. Why is this? Is it because of a B&G licensing issue? Seems like it just adds the insult of unnecessary expense to the injury my pride's already suffered! :mrgreen:

There's a small chance I'll be able to sort out the board I fried SOMEDAY, and so I plan on keeping that as a backup unit, or for use in my next project.

Thanks, mates.
5.0L 1965 Mustang coupe, V3 PCB/MS1, EDIS 8 (planned)
"Faux-SVO" Turbo 2.3L Foxbody Mustang Convertible, V3 PCB/MS3, EDIS 4 (in progress)
5.0L 1971 Ford Maverick, V2.2 PCB/MS2, MSD 5 ignition
billr
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Re: V3 PCB Weirdness (Excessive current draw, raised "pimple

Post by billr »

I'm confused here: which board has the "pimples", the MS3 daughter, or the V3.0 mainboard?

You said the MS3 stepper-driver chip blew, so I was thinking you need a new MS3. Now you seem to be ordering an MS1 kit just to get the V3.0 mainboard. Obviously (?), if both are bad, you need to order an MS3/V3.0 kit. When I thought it was the MS3 with the pimples, I figured you were going to need a new MS3 because of that and the blown stepper chip, but a V3.0 with burned traces may be fixable
DaveEFI
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Re: V3 PCB Weirdness (Excessive current draw, raised "pimple

Post by DaveEFI »

Myrrhstang wrote:I came to the same conclusion, so I have a whole new V3/MS1 kit on order from DIYautotune. I don't relish trying to desolder/unstuff the bad board... At all!

From the DIYautotune website, it looks as though the PCB cannot be purchased alone, but is bundled with the processor and MAP sensor. Why is this? Is it because of a B&G licensing issue? Seems like it just adds the insult of unnecessary expense to the injury my pride's already suffered! :mrgreen:

There's a small chance I'll be able to sort out the board I fried SOMEDAY, and so I plan on keeping that as a backup unit, or for use in my next project.

Thanks, mates.
I could be wrong, but think you may be able to buy the board or part kit on its own perhaps on an exchange basis? And yes, it is about copyright issues. Contact DIYautotune.

However, it is possible to repair burnt tracks on a V3 board. Easy to check which ones may be burnt out with a continuity tester and reference to the schematic. But it may look a bit untidy.
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Myrrhstang
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Re: V3 PCB Weirdness (Excessive current draw, raised "pimple

Post by Myrrhstang »

billr wrote:I'm confused here: which board has the "pimples", the MS3 daughter, or the V3.0 mainboard?
My sincere apologies for the confusion!

The "pimples" are on the V3.0 mainboard. The +5V plane was so loaded down that that the processor was seeing only +0.7V or so. At first I thought I might get off easy & find it was only a forward-biased PN junction to ground, but now it definitely looks like the +5V and ground planes are shorted together in spots. Sigh... :(
billr wrote: You said the MS3 stepper-driver chip blew, so I was thinking you need a new MS3...
The stepper-driver chip DID blow, so I obviously won't have that functionality unless/until I replace it. BUT, when I got power to the MS3 daughtercard (by putting it on a prototyping strip), TunerStudio could "see" it, and I could get some readings on the dash by putting voltages on the MC9S12XEP100MAL's analog input pins. So the daughtercard *may* be salvageable. My fingers are crossed until I have a known good mainboard to plug it into again.
billr wrote: Now you seem to be ordering an MS1 kit just to get the V3.0 mainboard. Obviously (?), if both are bad, you need to order an MS3/V3.0 kit.
This is where I left out a key fact -- I have another build planned. It's a Ford 302/5.0 NA V8, for my long-suffering wife's 1965 Mustang coupe. This will be a pretty plain vanilla engine, so it's needs are modest. The slower MS1 processor will be "good enough" for now.

Once I have a known-good mainboard to act as a testbed, I can complete my MS3 daughtercard tests, and determine whether or not it is salvageable.
billr wrote:...a V3.0 with burned traces may be fixable
That is my fervent hope, Bill! Please wish me luck... :P

Again, I apologize for the confusion I've caused. Thank you for your help!
5.0L 1965 Mustang coupe, V3 PCB/MS1, EDIS 8 (planned)
"Faux-SVO" Turbo 2.3L Foxbody Mustang Convertible, V3 PCB/MS3, EDIS 4 (in progress)
5.0L 1971 Ford Maverick, V2.2 PCB/MS2, MSD 5 ignition
Myrrhstang
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Joined: Thu May 19, 2016 2:05 pm

V3 PCB Weirdness UPDATE

Post by Myrrhstang »

My new Megasquirt kit arrived today (Thanks for the prompt shipping, DIYautotune!)

I thought I'd do a quick visual checkout of the "new" board, and compare it to the "old" one before starting on the "new" one. Here's what I found... The old board is (date-?) coded 3214*. The code on the new one is 0216.

There are a number of blems on the old board, that suggest to me that perhaps there were lamination problems at the PC fab. (Since I don't have a "before the disaster" pic of the old board, we'll never know for sure, of course!) My hypothesis is that these blems, COMBINED with my overcurrent abuse, were what caused a low-resistance fault to appear between the ground and power planes.

Many, many moons ago, I worked at John Fluke Mfg. Co. We made some of the first 6-layer boards for our products in-house, back then. Believe me, I know how tricky making multi-layer boards can be! I'll try to post comparison photos of the two boards, so you can have a look for yourselves.

I just wanted to mention this in case you might have any older boards in inventory -- you may wish to inspect a few to check for similar issues.

*I'm more than a little embarrassed to say that the kit sat around for more than a year before I started on it! :P
5.0L 1965 Mustang coupe, V3 PCB/MS1, EDIS 8 (planned)
"Faux-SVO" Turbo 2.3L Foxbody Mustang Convertible, V3 PCB/MS3, EDIS 4 (in progress)
5.0L 1971 Ford Maverick, V2.2 PCB/MS2, MSD 5 ignition
Matt Cramer
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Re: V3 PCB Weirdness (Excessive current draw, raised "pimple

Post by Matt Cramer »

Correct, the first two digits of the code are a week code (01 through 52) and the second two are a year code.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
Myrrhstang
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Re: V3 PCB Weirdness (Excessive current draw, raised "pimple

Post by Myrrhstang »

The saga continues.

I now have a known good testbed system, so I thought I'd TRY to rehabilitate the old MS3 daughtercard (the one with a blown stepper motor). I got a few A4970 chips (I think they cost about $5 each in qty 3 @ Digi-Key, or someplace), fired up the hot-air rework system for the first time, and set to work.

This was my first try at any serious SMT component work, so I was quite nervous. Rightfully so -- I pulled up some of the board traces when removing the old chip. :x Stripped some stranded wire, and used short sections of single strands to replace the traces I'd mangled. Then, I installed the A4970, using solder paste and a pencil iron with a very fine tip...

And... It works! Stepper function restored. :P :P :P

NOW, one question: what is the function/value of C10 on the MS3 daughtercard? Mine was missing somehow (probably happened when desoldering the old A4970, I reckon). I guessed it was just your standard power supply bypass capacitor, so I installed a 0.1 uF cap in its place.

After several abortive attempts at getting a teensy-tiny chip cap in there, I gave up & soldered a 0.1 uF through-hole cap in its place. It looks ugly, but it works! I'll post pictures when I can.
5.0L 1965 Mustang coupe, V3 PCB/MS1, EDIS 8 (planned)
"Faux-SVO" Turbo 2.3L Foxbody Mustang Convertible, V3 PCB/MS3, EDIS 4 (in progress)
5.0L 1971 Ford Maverick, V2.2 PCB/MS2, MSD 5 ignition
billr
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Re: V3 PCB Weirdness (Excessive current draw, raised "pimple

Post by billr »

On either SMD or TH I usually cut the leads, or cut up the device body, so leads can be removed one-by-one with minimum heating to the PCB.
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