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Old 07-10-2008, 12:44 AM   #1
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Default Megasquirt PCB assembly

First, I need to thank everyone who maintains the Megasquirt megamanual and who has put time into additional write-ups. I have used the https://www.miataturbo.net/forum/showthread.php?t=13676 and http://www.diyautotune.com/tech_arti...azda_miata.htm articles extensively.

I am building a Megasquirt I V3 for our 1997 Miata. Prior to this, the car has absolutely no modifications to the engine. I am building this primarily as a learning experience, but if there is some performance to be gained, Iíll be glad to take it.

For this installation, I will be running the Megasquirt in parallel with the stock ECU. This is mainly to simplify emissions testing, but should also make it easier to retain the air conditioning. We are currently in Jacksonville, FL, Jacksonville and do not have emission testing. The car will eventually be back in Gwinnett, GA. When I last lived in there, they inspectors looked for a working OBD-II connector. I donít want to deal with a non-standard inspection. The parallel install will also make it easier to revert back to stock if I really mess up.

I purchased everything in the ďwhat to buyĒ list except the boost control mod kit. I also purchased an LC-1. Iíve spent the last two weeks reading and assembling the Megasquirt. I believe I now have everything except the harness and the idle control mod ready.

I do have a few outstanding questions:
--Trim the nylon screws? The nylon screws by the heat sink are longer than they need to be. They just barely touch the top of the case. Are there any drawbacks to trimming them? I have a photo at http://www.flickr.com/photos/[email protected]/2654793944/
--Flux on the board. I cannot remove all flux from board. I still have a thin layer of haze. Iím using pure isopropyl alcohol. I started with 70% alcohol and, as the Megamanual warned, it didnít work. The 100% alcohol works much better, but how clean will the board need to be?
--Spray painting the board. The megamanual also recommends spraying a coat of Krylon Krystal spray paint to seal the board once everything is working and tested. I assume the processor must be removed, the socket masked, and the MAP sensor must be masked. Is there anything else? Should the proto area be masked?
--Preferred mounting location. I searched, but couldnít find a definitive answer to where the best place to mount the Megasquirt is. Since this is a later NA, the stock ECU is behind the passenger seat. I have not pulled back the carpet in the passenger footwell. Is the ECU location from the 1.6 NAs still open?
--Could anyone give my board a once-over. I posted pictures of the front and back of the board here http://www.flickr.com/photos/[email protected]/2654794216/ and http://www.flickr.com/photos/[email protected]/2653966751/ The idle control mod kit has not been added (see next question.
--Installing the idle control mod kit. I found the instructions for the idle control mod kit on the DIYautotune site and in the megamanual. However, it isnít covered in the Braineak how to article. I did install the D8 and the R39. I also installed the Q16. I believe that the Q16 is only necessary for a Megasquirt II install. Can anyone verify that it is safe to remove it and use the spot for mounting the TIP120? With the Miata-specific mods, should I still remove D8 and jumper R39?
--I have had the hardest time tracking down the harness plugs. I have responded to a few for sale items on Miata.net classifieds, but I havenít received anything for the cash Iíve paid out. I did get Tyco to send two of the plugs by asking for samples. They wonít give out pins as samples, so Iím stuck. Can anyone give me a lead? Iíll even go by a junkyard, but I donít know of any in the area.
--Do I have my stimulator configured correctly? http://www.flickr.com/photos/[email protected]/2653967045/ Switches 2 + 3 are on. All others are off. I have the 2nd trigger jumped to pin 25. It works in Megatune, but does this configuration accurately simulate the Miata?
--Finally, if anyone in Jacksonville wants to give me pointers in person, I'd appreciate the help.

Thanks in advance,
Chris Dobbins
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Old 07-10-2008, 01:52 AM   #2
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Well, that's a lot of questions.
--Trim the nylon screws?
Sure. No harm in doing so once they're tightened. Makes for a cleaner looking install.
--Flux on the board. I cannot remove all flux from board.
Hell, I'm an electrical engineer, I prototype stuff all the time, and I don't think I've ever bothered to thoroughly de-flux a board. Folks talk about "flux creep" and such, but I've just never known it to be a problem. Looks ugly, causes no harm.
--Spray painting the board.
Heh. I forgot all about that... The theory is that this will seal the board against moisture. All the OEMs do it, as do a lot of consumer electronics manufacturers. If you do spray it, you'll have a bitch of a time if you ever want to do any mods in the future. Like you said- if you really wanna do it, cover the CPU socket and the MAP sensor. And the proto area. And every single JMP and SPR point. And anything else you might ever want to touch with an iron from now 'till the end of time.

Or not.
--Could anyone give my board a once-over.
Too tired to trace wires right now... Later.
tion.
--Installing the idle control mod kit. (...) I believe that the Q16 is only necessary for a Megasquirt II install.
Q16 isn't necessary for anything on a Miata, regardless of processor. It's a high-current ignition driver that's available so people with V8 engines that use a distributor and a single ignition coil can drive the coil directly off the MS without external hardware. Yank it.
-- should I still remove D8 and jumper R39?
Yup. And pull Q20 as well. R39 and Q20 are an overcurrent protector for Q4. You don't want them there, as the new part will be sinking more power than they're set up for. Actually, you can leave D8 in place. It's just a harmless flyback diode.
--I have had the hardest time tracking down the harness plugs.
"Read the FAQ, Luke".

Message #3 here: https://www.miataturbo.net/forum/showthread.php?t=13676
--Do I have my stimulator configured correctly?
Looks good. You've got both ignition triggers set up, and the pullups are off. You'll need to run another two jumpers from IGN and I2B to get the ignition outputs to drive a pair of LEDs.
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Old 07-10-2008, 11:53 AM   #3
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Still reading through this but as an electronics tech, Ive had to deal with flux alot and Ive found pow-r wash very good at cleaning it and can be used on electrified boards, also it doesnt stink

http://www.google.com/products?hl=en...num=1&ct=title
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Old 07-10-2008, 12:51 PM   #4
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Why would you need idle control if you plan to piggy back it?

And you got a huge friggin cap for the hi res mod.

Nice first post, respect++.
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Old 07-10-2008, 02:40 PM   #5
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as far as a mounting location goes, I lengthened the wires that go to my fuel pump, wound up the stock harness and zip tied it under my passenger side dash, then mounted the megasquirt on the passenger side of the transmission tunnel with sheet metal screws. I love it. easy access to the serial port, and you can see the lights easily.
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Old 07-10-2008, 10:52 PM   #6
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Thanks for all the quick and thorough replies.

After the PMW idle mod, I'll clean the board again with alcohol and call it done. I like the pow-r wash suggestion, but it is a little expensive for a one-time use. The alcohol cost me just $1.50 or so.

Joe, I didn't realize what I was asking when I wanted a once-over on the board. That would be difficult to do by just studying the pictures. I hope you didn't spend any time on it. I'll be able to test it in the car faster than anyone could verify each part.

For the ECU plugs, I was having the hardest time finding a place that had them in stock and didn't have a ridiculous minimum order. I did finally get confirmation I have some on the way, so I'm all set there. For anyone else looking, requesting samples directly from Tyco might be an option.

Sam101, I understand that the idle control mod is not necessary with a parallel installation, but I really want to learn everything I can about the Megasquirt. My last fun cars were a 1969 Datsun 510 and a 1969 Porsche. Tuning those cars meant adjustments to the distributor and carb. That's it--I couldn't do much else. I had fun with that and got pretty good at it. I could even get the points dead-on without a feeler guage. I'm excited about being able to tune the Maita.

The cap I used for the hi-res mod is from Radio Shack. I got the only 0.1uF cap I could find in the whole store. It is labeled as a ceramic-disc capacitor - 50WVDC maximum - high K dielectric. I have no idea what the 104M marking means.

Thanks for the mounting idea! I had only thought about the trunk (hard to reach with a DB9 cable), under the dash, behind the seat, or under the floorboard (if that is even open).

Chris Dobbins
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Old 07-10-2008, 11:38 PM   #7
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I gotcha dude.

That cap will work, its just huge. I actually used a .22uf cap that was in the leftovers from my build of the MS.
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Old 09-01-2008, 12:38 AM   #8
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Quote:
Originally Posted by Cosmic_Eraser View Post
I have no idea what the 104M marking means.
Following up on an old thread as I'm sure this will come up again, so in the future I can just refer back to this.

Big electrolytic caps usually have their value written directly on them, however smaller ceramic caps use a code. It is read as xxyt, where:
xx = two digit value
y = trailing zeroes on value
t = tolerance.

You add y zeroes to xx to get the base value in picofarads. So 104 = 100,000pf, or .1uf.

For the tolerance, I can never remember all the different codes. I know that Z is the worst, at something like +/- 80%, and that J is 5%, simply because we have tons of J-spec caps in the proto bins.


edit: Table of tolerance codes. Forgot that Z and P were asymmetric.
B +/- 0.1pF
C +/- 0.25pF
D +/- 0.5pF
E +/- 0.5%
F +/- 1%
G +/- 2%
H +/- 3%
J +/- 5%
K +/- 10%
M +/- 20%
N +/- 0.05%
P +100% ,-0%
Z +80%, -20%
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