MS1 V3 Assembly Issue/Question
 

Referencing step 69c in the mega manual, there should be at least 60k ohms resistance between the metal tab of Q9 and Q12 and the heat sink. I'm getting upper 30k ohms resistance and tried sanding the heat sink lightly but it didn't change my results. Of course I missed this last half of the step before soldering it (last half of the step was on the next page of my printout) so its kinda tough to do anything about this but what else can I do to increase resistance here?

I did use the mica insulator and heat sink compound btw.

Upper 30s sounds fine to me. The important thing here is that you don't have a short circuit between tab and ground.

Funny, I just pulled up the datasheets for the TIP125 from Fairchild, ON, and ST, and none of them indicate that the tab is electrically active.

Ok, i'll trust your expertise on that and wont mess with it.

Now on to a tricky solder bridge I made when accidentally soldering on Q20 :vash:

I assume you mean the big TIP120 that you're installing in place of Q20, and not the little 2N3904, right?

When it comes to solder blobs, it occurs to me that a lot of folks who are newish to soldering probably don't know about desoldering braid: http://www.radioshack.com/product/in...ductId=2062744 This stuff is nothing more than a little strip of finely-woven copper thread, coated with flux. When you've got a blob somewhere you need to get rid of, just lay the braid over the blob and press down with the iron. The solder is wicked up into the braid and you have a clean pad left behind. Just keep braid properly trimmed so you're always working with the very end of it, and it works miracles.

I thought the TIP120 went on Q4, not Q20...Megamanual says not to install anything in Q20 for PWM.

Also, I know all about desoldering braid but unfortunately, i cannot eliminate this bridge and it is seeming to me as if I have actually newbishly bent the little metal parts into eachother. I may be screwed at this point.

Whoops- my bad. Yup, the '120 replaces Q4. Q20 is the overcurrent protection clamp which needs to not be there when you're running PWM (which, by definition, will be sinking a lot more current than that circuit was originally designed to deal with.)

Since the Q20 spot is going to wind up unoccupied in the end, you could always just break the pads off the circuit board with a X-acto knife if you've really munged them up that badly.

Ahh, a breath of hope. I'll try that tomorrow...to many drinks tonight to continue working with hot/sharp things.

I have another question though as follows:

Step 75 in the manual says to jumper R39 if PWM but brain didn't indicate that in his writeup (or more likely, i missed it). Should I jumper this use the resistor?

Well, remember that Braineack's instruction were written for a parallel install. It sounds to me like you're doing a standalone install, or you wouldn't be worrying about the IAC mod at all.

In the original design, R39 is there to create a voltage drop for Q20 to activate on. It's the setpoint for the overcurrent detector. Since we're not concerned with this, R39 is removed and replaced with a jumper. No sense in creating needless heat by passing current through a resistor when we don't need to.

Amazing, an answer with back information as well. Thanks so much. And yes, i'm doing a standalone.

Then you want to focus on the MegaManual, and go here for the Miata-specific mods: http://diyautotune.com/tech_articles...azda_miata.htm One thing- that writeup says to use 1k resistors on the SparkOut mods- use something smaller, like 270 or 330 instead.

So I already installed the 1k resisters. Is it actually worth the trouble of desoldering them and switching to smaller resistors?

The only thing one needs to do when following my writeup, when doing a standalone install, is performing the idle control mod as shown in the mega manual. Everything else should be the same.

Thats what I thought too...then I hear this about using something less than the 1k resistors...just wondering if its actually worth desoldering the 1ks and putting in the smaller ones.

It'll run fine with the 1ks. I went with a smaller value as a sort of thought-experiment after an exchange with the guys at DIY. It makes the trigger signal much prettier (if you happen to be observing it on an oscilloscope) but seems to make no functional difference.

Haha...he said munged!:giggle:

See usage #2: http://www.catb.org/jargon/html/M/mung.html

I got it! I read your other post. I think I may start using it myself. I have a few things around here that are munged!

Can the TIP120 do without the mica insulator? It didn't come with one from DIY like the other things that attach to the heatsink (that require an insulator anyway).

Like I said in post #2, the TIP12x family datasheets do not indicate that the tab is electrically active, however it's almost always good practice to isolate metal-tabbed devices.