IAC tuning. Am I crazy? (Solved!)

bluetrepidation · Post by **bluetrepidation** » Thu Apr 20, 2006 10:54 am

Alright I ordered all my parts. I also am bringing home a digital laptop based scope from work tonight. I'll post a few waveforms when I get time to test. I'm thinking IAC Start step sequence with and without the IAC motor connected to start with. I'll post ASAP.

A.J.

bluetrepidation · Post by **bluetrepidation** » Thu Apr 20, 2006 4:48 pm

Alright I busted out the scope. Channel zero is across 1A and 1B for coil one (green). Channel one is across 2A and 2B for coil two (yellow). My battery voltage is 12.5 volts. The chip seems to be outputting the full 12.5 under load. Now I ran three tests with the IAC start value set to 600. I cycled power with no stepper motor connected. Then a free wheeling stepper motor that I opened up for testing. Last, a stuck motor run. Well as you can see looks like I have a blown driver transistor! Agree? Having a duel channel scope is the only way to go.

A.J.

Philip Lochner · Post by **Philip Lochner** » Fri Apr 21, 2006 4:12 am

bluetrepidation wrote:Alright I busted out the scope. Well as you can see looks like I have a blown driver transistor! Agree?
A.J.

I'm following this topic with great interest. All 3 diagrams seem the same to me. Am I crazy?

Is it the kink in the green trace which you interpret as the blown tranny? Were you using balanced probes? I have an old dual channel scope but I'm reluctant to connect up both channels simultaneously as I'm worried that the earth leads on the two channels may have a common ground and then short out something.

My IAC seems to be working OK now except that now and then it seems to stick in the open position (when engine is cold) causing 2000rpm idle. Driving 2km's and then restarting sorts idle out - still a nuisance though.

bluetrepidation · Post by **bluetrepidation** » Fri Apr 21, 2006 5:28 am

Yes all three are very similar. This is a good thing really. Shows that even under load the chip is handling everything. I checked my probes before hooking them up and they don't have a common ground. On your scope I'd check this with an ohm meter before connecting. Now the more I look at this the more I think this may not be a blown transistor but more a fault mode. The chip should be switching the polarity back and forth. But the little glitch look like it waits for 45 degrees and then goes high like it should of right away. A completely blown FET this would never happen. It could be just damaged though. I'm going to email these to an electrical engineer friend of mine and get his opinion next.

A.J.

JSC · Post by **JSC** » Fri Apr 21, 2006 8:15 am

A.J.

Cool pics. Looks like whats happening is when 2A goes high it's shutting off output 1 until 1A goes high (it's half stepping). Goto http://www.allegromicro.com/sf/2916/, you can download the 2916 datasheet and also the Techincal Publication "UDN2916 Current Ratio/Timing Diagrams" these will help you understand the 2916. What I would check next (if I had my new scope) are the "I" inputs, these are used to change the current limit and turn off the outputs for half stepping.
These four inputs should be low (0 Volts) for normal operation. Check pins 1, 2, 12, & 13 with your scope with the IAC motor running.

Also, changed the components on another MSII last night, the IAC seemed to work good on the STIM, haven't had a report on how it works in the car yet, Will report later.

Scott

bluetrepidation · Post by **bluetrepidation** » Fri Apr 21, 2006 9:30 am

According to the MS II schematic those should all be pulled low by the IACEnbl output on the processor correct? That could be a problem if it isn't occurring! I'll check that out next. Yeah I have a National Instruments 5102 scope. It's a PCMCIA card for a laptop. Slick. Now if I could afford one for myself......

Alright I'll keep things posted.

A.J.

bluetrepidation · Post by **bluetrepidation** » Sat Apr 22, 2006 9:16 am

OK I checked out the "I" inputs and all are held low during the entire 600 steps. I can set to stepper moving only then they go to a logic level high right after the steps occur. This seems normal to me. I got the components in today to do the changes you suggested. Should I give that a go next? I'll be sure to remove my jumpers as well.

A.J.

JSC wrote:A.J.

Cool pics. Looks like whats happening is when 2A goes high it's shutting off output 1 until 1A goes high (it's half stepping). Goto http://www.allegromicro.com/sf/2916/, you can download the 2916 datasheet and also the Techincal Publication "UDN2916 Current Ratio/Timing Diagrams" these will help you understand the 2916. What I would check next (if I had my new scope) are the "I" inputs, these are used to change the current limit and turn off the outputs for half stepping.
These four inputs should be low (0 Volts) for normal operation. Check pins 1, 2, 12, & 13 with your scope with the IAC motor running.

Also, changed the components on another MSII last night, the IAC seemed to work good on the STIM, haven't had a report on how it works in the car yet, Will report later.

Scott

JSC · Post by **JSC** » Sat Apr 22, 2006 9:44 am

A.J.

Sounds like the "I" inputs are functioning properly, I'm still curious as to why your output is half stepping (would like to check mine but the new scope won't deliver until Wed.). Are you going to change your 2916? Either way, I would change the RC components, the two I have changed work much better, but I don't think they're 100% yet. Maybe change the RC components first, recheck the output, if it's still half stepping then consider changing the 2916.
I would like to check the output on some more 2916 drivers before assuming that yours might be bad. Another test I would do is scope the phase inputs to the 2916 while it's running. If you keep doing all the tests, I won't need a new scope.

Scott

bluetrepidation · Post by **bluetrepidation** » Sat Apr 22, 2006 10:15 am

I was just thinking phase inputs myself.... So I checked those too. Let me upload the pic.

bluetrepidation · Post by **bluetrepidation** » Sat Apr 22, 2006 10:19 am

Again Ch. 0 is phase 1 and Ch. 1 is phase 2: