REAL fix for ARC blinking lights - Page 2 - Alfa Romeo Bulletin Board & Forums

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post #16 of 156 (permalink) Old 04-12-2008, 05:57 AM
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Used a LM340t5, sub for NJM7805a or AN7805f. Went through several hot/ cold cycles &
viola, no more ARC disco shows. I feel so cocky now I might even try to fix the oil level
sensor. Thanks a million Tom.

John
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post #17 of 156 (permalink) Old 04-12-2008, 07:48 PM
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Tom - Roger B. & I swapped out the stock voltage regulator with a LM7805 ($0.69 at Halted), reused the original heat sink and ... IT WORKS

Yes, we do owe you a beer.
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post #18 of 156 (permalink) Old 04-12-2008, 09:10 PM Thread Starter
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Sweet. Sounds like we've got this mo-fo licked

Tom

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post #19 of 156 (permalink) Old 04-12-2008, 09:25 PM
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How do we pin this or make this part of the FAQ?
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post #20 of 156 (permalink) Old 04-12-2008, 11:10 PM
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No more use for Louis' GIF then. He should still post it here anyways..

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post #21 of 156 (permalink) Old 04-12-2008, 11:47 PM
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Quote:
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No more use for Louis' GIF then. He should still post it here anyways..
Hahaha. Just a picture of a blank ARC maybe?

I meant to pick up one from work, but forgot.

It's amazing though, it's taken 20 years for someone to finally figure out the real problem! A $1 problem.

ROCK ON
R~R
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post #22 of 156 (permalink) Old 04-13-2008, 11:21 PM Thread Starter
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Yeah, a one-buck part and an incredible number of man hours to figure out the problem. Somewhere there is an Italian electrical engineer who made my s--t list! I mean, seriously, Alfa sold these cars for how many years and couldn't fix this?

I'd been working on this quite a while, actually, swapping parts, checking voltages, checking grounds, checking current flows to ground, and just generally trying to figure out what was going on. Once I had enough parts stockpiled, I was able via swapping to nail down that the ARC computer didn't make a lick of difference but the display did.

After that, it took my buddy and I a couple of hours to figure out what the board was supposed to do. It's a pretty simple circuit, but we had a hell of a time figuring out the details for the driver chips so it took a while - just couldn't find them anywhere. Eventually we found a similar VFD driver chip with similar specs.

Once I knew how the circuit was supposed to work I spent an afternoon just looking at voltages on the board as various things happened, and even with a DVM I could see the voltage get noisy as things turned on and off. Using the freeze spray to further isolate the problem helped a lot. Hell, if I'd started with the freeze spray I probably would've figured the whole thing out a lot faster.

I actually bought an HP 1631D logic analyzer and oscilloscope to check for electrical noise and read the digital data stream but ended up not needing it. No big - been looking for an excuse to buy an oscilloscope for a long time.

So now I have a working ARC and a cool oscilloscope. Life is good

Tom

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post #23 of 156 (permalink) Old 04-13-2008, 11:29 PM
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You should make a roll call of all Bay Area Milano Mafioso (BAMM!) to fix their ARC's and come down to IHOP to show off their (working) ARC's
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post #24 of 156 (permalink) Old 04-15-2008, 03:46 AM
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I bought one of the VR's from Radio Shack this past weekend as I wanted to make the fix on one of my spares. I'm going nuts now trying to find even one of the two ARC's I know I have buried in the many totes of Milano and Spider parts I have in the basement! I feel like I'm on a Snipe hunt.

Thanks for posting this fix!

Kevin

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post #25 of 156 (permalink) Old 04-18-2008, 09:04 PM
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Thumbs up Wow

Gubi what you have done is the Milano electrical gremlin equivalent of inventing penicillin!
Congratulations and thank you. My Verde display works well but no doubt some day it will need this fix.

Jim
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post #26 of 156 (permalink) Old 04-20-2008, 10:17 PM Thread Starter
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Okay, maybe not *completely* fixed. I took a long drive on Saturday and by the end of it I was getting an occasional blink of the master warning light. As I mentioned earlier, I'm guessing the issue here is probably heat since this didn't happen on shorter trips.

Since I wasn't really happy with the tape method I'd used to attach the regulator anyway, I took it back apart and re-soldered it, this time properly attaching it to the board with a stand-off. I also took the opportunity to dab some thermal grease between the heat sink and the regulator to ensure good thermal contact (it was a little loose with my original rivet, and with no thermal grease the heat transfer may have been poor. This is what I get for rushing through a job)

We'll see if this shows further improvement. If not, I'm going to drill some holes in the plastic case to improve air circulation.

Tom

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post #27 of 156 (permalink) Old 04-20-2008, 11:22 PM
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Tom - when I reassembled mine, I found a standoff from my old PC that fit, along with using a generous amount of thermal grease to the (reused) heat sink. So far so good. I actually have to pay attention to it now because it actually does tell you what's wrong
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post #28 of 156 (permalink) Old 04-21-2008, 06:47 PM
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Here is an idea, they charge $500 or more to fix a 1994-1995 164 HVAC control system, so you should recondition these Milano units and sell them for $250! Now that the cat is out of the bag maybe its not so possible, but I am sure many a Milano owner will thank you. Good work and glad you have been victorious!

Again the proud owner of the White Dragon and a 2010 Jetta TDI
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post #29 of 156 (permalink) Old 04-21-2008, 06:57 PM
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I'm pretty sure by putting up a post on the BB, he wasn't planning on selling this fix =)

But yes, you were the talk of the town of ButtonWillow, Tom. I can't wait to get home to my stored ARC and see if I can fix it.

Thanks!

What's a Standoff?

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post #30 of 156 (permalink) Old 04-21-2008, 09:12 PM Thread Starter
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Honestly I'd rather just have the fix out there. The thought of offering to fix them for a fee did cross my mind, but then I realized that I already spend enough time sorting electrical issues on my own Milano. I'd hate to have people mailing me crap to fix on top of that!

A standoff is a little hex shaped post with a screw on one end and a female thread on the other. You can screw them together to attach them to things or make longer standoffs. You use them to separate electrical boards, usually. I just used a bolt and some nuts as a standoff in this case - same idea.

Tom

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