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

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 156 (permalink) Old 04-07-2008, 05:58 PM Thread Starter
But Mad North-Northwest
Platinum Subscriber
 
Gubi's Avatar
 
Join Date: Sep 2003
Location: SF Bay Area, CA
Posts: 8,433
REAL fix for ARC blinking lights

Like many Milano owners, I had an ARC that tended to go haywire when either it was very cold, or when multiple lights came on. So I spent some time with an EE friend, and I think we've found a fix for at least some cases of the ARC blinking lights.

Most people (including myself until I took it apart) assume that the issue lies with the ARC computer itself and that the display board is just "dumb" circuitry, but this isn't the case. There's some digital processing going on in the display board as well. Folks blame the ARC computer, but I've done a whole lot of parts swapping and testing it looks to me that a lot of the problems originate in the display board.

Here's the deal: the ARC computer talks to the display board via three wires in the connector. There's a data line, which encodes which lights to flash as an (up to) 30-bit data stream. This is interpreted by three 10-bit LED driver chips on the board. There's a clock line to keep the two boards in sync, and then there's a strobe line that's used to signal the driver chips to light the LEDs. In addition there's one transistor (which is used by the ICs to drive the 12V master warning lamp) and there's also a NOR gate chip (which possibly handles the big alarm light and the ARC clear button). All of this circuitry runs at 5V, which is stepped down from the car's 12V by a voltage regulator chip.

Other than that, there's not much on the display board. There's three capacitors that I thought might have gone bad with time, but they're only used to clean up the voltage on the 12V/5V lines and they tested good. ICs, transistors, and resistors don't generally go bad, and all the solder joints looked good. That left the voltage regulator. Using a can of freeze spray, I was able to isolate that cooling the regulator made the lights go haywire.

I also did some multimeter testing and here's what I think is happening. The LED's and the chips are both run off of the 5V output of the voltage regulator. When too much power gets drawn off of this line (i.e., when multiple LEDs light up) the output of the voltage regulator goes a bit haywire which makes the ICs start to malfunction. I'm not sure why cold makes the problem worse, but suspect that it's just a crappy part and doesn't have good thermal performance.

I pulled up the spec sheet for the voltage regulator and it's only rated for 500 mA output. Thinking this might be too little, I got a $1.59 voltage regulator from Radio Shack (P/N 276-1770) that has the same voltage in/out but is rated at up to 1 A output draw. I desoldered the old voltage regulator, drilled off the old heat sink (probably the toughest part!) riveted the heat sink to the new regulator, and soldered it into place.

The result is an ARC that correctly lights up multiple lights and doesn't go haywire! I did my work on a "bad" display board that I purchased for testing. As it came to me originally it would go haywire all the time, even when no lights should be lit. With just the change of a $1.59 part (and no changes to the ARC computer, cleaning grounds, or any other such stuff) it started working perfectly. The best part is, it now even works first thing in the morning when everything is cold.

The Radio Shack part is at the link below. The pinout of this is exactly the same as the existing chip.

+5V Fixed-Voltage Regulator 7805

The pic below shows the parking brake light and all four door lights working properly, with no blinking. Boo-freaking-ya!
Attached Images
  

Tom

1991 Spider
1963 Giulia Spider (1750 engine)

Last edited by Gubi; 04-08-2008 at 09:28 PM. Reason: Spec correction
Gubi is offline  
Sponsored Links
Advertisement
 
post #2 of 156 (permalink) Old 04-07-2008, 05:59 PM Thread Starter
But Mad North-Northwest
Platinum Subscriber
 
Gubi's Avatar
 
Join Date: Sep 2003
Location: SF Bay Area, CA
Posts: 8,433
And now a warning:

I THINK this is a likely fix for many ARC problems. I THINK that even if it doesn't fix the issues, it can't make things worse. I THINK everything I am saying here makes sense, and it definitely worked great for me. However:

1) I've only tried this on one board
2) I only did this yesterday and haven't subjected it to extensive testing yet
3) It's quite possible to blow things up if you mess something up. Case in point: while testing in the car, I slipped with my voltmeter probes on the display board and ended up smoking one of my ARC computers. Fortunately it ended up just being a burned PCB trace that I was able to bypass and fix, but it could have been much worse.

I suggest you proceed at your own risk until more data comes in. My hope in posting this is that someone else out there (likely with a disconnected display board who has nothing to lose) will do some work to validate my findings.

I will keep you posted of any updates in my testing.

Tom

1991 Spider
1963 Giulia Spider (1750 engine)
Gubi is offline  
post #3 of 156 (permalink) Old 04-07-2008, 06:00 PM Thread Starter
But Mad North-Northwest
Platinum Subscriber
 
Gubi's Avatar
 
Join Date: Sep 2003
Location: SF Bay Area, CA
Posts: 8,433
Procedure

1) Remove the ashtray

2) Remove the two screws on the ARC display and remove the display from the dash. Disconnect the three connectors.

3) Unscrew the two screws on the back and remove the clock.

4) Unscrew the three screws on the back holding the display panel together.

5) Gently separate the white back of the display panel from the black front. You can see the catches around the edges - pry these gently and separate. When you do this, there are two lenses over the master warning light that will probably fall out. Don't lose them.

6) Remove the black piece with the graphics from the white back of the display panel to reveal the circuit boards.

7) There are two boards: the front board with the LEDs and the smaller rear board with the plug connector. These are joined by a short flexible cable. Gently slide them out.

8) The voltage regulator is on the rear board under the big heat sink. The heat sink is riveted to the regulator and then attaches via a post to the circuit board. To remove it, I heated the underside of the board to melt the solder where the post goes through the board. Then I gently pried the post off of the board using a small screwdriver. Once I did this, I desoldered the regulator/heatsink and removed them.

9) I re-used the heat sink by drilling out the rivet. I then used a pop-rivet to attach the heatsink to the new regulator. BE SURE TO MOUNT THE REGULATOR IN THE SAME ORIENTATION or else you'll get the pins backwards. The pinout of the new regulator is exactly the same as the original one.

Edit: I suggest you use thermal grease in step 9 between the heatsink and the regulator

10) Bend the pins and solder the new regulator into place. the heatsink is grounded, so make sure it will not touch the other board when you reassemble everything. The post was there to keep the heatsink from vibrating and cracking the solder, so make sure you use some method to mechanically fasten the heatsink to the board to prevent this. I used tape but will probably try to come up with something better.

11) Reassembly is the reverse of assembly.

Tom

1991 Spider
1963 Giulia Spider (1750 engine)

Last edited by Gubi; 06-05-2008 at 12:37 PM. Reason: Wordsmithing, added need for thermal grease
Gubi is offline  
 
post #4 of 156 (permalink) Old 04-07-2008, 06:17 PM
Registered User
 
DonBeeson's Avatar
 
Join Date: Feb 2005
Location: Somewhere in Canada
Posts: 1,415
Someone should sticky this. I'll test my ARC display that went haywire when I go back home for it.
Thanks for the writeup!

'88 Alfa Romeo Milano Verde - 24V, '87 Platinum 3.0 (for sale), 94 LS parting out
DonBeeson is offline  
post #5 of 156 (permalink) Old 04-07-2008, 06:23 PM
Registered User
 
Potenziato's Avatar
 
Join Date: Aug 2003
Location: San Jose
Posts: 673
Hmmm, I'll go to Radio Shack and get a voltage regulator. I've noticed that in changing the displays that some are more erratic than others.

Keep it up Gubi! I'll report back if it works or doesn't.

Louis
2011 M3 e90 ZCP no sunroof, 2004 M3 e46 no sunroof , 1987 Milano 24v, 1987 Milano Verde

Last edited by Potenziato; 04-07-2008 at 06:25 PM.
Potenziato is offline  
post #6 of 156 (permalink) Old 04-07-2008, 10:46 PM
Registered User
 
alfaspence's Avatar
 
Join Date: Apr 2007
Location: ipswich, uk
Posts: 296
Oh Tom! This is awsome news! (but why couldn't you have done this a few months ago )
If this works, and continues to work, you may have found the cure for one of the most irritating gremlins that these cars suffer from
(in case you are wondering why i said about doing earlier, ive removed mine, and its wiring completely )

Spence
1972 Vauxhall Firenza 3.0 V6
alfaspence is offline  
post #7 of 156 (permalink) Old 04-08-2008, 12:55 AM
Registered User
 
Craig's Avatar
 
Join Date: Apr 2004
Location: Melbourne Australia
Posts: 1,885
G'Day Tom,

Sounds like a possible fix, I had assumed that the 5V regulator was a 7805 but have now opened one up to find a TEA7605SP rated at 500mA as you have stated.

The main differences between the two are output current (500mA v 1A) and input voltage (the TEA7605SP only requires an input voltage greater than 5.6V to give 5V out whereas the 7805 requires greater than 7V in to give 5V out).

So using the 7805 I think the only downside (apart from stuffing up the changeover) is that there could be funny things happening with your ARC during cranking with a less than fully charged battery. This may not be a problem at all.

Craig,
1988 75 TS, 1989 164
[COLOR="Red"]My web sites:[/COLOR]
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
&
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Craig is offline  
post #8 of 156 (permalink) Old 04-08-2008, 05:08 AM
Registered User
 
Rookie ROX's Avatar
 
Join Date: Jan 2006
Location: Brisvegas, Australia
Posts: 659
Sounds very interesting. I think I may wait for the testing to occur, but it'll be easy enough to get a regulator from work.

On a side note - Over the past two months or so, my ARC Trip Computer has been freezing. I'd come out to the car and find the clock had stopped and nothing would work, the three buttons would make no difference. I'd have to disconnect the battery and reconnect it for it to work again. It's done it three times now. Has anyone else ever experienced this before? I'm yet to get a chance to switch it over to the other trip computer we have, but it's incredibly bizarre.

ROCK ON
R~R
Rookie ROX is offline  
post #9 of 156 (permalink) Old 04-08-2008, 01:31 PM Thread Starter
But Mad North-Northwest
Platinum Subscriber
 
Gubi's Avatar
 
Join Date: Sep 2003
Location: SF Bay Area, CA
Posts: 8,433
That's what I figured from the specs, Craig. Interestingly I did notice it going a bit wacky today during cranking (car took a little bit to start) but it settled down once cranking stopped. Beyond that it's been working utterly flawlessly, which has been sweet.

I'm pretty certain they used different components depending on when these boards were built - I know that the ICs on the two boards I have are from different manufacturers. I don't remember the part number, but I know the regulator I pulled out was ST manufactured and rated at 500mA.

[Edit: it's an ST L4705CV]

Fry's Electronics around here carries NTE components and the NTE equivalent part was a NTE1951 (1A). Unfortunately this isn't one of the parts Fry's stocks on the shelves, so out of desperation I went to Radio Shack and was pleasantly surprised to find they had an equivalent in stock.

For the record, the web page for the Radio Shack part says 1A, but I'm 95% certain the packaging on the one I bought said 2A. Likely 1A is enough, but it's voltage regulated so no risk of blowing something up with a higher amperage version.

[Edit: I'm wrong, the Radio Shack one is a 1A 7805 as it says on the web page]
Attached Images
 

Tom

1991 Spider
1963 Giulia Spider (1750 engine)

Last edited by Gubi; 04-08-2008 at 07:01 PM.
Gubi is offline  
post #10 of 156 (permalink) Old 04-08-2008, 02:24 PM
Registered User
 
Craig's Avatar
 
Join Date: Apr 2004
Location: Melbourne Australia
Posts: 1,885
G'Day Tom,

Yes the NTE1951 would be a better choice with the lower drop out voltage but the 7805 should suffice and is as common as dirt. The 78xx series in the TO220 package is normally rated at 1A but since the theory here is that 500mA is good enough most of the time (but only just), 1A should be more than enough.

I guess we need more people to try this on known dud ARC's and report their findings.

Craig,
1988 75 TS, 1989 164
[COLOR="Red"]My web sites:[/COLOR]
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
&
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Craig is offline  
post #11 of 156 (permalink) Old 04-08-2008, 05:03 PM
Registered User
 
Potenziato's Avatar
 
Join Date: Aug 2003
Location: San Jose
Posts: 673
I just finished trying to repair an ARC using the GUBI mod. The display I used was totally dead and was completely erratic. IT WORKED!. The display worked perfectlly from cold. No Milano Christmas tree. I couldn't believe my eyes. I swapped back to the one that I used before and sure enough, dancing lights. On the repaired one, the connection between the cable and the display was a little dirty so I used CAIG contact enhancer and it was working 100%.

I did this one fast. I think I'll use thermal compound between the heatsink and the voltage regalutor. I used an aluminum rivot to hold them together.

I'll report back after testing! If it works without fail I'm buying GUBI pancakes!

Louis
2011 M3 e90 ZCP no sunroof, 2004 M3 e46 no sunroof , 1987 Milano 24v, 1987 Milano Verde
Potenziato is offline  
post #12 of 156 (permalink) Old 04-08-2008, 07:04 PM Thread Starter
But Mad North-Northwest
Platinum Subscriber
 
Gubi's Avatar
 
Join Date: Sep 2003
Location: SF Bay Area, CA
Posts: 8,433
Pancakes? Dude, if this works, every Milano owner in the world owes me a beer

Glad to hear of some confirmation. I wonder, perhaps, if one reason these got worse with time was that the regulator gets hot and degrades over time? I haven't checked how hot that heat sink gets in normal operation.

I suppose if that's a contributing issue it's easy enough to add some vent holes to the housing.

Tom

1991 Spider
1963 Giulia Spider (1750 engine)
Gubi is offline  
post #13 of 156 (permalink) Old 04-09-2008, 11:30 AM
Registered User
 
Join Date: Feb 2008
Location: NJ
Posts: 30
Nice work

Great job. I don't know why I didn't check that.
One word of caution though, NTE doesn't have the best QC, but since that
component is obsolete & the markets flooded with knock offs & remarks, you have to get what you can.

Regards,
John
Attached Images
File Type: pdf AN7800_E_discon.pdf (622.6 KB, 544 views)
crankCase is offline  
post #14 of 156 (permalink) Old 04-11-2008, 04:10 PM
Registered User
 
Join Date: Mar 2005
Location: Milpitas CA
Posts: 2,984
hmm I took out the part above the glove box and it seemed to be fine I even changed out all the caps.
I did not know there was anything on the other part I will take mine out and take a look.
I was starting to think that the flash in the MCU was starting to lose the program. but I never went back to look at it anymore. I was going to go log all the voltages and see if they were in the right range but never got to it. I was thinking I might have to make a new box from scratch. but all this time I was thinking the display PCB had no active parts on it.

1987 black Milano Verde, 1987 (made in 1986)blue $200 gold with ABS and LSD
1972 White spider 2000 Veloce
slyalfa is offline  
post #15 of 156 (permalink) Old 04-11-2008, 06:11 PM
Registered User
 
Join Date: Mar 2005
Location: Milpitas CA
Posts: 2,984
I pulled it out and swaped in a normal 7805 I have a box of them.
I did not reuse the riveted thing I just put in a standoff with some locktight
I think the whole thing took like 15min. start to finish. And it looks better allready. the break light went off as soon as the ABS pump pumped up. and the hand break light went on/off with the hand break.

I have not driven yet. but it looks like it is working.....

1987 black Milano Verde, 1987 (made in 1986)blue $200 gold with ABS and LSD
1972 White spider 2000 Veloce
slyalfa is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Alfa Romeo Bulletin Board & Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
Replace with
For the best viewing experience please update your browser to Google Chrome