Sidelights blinking twice the speed they should

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balto8
Knows an Aerodeck isn't a 480
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Sidelights blinking twice the speed they should

Post by balto8 » Tue Mar 29, 2016 4:29 pm

After going through the 33 index pages of the Electrical System index I have to plant this.

My sidelights have started blinking twice the speed they did before. This happens when I pull the lever right or left but not when I push the warnings button where the interval stays normal .

I have recently replaced my DRLs and front blinkers for LED bulbs but everything has gone OK for a couple of weeks so I don't think this to be related.

Where to look at? Who controls the blinking interval? Why does it stay on it's frequency when I push the warning button?
1991 480 Black Turbo
2012 Seat Exeo ST
2013 VW Polo TSI DSG

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jamesy12345
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Re: Sidelights blinking twice the speed they should

Post by jamesy12345 » Tue Mar 29, 2016 6:00 pm

Maybe one of the bulbs has gone
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dcwalker
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Re: Sidelights blinking twice the speed they should

Post by dcwalker » Wed Mar 30, 2016 8:22 am

Standard way of letting you know that an indicator bulb has failed. Including side repeaters.

If they all appear OK then it may well be to do with the LEDs. Try putting normal bulbs back in and see if that cures it...

David
Current: 1994 480 GT, 1995 480 Celebration 467/480 (plus 2004 C70 Collection)
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balto8
Knows an Aerodeck isn't a 480
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Joined: Tue Jul 22, 2014 3:02 pm

Re: Sidelights blinking twice the speed they should

Post by balto8 » Wed Mar 30, 2016 5:18 pm

Yes. That's the problem probably.

I remember that I changed DRLs for LEDs 10 days ago, but front blinkers were replaced for LEDs just 3 days ago, and I had only tried them working with the warnings button, not with the lever. So I guess having front blinkers in LED and the rest in standard bulb has to have CEM receiving different voltage responses from the front ones an therefore interpretating there must be a fused one.

I'll try later this week as I receive more LED bulbs to replace all blinkers for LEDs ( including lateral ones) and see If it persists. I'll report back.

Thanks
1991 480 Black Turbo
2012 Seat Exeo ST
2013 VW Polo TSI DSG

Robou
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Re: Sidelights blinking twice the speed they should

Post by Robou » Wed Mar 30, 2016 8:53 pm

The blinking function is hidden in the CEM. The current through the indicators is measured over a reference resistor and compared with a set value. The small current through the LEDs causes an "unwanted" situation and the CEM acts appropriatly by raising the speed.

The dirty solution is to connect a resistor in parallel with the LEDs which dissipates as much as the standard bulb. As the indicators on each side are connected in parallel one resistor for each side would do. This resistor should draw a current equal to that of two bulbs of 21W=3.5A. A resistorvalue of 3.3 Ohms will do. Mind that the resistor dissipates a lot of heat so the specs should be at least 15W and heatsink, mounted to the chassis.

More sophisticated is to change the reference resistor in the CEM. This is a shunt of a few hundredths of Ohms, situated between relais 6 and 9 (CEMIII)and marked RM1. Replace the shunt by a resistor of approx. 0.18 Ohm, 5W. As the value depends on the current running through the LEDs some trial is needed. But now also the warning function for a broken LED is intact.
Too old to bother
480 Turbo midst '91

balto8
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Joined: Tue Jul 22, 2014 3:02 pm

Re: Sidelights blinking twice the speed they should

Post by balto8 » Thu Mar 31, 2016 11:18 am

All understood, well... kind of Thanks a lot.

Last night I went down to the garage and made a few tests.

I had to go back to front and rear filament bulbs again and the blinking interval became again right. Side blinker I replaced for a canbus T10 bulb and it doesn't seem to afect anything. Don't know if the side blinker voltage will affect the CEM.

So next thing is I will try all canbus LEDs and report.
1991 480 Black Turbo
2012 Seat Exeo ST
2013 VW Polo TSI DSG

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