2001 Turn Signal Circuit (LED Lamp Related)

[Shelby Griggs]

As many of you know I have a flatbed with LED lamps. I as well as others have posted about the rapid flash of the turn signals due to the low current draw of the LED lamps.



I finally found an after market flasher, a Tridon EP27 that is a direct replacement, as a matter of fact I would bet they make the OEM units. The good news is that they are $12. 99 at Autozone instead of the $40-50 the dealer quoted.



The EP27 has the same problem as the OEM (rapid flash with LED's), like I said, I think it is the same guts in a different color case.



The challenge is to figure out the turn signal circuit and then modify my new flasher. Didn't want to experiment until I found a more reasonably priced replacement.



I have the replacement unit open, and it looks fairly simple, a few resistors, a diode, a capacitor, a coil to actually make and break contact (the clicking) and a small IC chip.



I am lacking a schematic. Is there a schematic of the flasher in the full service manual? As a minimum, could somebody scan and e-mail to me the turn signal circuit diagram out of the service manual? Better yet, would be an analysis and recommendation of what modifications would be necessary to the flasher to eliminate the current sensing aspect of the operation. A chore for the lurking EE's



I have e-mailed Tridon, but I doubt if they will be forthcoming with a schematic or a way to modify their product.



I am hoping that this will be a simple modification of the flasher to cure this problem once and for all.



Any help, assistance or comments would be appreciated by myself and I am sure by several others on this board who have posted about this problem.



TIA



Shelby

 

[Alaskaskiff]

I think you would have better luck finding an electronics book that has the schematic for such a thing. I had a couple from an engineering class, but they went unused for over 10 years and I got rid of them. You need to add resistance into the circuit outside the flasher or lower the resistance inside the circuit (resistors are color coded with rings of certain colors for their impedance).

 

[Shelby Griggs]

Alaskaskiff,



Thanks for the comments. I want to modify the flasher internally, not add resistance to the circuit externally. I understand resistor color codes and so forth and have some electronics background, so am not intimated at trying to modify the internal circuity, just trying to figure out what to modify.



Shelby

 

[Alaskaskiff]

Shelby,



How about a smaller capacitor?

 

[Alaskaskiff]

Reverse Engineering

On my 96 they gave me two flashers. One was a regular and the other was a heavy duty one for the trailer lights. Same idea as your problem, but the other direction. Bet if you pulled one of those apart you could compare to see the difference.

 

[Shelby Griggs]

Will definitely need to reverse engineer, but the 2000 and newer trucks use a totally different flasher, one is supposed to work for varying loads. The older flashers were / are what is known as a thermal flasher, and adding a trailer caused more draw, more heat and a faster activation, thus the need for the so called heavy duty flashers that could handle the higher current load without going to the rapid mode.



What we need to find out on the newer flashers, which are electronically controlled is which part of the circuit is the current sensing portion, and either eliminate it, or modify it, to fake it into thinking there is a standard amount of current flowing though the LED's.



Shelby

 

[Alaskaskiff]

Shelby,



You might post the number on the chip. S1227, or whatever. I don't doubt someone could get the logic for you. This may very well hold the answer.



I was still operating in the simple world. Had no idea that there was a variable flasher running around out there.

 

[tgbol]

Shelby

I was going through the Signal Stat lighting catalog last night. Came across this number 285 "turn signal flasher for LED systems" works with draw of 1 milliamp to 16 amps. I ordered 2 of them to check out. Signal-Stat numbers are also the same as Napa Lighting so you might be get one locally. Let me get mine and we will see how it works.

Tom

 

[CJ Johansson]

Electronic Flashers

So, the one you're looking at has an IC in it? And it still changes the flash rate with varying current? And with a smaller load (the LEDs) it goes faster? Interesting. Usually, the IC controlled ones use some simple timer chip like a NE555 to generate the ON-OFF pulses, driving a relay (the coil thing) to control the actual lights. The old thermal flashers changed speed based on how long the element tok to heat and bend - more current gave faster flash. Why they would desing an electronic circuit that depended on current is beyond me.



OK. All that aside, it should be fairly easy to reverse engineer the circuit, assuming they didn't do anything nasty like sand off the IC designator markings or get a custom made IC. We need to have the numbers off the IC, there may be a few sets of numbers, some are date codes, etc. , but if you give them all, I can probably figure out what ones are the right ones. Then, I'm going to assume the circuit is on some sort of PC board, most likely single sided - it only has copper traces on one side, the parts mounter on the other side. This makes it fairly easy to trace the circuit. The IC will have a dot or bump or some such near one corner, or possibly a notch in one end. This tells you where pin 1 is on the chip.



If you can trace the circuit out, and we can figure out some way to get it to me, I can probably figure out how it works.



-cj

The EE Rancher...

 

[Shelby Griggs]

CJ,



I appreciate your offer. I have some electronics background, so am not afraid to do the actual mods, BUT, I haven't been in that field for 12 years now, so am a little rusty on trying to reverse engineer this thing. I just talked with tgbol, and his find will not work, two terminals instead of five. If you want to hack on my flasher, I would be happy to forward to you, and if it gets destroyed, no big deal. It will only cost me $13 + shipping to you.



The stated reason for the current sensing circuit is to let the operator know when a bulb is out. Like I don't have sense enough to check my bulbs on a regular basis. I suppose most people don't.



Let me know if you want to tackle this. If you do, send me a PM or e-mail with shipping instructions.



Thanks,



Shelby