Daylight running modules (DRL)

1990 Buick PA. The module died. I belive '90-91 used the same module and likewise Olds. I know the 1991 Olds Delta 88 Royale does have the same module anyway.

Anyone have information on how they work, schematics for the internals or anything at all on how they can be repaired? The FET (field effect transistor) output overheats in time and destroys the unit. It uses a BTS129 FET which I have on order hoping that will fix the module. My guess is that the module uses a freq or oscillator circuit which puts out a square wave output voltage reducing the voltage to the high beam lights, extending bulb life and conserving energy. Can anyone confirm how these boxes work, or add any information? They are a problemsome unit it seems. Lots of wrecks have similar deteriorated or none working units so good ones are not so easy to find. Besides it's a good challenge. :)

TIA

Think they were called LCM's, light control modules.......

As a tech, it's considered a black box, just like any other module.....if it has power, ground, and inputs, and doesn't work, it is replaced......there is no fix.....it doesn't pay a tech to fix it.....so in a sense we are parts changers, but educated parts changers....we don't replace parts unnecessarily.....or hopefully we don't....

However, necessity is the mother of invention......if no parts are a available, all you can do is bring it to a radio repair facility, if you don't have the expertise of diagnosing circuit boards.....

Thanks for the reply.

I've have studied and done repairs of this sort for quite a number of years. The problem with these units is they use proprietary parts numbers on the integrated circuits so it's difficult to determine what the part really is. The rest of the parts are standard components. Have access to a scope so I will follow up on what the output looks like on a good working unit. I expect to see a chopped square wave output. Maybe I'll be lucky to just replace the final output FET. If successful there won't be a shortage of units to repair!!

Was just a long shot but was hoping someone might have researched these units or a techy electronics guy was lurking.

Think they were called LCM's, light control modules.......

As a tech, it's considered a black box, just like any other module.....if it has power, ground, and inputs, and doesn't work, it is replaced......there is no fix.....it doesn't pay a tech to fix it.....so in a sense we are parts changers, but educated parts changers....we don't replace parts unnecessarily.....or hopefully we don't....

However, necessity is the mother of invention......if no parts are a available, all you can do is bring it to a radio repair facility, if you don't have the expertise of diagnosing circuit boards.....

Here is the update on the module. It's actually quite easy.

If you take these modules apart (just release the tabs and pop it open) you will see the heat sink and a MOS FET. (metal oxide semiconductor, Field Effect Transistor). The board may have some heat damage but every unit I've examined is still recoverable. The FET is a BTS129. I paid less than $10 for a replacement. Clean it up, and re-solder the heat sink etc. Re-install and it should work fine. The FET ouput is giving the headlights pulses of 12 volts, reducing the effective voltage to the headlights during daylight. Saves the bulbs and energy use. It would be possible to make changes to the unit by installing a separate larger external heat sink. The box would likely last forever. It's a little under designed in my opinion.


Thanks for the reply.

I've have studied and done repairs of this sort for quite a number of years. The problem with these units is they use proprietary parts numbers on the integrated circuits so it's difficult to determine what the part really is. The rest of the parts are standard components. Have access to a scope so I will follow up on what the output looks like on a good working unit. I expect to see a chopped square wave output. Maybe I'll be lucky to just replace the final output FET. If successful there won't be a shortage of units to repair!!

Was just a long shot but was hoping someone might have researched these units or a techy electronics guy was lurking.