Repairing the Room Lamp Control Module aka Ignition Key Cylinder Light Relay

[Timpanogos Slim]

I am pleased to report that with my key cylinder illumination has returned to nominal function.

And hey, look at that poor little zener diode this way: It was designed to protect the circuit. Whenever a voltage spike came along, it took it. Years and years of selfless, thankless duty in the service of the proper illumination of your ignition switch. So you could figure out where to put your key even if the dome lights were all burned out. And then, it failed. It gave it's life so that you don't have to fumble in the dark.

Clipping it's leg is just releasing it from the bonds of this mortal coil to rest in peace forever. Replacing it with a new zener shows it respect by displaying that we found it's function to be worth continuing.

There should be an IAQ for this kind of thing.

As promised, the solder side of the board:

 

[landcrshr]

Cool, glad you were able to isolate the bad component. Geeks like me want to know. Not sure why they used a zener for protection, seems a regular rectifier diode would do the same job.

But in thinking about this, why settle for just the key cylinder when you can have the whole interior stay lit upon entry (until it fades out).

Here's your new project:

 

[Timpanogos Slim]

Cool, glad you were able to isolate the bad component. Geeks like me want to know. Not sure why they used a zener for protection, seems a regular rectifier diode would do the same job.

But in thinking about this, why settle for just the key cylinder when you can have the whole interior stay lit upon entry (until it fades out).

Here's your new project:

View attachment 789913

Haha. I've been considering that project.

They're using it as a transient voltage suppressor. If you look at any of the LED threads, people insist that although the power system in most cars is "12 volt" it's really 13.8 volts and sometimes spikes well over 50 volts.

Which is probably true, since alternator regulation is imperfect.

In theory a zener is more of a high ohm resistor until the voltage across it exceeds it's breakdown voltage. I'm guessing that the part was rated somewhere between 14 and 16 volts but could have been rated to start zenering at some higher voltage. The worn-out, broken zener is little more than a rectifier and possibly a lot less. A properly working zener used like this is like a bouncer at a club keeping out people who are too tall. But eventually the tall guys overpower it.

I briefly considered searching mouser for a 16v TVS part but decided that i Don't Care. For all I know, the zener in my room lamp control module failed 100,000 miles ago, and the rest of the circuit is working fine. The original electrolytic cap may have had a few pinholes in it's dielectric from over-voltage. The transistors are rated for far more volts than they will see in a car. The zener took the abuse until it could take no more. They should have used a 1W rated zener maybe.

But i went ahead and put four 4.3v zeners in a string and installed that. And it works.

I left the bigger transistor in the output stage because I'm lazy.

If anyone ever finds either transistor cooked, they can probably replace both with MJE253. Metal side facing the resistors. Ic of 4A, so, 8 times as tough as the original tall transistor. Though I'm sure the 4 amp rating is with adequate heat sinking, and i figure only the output transistor is needed.

So yeah that's what I'm considering, a high power PNP on the output, with a heatsink, that will do fade-to-black on all the domes. Which are 48-led panels for me.

There is an unused output on these modules. maybe i will trace out the board after all.

 

[Timpanogos Slim]

Alright the whole-car-fade-to-black on closing the doors has been slowly stirring on the back burner of my mind because my volkswagen has that. and i love my volkswagen.

This is going to be especially hard to follow unless you're familiar with circuits and have thought about this particular circuit as i still haven't bothered to trace it out and name the components.

Right. So.

The big transistor would need to be bigger obviously. We may as well aim high as the parts cost is negligible compared to things like shipping.

MJE2955TTU is rated for 10 amps (clearly with adequate heatsinking) and costs 64 cents from Mouser.

It's nice and slow and "general purpose" for switching, etc. which is what we want.

We'll also need some bigger diodes and possibly resistors with higher current capacity but i haven't traced things out yet. tab 2 is not connected but we can upgrade this output to handle the dome lights.

Ohm tells us that power will flow through the path of least resistance, so if we tie tab 2 of the RLCM into lets say IE1 in the left kick panel this will mean that when all of the doors are shut the dome lights will suddenly have no power source except the RLCM and will then begin drawing from tab 2.

The only trick is that the RLCM is still only triggered by opening the driver's door. If we delete D8 and replace it with jumper wires, have we created an oscillator? Have we created an oscillator anyway? Do we add more diodes?

 

[landcrshr]

Dude, don't over think it! (you knew I'd chime in right?)

All you need is to add the NPN transistor and the resistor I drew in for you.

The module has a sourcing output (PNP), it will not drive the dome lights like that (from the negative side). You need to sink the current at that point, just like the door switch does.

Also, no need to go crazy with the size of the NPN. When it is saturated (on, like a switch) it really isn't dissipating much power (no voltage drop). It is only going to heat up for the brief time during fade-out.

 

[Timpanogos Slim]

hmmm.

ok. will consider this.

 

[Timpanogos Slim]

also, I4 is up in the roof. IE4 is easier to get to.

 

[landcrshr]

Yes, the connector in the kick panel would be most accessible.
I just drew it to I4 because that was easiest.

 

[landcrshr]

I should also add that doing this would cause complications for an alarm system.
Arming the alarm when the dome light is still on would cause it to think a door is still open. But there's a way around that.

 

[TicoCafe]

Edit 8/6/2013: SOLUTION FOUND. It's the little glass component on the far side of the brass tabs. Cut it off. Or replace it. See if i care.

I have that "ignition cylinder light never turns all the way off" issue.

We've seen the threads - here and here. The part number is 85965-60010 and it costs over a hundred bucks new and $50 used.

Or you can just remove the bulb. Or, even easier, remove the module. On my truck it is behind the passenger side kick panel, right under where the diff lock ecu would be if i had lockers.

But those options are the easy way out.

It turns out to be a fairly simple electronic circuit:

This probably cost a buck to manufacture in 1990.

I see two transistors, two capacitors, four diodes, and half a dozen resistors.

The only components that are at all likely to fail are the transistors and maybe the electrolytic cap. And it's not the electrolytic cap (already replaced it).

The contacts were dirty, but a judicious cleaning with 1000 grit sandpaper and then deoxit d5 didn't make a difference.

The taller transistor is a 2sb647c and is easily sourced on ebay.

The shorter one is 2sb637c and a bit harder to find, though there is an NTE equivalent available from Fry's for less than $4 shipped:

http://www.frys.com/product/1975880?source=googleps&gclid=CI202b3v5LgCFQnhQgodzRoA6g

But i don't like NTE's business model so i consider them a vendor of last resort. Ironically, their business model involves cornering the vendor of last resort market.

So I'll be frank: I want my ignition switch lamp to switch off properly, and I'm willing to debug this issue to do it. And unwilling to buy another module.

if one of the black diodes is cooked, the one in the middle is not connected to anything (wire harness is only 3 pins - unused output?) so i might try swapping them around. I haven't identified them yet but i would not be surprised if they are plain old rectifiers and i could just drop in 1n4001 diodes which i have a-plenty.

Perhaps i should pull out the unused diode and see if i can identify it.

I will probably order a baggie of the tall transistor from a chinese ebay vendor tonight. Though, a real man would just find a modern part with the same hfe curves.

Great post...thanks for sharing.
I am running into the same issue. I was wondering, for us mortals to point out in the pic which one is the Zener you had to replace??

 

[Timpanogos Slim]

Great post...thanks for sharing.
I am running into the same issue. I was wondering, for us mortals to point out in the pic which one is the Zener you had to replace??

Think I specified in another post - the component off by itself on the edge past the brass tabs. The one obviously made of glass. You could also just cut either leg of it. If you have this problem it hasn't been protecting the transistors for some time now but they still work anyway.

Or replace with a 1 watt zener rated from say 16 to 24 volts or so.

 

[TicoCafe]

Thank you for your reply... Got it working again by just cutting the Zener off as you mentioned. The Zener was looking a little over worked when I opened it up. This is from a 1997 fzj80.

 

[Rock40]

This is a very helpful thread for a very common problem, thanks. I replaced the zener diode in my 96' (wanted it protected and the damn light was on all the time) and I also swapped out to a 220UF capacitor to increase the amount of time the lamp stays lit. It works GREAT and the key ring stays lit for roughly 10 seconds now.

 

[adamf]

I know I know it's an old thread, but I just completed this repair on my '96 and it worked great. Thanks to Timpanagos Slim!

 

[Timpanogos Slim]

Welcome! Good to hear!

 

[Rigidarm]

I've had this same problem for a few years. Now it's off to find the green devil behind the kick panel and give it a snip snip ..... vs $150. for a new one. (Great thread that needed to be brought back up)

 

[Visuals1134]

Just clipped the end of my board .the one that looks like glass.hope this does the trick.thanks for the info guys!

 

[thelal]

just tried it on mine and hasn't made a difference on my parasitic drain. back to measuring ...

 

[enox]

Thanks for this, however I cut the glass diode off and still don't have the light working. As a matter of fact I don't even have power going to the plug that the lamp is running off of.

Door switches are good. Everything else works minus the keyring light and the ash tray light.

Am I missing something here or perhaps a fuse that is on both of those?

*Edit*
I got the ash tray light to work, the bulb was not oriented correctly.

I removed the lock cylinder and that was not hindering function nor produced any light.

Can I jump the brass tabs to illuminate that circuit? Just wondering otherwise I'm thinking about trying to wire the keyring light to the dome light circuit....

*Edit 2*
I ran a jumper on the plug so the problem does lie in the board, however cutting the glass diode did not solve my issue...

 

[Timpanogos Slim]

Saw your DM but for some reason i cannot reply to it?

I don't remember much about this. Best i can do is hope that you can find a copy of the electrical wiring diagram.