Hi All
Does any one have a circuit diagram for a 1983 K100 bulb monitoring unit? Plenty of schematics around but need the actual circuit diagram.
Fortunately I had a spare but the original has failed for the rear brake monitoring and I would like to repair it.

Cheers
Mike

robmack wrote:https://www.k100-forum.com/t13127-reference-bmw-instrument-cluster-schematics

Many thanks, I will see if it ties up with the one I have.

robmack wrote:https://www.k100-forum.com/t13127-reference-bmw-instrument-cluster-schematics

Unfortunately those cct diagrams are totally different to the bulb monitoring unit I have, mine is a very early K100 frame No 0003438

This is what mine looks like.

ULN2003 looks like a NPN Darlington pair array, cant find any info on the coils Clare CUP S 1000
3x 4004 diodes
4x 1uf 63v caps
and I can just see a '48' on one of the other diodes not covered by epoxy
Looks like a 3.3 ohm resistor (orange, orange, gold, gold )

The board layout and components is completely different, I'll give you that,  The three Clare CUP S 1000 devices are reed relays.  Two pins are the NO contacts and the other two contacts are the relay coils.  The diode marked with a 48 might just be a signalling diode like a 1N4148.  Is it glass or plastic?  The 1N4004 diodes are standard.  The ULN2003 is indeed a motor driver IC. What's that piece of black stuff near pin 3 of the IC on the underside?  Dirt or something else?

I'd check the diodes with a ohm meter to make sure none are shorted or open circuit; that they are doing their diode thing.  With the age of the board, I think the electrolytic capacitors are dead and should be replaced with new ones as a matter of course.   If you have the tools and feel confident, you can try and remove the IC and replace it.  You'll need soldering iron, solder wick, and liquid flux.  Take your time and make sure each pin is loose before attempting to yank the chip off.  You don't want to rip up any copper traces.

Depending on how much desoldering you think that you'll do in the future, my preference is for one of these:

https://www.ebay.co.uk/itm/144373686542?epid=12003303625&hash=item219d57a10e:g:MmUAAOSwSLpgLQz-

I've a couple of 'original' Radio Spares ones that have seen service for over 40 years now. I never got on with solder wick.

I would also recommend avoiding the solder wick.  It's okay for removing solder from the metal terminals on switches, but I've damaged too many circuit boards using that stuff. 

I have one of those solder suckers.  The spring loaded vacuum plunger does a great job of instantly pulling the solder out of the joint so you don't have to keep reheating the joint to get the part loose.

My experience has been the opposite.  I have a dedicated Weller desoldering machine on my bench and a variety of solder wick.  I've even owned portable solder suckers like referenced.  My success rate desoldering through-hole and surface mount components using solder wick is greater than with the dedicated machines.  Once the wick has sucked up 90% or more of the solder, pressing the pin using a jeweller screwdriver releases the pin from the board.  It helps a great deal to soak the wick in liquid flux as that promotes solder to wick up quicker and more completely.

But if solder suckers work for you, all the power to you.

You mention flux.  I wonder if that is the problem with the solder wick I have around here.  It's very possible that the flux has degraded in the 25 year old spool I have on my bench.  I know it's been pretty difficult to get good solder absorbancy on it for quite a while now.  It seems when I use it I have to overheat the joint to get the solder to flow into the wick, and even then there is always enough solder left to make breaking the joint difficult.

Again, with the demise of Radio Shack, I have been working with my very old inventory of tools and supplies.  I suppose I should get some liquid flux on line.  And to think I used to do business with a company that made solder flux.

Suckers of the world UNITE!!!!






(Just thought I'd get there before somebody else did )

Gryph what about Jaycar? They will deliver and it's free if you spend over $99.00. Amendment, I just had a look at Jaycar USA and they only have 3 stores we've got 5 in a 20 Km range closest is 2.8 Km. We have only one other choice locally Altronics. We've lost Tandy and Dick Smiths which slowly morphed into an appliance store before disappearing.
Regards Martin.

robmack wrote:The board layout and components is completely different, I'll give you that,  The three Clare CUP S 1000 devices are reed relays.  Two pins are the NO contacts and the other two contacts are the relay coils.  The diode marked with a 48 might just be a signalling diode like a 1N4148.  Is it glass or plastic?  The 1N4004 diodes are standard.  The ULN2003 is indeed a motor driver IC. What's that piece of black stuff near pin 3 of the IC on the underside?  Dirt or something else?

I'd check the diodes with a ohm meter to make sure none are shorted or open circuit; that they are doing their diode thing.  With the age of the board, I think the electrolytic capacitors are dead and should be replaced with new ones as a matter of course.   If you have the tools and feel confident, you can try and remove the IC and replace it.  You'll need soldering iron, solder wick, and liquid flux.  Take your time and make sure each pin is loose before attempting to yank the chip off.  You don't want to rip up any copper traces.

Awesome, yes agree the diode could be 1N4149 as they are glass.
Was very proficient in the past working on cct boards, just need to get the eye back in, got solder suckers and all the tools.
Good to know the CUP devices are reed relays.

The black blob on the back of the cct board is resin, will scrape it off to see what's underneath.

So the fun begins, good job this is the spare now.

robmack wrote:The board layout and components is completely different, I'll give you that,  The three Clare CUP S 1000 devices are reed relays.  Two pins are the NO contacts and the other two contacts are the relay coils.  The diode marked with a 48 might just be a signalling diode like a 1N4148.  Is it glass or plastic?  The 1N4004 diodes are standard.  The ULN2003 is indeed a motor driver IC. What's that piece of black stuff near pin 3 of the IC on the underside?  Dirt or something else?

I'd check the diodes with a ohm meter to make sure none are shorted or open circuit; that they are doing their diode thing.  With the age of the board, I think the electrolytic capacitors are dead and should be replaced with new ones as a matter of course.   If you have the tools and feel confident, you can try and remove the IC and replace it.  You'll need soldering iron, solder wick, and liquid flux.  Take your time and make sure each pin is loose before attempting to yank the chip off.  You don't want to rip up any copper traces.

Would you happen to have a spec sheet for the CUP S 10008 reed relays? I seem to be able to find every thing else made by CLARE
Cheers