Hyundai trailer module 5D033 blown component

[Mandarin47]

Hi, I have a Hyundai trailer module that I got about 2 years ago (so I can't return it) and I am now trying to fit it to a car. Its simple enough wiring so I am sure that that is correct but the fog lights and brake lights don't work. One hazard light on the trailer will stay lit but won't flash. I took out the module and had a look at the board and I found a blown component but I can't tell what it is. I am assuming its a diode but all the markings on it say M8. D17 is on the pcb beside the component.
I have a very basic level of electronic knowledge. I removed another M8 component from the board to test with a multi meter. I have labelled the pins 1, 2, 3 in one of the images. When tested with a diode test on a multimeter there is a 0.7V drop going from Pin 2 to pin 1. There is no other drop with any other sequence of pins.
There is a kilo ohm resistance between all pins that seems to fluctuate between 30-50 Kilo ohms.
I have tried to find what the component actually is but I can't find it anywhere.
I would appreciate any help with this

[Manul]

So 0.7v drop is with positive to "2" and negative to "1"?

I was not successful to find likely part by SMD code.

But I have idea that it may be a zener. Possibly 4.7v

Mandarin47, do you have some spare components, like 10K resistor laying around? Can you test if it is zener?

[Mandarin47]

Hi Manul, thank you for your reply.
Yes the positive is at pin 2 and the negative is pin 1.
I have loads of different values of resistors and a variable power supply. How do I use the 10k resistor to test if its a zener diode?

[Manul]

I attached a circuit diagram. Basicaly you take a power source around 10 to 20v and try to drive your diode in reverse (negative to pin 2, positive to pin 1) through a 5 to 10 kiloohm resistor. Observe a voltage on a diode with multimeter. If you see a voltage similar to your power supply, then it is a simple diode. If you see some clearly lower voltage it is a zener.

[Mandarin47]

Hi, thanks again. I built the circuit. I started the power supply at 1v and the drop across the component was 1v.As I turned up the voltage on the psu, the voltage on the multimeter remained the same until 3V and then they started to separate. At 4v I was still at 3.2v on the multimeter and by the time I was at 8v on the psu I was still at 4.2v at the component. I didn't want to go any higher in case I damaged another component. I'm assuming so that its a zener diode. What would your advise be on replacing the component, ie voltage and current ratings?

[Manul]

Yes, that is similar to a curve of 4.7 volts zener diode. If you would go higher and higher current it would stabilise somewhere around 4.6 - 4.8v.

And as it seems from pictures pin3 is not used, it means it is 1 zener diode in a package.

So you need a 4.7v zener diode in same package and same internal orientation. I will try to look quickly what can be found. But, keep in mind, that it is not very likely to be the only fault.

By the way, is damaged diode shorted or open?

[Manul]

The original part is very likely BZX84C4V7

Power dissipation specification varies a bit depending on manufacturer, there are versions from 250mW to 350mW. So 300 to 350mW will be a good bet (middle to high end).

[Mandarin47]

The damaged diode is shorted  While nothing else looks damaged I'm sure there's a chance that something else is. Thanks so much for your help. I'll look at getting the part that you suggested and I'll post back here once I've put it on the board. Thanks again for your help 

[Manul]

In this case shorted should be better Because obviously it was a serious overvoltage or reverse voltage event. So by shorting, it absorbed this event.

Don't buy 1, buy 10

[Manul]

While waiting for components, you can try to look where pin 1 goes on a board. It probably has a direct connection to PIC16 microcontroller (U2) pin. Because there is a few identical circuits: 2.7K resistor --> 4.7K to ground + zener to ground --> PIC16. Because 2.7K resistor can not carry enough current to destroy a zener, it means that this current came from PIC16. That would be strange and unexpected.

[Mandarin47]

Hi I have checked the board with a multimeter and i have included a basic DaveCad diagram of what I have found

[Manul]

Can you post pictures of both sides of the board? From top, close to 90 degrees angle and similar distance.

[SL4P]

Just curious...
What’s a trailer module, and what does it do ?

[Mandarin47]

Hi I have attached the pictures. If you need better ones let me know. I soldered the red and black wires so that I could test the board inside my house. I measured the input voltages that the car sends to the board so I was able to simulate that inside. Also the black writing on the  back of the board was also done by me. I had thought there was a problem with the relays as I only ever heard one click before I found the blown diode.

[Mandarin47]

It's used to power the lights on a trailer thats attached to a car. The lights of the trailer are not directly attached to the lights of the car. The module gets the signals from the cars lights and then switches relays in the module to turn on and off the lights on the trailer.

[Manul]

Ok, so it seems that disaster came from this connector pin. What is the function of this pin? What signal, what voltages? Bad thing is that there is a direct connection to microcontroller, hard to say if it survived. Bad design to not have a series resistor here...

[Manul]

It looks like a stupid circuit. I mean, with a series resistor it would work like a voltage clamp to convert input voltage to microcontroller voltage levels. But because there is no series resistor, any voltage at this input above ~4.7v (or < -0.7v) will start a big current in a zener and it will act like a "hard clamp". Until of course the zener burns. Also possibly U2. So it is like a protection, but not really.

It seems to me, that the designer of this board "wanted to do good", but the result was "as always"

[Mandarin47]

I was just looking at the connector and that pin and the pin beside it are blank. I was at a loss but my 10 yr old son just told me that he was watching what I was doing, probing the circuit and he touched some of the pins with a lead from the psu when I wasn't there. So I guess thats that mystery solved. I've ordered the diode and the resistor so hopefully the microcontroller won't be damaged.

[Mandarin47]

But there was still a problem with the the circuit before the component was shorted which is why I was looking in the first place. Only the parking lights worked, the hazard lights would stay on, the brake lights would light a test probe but not a bulb (it had 13V @ 0.04A on the pin) and the fog lights never worked.

[Manul]

Was it behaving differenly after your son touched that pin? Or you just noticed burned diode and nothing else was strange? Maybe it survived after all.

It is almost impossible to have that resistor shorted. Did you remove burned diode before testing resistor?

[Mandarin47]

When I started testing it again before I spotted the blown diode, the parking lights worked but there was no voltage on the brake pin (this had 13V@0.04A before the diode was blown). Thats when I looked at it again. The fog light pin never had any voltage. Just to be clear about the hazard lights,when I originally connected the trailer the hazard light on the trailer stayed on (wouldn't flash) . When I probed the pin when it was connected to the car the voltage was up and down on the pin (2-12v). I can't simulate that on my bench but when I connect a 12V signal to the hazard input pin the output pin lights a bulb. It did this before my son got near it and it still does it.

[Mandarin47]

No, I tested the resistor on the board. I thought it was strange too that it seemed shorted but my experience is very limited

[Manul]

Off topic: my father was an electronics hobbyist and I broke a lot of things for him. But now, after many years, he is sometimes calling me and asking for technical advice. I guess he is not angry anymore

[Manul]

If shorted diode is still on the board, point of its pin 1 is shorted to the ground. Another end of resistor is connected to ground. So it makes this resistor seem shorted. But it can also be U2, because it is also connected to same point. So if you remove burned diode and the resistor does not look shorted anymore - that is good. If it looks shorted - U2 is burned and that is bad...

[Mandarin47]

  If my parents really knew how much stuff I opened and broke when I was small just to see how it worked I'd owe them alot of money  I'm delighted hes taking an interest in seeing how things work

[Mandarin47]

I removed the diode and you were right, the resistor isn't showing a short anymore, its reading a value of 4k7. So I'll just wait now for the diodes to arrive.

[Mandarin47]

Diodes arrived today and interestingly they have M8 printed on them as their only marking. I replaced the blown one an put back the one I removed for testing. The U2 appears fine at least no worse than it was before the damage. The hazard and parking lights work as before but the brake lights now work too. Before there was only 13V @0.04A on the output pin but now there is enough to light the bulbs (13V@1.4A). The fog lights started to work intermittently. After testing all the other lights I tested the fog lights and it worked. I turned off the PSU and turned it on again and now they didn't work. After a bit of testing it seems that the fog lights will work after I have had either of the hazard lights turned on (they don't have to remain on). Its as if the relay for the fog light gets energised by the hazard lights and remains closed as long as power is provided to the input pin of the fog lights. As soon as I remove the power from the input pin I hear the relay click off so I have to repeat the process again. I attached the board to my car and the same thing happens. However what I did find out by mistake is that with an input to the fog lights and an output to a bulb, if the fog lights output shorts to a hazard output the fog lights will work. There is 0.5V on the hazard output pin when not in use.

[Manul]

I'm not sure, but it may be that low current output you measured is the result of module just checking if the bulb is not broken. Like a car computer does that, when you turn on ignition. It gives low current to all bulbs to check continuity. In that case it is not a failure. Also it rises a question, just how sofisticated is this module? Maybe it does not work correct because it is sensing some fault?

[Manul]

The best I can suggest is to go methodically and check things. Because at this moment it is really hard to say, what is wrong with it.

[Mandarin47]

I have done some probing and this is the schematic of what I have found so far

[Manul]

Check voltages on D5050 outputs (idle state without any inputs to the module). Also there is 1K resistors on the inputs of D5050, this is the control signal to D5050. When it is high (~ +5V) the output of D5050 is switched to +12, and when it is low (~0V) output is disconnected from +12. Check what are voltages on these resistors and check if any of them gives noticeably different voltage on different sides of resistor.

[Manul]

Also noticed something suspicious. Is it a solder piece shorting two upper pins? Board should be checked good, maybe use compressed air and some soft watercolor brush for artists.

[Mandarin47]

Everything was fine with the resistors, same 5V on each side and the D5050 outputs was 12V. Theres no D5050 going to the fog lights output, only a relay, so I'm trying to trace the connections to the relay now. Would you have any idea the part number of the relay so I can see what pins are what? I've googled the BD-SS-112d but can't find a pinout for it. I'm wondering like the M8 diode does the relay have a different part number.

[Manul]

I don't know much about relays, but a quick search gave me this:

[Mandarin47]

I looked closely at the board just now and whatever that is in the picture is no longer there but the board still acts the same. I was hoping that was the problem 

[Manul]

Datasheet

[Mandarin47]

Thanks so much for all your help with this so far and finding the correct diodes for me. You've been a great help. 

[Manul]

Just having some free time and fun By the way, are you 100% sure, that wiring is correct? Also, have you checked all diodes and transistors with multimeter for voltage drops and resistance? It can reveal some suspicious components. They do not always fail with a burn mark. Of course it is to some extent hard to judge while they are on the board and connected to other things. In that case comparing them to others, which are connected in a similar way can give useful observation. For example on the lower right side of board there are 4 copies of identical circuit blocks which can be compared to each other with a diode test mode on differerent points and polarities.

[Manul]

What I often do with a diode test mode is to connect negative multimeter lead to board ground and go through points on a circuit. Then I connect positive lead to board ground and also go through circuit points. This relative to ground and both polarities measurement and comparing similar points (like multiple similar microcontroller inputs) is often revealing suspicious things.

[cs.dk]

The fog lights started to work intermittently. After testing all the other lights I tested the fog lights and it worked. I turned off the PSU and turned it on again and now they didn't work.

Some cars have a switch in the trailer connector, it'll disable foglights on the car, when a trailer is hooked on. The switch (or wiring) could be the problem.

[Mandarin47]

Hi, thanks for your suggestion. There is a switch in the trailer module as I has to cut the wire for the fog lights in the car and attach 2 wires from the module to it. One of these wires is the input pin for the fog lights and the other appears to be connected to ground. I also read that the circuit might have to have a proper load on it for the switch to operate so I got 2 car bulbs to test the circuit inside my house. I also connected the module back to the car after I fixed the burnt diode (just incase I was not giving the module the correct inputs) and it still would not light the fog lights.

[Mandarin47]

The wiring is fairly simple, one ground wire, one plug and the 2 wires for the fog lights. I have attached the ground to a ground wire that is bolted to the car body so thats ok (alot of people online suggest grounding issues for faults with trailers), the plug connects directly to a an empty socket in the car and the fog light wires connects to the wire I cut. I will have to go through the circuit like you suggested as I can't see anything obvious.

[Mandarin47]

Hi again Manul. I haven't had much time to work of the module but I have done some tests. There are some components on the board that seem to be transistors because they are marked with a "Q" but the don't measure like transistors. there's nearly a voltage between all the 3 pins on them no matter which way I have the positive and negative test leads.
I have also included a schematic of part of the circuit with some voltages at certain points. In test one I connected an input to the foglight input and again there was no output and I recorded the voltages.
In the 2nd test I again had the foglight input connected, but what I haver found is that if I connect one of the hazard lights and its illuminated and I then connect the 14v to the foglight input, the fog light bulb illuminates. I have also these voltages recorded. Can you take a look and see if you can spot anything. What I did find odd is that in the 2nd test when the fog light is illuminated that the ground voltages are -22mv- -34mv. I would have thought these would have been zero throughout.