Hyundai trailer module 5D033 blown component

[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.