16 replies to this topic

[cal844]

Hiya folks

I've been asked to source a replacement 5AS module (clips onto top of brake servo) on an SPI mini.

The owner has replaced the alternator after the old unit failed. Once replaced the car started and run well, then a sudden burning smell and smoke from the 5AS unit.

I was given the unit with the case unfastened. Here is my initial issue....



The red wire runs from lower left terminal (viewed looking at the connector end) to a diode or resistor next to the Front Left relay (again viewed from the connector end). This has been repaired previously and the soldering looks professional.




Apologies for the poor quality image, couldn't get my phone to focus.

The small brown diode (located between the small connector block and left hand relays) has a small area of melting but no blackening, presumably from the previous repair.


Is there any way I can test this unit with a power probe or multimeter?

Can it be repaired, or would it be easier to replace?


(ADMIN, I'd posted here to get a more general opinion, please move of needed)

Thanks and kind regards

Cal

Edited by cal844, 21 April 2020 - 06:17 PM.

[RustyAutoCityE]

If it was me, I would start by checking the continuety of all traces, especially since it has suffered corrosion before, that the red wire has repaired.

 

The I would check the resistance of the brown resistors against what they are rated at (Can't make out the colour code from the pictures).

 

Then the diodes to see if any have failed.

 

Also check the relays are free to move, if one is stuck it might have caused the heat/smoke.

 

Is that all there is to the board? No logic on the back?

[cal844]

If it was me, I would start by checking the continuety of all traces, especially since it has suffered corrosion before, that the red wire has repaired.

The I would check the resistance of the brown resistors against what they are rated at (Can't make out the colour code from the pictures).

Then the diodes to see if any have failed.

Also check the relays are free to move, if one is stuck it might have caused the heat/smoke.

Is that all there is to the board? No logic on the back?

I can get the resistor colours and also the diode colours, I assume you need main and trace colours that are around the body of them?

I assume I just need 12v and an earth to test each relay?

I will post a picture of the back of the board to confirm, and I will try to list the colours on each resistor and diode.


Thanks for the help

[RustyAutoCityE]

No worries, hope I can help even if it is just a bit.

 

If you put up all the colour bands in order that they appear on the resistors, the value can be worked out (one band will be a tolerence value, possibly gold).

 

Any writing on the diode as well, in case it has failed and you want a replacement.

 

With the relays, rather then powering it up just give the little copper arms a poke and see if they are free of the contacts. It is porbably the angle of the picture, but the bottom right one looks like it is stuck closed?

[cal844]

Are these any better?

Diodes


Rear of board



To my untrained eye all factory solder looks good, the additional wire (bypassing water corrosion) is fairly strong too.

Do I just test the resistance test the circuits, then apply voltage and earths as per the diagram on here?

Thanks

Cal

Edited by cal844, 21 April 2020 - 08:43 PM.

[RustyAutoCityE]

Do you have a multimeter with a diode check/continuety setting (makes a beep when you touch the probes)? Use that and go point to point on all the traces, between the components, to make sure everything is still connected.

 

I can only see the one Diode (the black and silver part), the rest look like Yellow-Violet-Brown-Gold resistors (470 Ohm 5%+/-), you should be able to check them in circuit with a meter.

[cal844]

Do you have a multimeter with a diode check/continuety setting (makes a beep when you touch the probes)? Use that and go point to point on all the traces, between the components, to make sure everything is still connected.

I can only see the one Diode (the black and silver part), the rest look like Yellow-Violet-Brown-Gold resistors (470 Ohm 5%+/-), you should be able to check them in circuit with a meter.

I dont own a meter but I can borrow one, I assume I resistance check the ciruits with the resistors

I'm new to all this control unit testing, however with guidance I will give it a go.

Thanks for all the help, apologies for the basic questions, I dont want to cause damage as the unit is a friends and is expensive new if I damage it.

Cal

[KTS]

Is the owner certain the smoke was from that unit ? From the photos there doesn't appear to be anything suggesting any heat damage or discolouration

Does it smell burnt ?

[RustyAutoCityE]

Honestly seeing the back of the board there is not much you can damage there, it looks like all the control is done by the external ECU, there is no logic on that board at all.

 

To do any sort of troubleshooting you will need a Multimeter, even a cheap one will do (just make sure it has a continuety buzzer, makes it a lot easier).

 

You will need to set the meter to resistance (one step up from the resistance you are testing, in this case 470 ohms, so it would probably be 2000 ohms) then just put one probe on one leg of the resistor, and the other on the other side and see if the meter reads 470 ohms +/- 5%. If it does, that part is good. If not, either the part is bad, or you will have to clean up the legs to make a good connection.

Edited by RustyAutoCityE, 21 April 2020 - 09:01 PM.

[cal844]

Is the owner certain the smoke was from that unit ? From the photos there doesn't appear to be anything suggesting any heat damage or discolouration

Does it smell burnt ?

No burning smell from the relays, the ecu seemed to have damage to the tracks in the board and a small amount of damage to one resistor but we will find out tomorrow

[Bobbins]

Cal, the unit you're looking at is not the 5AS, it's the MFRU (Multi Function Relay Unit) which is basically an assembly of relays including for the starter motor, lambda sensor and fuel pump. They're pretty rugged but the relays are quite small so failure is usually based around one of the relays no longer working. If you have overheating from the unit I think you need to investigate whether you have something else that is causing a short circuit. Has the alternator definitely been connected correctly?

For info, the 5AS is a rectangular box of similar size (but thinner) and is associated with the immobiliser.

Stu.

[cal844]

So upon further inspection of the unit I cant see any burnt tracks, the diode and resistors look ok but I will get a multimeter and check the circuits

[GraemeC]

Isn't it normally one of the pins in the connectors that burn out on these?
I'd check there (and the corresponding plugs in the loom)

[cal844]

Isn't it normally one of the pins in the connectors that burn out on these?
I'd check there (and the corresponding plugs in the loom)

I'd had a brief conversation this morning, the main relay had burnt contacts so the owner had tried cleaning it up but it still didn't work so I think I'll order a new unit

[GraemeC]

I have a spare SPI one if it would help?