Thrustmaster T150 racing wheel pcb faulty (no voltage to cpu)

[trez0r]

Hi!

The wheel is not recognized by the pc and does not show any signs of life.

The origin USB 5V and PSU 25V are present but later the voltage "gets lost".

Pins 8 and 44 on the cpu (nxp lpc11u35) which are the VDD do not have any voltage on them.
Retracing back to coil which supposedly converts 24->12V - also have no voltage present.
Also half of the "big" caps at the start of the supply lane don't get any voltage.

By no voltage here I mean nothing much above 0V, there may be something like 0.1V or so, but I don't remember now - I'd have to re-measure to get exact numbers.

Short circuit somewhere? It's a multilayer pcb.
Hoping to get some pointers on finding out / fixing the problem. I don't have a strong background on electr(on)ic stuff, but I can solder and have a fairly good multimeter to work with.

A picture is worth a thousand words - see attachment

Thanks in advance!

[LateLesley]

First step, check the 0 ohm link resistors (all the ones marked FB17 - FB24), you can also check for power at each side of each one.

I've circled the bits to check in Red.

Also I'd maybe check the  Large Diodes around the Caps, D8 and D9, the Diodes next to the coil D2 and D4, and the one at the bottom next to the 2 pin connector (I can't see what this one is labelled)

[trez0r]

Hello!

First, thanks for chiming in!

I checked those resistors you circled and they all came up empty.

I suppose there's no other way to check the diode unless one end is desoldered?

I'll give it a shot later when I have some more time to tinker around.

Thanks!

EDIT:
I checked the diodes and they seem not too far out, please see attachment.
Or is 0.2V considered low for a typical silicon smd diode?

Actually I just looked up their datasheets:

D2/D8 - B260 (SCHOTTKY) datasheet max FVD 0.5-0.7V (https://www.diodes.com/assets/Datasheets/ds13004.pdf)
D4      - B120 (SCHOTTKY) datasheet max FVD 0.5-0.7V (https://www.diodes.com/assets/Datasheets/ds13002.pdf)
D9      - B560 (SCHOTTKY) datasheet max FVD 0.55-0.7V (https://www.diodes.com/assets/Datasheets/ds13012.pdf)

Forward voltage drop specified in chart of the datasheet is a bit higher than the measured even at lowest current at room temp. Not sure what to make of it.
Manual of my multimeter states 1mA is used for diode test. Maybe these readings are on point then at such low current.

[LateLesley]

0.2V does seem a little low, but I think since they are BIG Schottky diodes, they may be fine. Another way to check would be to apply power to the board, and just check the DC voltage at either side of the Diodes in relation to ground. You should see voltage at either side, with a small drop across it.

I'm having a bit of a hard time tracing the circuit, is there any tracks on the underside, as it does look like the board had a lot of via's in it, some of which I'd like to follow, to figure out how the circuit is set up? If you could get a better picture of the left half of the board top and bottom, it might help in tracing the circuit and finding out what's wrong.

I'm also trying to see what the markings are on the 6 pin IC under the inductor L1. I'm wondering if it's a PWM controller for the power, and maybe a feeder resisitor to power it is gone. Could be one of the SMD caps pulling things down too. It's hard to tell without knowing if there is anything under the board.

One wee trick i've seen, is to pour 99% isopropyl alcohol on the board with it powered, and watch for what gets hot, the alcohol will evaporate quicker on hot components. If it all seems ok, then chances are its maybe a feed resistor to the PWM circuitry for the DC-DC converter, or a shorted FET somewhere not switching. At this point, a lot of components are suspect, and we need to build a picture of the circuit, and follow the voltage, to see where it disappears. That narrows down where to look for the faulty part.
 

[trez0r]

Here's a slightly better pic of the board. And a pic showing both sides (on this I haven't yet soldered the diodes back on).
Actually there are more diodes on the underside, I should probably test those too.

EDIT:
Just checked them, they too appear to be fine (one way 0.185V FVD)

In fact I have a simple infrared camera (seek thermal), but the bad news is that I had already used it to watch the board when powered and didn't find any parts reaching excessive heat.
I can take a picture with it if you'd like.

EDIT:
That 6 pin IC under the inductor seems to be a controller similar to this https://www.diodes.com/assets/Datasheets/AP4313.pdf - the ground pin matches that of the diagram. There's no meaningful voltage on any other pin though.

[trez0r]

Attaching  a thermal image of a powered board. The t° delta is just 4 degrees, so basically none.

[LateLesley]

OK. This is gonna be difficult. It's a multi layer board. So we can't see some of the tracks. But we can trace some of the stuff.

Can you power up the board, and with a multimeter, set to voltage, Black lead on ground, Probe the following points, and give me the voltage reading?

either side of FB26, top left of the board, component side.

Reading of the middle and edge pin of Q13 (marked 2A next to the C48 label, top edge of the board)

The reading on D4, near the inductor L1. Right hand side should have power.

This is just testing the initial power rail.

Edit - also just noticed what looks like a damaged component trying to escape, just above the 4 pin connector (D5??) just down from the R53 marking on the board. It needs checking out.

[trez0r]

Here are the readings:

FB26    - 4.929V
D4 R/L - 4.919/4.944V
Q13     - 4.929V (M), 4.233V (L), 4.944V (R)

The suspect you mentioned is a diode - it appears to be in contact despite it being out of position. I added a blob of tin on that end to be sure. It tests out ok - 25.8/25.7V.

Waiting for your input on next things to test. Thanks!

[LateLesley]

OK! So we do have a 5V rail. Now we just need to figure out where it going missing. 

There's a resistor next to the label R25 (E62  on it, next to a Via) , can you check that there is 4.9V on the top pad of that, and can I get the part code off of U2? Just so I can grab the datasheet, it might help me figure out more of the circuit.

[trez0r]

U2 is lpc11u35f see here https://www.nxp.com/docs/en/data-sheet/LPC11U3X.pdf

R25 has 4.94V on pad closest to edge and 3V on the other.

[LateLesley]

ok.... I'm trying to trace the rest of it, and it's now getting too difficult to do with just pictures. pin 44 I suspect is the main power to the chip, but seems to be coming from an inner layer, just below the left side of C17, below the chip. it seems to have C17,C18,C22 and C21 on the powerline before the chip. Can you do an ohms reading across one of those caps?

Can you also check C13 and C16?

And can you clean the solder off the crystal pins, and resolder them? (the two solder joints next to SCLK on the underside of the board) They don't look too clever.

I don't know what tools you have, but you need a solder sucker or desoldering braid, clean off the old stuff, and resolder with fresh stuff.

It is getting hard to help now though, we're into trying to trace layers inside the board, and that's hard to do without having it to hand to probe about.

I'm beginning to think it might be a bad Via, not passing power through. Cos the power seems to get close to the chip, but not actually getting to it.

[trez0r]

C21/22 stop around 1.5 kOhm
C17/18/13/16 all stop around 20 kOhm

That sloppy soldering on crystal is my doing.
When I started this debugging ordeal, I replaced it with another same mhz unit just because someone said they had crystal fail on them in similar wheel.

[LateLesley]

ok.... so we don't have a shorted cap.   I just just looked at the spec's of the chip, it seems to run of 3.3V - so that means there's going to be a regulator (probably a 5V - 3,3V LDO) to power the chip. Thats what we need to find next. I'm going to have a hunt around the board. might be tomorrow before I reply though, I'm kinda tired now.

Edit - OK, VR31 is on my radar, the 4 pin package top middle, Above the microcontroller U2. What's the marking on that component, as I can't see it clearly.

[trez0r]

VR31 is "WR1 63".
I measured it's pins - lower left has 5V, right 0V, top left 0.015V, right 0.019V (top being closer to edge of the board).

About crystal - it appears to connect just fine - it's legs measure connectivity to chip pins 6 and 7 (XTALIN/XTALOUT).

Today I'm going offline till late afternoon, so I'll not be able to give any feedback till then. Again, really appreciate your help (and the debugging is exciting in its own way)!

[LateLesley]

Well, I'm afraid I'm kinda at the end of the road. I can't find the datasheet for VR31, I suspect it is an LDO, but I cannot confirm or get the pinout. It could be a transistor, there's a few different components use that type of package. If it is an LDO, it'll have an enable pin - which I suspect isn't getting powered due to the low readings, and I'm scared to inject 5V, as if we do it to the wrong pin, the microcontroller might get 5V and fry it.

You could try a continuity measurement between the bottom of C16, and the top 2 pins of VR31, that would confirm it's what supplies the microcontroller power. But even then, I can't trace where the enable signal is coming from, you'd need to probe about to find it. And that's assuming it IS an LDO, and not a transistor. I'm getting kinda stuck I'm afraid! Without the circuit diagram, or datasheets, it's difficult, unless it's a simple fault.

[trez0r]

What if we inject 3.3V? Could be easily doable from PC PSU.

Bottom right is ground for that 4pin IC. Top pins measure 6 and 10 MOhm to C16, so not really connecting.
EDIT:
Top pins are actually (L) USB Data (+) and (R) Data (-), lower left is USB 5V and lower right is ground.

[trez0r]

Did some probing.
Almost all of the underside "lone" vias are connected to U2 power supply lanes (C21/C16/etc). Except the two + two marked in picture - those are connected in pairs one to unknown point and the other closer to 4pin power connector - to 26V input.
Do you think it would be helpful to mark all these vias on the front side? If so I'll do it later.

[LateLesley]

OK, so that kinda eliminates VR31. The microcontroller runs off 3v - 3.3v, and that must be getting generated somewhere on the board. So there must be a regulator circuit, an LDO, DC-DC, and Power Management chip of some sort doing it. What you need to do is probe the positive rail side of C16, and/or C21, and find where it is connected to. Hell, even just check continuity on both C16 to C21 to make sure they are on the same rail. If we can find the points where that rail goes, it could narrow down where it's being generated. I'd poke around that 6 pin device under the inductor,  and around U1, and even U3, although it's a motor driver chip, so I don't think it'll be anything to do with it. But it's got to be being made somewhere! It's frustrating when they don't make it easy. :-)

[trez0r]

Ok, I'm pretty sure I marked them all. All the red dots connect. Which makes me think that inductor is actually supposed to convert to 3.3V if it had anything incoming (or am I wrong?).

[LateLesley]

No, I do not think you are wrong. I think we are on the right track, I'm suspecting that 6 pin package. I think the circuit is similar to this :-



The problem is, I can't find any datasheet for that chip. (It is marked BN0U 15? )

In fact, I think the circuit is more like this one -



So, upshot is, I think that's the faulty component, and we either need to find that part, or rig something similar into place. I think what you need to do now, is try and figure out the pinout of that package. Find out what pin is Vin, and what voltage it is, we pretty much know pin 6 goes to the inductor, we need to find the enable and feedback pins. one will have a resisitor to Vin, feedback will have resistors to V out and ground. Probably high value ones.

[trez0r]

It's either BNOU or BN0U (yes, underscore below last symbol) 15.
I couldn't find anything on it in web as well.

I probed that IC and it seems it doesn't get any volts on any leg, so I guess the problem might be somewhere earlier. Also could it be that we are looking at it from wrong direction - as in we expect volts from it to inductor, but in reality it's the other way around (if that makes sense)?
Anyway please see the picture, I mapped the close proximity to that IC (green is ground).

[LateLesley]

NO, I do think we are looking at it right, because the inductor is connected to the powerline for the microcontroller which is 3.3V, and we already know the other two lines are 4.9V and 25V - so if they landed on the inductor, it would fry the MCU.

The fact that you can't find power on the 6 pin IS a problem though, I would have expected to find the 25V there, if not the 4.9V. This could mean it is earlier in the circuit that the problem lies. So now we need to find which pin is the voltage in, and trace that circuit back. I'm guessing since it's at the bottom on the board, it's meant to come off the 25V line. Now if I remember right too, there were two caps with no power too, wasn't there? Can you probe out if either of them connect to any pin on the 6 pin converter? (I suspect pin 5.) In fact, can you find out where pin 5 connects to? I can see it on R42 (which I suspect is the enable resistor) and C28, but there is a Via, so it goes elsewhere. If we can find where, it'll help.

[trez0r]

You remember right. The closest I could find these 2 caps connect to is the driver chip of the motor (diagonal pin to the orientation dot).

I updated the pic with your request on pin5. It in fact is leading to one of those 2 pairs of "lone" vias I mentioned in earlier post.

[LateLesley]

where does the top left of Q10 go? And are you sure about that purple line to the big cap? cos I think it's top edge is ground, and may be something to do with the fault. I'm wondering of Q10 is shorted. That motor driver chips coming on the radar too, I'm wondering if it has something to do with generating the rail. It might be worth poking about its two top left pins, see where those Via's lead it to.

[trez0r]

Q10 checks out and does not short. Top of Q10 goes back to 5V actually (it's more like 4.3V near Q10 though). You are right about ground being at top of that cap, I updated the pic (does it still seem fishy?).  Those resistors on purple line are ~80/100kOhm. Driver's chip's two top left pins go to the diode cluster on the backside (which I think play role in operating the motor).