Car Double DIN Stereo Head Unit SD Cards Fighting

[Skezza]

Hello,

Firstly, I'm Joe, I'm a 23 year old software engineer by day (work in Wilmslow near Manchester) and a hobbyist electronics enthusiast.

Basically, my head unit has 2 slots on the front for a microSD and a full-size SD card. The full-size SD card contains the software and maps for the sat nav unit. The microSD card is for music, aka fill up with MP3's and you don't have to carry dozens of CD's with you. The music feature has always been buggy e.g. sometimes you'll listen and then the music stops and restarts from the start of the track. I've always thought it was because of a cheap SD but I'm starting to think there's an electrical fault, especially as the music player is totally independent to the sat nav from a software perspective (And probably hardware), so I doubt they're even sharing the same bus, the only thing they're sharing is the same ribbon cable from the sockets to the board perhaps?

Say I put the microSD first and start playing some music. If I then put in the SD for the sat nav software, the music will instantly stop playing, the software will reset and start from Track 1 on the microSD. Second, say I'm listening to some music, and I decide to load the Sat Nav software (So not even touching the SD card), the same result. It seems that whenever there's a burst of data from the sat nav side of the unit, there's a fault, like the two SD's are fighting, resulting in the music restarting or in one or two cases the whole thing crashing. Now this one has completely stumped me as I've owned dozens of sat nav style head units before and never had this issue with music SD card. If I remove the sat nav SD and just listen to MP3's it'll play all day, won't crash at all. However, if I've inserted the sat nav SD card, and start playing music, it's only a matter of time before it crashes. Sometimes this is one song, sometimes this is two or three, but it will inevitably crash.

So, what do we think? Are the SD cards not receiving enough power to supply the necessary data at the correct speed? Is it a wiring fault, perhaps they're sharing a ribbon cable that isn't able to cope with the amount of data? Alternatively, could it be because I'm using one very fast SD card and one slower SD card?

Thoughts, opinions, and advice would be brilliant.

Thanks

 

[zenith]

Perhaps the head unit can only read one card at a time, try putting all the data on just one card (nav + music) and see what happens.

 

[Skezza]

Hi zenith,

This shouldn't be the case as the device is obviously advertised as being able to read both simultaneously. I've owned many of these before now and this is the first that's encountered this issue. They also don't share the same hardware bus as far as I can tell which means if one is removed, that piece of functionality will be rendered disabled, even if there's music/software on the other SD.
I had a read up yesterday of the instructions and it says it can support up to 16GB in either slot, so I'm not pushing anything there.

I guess it's theoretically possible that size can make some difference on power consumption. I will move the maps over to a 4GB card and see if anything changes. For me, the biggest concern is that being an electrical issue, perhaps the device isn't drawing enough current to operate correctly? Diagnosing this will be pretty hard right? Any tips or things I should look out for?

Unfortunately, the device is out of the warranty period and the company who sells them have a reputation for saying "I'm sorry, it's out the warranty period, but we'll give you a discount on a new one". Worst case scenario I have to put up with it.

 

[Skezza]

After consulting with a couple of experts who work on these devices every day, they are pretty convinced it is probably a voltage drop which is causing the SD card with music on to unmount. They reckon the other side is probably protected by the WinCE operating system which can handle voltage drops.

They think the most likely cause of this is a poor/iffy component on the circuit board. Unfortunately, I have no warranty with the unit. I may contact the company to ask if they'll honour the warranty as a goodwill gesture, but goodwill doesn't seem very common these days.

How easy are these PCB boards to work on realistically? Could I get a multimeter in there and find the voltage drop? Obviously a lot of these components are surface mount. Would putting a capacitor somewhere smooth that out slightly? The voltage is 3.3v. I know there's a ribbon cable linking the SD slots to the board.

Thanks

 

[Harald Kapp]

If it's a permanent voltage drop, you can measure it using a multimeter.

More likely it's a sporadic dip in the voltage which could be detected using an oscilloscope but not a multimeter.
Adding an additional electrolytic capacitor from 3.3V to GND may be worth giving a try. Get a 220µF or 470 µF or 1000µF capacitor rated for at least nominally 6.3V (or more) and solder it between 3.3V and GND using very short leads. Observe the polarity of the electrolytic capacitor.

 

[Skezza]

Thanks for your reply Harald.

It's definitely sporadic, because without a sat nav SD it's perfect, it's only when the SD nav is inserted that we start to see problems. The card runs at 3.3v so I'm wondering how much of a voltage drop there would be, clearly enough for the card to unmount.

When you say put a capacitor between the 3.3v and ground, are you saying snip the 3.3v cable to the SD reader and then wire a capacitor inline (observing polarity of course? Or are you saying merely splice the 3.3v and go direct to the ground. e.g. the casing?

 

[Harald Kapp]

A blocking capacitor as suggested should be placed onto the PCB of the card reader. Presumably you will find at least one capacitor from 3.3V to GND already on the PCB. Connect the additional capacitor in parallel.
In no case must the capacitor be placed inline with the power supply. It will block the DC power supply completely. See this sketch:

 

[Skezza]

Thanks for that Harald. I obviously need to get the unit apart and have a good look, if it's a SMT capacitor what would be the best way of patching in? Would you heat the solder for that component on the board? The big issue will be finding where I can join in parallel. I was reading on the Internet about Arduino's with the same issue and they suggest a >10uF cap? I also read that you can buy specialist 'low voltage' cards. I wonder if that's an option in case it's not possible?

Once I've got it apart I can obviously take some photos and work out what's going on. I've never done this kind of electronics before, I'm used to building guitar pedals and automotive wiring which is noddy compared this kind of stuff

 

[Harald Kapp]

Let's see what you find inside..

 

[Skezza]

Going to take it apart tonight and see what I find. In the meantime, I've found a workaround:

SD card in USB Adapter into the USB input.

Confirms to me the issue is a power drop problem.