Sunday, December 07, 2008

Video iPod won't charge via USB, won't turn off from Rockbox

I've decided to document this problem because I've seen it several times on the Rockbox Forums.

This applies to Video iPods (5th or 5.5 generation). The symptoms are constant detection of USB power, inability to charge via USB, and inability to turn off from Rockbox.

USB power management and battery charging is done via an LTC4066 IC. The USB power part of the IC may fail so that USB power cannot be used and power is output via the IN pin (#9, 3rd from the left on the bottom). This causes the USB power input to stay at a few volts when nothing is connected, which makes other circuitry detect that USB power is present. This voltage can even be measured from the end of a USB iPod cable. This is an easy and non-invasive check which could be done first.

The iPod cannot stay off because false detection of USB power turns it on. The original firmware's "off" is actually sleep, so that still works. When Rockbox tries to turn off the iPod, it restarts.

There are several things which can be done about this:
  • Use the original firmware. Its off is sleep, and sleep is still possible.
  • Cut the trace leading to the IN pin of the LTC4066. This is what I did. The power output from the IN pin doesn't get to the USB power detection circuitry, so it's possible to turn off from Rockbox.
  • For power while connected via USB, use a USB+FireWire cable and a FireWire charger on the FireWire end. (For example, here are some cables at Amazon.)
Other possible solutions I've thought of are:
  • Replace the LTC4066. I thought this was too hard because there is a large solder tab under the chip for heat sinking and there are very tiny parts very close to the chip.
  • Cut the trace and connect a diode from the USB +5V input to OUT of the LTC4066 to restore USB charging ability. I wanted to do this but there wasn't enough space for the diode. I also had some concerns about voltage drop and the diode's heat dissipation.
  • Short the USB +5V input to ground when not using USB, eg. via a modified dock connector. It should be easy, but would waste power. I didn't try this.
  • Replace the motherboard.
  • A purely software workaround which allows Rockbox to shut down the iPod. In firmware/drivers/pcf50605.c, pcf50605_standby_mode() sets conditions which turn on the iPod. Removing the condition relating to USB charging, probably CHGWAK, would allow the iPod to stay off, though FireWire charging might not turn it on either. But be careful, because according to the comment, it is possible to turn off the iPod in a way that requires disconnecting the battery or waiting for it to discharge (a month or more I guess).
Here is a photo of the front an iPod motherboard with a blue circle around the LTC4066 and a red line showing which trace needs to be cut and suggesting a location for the cut. (Click on it to see the full-resolution version.) Note that the wheel has been swung away and that the wheel's ribbon cable passes right below the LTC4066.

Here is a closeup of the LTC4066 area. Remember that this is a small part of the iPod, and what you see here is actually very tiny.
(Both images are from another iPod which doesn't have this problem, which is okay because the LTC4066 doesn't have to look any different when it fails.)

10 comments:

Anonymous said...

Hello Boris-

I just installed Rockbox on my 80gb Video iPod yesterday and loaded several FLAC files onto it to verify that everything was properly installed and working. Upon returning to my iPod about 12 hours later, I discovered that it appears to be dead and won't charge. I assume that I've encountered the same problem that you've documented here. I was hoping to verify several things with you before I decide to dissect my iPod. How should I "cut the trace" that you've indicated? Do I simply use a hobby knife or is there a more appropriate technique? Do I understand you correctly that after I cut this trace I should be able to charge my iPod but only via a FireWire port?

Thanks,
Craig

Boris Gjenero said...

Yep, a hobby knife will work. Be careful, just cut the trace and don't cut deeper into the board as that may get to other layers. I cut via multiple light passes instead of applying enough force to cut the trace in one pass.

If I was in this situation right now, I would try the pcf50605_standby_mode() change I described.

tiredtonto said...

It's worth adding that if your iPod refuses to go into Disk Mode and you hear a noticeable clicking sound, it's likely a faulty hard drive. If the unit is a Fourth Gen, however, the problem might just be corrosion on the HDD cable and will need cleaned periodically. Good luck & I hope this helps.

ipod wont turn on

Anonymous said...

Awesome! Just did it and my friends iPod works again. Good call on that IC messing up. All the problems it was having made sense after reading this. Thanks again!

The Overworked Barista said...

I found this elsewhere and was wondering if the ipod would then receive too much power or if it would stay regulated enough in the firewire mode.

"As long as there is power available from the USB port, the port powers the iPod not the battery. If the battery needs charging, it will charge while USB powers the iPod--mostly.

Here are the gory details: Battery charging and iPod power is controlled by an integrated circuit from Linear Technologies. Older iPods used the LTC4055. The 5G and Nano use the LTC4066. They are similar, I think.
Linear Tech doesn't let you easily see the LTC4066 data sheet. Both parts have similar pinouts so I think it's safe to assume the 4066 works much like the 4055. I think Apple might have a hand in suppressing the data sheet because the Wolfson CODEC data sheet isn't available either. GO figure--anyway...

The USB specification allows 500mA (half an Amp) to be pulled from the port. The LTC4066 manages that current so that the iPod power and battery charging current never exceeds 500mA. So... most of the time while USB power is available, it powers the iPod. If you get a high current spike like when the HDD spins up, you may have to pull some of that peak current off the battery.

The LTC4066 also monitors the battery charge state and temperature. When the battery is charged, it quits supplying juice to the battery so it's OK to leave your iPod connected to a USB port indefinitely without damage to the battery. That's my engineering view of it for what it's worth."

Boris Gjenero said...

FireWire charging is as safe as USB charging. The iPod is designed for that.

FireWire input voltage can vary widely, so it is first stepped down to around 5V using a switching power supply. Then, that gets to the LTC4066 chip, and charging is regulated in the same way. The USB power and battery charging parts of the LTC4066 are functionally separate. The charger does not depend on the USB current limit.

The data sheet for the LTC4066 is available: http://cds.linear.com/docs/Datasheet/4066fc.pdf

The iPod never uses 500 mA, even when the hard drive is spinning up. So, if 500 mA is available via USB, the iPod shouldn't need battery power. Maximum charging current plus maximum power used is more than 500 mA though, so charging can slow down while the hard drive is being used heavily.

Stelly said...

Here's the thing, though. I first used Rockbox almost 3 years ago and, just within the last year, I've been having issues not unlike everyone else here. Would it be safe to say that it is a software issue and not a hardware one?

Boris Gjenero said...

This hardware problem can be checked for independently of Rockbox. USB charging didn't work in the original firmware. The battery indicator in the original firmware sometimes showed the iPod is on external power when it wasn't. Also, I could measure voltage on the +5V line at the end of the USB cable when the cable wasn't plugged into a USB port.

wes said...

I cut the trace as described and my iPod will still mot charge I don't know what to do now.

Boris Gjenero said...

The trace cutting is only to fix the inability to turn off the iPod in Rockbox. It won't re-enable USB charging, and in fact, it creates an interruption in the circuit used for charging.

You can still use FireWire charging. When using USB for data, you can use a Y cable with the USB end connected to a USB port and the FireWire end to a FireWire charger.

If you really want USB charging, the only sure solution is replacing the LTC4066 chip. Alternatively, maybe you can connect a Schottky diode between USB +5V and OUT of the LTC4066 chip. This is just a theoretical idea; I never tested it.