Continuing on from the Link-Depot sucks + USB debugging post, we know:
- The Link-Depot 4 Port LD-USH-4POW hub sucks. But how bad and why?
- The hub is reporting itself as USB 2.0 capable (Hi-Speed = 480 Mbps)
- In reality, the hub can only ever achieve USB 1.x speeds (Full-Speed = 12 Mbps)
- The hub reports a vendor ID of 1A40 which is reserved for Terminus Technology Inc.
- Suspect that the USB IC is actually High-Speed capable, but the overall circuit isn't
It's got a brand (Link-Depot) so surely it has to be better than an eBay sweatshop special. Oh wait... the Link-Depot brand only shows up on the packaging and no where on the actual hub.
Let's start pulling things apart!
Yuck! I feel dirty just looking at it. Right away you notice that the USB connectors have a shell pin that isn't soldered and the ones that are soldered aren't done very well. And what is that white crap all over the board? Some kind of flux residue? The random drops of solder are a nice touch, but my favorite is below!
I love that R7 actually works! I guess it is only for a simple LED, but MAN is that bad. Hahaha. Actually, it kind of makes me sad to think how fast that person must have been working to make a living.
Like strapping a jet engine onto a car held together with duct tape while driving through a forest...
Sure enough, the circuit does use a USB 2.0 capable IC made by Terminus Technology Inc, but the entire rest of the "USB 2.0" layout is complete hogwash. The PCB is a standard dual sided FR4 board which makes matching the required 90 ohm differential impedance of the data line traces impractical, but they don't even try! The data lines are also way too close together (coupling), there isn't sufficient decoupling / bypassing... this kind of tomfoolery will probably scrape by for lower speed circuits, but there is no freaking way it will work for 480 Mbps! At these speeds, this design is like strapping a jet engine onto a car held together with duct tape while driving through a forest and expecting to break the sound barrier. Hope you have a fire extinguisher for your charred dreams Link-Depot. Here's a document that outlines proper layout techniques.
Let's not forget to mock the solder balls on the 10uF cap's pads and edges [mocking not provided].
No big surprises here: some LEDs, switches, missing capacitors, non-twisted data wires, and a 12 MHz oscillator.
I skimmed the datasheet for the USB IC used (FE1.1s) and noticed that the crappy hub circuit followed the majority of what was written in there so I guess they tried. The datasheet doesn't contain a reference circuit, just a number of what I would call absolute minimum requirements that the hub met. That said, the USB 2.0 IC manufacturer (Terminus Tech) does have a reference board available (shown below).
Night and day difference between the Terminus Tech reference board (shown above) and the shady Link-Depot hub.
See page 4 of this document if you are curious about the operation of the block diagram used in the FE1.1s.
I no longer feel the need to put the Link-Depot hub under an oscilloscope anymore. We know what's going on :P