Very low data speed on USB camera

Hello there,

I have a 5 meter long inspection camera bought on ebay (**broken link removed**), getting 30 fps @ 640x480. I was measuring the resistance between D+ and D- while connected (DP, DM in the actual image), just for fun, during which the buzzer of multimeter beeped. I'm suspecting that i touched the tips of probes to somewhere else and/or shorted D+ and D-.

Then i plugged it in and now i'm getting 4 fps max. at 320x240 resolution. The resistance between D+ and D- now is ~4.4Kohm. I know it's way too high and it's supposed to be 90ohm.

Well since i don't want to break the camera head, i can't replace the shielded USB cable. So is it gone forever or recoverable for instance with a ferrite bead?

2072e said:

I was measuring the resistance between D+ and D- while connected (DP, DM in the actual image), just for fun, during which the buzzer of multimeter beeped. I'm suspecting that i touched the tips of probes to somewhere else and/or shorted D+ and D-.

Click to expand...

Just to check if I got the point: Are you saying that you really probed the resistence of the cable with multimeter while USB bus was energized ?

Yes i did
Somewhat it's downgraded to usb 1.1, not sure whether full speed (12Mbits/s) or low speed (1.5Mbits/s)

Now i found out that putting any load, including measuring the resistence, on data pins while working is bad idea.

But since it's not completely fried, i'm hoping to revert it back to usb 2.0 speed again.
I'm currently reading this and this

Here's an excerpt from the first link:

...all high-speed hosts and devices initially operate at full-speed and a high-speed handshake must take place before a high-speed capable device and a high-speed capable host can begin operating at high-speed. The handshake begins when a high-speed capable host sees a full-speed device attached. Because high-speed devices must initially operate at full-speed when first connected, they must pull the D+ line high to identify as a full-speed device. The host will then issue a reset on the bus and wait to see if the device responds with a Chirp K, which identifies the device as being high-speed capable. If the host does not receive a Chirp K, it quits the high-speed handshake sequence and continues with normal full-speed operation. However, if the host receives a Chirp K, it responds to the device with alternating pairs of Chirp K’s and Chirp J’s to tell the device that the host is high-speed capable. Upon recognizing these alternating pairs, the device switches to high-speed operation and disconnects its pull-up resistor on the D+ line

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.

So i presume the problem is that the device doesn't respond with a "Chirp K" thus the pull-up resistor on D+ line is not disconnected, thus the camera continues in USB 1.1 speed.

Actually, i'm not 100% sure if it's USB 2.0. It's what the product description says. So a full speed USB 1.1 can give 30fps @ 640x480?

Just to check if I got the point: Are you saying that you really probed the resistence of the cable with multimeter while USB bus was energized ?

Click to expand...

That's also my understanding. If so, it won't be surprising if either the host computer's USB port or the camera device has been damaged.

The only surprising point is that it seems to be still working somehow. Possibly forced into low speed mode by a defective driver. I don't see how a ferrite bead can heal it.

90 ohms is the nominal USB transmission line impedance, nothing that can be measured with a multimeter, neither in operation nor in unplugged state.

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Hearing that the camera was originally supporting high speed (480 Mbit) USB makes even more sense, because the mode use a second set of drivers and receivers. So there's a certain chance to burn the high speed drivers and keep the low/full speed drivers working. It's surely not only the pull-up resistor...



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Popular misunderstanding, USB 2.0 support doesn't mean that a device is high speed capable. MPEG compressed video can run over full speed USB under circumstances, uncompressed however can't. It should be mentioned in the specification. But anyway, very likely the camera (I presume you verified that it's not the host computer) is seriously damaged. Consider total loss, unless you have a use for a still camera.