OK, so I was wrong about those kernel versions! Very polite of you not to emphasise the point but instead just show me how to proceed. Both machines now on same kernels, 5.4.0-39-generic; the laptop still works fine. Have performed sudo modprobe uvcvideo
on the desktop, with this result now:
uvcvideo 94208 0
videobuf2_vmalloc 20480 2 pwc,uvcvideo
videobuf2_v4l2 24576 2 pwc,uvcvideo
videobuf2_common 53248 3 videobuf2_v4l2,pwc,uvcvideo
videodev 217088 4 videobuf2_v4l2,pwc,uvcvideo,videobuf2_common
mc 53248 5 videodev,snd_usb_audio,videobuf2_v4l2,uvcvideo,videobuf2_common
This seems to be missing a line from the laptop version, but perhaps this is because it's temporary?
However, Cheese still isn't playing - and has this new message:
(cheese:7619): cheese-WARNING **: 12:12:42.592: Failed to allocate required memory.: gstv4l2src.c(658): gst_v4l2src_decide_allocation (): /GstCameraBin:camerabin/GstWrapperCameraBinSrc:camera_source/GstBin:bin18/GstV4l2Src:v4l2src1:
Buffer pool activation failed
As for changing the USB port - well, I'm afraid I didn't because (a) it had worked with 18.3 (b) it's the only easily accessible one on the case. The other is in use for a mouse receiver and round the back is awkward for an item I move around. I have now switched the two case ports round - no difference.
Anyway, here's what happen if I plug straight into a motherboard USB2 port:
Webcam is identified on the new port with lsusb:
Bus 004 Device 005: ID 046d:08b2 Logitech, Inc. QuickCam Pro 4000
Still no result from Cheese:
(cheese:10511): cheese-WARNING **: 14:23:17.811: Device '/dev/video0' is busy: gstv4l2object.c(3754): gst_v4l2_object_set_format_full (): /GstCameraBin:camerabin/GstWrapperCameraBinSrc:camera_source/GstBin:bin18/GstV4l2Src:v4l2src1:
Call to S_FMT failed for YU12 @ 640x480: Device or resource busy
If I use the USB3 port on the desktop's internal card reader, cheese behaves a bit better - no message such the one about setup below. But Cheese still only shows a blank screen or the green screen effect. Zoom sees the camera name but shows a black rectange.
The handy USB3 ports on the monitor never seemed to play with this camera (or some USB2 drives, though happy with most): here's what Cheese says if I try one: 'no device found' on screen. (Zoom doesn't see the webcam at all.)
** Message: 12:50:05.303: cheese-application.vala:211: Error during camera setup: No device found
(cheese:8380): cheese-CRITICAL **: 12:50:05.315: cheese_camera_device_get_name: assertion 'CHEESE_IS_CAMERA_DEVICE (device)' failed
(cheese:8380): GLib-CRITICAL **: 12:50:05.315: g_variant_new_string: assertion 'string != NULL' failed
(cheese:8380): GLib-CRITICAL **: 12:50:05.315: g_variant_ref_sink: assertion 'value != NULL' failed
(cheese:8380): GLib-GIO-CRITICAL **: 12:50:05.315: g_settings_schema_key_type_check: assertion 'value != NULL' failed
(cheese:8380): GLib-CRITICAL **: 12:50:05.315: g_variant_get_type_string: assertion 'value != NULL' failed
(cheese:8380): GLib-GIO-CRITICAL **: 12:50:05.315: g_settings_set_value: key 'camera' in 'org.gnome.Cheese' expects type 's', but a GVariant of type '(null)' was given
(cheese:8380): GLib-CRITICAL **: 12:50:05.315: g_variant_unref: assertion 'value != NULL' failed
** (cheese:8380): CRITICAL **: 12:50:05.315: cheese_preferences_dialog_setup_resolutions_for_device: assertion 'device != NULL' failed
Hope you can advise, as you have so far! Thanks again - feels as though I'm almost there!