Volume control not working. Only intermittently can I turn it down,

Hi,

Seems as though you have a faulty Volume Down button.

Here is a link to the Ifixit repair guide for your Kindle.

Kindle Fire HD Teardown

Here is an image taken from Step.16 in the guide. I have highlighted the power/volume button flex ribbon cable to show what it looks like. Obviously you do not have to dis-assemble the tablet fully (as shown in the picture) to access the cable.

(click on image to enlarge for better viewing).

Here is a link to a replacement part (I think - check the kindle model number against yours). It's not a recommendation to use the seller. It is just shown to give an idea of the cost of the part. There are others online that may suit you better.

Just ensure that after you have opened the Kindle that you disconnect the battery from the systemboard first before attempting any further dis-assembly. This is in case you accidentally slip when using any tools. That way at least if you do you will only cause mechanical damage (which may be bad enough) but at least is easier to find than any electrical problems that may arise.

Looking at the teardown image and the spare part, you may only have to replace the orange cable/buttons section and perhaps not the board or the other silver (white?) cable, which should make the replacement even easier.

With the Kindle opened you could also check before ordering any parts whether the Volume Down button actuator is actually pushing the Volume Down button contact far enough. Compare it to the Volume Up. It may be a faulty button actuator rather then a faulty contact. If it appears that it may be broken (as compared to the Volume Up try padding it out with a sliver of paper etc., between the button and the contact to ensure positive action.

Don't forget to reconnect the battery after you have finished and test that it works properly before closing the tablet.

Hopefully this is of some help.