JVC HR-S9900U won't stay powered on
 

I've been using my JVC HR-9900U to record tapes to my computer. It was working fine until a while back when it wouldn't stay powered up. Turn it on and it stays on for a couple seconds, then shuts itself off. At that time I unplugged it and came back a couple days later to try it again. It worked fine and I got 3 tapes recorded. It's been a couple weeks now and it's back to turning itself off again. It will load a tape but after that it just shuts down.
Any ideas why this is happening and what it might take to fix it? Thanks.

As a safe guard procedure if certain sensors are not tripped within 1 to 2 seconds during loading, or entering playback or fast forward it will automatically disengage and eject a tape.. or at least power down.

The cause can be from a stretched loader drive belt, or from a main drive belt.. or it can be the "position encoder" for the CAM that moves all the gears in the main drive has become corroded or dirty.

There are too many variables to tell without more information and careful observation.

I believe the JVC model your speaking about had a "special service remote" which could shoot specific Infared signals at the recorder to "Self Diagnose".. it maintained a buffer of the last few Error codes.. which when translated into English would indicate the specific part of the path, or the sensor responsible for safe guarding that "Step" as the one that caused the shutdown.

Sounds like the Dynamic drum to me, You can't fix it as there is no parts for it, You can sell it as is and get a non dynamic drum VCR or disable it according to this thread if you have the skills:
https://forum.videohelp.com/threads/...m-Ultimate-Fix

Thanks for the ideas. It's the strangest thing, but I turned it on this morning and it worked fine. Still am not sure what's causing it to act up but I'm good to go for the time being...

The cracked gear in the DD system has a large gap between the teeth, sometimes it skips it and works fine but when it randomly stops at the gap it's hard to start from that position unless you try several times, It only going to get worse and it will start to loose alignment (the neutral position).

http://www.digitalfaq.com/forum/vcr-...0am-keeps.html

Here's a thread with the same problem and a fix. Although it's a different model JVC, it seems this is a good fix for many models.

It depends on how big the crack, If it's bigger than the gear tooth it will always fail unless the system is disabled by removing one or two gears.