Sorry for my terrible english ! - I load a drumgroove and the overdubbing stops at second 25, ... after 1 minute of recording, the recording system doesn't allow me to record any longer

Zoom would be a possible source.

There could be a few different reasons why your keyboard is stopping recording after a minute. Here are a few things you can try to troubleshoot the issue:

1. Make sure that you have enough free space on your device to save the recording.
2. Check to see if there are any other programs or processes running on your device that could be causing the issue. If you have other programs open, try closing them to see if that helps.
3. Try turning off any antivirus software you have running on your device, as it could be causing conflicts with the recording process.
4. Make sure that your device is updated to the latest version of its operating system.
5. If you're using a digital audio workstation (DAW) to record, make sure that you have the latest version of the DAW software and that it is compatible with your device.

If you've tried all of these steps and you're still having trouble, it's possible that there could be an issue with the keyboard itself. In this case, you may want to try contacting the manufacturer for further assistance.

It's doubtful that the LED itself is burnt out, so it's most likely a problem in the circuit. I doubt it will be user-servicable, so take it into the repair shop.

I can totally relate, Tom. Good old multitrack recorders!
This may sound stupid, but you don't have like a slap back delay turned on by mistake, do you? Other than that, I'm afraid I'm not much help.

You can make a backup on your pc and load back Default settings or restore to default settings. Normally you should have I quote ' with up to 49 minutes of mono recording time (or 24 minutes in stereo), the RC-50 can function as a song recorder as well as a looper'

I have the RC300 which has 3 hrs recording time. But when i reach the limit. I make a backup and load back in a initial default setup which I have downloaded somewhere. But you can also restore to default from the unit itself. Hope this helps

With the sensitivity set very high, you might be getting false triggers from static discharges. It sounds like your snare trigger is either bad or possibly the cable from it may have a problem as you should NOT have to set the sensitivity so high.
It will take an oscilloscope to test the pad unless you can find a system to do a sensitivity comparision. The second problem regarding the recording/overdubs I cannot help you solve.

You have to make sure that the clockspeed of the program that you use to play the files back with matches the clockspeed of the program that created them. I might be wrong about that. Here is a good resource:http://forum.recordingreview.com/f18/midi-troubleshooting-101-a-5208/ You will have to join to access but its free and the Killer Home Recording setting up is also free from the site and is full of good info.

This is a common problem with digital recording. Simply put, it takes some time to convert analog (audio) to digital and then more time to convert it back. So, your playback track goes through conversion and introduces some delay. You don't hear this because you have no zero reference. Your recorded sound goes through the A/D converter and also incurs some delay. When you play them back together, you hear the difference in time from one track to another. Most pro recording programs have some method to minimize or cancel the delay like slipping the tracks so they all start together. Pro Tools just introduced a version that automatically does this. They have always had what it called "low latency" monitoring which attempts to keep the "shortest" digital/analog path so overdubs are close enough that we don't hear any issues. So, since you talk about the mixer but not the recording program, I can't tell you specifics but I'd look into the recording program for time alignment settings and options. If you have a manual for the recording program, try to look up latency.

Here is a link for you to look at:http://www.tascam.com/products/2488mkii.html Look under resources to download the manual or a Beginners Guide to Recording.