Shortest period to switch off electronic equipent for before switching on

You might want to regulate your relatives when they are in YOUR HOME. As you say some things need a few seconds to reset.

My Humax HDR Fox T2 says to wait until you hear the HDD wind down before turning it on again. Otherwise, I generally try to wait for 30 secs. as a rule of thumb, although I'm not always that patient. Not that I have to reset stuff much anyway.

If they're in your home, then visitors work to your rules!

There are two issues here:

On the second point, PVRs, in particular, do not seem to be designed to be really safe to power down at any time, as there is no way of putting them into a soft power down state. You have to make sure that there are no recordings scheduled and put them into standby. On my Humax, you then need to wait until the red light dims

Otherwise, you will be relying on the consumer user defences built into the disk drives ensure that the current write completes and the heads park, and also to recover any logical damage to the filesystem. Even PC's are quite good at this these days, and should never be given a hard power down until a soft power down has completed, unless they have completely locked up and there is no reset button.

On the first point, it depends on the design of the electronics as to how long it takes for all capacitors to discharge sufficiently to put them into a clearly off state. Remember that some devices will detect a warm start by reading RAM, and maximum retention times, without refreshes, are not characterised for dynamic RAM, only minimum ones.

Also the time constants associated with some faults that require resets can be hours.

Where a hard power cycle is needed, I would probably go for about 30 seconds for the first attempt, and then overnight, if the first attempt doesn't succeed.

Of course, you should not need to reset the device this way at all, unless there is a fault, so it is probably something that you should not allow visitors to do at all.

A few days ago, for the first time that I have ever seen, my Humax refused to respond when I tried to turn it on. Neither the remote control nor the big button would make it work. I turned it off with the switch on the back panel, waited some time, probably less than 30 seconds, and then turned it on again. Since then, it's worked fine. The log showed nothing of any use, so I have no idea what the problem was. The unit is now about 4 years old, and was a refurbished unit when I got it, so I have had my money's worth if it failed at any time.

To my young relative 30 seconds is like an eternity. If I advised him to wait 30 seconds before turning equipment back on again, he would never manage it.

However his OFF-ON is so quick that it makes me think on some occassions he could create a power surge.

to

My Humax (old 9200T) will record even when in standby. On the other hand, it sometimes gets stuck and has to be powered down to reset it. And I give it several seconds, but not as many as 30!

Mike.

You can't just lump everything into the same bracket - a lot of people just turn the TV off "cold turkey", its a lot better than leaving it unattended on standby.

Anything with a hard drive can trash a file if you power down in the middle of a write operation.

Some designs of SMPSU can go bang if you switch back on before the reservoir caps discharge and those with inrush surge limiting have a thermal recovery time for no protection - but it just stresses the components a little more than usual. Most user manuals seem more or less unanimous for about 30s.

I have a small low powered solid state stereo receiver. I noticed that things is always using power when it's turned off. A few weeks ago, while this receiver was OFF, I removed the speaker wires to test another amp. I then unplugged the receiver. Last week I put the speaker wires back on that receiver (it was still unplugged). There was a loud pop on each channel when I put the wires on it. (That was around 16 days later). Those caps must hold power for a real long time..... (There is no battery of any sort in this thing).

Another thing, I have an external 56K modem that I use to connect (on dialup). Once and awhile if I shut off connection, later on, I have trouble connecting to the internet. I found that if I just shut the power off to that modem, it seems to reset it and thn it connects fine. BUT. I have to shut it off for about 30 seconds. Just ON-OFF dont work. I assume the caps need to discharge to do the reset....

Most of this is dependent on the carefulness of the design. If power loss or brownouts is given consideration by the designer, none of this is a problem.

There is absolutly nothing wrong with "standby".

Nonsense. There are many ways to design a device that will survive a power failure during disk write. A bit of reserve power is probably the best solution but a JFS works, too.

Only if it's designed by a moron.

Twenty years ago 5 seconds may have caused a problem due to the possibility of surges due to mains input filters.

Often if the switch off is to cold boot crashed software then the internal PSU voltages have to decay. My rule of thumb is 30 seconds after any front panel LED has gone out.

That's why I said you must make sure there are no recordings scheduled!

In my view all devices should have a little pin hole switch that does this for you. It really depends on the device I think. Things like my Smart talk freeview box almost instantaneous resets are OK if done via the little plug from the psu on the back, but if you do it from the mains it needs a little longer as I suspect the wall wart has some capacitors in it.

Phones are awhole other ball of nuts. Some seem to remember crashes indefinitely. there is one which is not out of production where the software crashes and stops the voice from working at all, even if you take the battery out. Sadly as nobody has the gear to reblow the software any more its a brick. Brian

Not many people understand computer shut down via the button either If software has locked up or is doing odd things, then a short tap on the power button, ie NOT the reset is normally the way to get a good shutdown. If that fails, then hold in the power button, NOT the reset button as this normally protects the hard drive from corruption. all these folks wo either press reset or worse, just pull the plug out deserve the reinstall they evenntually end up having to do. Brian Of course if there is a power cut this can happen anyway, and I've often thought of putting in an uninteruptable supply to allow proper shut down. they are not that expensive these days, and laptops of course have one built in. Brian

I suppose anything with disk-like storage (including flash drives) can be trashed if the power goes off during a write, though the time during which the files is in an inconsistent state between data sectors and sector map may be less with solid state than a mechanical rotating disk.

It depends what filesystem they use. NTFS is pretty robust but it requires a licence to be paid to the inventors which is why a lot of PVRs use/read only FAT/FAT32. If they are Linux-based they will be able to use filesystems which are more robust (I'm not very clued up on Linux).

But I'd say that a design which trashes the file that is being written to or the whole filesystem when the power goes off (eg due to a power-cut, which is not totally unexpected) is a bad design: you need some form of resilience in terms of battery-backed supply until the file write is complete and consistent.

I use my Windows 7 PC as a PVR (either Windows Media Centre or NextPVR) and I've occasionally had power cuts during recording. I've never yet lost the recording that was being made or the filesystem of the recording HDD (NTFS). OK, Windows may do a chkdsk repair after the PC reboots, but it seems to sort itself out.

A UPS would be useful for graceful shutting down during power cuts, but it might be more trouble that it's worth. At present my BIOS is set to reboot the PC automatically after the power is restored. If the UPS keeps the power up and initiates a graceful shutdown, the PC may not boot back up once the power comes back.

My wife bought a 3kVA UPS with her big Dell PC about 10 years ago. We didn't get round to setting up the UPS for a couple of years. By the time we did (and after the warranty had expired, inevitably) we found that it had virtually no battery capacity: the battery monitoring software (monitored by USB connection) showed the battery accepting charge and gradually charging up and eventually showing as fully charged, but as soon as the mains was removed, the battery discharged within about 10 seconds with a nominal 40 W lightbulb as the load. Utterly useless, and it wasn't even worth buying a replacement battery for it because the fault may have been in the charging circuit rather than the battery itself. APC didn't want to know when we asked what a repair might cost, so it went in the skip - a waste of money as it was never even used.

Moral of the story: always try any new hardware during the warranty period!

not to discharge totally and if on again during this state, the result is unpredictable.

Thje more the device uses power, the less this time is needed.

Today, it seems that 10-15 s are enough.

For a modem (ADSL or cable) it's OK.

For a LCD or plasma TV too.

To be secure, count on 20s.

That's an economics decision. There is nothing cast in jello that says they have to cheap out, or even use an existing FS. JFS techniques are well known. Even if they do want to use a vulnerable FS, a proper power system design can guarantee a safe shut down.

Exactly so. This is common with flash-based systems. The power system has to guarantee at least the current block has been written.

NTFS?

Always test your emergency system. When I was in IBM, they tested the emergency generators once a month. I have no idea why they had such in the building I was in (just offices and a few labs at that time) but they were there, so the were tested.

It's a really good idea to test your system backups from time to time, too. You may find the restore doesn't work. :-(

Anything that's important has to be tested.

As I understand it, a long press is handled by the hardware and forces a dirty shutdown. If it were handled by the firmware, it could be difficult to shut down a battery powered device which had locked up. RESET should be more gentle than a long press.

Typically, power supplies will not have decayed before any sector write in progress has completed and disks should park. However, you are basically relying on fault recovery mechanisms to protect the physical media, and the low level formatting.

Journalling file systems may protect the basic file structure, but data buffered in user space, and write back caches (OS and device) will not get written and very few application designers will have designed them to be completely safe against partially written files.

Consumer devices have to be tolerant of such abuses, but whenever you start relying on fault recovery mechanisms, for normal operation, you are on dangerous ground.

The office building where I worked had huge diesel-powered generator to cope with power cuts. My office was near it, and I know it wasn't tested during office hours for five years. One day there was a power cut that affected the whole town, and the diesel engine fired up, amid a tremendous roar and lots of filthy black smoke. Power returned for about a minute and then there was a huge explosion and a jet of flames. Apparently the generator couldn't handle the load, even with the engine working as hard as it could (a good diesel grunt!) and something caught fire, igniting the diesel tank. Turned out that it had been specced back in the days when there wasn't a PC on every single person's desk, and it was woefully underpowered for the modern demands that were placed on it.