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Random Black Screens

M

motrek

macrumors 68030
Sep 14, 2012
2,613
305
apple-win said:
No, the equipment in the Youtube video is not an *analog* oscilloscope. Please take a look at 2:43 in the video. It looks like it is Tektronix DSA8300 Digital Serial Analyzer Sampling Oscilloscope.
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This equipment is made for BER analysis(Bit Error Rate) for serial data link.
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By the way, BIOS setup can only do certain things. If this is a CPU timing, RAM timing, or PCI-e timing issue, mini display port should have the same video problem. But many users said that only HDMI has problem.
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Yes, yes, okay, fine, it's obviously a digital oscilloscope that does digital sampling of ANALOG waveforms. That's obviously what I meant.

I don't see the point of looking at a digital signal and discussing how clean the rises and falls are, which is what they were doing in the video, without having any actual discussion about whether or not the signal was stable and correct at the times it was supposed to be sampled by the receiver.

In other words, if the device was made to analyze bit error rate, why did nobody mention whether or not there WERE any bit errors rather than just discuss how pretty the signal looked?

As for my BIOS comment, my point was not that you can change the CPU clock specifically and that might fix the problem. My point was that these signals are programmable, and there's no reason to believe that the timing of the signal coming out of the HDMI port is not similarly programmable. In a previous post you made a comment that seemed to imply that signal timing could not be under software control and I was contradicting you.
 
philipma1957

philipma1957

macrumors 603
Apr 13, 2010
6,365
251
Howell, New Jersey
motrek said:
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As for my BIOS comment, my point was not that you can change the CPU clock specifically and that might fix the problem. My point was that these signals are programmable, and there's no reason to believe that the timing of the signal coming out of the HDMI port is not similarly programmable. In a previous post you made a comment that seemed to imply that signal timing could not be under software control and I was contradicting you.
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you are correct this can be fixed via software/firmware. it was done with the 2009 minis it will be done with the 2012 minis.
 
M

motrek

macrumors 68030
Sep 14, 2012
2,613
305
Mac... nificent said:
Really? That's a $28,000 Tektronix scope, who convinced you that it was analog? LOL :D

The problem with this "cheap as good as expensive" cable myth (started by cheap cable manufactures) is that it doesn’t hold up under scrutiny. One of the things the nay sayers seem to forget is right in front of their eyes, which is while the signal STARTS out as being digital, the cable is still made out of the same material as a analog cable is made out of, copper. When a digital signal is run through copper there is (among other things) lag and the signal becomes minimized and distorted over time. The thinner and cheaper the wire used, the more pronounced the signal errors. The inductance and resistance of the copper also plays a part in this. The end result is washed out color, and what is known as digital blockage and drop outs. If you don't have a way to compare the original signal to what is coming through the cheap cable, then you may feel as they say 'ignorance is bliss' and all will seem fine. You will learn more about this as UHD becomes more prevalent because cheap cables won’t hack it for UHD.
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(See my other comment about the scope.)

As for cables--of course in some rare cases a cable can be so crappy that it can't transmit data correctly, and a more expensive cable might be more durable than a less expensive one, but the point of digital is that as long as the signal has the right value at the right time (with a huge margin of error) it *doesn't matter* if it's ringing, or has distortion from reflections, etc.

Regardless, there's no way a bad cable can give you "washed out colors" with a digital signal. Let's say you have a hypothetical single bit error in an HDMI signal. It will just as likely affect a higher-order bit of an RGB byte as a lower-order bit, meaning the color of a pixel will often be *completely* wrong, i.e., if a pixel is supposed to be green and you change a random bit, it will very likely become black or yellow or cyan, but there's no way it will become "washed out."

If you just have one bit error it will be imperceptible because you have so many pixels and the refresh rate is so high, but if you have constant random flipped bits then it will look like "sparkle" if anything, not bad color reproduction.

Over the last ~30 years that I've been using computers I've made a point of buying the cheapest possible cables for digital signals that I can find--USB cables, SATA cables, HDMI cables, network cables, coax cables for digital signals, etc. Admittedly in a lot of cases the digital data being transferred on the cables has error correction and I wouldn't know if there were a lot of errors, but if the SATA cables I bought for $0.50 from Monoprice can correctly transfer hundreds of megabytes per second, how bad can they really be?

Currently I'm using a cheap Monoprice DVI cable with my Mac Mini which I used without problems for the last ~8 years with a Hackintosh, i.e., no black screens ever. Now I have seen two black screens with this cable and the Mini so I'm 100% certain that the problem is not with the cable.
 
M

Mac... nificent

macrumors 6502a
Nov 20, 2012
943
498
motrek said:
In other words, if the device was made to analyze bit error rate, why did nobody mention whether or not there WERE any bit errors rather than just discuss how pretty the signal looked?
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Because that's precisely how digital signals get corrupted over time.
 
M

motrek

macrumors 68030
Sep 14, 2012
2,613
305
Mac... nificent said:
Because that's precisely how digital signals get corrupted over time.
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Uh, so your point is that if you're constantly bending and flexing the cable it might eventually degrade the signal enough that you get errors? I suppose. Most of my cables go for years without me touching them though so I would be immune to such a problem.
 
M

Mac... nificent

macrumors 6502a
Nov 20, 2012
943
498
motrek said:
As for cables--of course in some rare cases a cable can be so crappy that it can't transmit data correctl
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Sorry, you can't have your cake and eat it too. Either a cheap cable can alter a digital signal, or it can't. Pick one.

there's no way a bad cable can give you "washed out colors" with a digital signal.
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That's a very ignorant thing to say publicly. I take it digital photography isn't your strong suit. LOL :D Your problem is your simplification of what a digital signal is.

I bought for $0.50 from Monoprice can correctly transfer hundreds of megabytes per second, how bad can they really be?
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Price does not necessarily make a cheap cable, build quality does. Actually monoprice has a few inexpensive cables that have fairly good build quality. What you are forgetting is that it doesn't matter how badly the digital signal becomes corrupted, if at the end of the cable the bitstream can be fully and correctly reconstituted - once that information is reconstituted at the receiving end, it's as good as new. But that's a BIG if ...and greatly dependent on how much degradation the signal suffered while being run through the cable.

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motrek said:
Uh, so your point is that if you're constantly bending and flexing the cable it might eventually degrade the signal enough that you get errors?
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Nope, that's not what I was saying at all.
 
M

michael_aos

macrumors 6502
Jan 26, 2004
250
0
I hadn't had many black screens on my new mini w/Thunderbolt Display lately, then I've had 3-4 within the last 2 days.

There seems to be a correlation between system load / heat / activity and the black screens.

I've been copying several TB from my NAS to a USB3 RAID-10 (4x 3TB) array on the Mini (at ~100MB/s). The mini gets hot and the fan ramps up. kernel_task sits around 70% for many hours.

I'm using both the gigabit port on the Thunderbolt display AND the gigabit port on the mini. LACP with an HP switch.
 
M

motrek

macrumors 68030
Sep 14, 2012
2,613
305
Mac... nificent said:
Sorry, you can't have your cake and eat it too. Either a cheap cable can alter a digital signal, or it can't. Pick one.


That's a very ignorant thing to say publicly. I take it digital photography isn't your strong suit. LOL :D Your problem is your simplification of what a digital signal is.


Price does not necessarily make a cheap cable, build quality does. Actually monoprice has a few inexpensive cables that have fairly good build quality. What you are forgetting is that it doesn't matter how badly the digital signal becomes corrupted, if at the end of the cable the bitstream can be fully and correctly reconstituted - once that information is reconstituted at the receiving end, it's as good as new. But that's a BIG if ...and greatly dependent on how much degradation the signal suffered while being run through the cable.

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Nope, that's not what I was saying at all.
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#1 -- Of course you can have a BAD cable, i.e., one that's simply broken. And sometimes cables are made with such poor manufacturing and quality control that they are shipped broken. I would be an idiot to argue otherwise, since every manufacturer occasionally ships a broken product. But in general I am happy to argue that the VAST majority of cheap cables are just as good at getting a digital signal from point A to point B as expensive cables. Given that, it's pointless to buy an expensive cable.

#2 -- I have a degree in electrical engineering and took classes in digital signals and digital signal processing. I told you exactly how errors would affect an HDMI signal and stand by what I said. If you want to contradict any argument I made, then please do so, but don't just state that I'm being ignorant and wave your hands about photography. If you want, I can write a program that will randomly flip bits of an image in any format and you can see the effects of those bit "errors." I guarantee that no amount of bit flipping will give you a "washed out color" effect as you claim. Washing out colors would actually require a very precise mathematical transformation of every pixel in an image and that certainly can't be reproduced with a bad cable.

#3 -- Re: "that's precisely how digital signals get corrupted over time." If you aren't referring to stressing cables over time, then what in the world ARE you talking about? Digital information is either correct or it's corrupted, but there's no state where it gets corrupted "over time."
 
M

motrek

macrumors 68030
Sep 14, 2012
2,613
305
motrek said:
... I told you exactly how errors would affect an HDMI signal and stand by what I said. ...
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Out of boredom apparently, I wrote a program that flipped bits in an uncompressed image of the sort that's transmitted over HDMI.

To prove a point I flipped 1% of the bits randomly... a cable would have to be truly horrific to have this kind of error rate and I bet it actually wouldn't work at all since the handshaking data couldn't be transmitted reliably.

But if you COULD see an image, this is what it would look like. Notice the "sparkles" that I predicted. Otherwise color reproduction is perfect.
 

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philipma1957

philipma1957

macrumors 603
Apr 13, 2010
6,365
251
Howell, New Jersey
michael_aos said:
I hadn't had many black screens on my new mini w/Thunderbolt Display lately, then I've had 3-4 within the last 2 days.

There seems to be a correlation between system load / heat / activity and the black screens.

I've been copying several TB from my NAS to a USB3 RAID-10 (4x 3TB) array on the Mini (at ~100MB/s). The mini gets hot and the fan ramps up. kernel_task sits around 70% for many hours.

I'm using both the gigabit port on the Thunderbolt display AND the gigabit port on the mini. LACP with an HP switch.
Click to expand...

yeah thats right. I had many blackouts running ,prime95 ,cputest and handbrake all 3 programs come close to 99 or 100% of each core. Also long tests of rember ram test made more blackouts.
 
M

Mac... nificent

macrumors 6502a
Nov 20, 2012
943
498
motrek said:
Of course you can have a BAD cable, i.e., one that's simply broken.
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Who said anything about broken cables? The subject is your "theory" that inferior cables are the same as expensive cables. Too bad for you that it's not provable with science, and your opinion doesn't count :)

I have a degree in electrical engineering and took classes in digital signals and digital signal processing.
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Who are you trying to convince, everyone here or yourself, because from what you've said so far I don't believe your claim for a minute. Fortunately this isn't about you or me or anyone else, so back on topic :)

Washing out colors would actually require a very precise mathematical transformation of every pixel in an image and that certainly can't be reproduced with a bad cable.
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Both of your assumptions are not true. I guess in your world there is no binary code for color intensity. Apparently you missed 'school' when they were going over integer numbers and color quantization. Listen, I'm not here to convince you of anything. In the real world your ignorance on this topic will not effect anyone else but you, and I'm perfectly fine with that outcome :)

there's no state where it gets corrupted "over time."
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Amazing.

You claim you went to 'school' but you don't even know how digital works :rolleyes:

If what you claim was true then a digital signal sent over a telephone line would not suffer the same distortion, attenuation and degradation as does a analog signal.

Your theory is easily proven false by simply using a long cheap cable in place or a quality 3 foot cable, and noting the differences in picture quality. The first thing a in-house tech will do when diagnosing picture quality issues is to try a shorter cable. Weird.

BTW, apple-win is right ;)
 
M

motrek

macrumors 68030
Sep 14, 2012
2,613
305
Mac... nificent said:
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Both of your assumptions are not true. I guess in your world there is no binary code for color intensity. Apparently you missed 'school' when they were going over integer numbers and color quantization. Listen, I'm not here to convince you of anything. In the real world your ignorance on this topic will not effect anyone else but you, and I'm perfectly fine with that outcome :)
...
Your theory is easily proven false by simply using a long cheap cable in place or a quality 3 foot cable, and noting the differences in picture quality. The first thing a in-house tech will do when diagnosing picture quality issues is to try a shorter cable. Weird.
Click to expand...

Okay, first of all to address this "over time" nonsense. Yes, it is absolutely true that reflection etc. will distort a signal more across a longer length of cable. You might have a spectacular point if we could magically make cables longer. But where I come from (Earth) you buy a cable of a certain length and it either works or it doesn't. You can't argue that "if you made this cable longer it wouldn't work" because you can't make that cable longer.

Second, as for color intensity, now you are referring to a YCbCr encoding instead of RGB. That's fine, it's the same principle. It's still just bytes representing values from 0 to 1, or 0 to 255, depending on how you look at it. A single bit error can just as easily flip the high order bit as the low order bit, meaning for example that a black pixel can turn white or now a blue pixel can turn green (instead of cyan or magenta). Either way you get sparkles, not washed out colors.

I would run my program to demonstrate this for you but I don't know of an uncompressed image format off the top of my head that's YCbCr instead of RGB and I have to go right now. But if you can send me an image encoded that way I'm more than happy to demonstrate what bit errors would do to it.

If you're going to argue that it's very "convenient" for me that I can't demonstrate this then I suppose I could write my own conversion programs to get between RGB and YCbCr, but really all you have to do is think about this a little. For the colors of an image to change, or a region to change, then every pixel in that region has to change, right? So that means instead of random bit errors you are talking about a very particular error every 24 to 32 bits depending on how many bytes per pixel. How is a cable going to be able to count how many bits come across it and only change every 24th bit? Do you think cables can do math?
 
M

Mac... nificent

macrumors 6502a
Nov 20, 2012
943
498
Good news guys, click on your Software Updater....

Looks like Apple has released a Mac mini EFI Firmware Update 1.7 :apple:

Please try it out and report back how it's working out for you :)
 
A

apple-win

macrumors regular
Dec 4, 2012
226
0
Mac... nificent said:
Good news guys, click on your Software Updater....

Looks like Apple has released a Mac mini EFI Firmware Update 1.7 :apple:

Please try it out and report back how it's working out for you :)
Click to expand...

If it can fix HDMI problem, I will buy a Mac Mini base model to replace my i7 quad core HTPC. :) My HTPC is too noisy. I have an USB TV tuner ready, just need to buy another Windows 7 DVD and an external Blu-ray drive. I have a superdrive (few weeks old), it cannot pop out some DVDs, I have to flip it so that the DVD can drop out.
 
J

jmhart

macrumors regular
Jun 14, 2012
127
0
Mac... nificent said:
Both of your assumptions are not true. I guess in your world there is no binary code for color intensity. Apparently you missed 'school' when they were going over integer numbers and color quantization. Listen, I'm not here to convince you of anything. In the real world your ignorance on this topic will not effect anyone else but you, and I'm perfectly fine with that outcome :)


Amazing.

You claim you went to 'school' but you don't even know how digital works :rolleyes:

If what you claim was true then a digital signal sent over a telephone line would not suffer the same distortion, attenuation and degradation as does a analog signal.

Your theory is easily proven false by simply using a long cheap cable in place or a quality 3 foot cable, and noting the differences in picture quality. The first thing a in-house tech will do when diagnosing picture quality issues is to try a shorter cable. Weird.

BTW, apple-win is right ;)
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No, sorry but you're mistaken and you're just digging yourself a deeper hole the more you defend your position. I've done enough cabling jobs to tell you with confidence that HDMI/DVI/DP signals don't start to break down until you get into cable runs longer than 15-20 feet. Certainly if you use a poorly shielded cable using copper finer than 28AWG then sure it could degrade over shorter runs, but cables that break spec like that are incredibly rare.

When a digital video signal degrades, it does not "wash out colors". That sort of video signal degradation only occurs in analog video signals such as S-Video where you are correct, one of the signals is indeed for color intensity. When a digital signal degrades beyond a certain point, the picture breaks up. Entire macro blocks will be missing and it'll be quite obvious that you're losing data, it won't be anything so slight as a blurry picture or a washed out colors.
 
W

Woyzeck

macrumors 6502
Nov 2, 2012
441
499
Mac... nificent said:
Sorry, you can't have your cake and eat it too. Either a cheap cable can alter a digital signal, or it can't. Pick one.
Click to expand...

Sorry, but I'm holding a communication engineer's degree, too, and your theories regarding digital communication are very bizarre.

HDMI uses sophisticated protocols (TMDS) to transmit a video image that are totally capable of detecting signal errors, including almost any forms of (analog) signal degradation that might be introduced by bad cables, electromagnetic fields etc.
There are several layers of error detection implemented (including parity data) that will be used by the display to detect (almost) any altered data.

The effects of an error rate that is higher than the protocols ability to compensate it are never ever washed out colors, but omitted pixels or lines.

However it's very unlikely that an off-the-shelf HDMI cable of reasonable length will render an HDMI signal unusable. Those gold-plated expensive HDMI cables are for freaks that have no idea about communication electronics.
 
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