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Scope for Diagnostics
Posted by
ehcaes
on 14 Sep, 2011 09:01
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Looking at using a scope for diagnosing PC hardware, as a way of providing better and more efficient service to my customers and also for hobby use.
Can they be used to determine if a CPU or Motherboard is bad? What else can they test?
Given current CPU speeds does this mean I would need one with a bandwidth of at least 3.5ghz,and at whatever point in the future when faster clock speeds come out it wont be good for CPU testing? Think this would be a great thing to be able to do but as you can tell I don't know much about them to determine if It would be a feasible option. sure if it could find problems with a BGA slot great but if that means I then need a BGA rework station one thing just leads to another....
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#1 Reply
Posted by
alm
on 14 Sep, 2011 13:16
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How much labor do you spend on a $100 mainboard? Parts exchange is by far the most economical option. PCs are way too complex for component level troubleshooting. For example, I once encountered an issue of a mainboard not having enough decoupling on the reset pin of the CPU, resulting in a too high noise level, triggering a reset once in a while. Do you plan on probing those 775 (or 1155) pins to find it? Can you even get the proper documentation without NDA? Can you get spare parts in reasonable quantities?
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#2 Reply
Posted by
bullet308
on 14 Sep, 2011 14:11
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IMHO, about the only thing that is practical/cost-effective to do with PC mainboard troubleshooting is look for and replace bulged and blown electrolytic caps. All you need for that is a calibrated Mk. 1 eyeball and perhaps a multimeter, not an o'scope.
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#3 Reply
Posted by
ehcaes
on 14 Sep, 2011 14:41
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IMHO, about the only thing that is practical/cost-effective to do with PC mainboard troubleshooting is look for and replace bulged and blown electrolytic caps. All you need for that is a calibrated Mk. 1 eyeball and perhaps a multimeter, not an o'scope.
I would beg to differ that you can always identify a bad cap by its bulge. Wouldnt say they have to bulge to be bad if in early stages. I do stand corrected if im wrong.
How much labor do you spend on a $100 mainboard?
How long is a piece of string? Motherboard prices vary.
Sure parts exchange can be economical, not always however, for example if I find a busted cap how long is it going to take to replace that vs order and install a new board. its also difficult to have a spare i7 990x to do a swap to determine whats gone bad as rare as it is that a CPU fails.
Can you get spare parts in reasonable quantities? Possibly, however a scope would give me the ability to repair old and difficult to source equipment, sometimes as well people cant wait for parts to arrive. I once had a customer with an old dell and an old form factor PSU I could only source from overseas the weight of the thing alone would have cost a fortune in freight. I didn't have the tools to diagnose the PSU properly. So had to sell him a new PC less his hdds/optical.
Just after a general idea of the whole scope of things really. Another reason is this allows you to offer an extra service to your customer whether it be the quicker turn around, nice diagnostics,. If nothing it lends your business an extra layer of credibility. Something I strive to do.
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#4 Reply
Posted by
dimlow
on 14 Sep, 2011 21:44
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You seem to have convinced yourself its the right thing to do, go ahead and buy a 3.5 GHz plus scope and shout to your customers you have one, to get the extra sales. Also please send me your contact details so that i can call you in a couple of years when the scope has gathered lots of dust, i will be due for an upgrade by then.
Sure scopes are handy, but really, not for what you are doing. I was IT manager for 15 years for several large company's, never once did I or my engineers need a scope, if you're having to source parts from overseas because you don't have a supplier, you need to expand your contact book, not waste silly money on toys, cos that's all a scope will be for a pc repair engineer.
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#5 Reply
Posted by
Psi
on 15 Sep, 2011 00:32
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I've been doing quite a lot of capacitor replacement on the pc motherboards in airport XRay machines.
The XRay machines here use a typical consumer grade computer motherboard and the caps are all failing. It's mostly due to the fact that the boards were never designed to be used 24/7 for 5+ years (some of them are 10 years old now). Some of the xray cards are ISA and buying new boards with ISA slots is almost impossible so replacing all the capacitors is a cost effective repair.
Takes around 2 hours to replace them all with solid caps.
I don't bother testing the caps, we replace them all, even if only 1 looks bad.
Only test I do is a quick DMM probe to make sure there isn't a short after soldering.
If testing the capacitors was necessary i'd probably buy the peak ESR meter.
There really isn't a need for a scope, although i did use the scope once in the beginning to check that the ultra low ESR of solid caps didn't cause any unexpected issues on the supply rails.
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#6 Reply
Posted by
alm
on 15 Sep, 2011 01:07
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The XRay machines here use a typical consumer grade computer motherboard and the caps are all failing. It's mostly due to the fact that the boards were never designed to be used 24/7 for 5+ years (some of them are 10 years old now). Some of the xray cards are ISA and buying new boards with ISA slots is almost impossible so replacing all the capacitors is a cost effective repair.
Takes around 2 hours to replace them all with solid caps.
Note that new motherboards with ISA slots are still being made for exactly this application. They won't sell for $100, though.
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#7 Reply
Posted by
Psi
on 15 Sep, 2011 03:39
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The XRay machines here use a typical consumer grade computer motherboard and the caps are all failing. It's mostly due to the fact that the boards were never designed to be used 24/7 for 5+ years (some of them are 10 years old now). Some of the xray cards are ISA and buying new boards with ISA slots is almost impossible so replacing all the capacitors is a cost effective repair.
Takes around 2 hours to replace them all with solid caps.
Note that new motherboards with ISA slots are still being made for exactly this application. They won't sell for $100, though.
Yeah there are some available but as you say, they are expensive.
They use newer cpus/chipsets and we're not 100% sure they would work.
Currently it's cheaper to just replace the caps than to investigate new boards.
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#8 Reply
Posted by
bullet308
on 15 Sep, 2011 12:14
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IMHO, about the only thing that is practical/cost-effective to do with PC mainboard troubleshooting is look for and replace bulged and blown electrolytic caps. All you need for that is a calibrated Mk. 1 eyeball and perhaps a multimeter, not an o'scope.
I would beg to differ that you can always identify a bad cap by its bulge. Wouldnt say they have to bulge to be bad if in early stages. I do stand corrected if im wrong.
Oh, you are quite correct...I have had dead caps that looked perfectly fine, and I have had boards that had leaky caps all over them and still seem to be quite stable. I have one client that is a private non-profit organization and they take in a lot of donated hardware. The most popular thing for businesses to dump on them are those mid-2000s Dells suffering from the cap plague. Even at an initial price of "free", they are not very cost-effective to recap but I did repair a few of them to fulfill a specific requirement they had.
But what else can you productively troubleshoot? Stuff on the PCI bus? PCI-E is a multi-gHz proposition. Not very much else, I imagine.
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#9 Reply
Posted by
alm
on 15 Sep, 2011 17:17
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Even if you spend the $$$ to measure those fast buses, and assuming you can troubleshoot those complex signals, what are you going to do with that information. Say the ~1000 ball PCH with fine-pitch BGA package is fried, now what? Do you have the technology to replace one? How fast do you get a replacement? AVnet has a minimum order quantity of 450 pieces and wants about $60 each, not in stock, call for delivery. Ordering a new motheboard is both cheaper and faster.
Replacing caps may be cost effective, like in the case of Psi. Just look for the bulging caps in that case, or get an ESR meter. I wouldn't bother for consumer applications, though. If the board is out of warranty, it's not worth spending much money on. Consumer hardware is just too cheap.
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#10 Reply
Posted by
ehcaes
on 18 Sep, 2011 11:20
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Well, looks like with the way the future is going not going to need one for PC repair. Just doesnt seem worth it. Think ill just stick to the old knowledge and experience and get a hobby scope and maybe get one of those uxd phd pci2 diag cards they look pretty awesome. Can test north and south interconnects. Anyone used these? and more future proof and when I realised the $$$ for multi GHz scope
no way. thanks for the helpful replies all. I now remain humbly seated before my audience after having my mind made up I just want one
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#11 Reply
Posted by
EEVblog
on 18 Sep, 2011 12:10
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Looking at using a scope for diagnosing PC hardware, as a way of providing better and more efficient service to my customers and also for hobby use.
Can they be used to determine if a CPU or Motherboard is bad? What else can they test?
In the case of PC motherboard servicing, not much at all, bordering on nothing.
Given current CPU speeds does this mean I would need one with a bandwidth of at least 3.5ghz,and at whatever point in the future when faster clock speeds come out it wont be good for CPU testing? Think this would be a great thing to be able to do but as you can tell I don't know much about them to determine if It would be a feasible option. sure if it could find problems with a BGA slot great but if that means I then need a BGA rework station one thing just leads to another....
As others have pointed out, a scope for testing modern motherboard processor signals is just not feasible, any way you look at it.
And realistically, if you have to ask such a question then it is almost certain that you don't have the very advanced skills needed to accurately probe and interpret such high speed systems to begin with.
The special high speed probes alone will cost many thousands of dollars each, and a 3.5GHz scope CANNOT measure a 3.5GHz digital signal anyway (classic beginners mistake). You could easily spend $50K on such a specced scope and special probes, and it would be next to useless.
An good argument could be made for such testing on very niche and valuable equipment, but general PC hardware - never.
A $50 2nd hand analog scope might be handy for checking basic signals and PSU ripple or something though, and for hobby use you should have one anyway. Or something like a basic Rigol DS1052E digital scope.
Dave.
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Unfortunately pc motherboards are a throw away item, sad but true. The repair costs far outweigh the replacement costs even if you could get spare parts. Some years ago I bought a POST board. It was great at identifying probable motherboard faults but it was no help in repair as you cannot get a new (for example) bios or even the driver chips etc. AS a quick check for a failed MB then it worked ok but thats about it.
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#13 Reply
Posted by
Alex
on 19 Sep, 2011 00:48
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This thread reminded me of this video:
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#14 Reply
Posted by
AlsInd
on 03 Oct, 2011 07:16
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well... when i was doing pc work professionally, i always tested at least the psu with an analog scope. you would be surprised how many of the problems people have with their pcs is power related. there are so many crappy cheap psus that are used in pcs, both major brand and cheapo local junk. our pcs never had the huge problems others did because when i was checking quality of parts in my builds, the scope spotted noisy crappy components in a heartbeat. so... will it help? hell yes it will help. i applaud you for even thinking of it. as far as i know, i was the only one who bothered with this. if more people bothered to check their psus and other components on their pcs, they would be shocked i think. many of the most popular brand psus out there are pure crap. get the scope... you do not need a fancy one. i use an old hitachi which has served for pc and audio work for over a decade.
i have repaired items too but in reality that is rare because it is cheaper to replace the part. but with the scope you will be able to choose better parts.
cheers :-)
al...
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#15 Reply
Posted by
Psi
on 03 Oct, 2011 07:28
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A 60mhz scope worked fine for me when repairing an old 1U SGI rack machine were the cpu regulators had died. Since it was just a 1mhz dcdc the scope was fine for looking at that.
But yeah, you're not going to be able to probe the cpu logic without a 10ghz scope or such.