Author Topic: Which Oscilloscope to buy for Computer repair  (Read 15978 times)

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Offline dev9393

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Which Oscilloscope to buy for Computer repair
« on: September 07, 2013, 07:24:47 pm »
Hi there to all masters , Sir's actually i am an Automobile engg (32yrs back )For last 1to2yrs i am repairing computers (hobby) and want to shift permanently to this field   , now i want to buy an oscilloscope and i am a big ZERO when it comes to the finer points of electronics .The frequencies used are (1)32.768KHz -South bridge  (2) 25MHz-- Ethernet (3)Audio Codec--24.567 MHz  (4)Clock Synthesizer--14.318MHz  (5)Micro controller--10MHz (6)Embedded Controller--32.768KHz (7)DSP--14.318MHz (8) GPU (MCH+ICH+CLK)--25MHz,27MHz,32.768KHz .I am not taking RAM in a/c.Now i have read that the accuracy of oscilloscope is 1/5 (one fifth) of its band width is it true? AS i am planing to buy Rigol 1102e 100MHZ is it sufficient for above mention frequencies also checking gate signals of Mosfet etc.OR should i get 1102d of which (analyzer )i know nothing.Please advice 
 

Offline Legit-Design

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Re: Which Oscilloscope to buy for Computer repair
« Reply #1 on: September 07, 2013, 08:18:41 pm »
What are you going to repair in computers? As far as I know computer repair is finding the fault and replacing whole modules, replace power supply, replace motherboard, replace what doesnt work since repairing it is going to cost alot unless you work for free or still as a hobby. Normal repair of non functioning laptop is a motherboard replacement. When computer power supply craps out it is just cheaper to get new one, or get a proper good quality psu so it will run for years. Depending where you live repairing something electronics level will not pay, compared to getting functioning part and just replacing it.
Even replacing faulty caps falls into hobby category, I can't see anyone doing it full time and getting good pay out of it.

If you just want to get oscilloscope and tell yourself it's for computer repair, there are already lots of threads discussing about buying proper scope. Rigol 1052E or 2072 seem to be popular and proven themselves in use.
« Last Edit: September 07, 2013, 08:22:52 pm by Legit-Design »
 

Offline amyk

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Re: Which Oscilloscope to buy for Computer repair
« Reply #2 on: September 07, 2013, 10:32:56 pm »
What are you going to repair in computers? As far as I know computer repair is finding the fault and replacing whole modules, replace power supply, replace motherboard, replace what doesnt work since repairing it is going to cost alot unless you work for free or still as a hobby. Normal repair of non functioning laptop is a motherboard replacement. When computer power supply craps out it is just cheaper to get new one, or get a proper good quality psu so it will run for years. Depending where you live repairing something electronics level will not pay, compared to getting functioning part and just replacing it.
Even replacing faulty caps falls into hobby category, I can't see anyone doing it full time and getting good pay out of it.
Take a visit to southeast Asia sometime...
 

Offline dev9393

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Re: Which Oscilloscope to buy for Computer repair
« Reply #3 on: September 07, 2013, 11:41:36 pm »
Hi, I  live in India and here we do not replace  but repair the boards right down to chip level (reflowing,reballing or replacement  of chip),some times it is just a faulty mosfet, pwm chip,  or a SMD (Resistor, Capacitor, transistor, Gates etc) and mother board(laptop or desktop)is working again.So it is necessary to pin point the fault,as the working is mainly of Voltages and Signals,hence the need of an oscilloscope. 
 

Offline Legit-Design

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Re: Which Oscilloscope to buy for Computer repair
« Reply #4 on: September 08, 2013, 12:50:21 am »
My bad, I was thinking everyone lives in a modern western country. Countries where trashbins are just filled with working stuff that people throw away because it's old, noisy and big, so they can replace it with iPads and such.

My sources for parts aren't as good as dumpster room at EEVBlog corporate headquarters, but if I am at the right place at right time, then free working stuff is guaranteed. Also where I live selling reflowed computer equipment is considered grey area, since it might last anywhere from an hour to a year, so it cannot be guaranteed to work and therefore shouldn't be sold. But I can see it has it's place when there is no option, or it literally might cost you a kidney.
 

Online AlfBaz

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Re: Which Oscilloscope to buy for Computer repair
« Reply #5 on: September 08, 2013, 01:10:23 am »
Hi, I  live in India and here we do not replace  but repair...
India and its people would have to be one of the best recyclers in the world, they waste nothing and we should all be following in their footsteps :-+
 

Offline Hydrawerk

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Re: Which Oscilloscope to buy for Computer repair
« Reply #6 on: September 08, 2013, 01:33:56 am »
Hi, I  live in India
BTW I have in my kitchen a great radio made in India. You are apparently good at electronic. It is named Olympia ATS-803A. It was manufactured probably in 1990 and it is still going strong. http://cbradio.cz/hamshack/Scanner/Olympia_ATS_803A.jpg
I still listen to it.
Amazing machines. https://www.youtube.com/user/denha (It is not me...)
 

Offline gibbled

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Re: Which Oscilloscope to buy for Computer repair
« Reply #7 on: September 08, 2013, 05:23:23 am »
Looks just like the Sangean of the same model number and my radio shack dx-440.
 

Offline Hydrawerk

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Re: Which Oscilloscope to buy for Computer repair
« Reply #8 on: September 08, 2013, 08:18:27 am »
Yes, it was sold under many brands.
Amazing machines. https://www.youtube.com/user/denha (It is not me...)
 

Online rdl

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Re: Which Oscilloscope to buy for Computer repair
« Reply #9 on: September 08, 2013, 08:48:21 am »
I have a DX-440 that I bought new back in the late 80s from Radio Shack and a Sangean ATS-803A that I got off eBay about 6 or 7 years ago. I'm pretty sure Sangean was the actual manufacturer of these radios, and both of mine are labeled as being "Made in Taiwan".
 

Offline PedroDaGr8

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Re: Which Oscilloscope to buy for Computer repair
« Reply #10 on: September 08, 2013, 12:46:11 pm »
In india, there was a period where they decided to try to show the world they were self sufficient. Foreign companies had to team up with a local company if you wanted to make or sell anything there. A prime example is Maruti Suzuki. So it is quite possible that this company was the Indian arm of a Taiwanese company and made this in India.
The very existence of flamethrowers proves that some time, somewhere, someone said to themselves, "You know, I want to set those people over there on fire, but I'm just not close enough to get the job done." -George Carlin
 

Offline iceisfun

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Re: Which Oscilloscope to buy for Computer repair
« Reply #11 on: September 09, 2013, 11:55:42 am »
I administrate many servers and assemble/repair/maintain many server class machines

75% of all failed hardware I pull/trash has small faults that I doubt could be fixed, such small things that they are just not usable for anything important and so cheap to replace its too expensive to put a probe to a board, and so complex unless its a power issue you could spend forever just hunting.

Even older stuff is this way, I have a scope and other stuff just for fun though, its fun knowing how computers work and I'm working on a Z80 just for fun, maybe I'll do another one if I have not had enough when I'm done with the Z80 :)

If you want some old broken hardware to trouble shoot I could probably send some, I even know whats wrong with some of it.
 

Offline amyk

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Re: Which Oscilloscope to buy for Computer repair
« Reply #12 on: September 09, 2013, 06:26:08 pm »
Hi, I  live in India and here we do not replace  but repair...
India and its people would have to be one of the best recyclers in the world, they waste nothing and we should all be following in their footsteps :-+
It's much the same for electronics in China. There are shops where you can get your laptop/tablet/phone/etc. reballed and/or parts-swapped while you wait and watch.
 

Offline madires

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Re: Which Oscilloscope to buy for Computer repair
« Reply #13 on: September 09, 2013, 08:03:09 pm »
Hi, I  live in India and here we do not replace  but repair...
India and its people would have to be one of the best recyclers in the world, they waste nothing and we should all be following in their footsteps :-+
It's much the same for electronics in China. There are shops where you can get your laptop/tablet/phone/etc. reballed and/or parts-swapped while you wait and watch.

That's great! I've fixed some mainboards with bad caps, nothing fancy but much better than throwing more stuff on the huge pile of e-junk. Rare earths are so expensive that some companies are trying to figure out to extract them from e-junk. I hope we'll see some change in the future, products built to last and designed to be repairable.
 

Offline flolic

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Re: Which Oscilloscope to buy for Computer repair
« Reply #14 on: September 09, 2013, 08:24:39 pm »
For years I do laptop and game console motherboard repairs on a component level. BGA reflowing, reballing, mosfet, IC, electrolytics change... It's a good money once you gain enough experience and collect all necessary equipment.
 

Offline amyk

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Re: Which Oscilloscope to buy for Computer repair
« Reply #15 on: September 09, 2013, 10:50:24 pm »
That's great! I've fixed some mainboards with bad caps, nothing fancy but much better than throwing more stuff on the huge pile of e-junk. Rare earths are so expensive that some companies are trying to figure out to extract them from e-junk. I hope we'll see some change in the future, products built to last and designed to be repairable.
Those services are available in Shenzhen at the SEG and Yuanwang digital mall, the tradeoff is that you probably won't be getting real name-brand components. And as alluded to above, they really love recycling, so new/unused is not easy to find. On the other hand, the prices also reflect that.
 

Offline dev9393

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Re: Which Oscilloscope to buy for Computer repair
« Reply #16 on: September 14, 2013, 06:27:38 am »
If you want some old broken hardware to trouble shoot I could probably send some, I even know whats wrong with some of it.
     please let me know what .hardware it is????and thanks for the offer :). sorry if my reply is in incorrect format as i am to the forum & do not know how to high light & using the forum.
 

Offline toni31

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Re: Which Oscilloscope to buy for Computer repair
« Reply #17 on: September 21, 2013, 05:01:21 am »
but is a good buy an oscilloscope for pc and laptop repairs
i mean it's useful?
 

Offline analiachester

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Re: Which Oscilloscope to buy for Computer repair
« Reply #18 on: April 04, 2014, 11:21:40 pm »
Seriously, there's not much scope in computer repair, you would not earn enough, especially in India. If you're doing this because of interest then it's total absurd because only money matters in the society. You should contact some tech store who can guide you well,
« Last Edit: April 05, 2014, 03:06:25 am by Simon »
 

3DG4

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Re: Which Oscilloscope to buy for Computer repair
« Reply #19 on: September 08, 2015, 12:14:58 pm »
I know this is a very old thread but, I wanted to share my thoughts on the OP's question.


If you are going to do troubleshooting and repair of laptop motherboards, then an oscilloscope is certainly a requirement. You won't be measuring CPU or RAM clock speeds with a scope in this application. Don't get hung up on all the bandwidth and sample rate tomfoolery that is so pervasive in these types of discussions. ANY analog or digital scope with around 50 MHz of bandwidth (or more if you desire) will be more than sufficient for the task. In my personal experience doing laptop motherboard failure analysis (troubleshooting all the boards that level II repair techs can't figure out) a good 90% of the failures are "no power" issues. In addition to performing voltage checks on the various regulation and startup circuitry with a good multi meter, it is often necessary to analyze the PWM signals coming from the half-dozen or so buck converter driver IC's on the board. In this instance, it's more about determining if a signal is present rather than the parameters of the signal itself. Also, checking for acceptable power supply ripple level on the outputs of the buck converters can only be achieved with an oscilloscope. Another way that a scope is indispensable in this application, is observing high to low or low to high logic level transitions when the power button is pressed. I find it much easier to look at the crisp clear trace on my Tektronix 2465A going from 0V to 3V and vice versa, than watching my Fluke DMM bounce around before settling on a measurement.

Just as a side note, I would like to add that the computer repair industry is far from dead. I work for a very large company that repairs tens of thousands of laptop computers a year. Sure, not all of them are motherboard related issues, but a lot of them are. I think it's important that we try our best to give clear and accurate responses to questions that are posted here. If you don't have experience on a particular topic, don't post nonsense. By doing so you very well may be driving away future generations of nerds like us that have a vested interest in electronics.

 

Offline BradC

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Re: Which Oscilloscope to buy for Computer repair
« Reply #20 on: September 08, 2015, 12:58:58 pm »
If you don't have experience on a particular topic, don't post nonsense.

You've just described 99.99% of "the internet". Wikipedia and Google experts abound.
I agree however.
 

Offline OldSchoolTechCorner

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Re: Which Oscilloscope to buy for Computer repair
« Reply #21 on: September 08, 2015, 02:03:31 pm »
You really don't need Oscilloscope to get into computer repair, it end up more likely becoming a door stop, or expensive paper weight and if you have to ask, then you don't need it.  Learn the basics first. Like how to replace LCD screens on tablets, phones and lvds connectors on mainboard, as with apple laptops to much current on one pin end up melting the connectors and shorting rail to ground, so is a common issue and then people break the power jacks, or USB mini jacks on various devices, so another common issue your come across a lot. Learn how to clone hard drives, or SSD drives and how to remove virus without having to wipe out drive, testing and replacing memory. For component repair, you need basics component knowledge and troubleshooting skill and be able to read and understand schematic diagrams as you se a lot of defective buck DC/DC controller and resistors that go bad on main board. Then you have to know how to check ESR on capacitors and absolutely need a ESR meter to start with, as they use low hour rated cheap capacitors and they go bad in power supplies and motherboards. Not all capacitors will bulge out and vent. That will cover most standard repairs. 

To do most advance repairs at component level, is where you start to making good money,  but you really do have to know what you are doing having extensive knowledge in circuit design and troubleshooting and invest in other equipment and a BGA rework station which is a whole another science to learn, as even for more common issues of crack solder balls under BGA. You have to be able to source new chips, as you can't use old one as substrate material and heat was the issue, using old chip it will just fail again and know how to set temperature profiles for ramp up and down and ETC. So you don't damage and warp board and for humidity control to get a successful replacement of the chip and reball done. One profile is different from another, as a lot of factors you have to consider when creating a good profile. I use to SMD rework by hand with just a heater with glass to use as a preheater and heat gun back before rework stations were popular. and can solder most chip by hand in seconds, took a while and ton of practice to become good and am a EE.

« Last Edit: September 08, 2015, 09:53:21 pm by OldSchoolTechCorner »
 

3DG4

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Re: Which Oscilloscope to buy for Computer repair
« Reply #22 on: September 08, 2015, 02:38:48 pm »
You really don't need Oscilloscope to get into computer repair, it end up more likely becoming a door stop, or expensive paper weight and if you have to ask, then you don't need it.  Learn the basics first. Like how to replace LCD screens on tablets, phones and lvds connectors on mainboard, as with apple laptops they pass to much current end up melting the connectors and shorting rail to ground, so is a common issue and then people break the power jacks, or USB mini jacks on various devices, so another common issue your come across a lot. Learn how to clone hard drives, or SSD drives and how to remove virus without having to wipe out drive, testing and replacing memory.
 

The OP was not talking about sub-assembly level repair of computers. They specifically stated that they were interested in doing component level repair on motherboards. Not every failure leads back to a cracked solder joint on a BGA. I suppose if you were only interested in swapping parts (shotgun troubleshooting) and re-flowing chips at random to try and fix a dead board then the advice you give might hold water. This is not the correct way to troubleshoot electronics. Again, why are we trying to deviate WAY beyond the scope of what the original question was?

understand schematic diagrams as you see a lot of defective buck DC/DC controller..........that go bad on main board.

How do you hope to accomplish this task? By replacing every chip in sight and with your fingers crossed hope that it fixed the problem? You can't substitute knowledge and critical thinking for all the latest whiz-bang technology on the planet. I'm doing my best to keep this constructive but it seems to be to no avail. When I take a motherboard that I've diagnosed to the BGA rework department to replace a chip, I do so with 100% confidence that the part in question is the source of the failure. We need to start teaching REAL troubleshooting again instead of pushing the ubiquitous spray and pray mentality. I mean no disrespect to you sir, but you are painting an all too familiar picture of this trade. As far as not needing an oscilloscope to properly troubleshoot a laptop motherboard, to put it lightly, you're dead wrong.
 

Offline OldSchoolTechCorner

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Re: Which Oscilloscope to buy for Computer repair
« Reply #23 on: September 08, 2015, 02:53:12 pm »
I have extensive knowledge and your just a your typical tech of trade and am a Engineer. So just don't guess and don't use shotgun approach and always narrow down the issue and cause of failure and know that board will work and fix 1000's of boards with various issue to component level and fix much more then just tablets and computers. Yes do have mixed signal scope, logic analyzer and various other lab gear and it needed, but also have the knowledge to be able to use the tools effectively and pretty sure you have the knowledge and training to, but not everyone does and that the point you missed.

It nice to have people learn I just can not recommend to someone just to get a scope, or any piece of test gear without getting the basics down first. Learn how components work and circuit design and troubleshooting first. You just don't buy test gear to buy it, as it then not really a tool at that point and waste of money. I don't want hacks doing repairs and guessing, as get boards all the time that someone attempted repair on and failed. Never do a simple reflow, or clamp trick, or towel and oven trick I see people do for BGA chip repairs, it will not only temporary at best if it does somehow manage to actually work and but more likely destroy the board in the process and more likely won't be repairable again. If someone starting off there also a market for basic repairs as screen replacement, power jacks replacements, data recovery and ETC on the computer repair side. Just won't make as much, as pretty common knowledge and prices of laptops and desktops are pretty cheap and live in a throwaway society.  Now if someone willing to take the time and buy the equipment and learn electronics and troubleshooting to start. Then any a good working analog crow, as they can be had cheap, or digital scope of 50 MHz and up of bandwidth will be more then enough to start with. The Rigol scopes are decent for the money.



« Last Edit: September 08, 2015, 09:54:20 pm by OldSchoolTechCorner »
 

Offline OldSchoolTechCorner

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Re: Which Oscilloscope to buy for Computer repair
« Reply #24 on: September 08, 2015, 04:05:16 pm »
We need to start teaching REAL troubleshooting again instead of pushing the ubiquitous spray and pray mentality.
I do agree with this part and that the point I am trying to get across.
 

Offline feipoa

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Re: Which Oscilloscope to buy for Computer repair
« Reply #25 on: November 13, 2017, 12:21:44 pm »
I am in strong agreement with what the guest named 3DG4 has been proclaiming.  It reminds me a lot of mechanics who just want to replace parts and not diagnosis the real problem.  I have my Master's in EE and nowhere did academia teach me how to troubleshoot something like a motherboard with an oscilloscope.   I do think that this may be where the more specialised workforce comes in, with motherboard repair techs, etc. 

What I find troubling about spending 20 minutes reading this thread is that I came out of it without any additional information as to how to begin troubleshooting a motherboard with an oscilloscope.  Could someone perhaps link a few good self-help tutorials with vivid detail on how to troubleshoot a motherboard with an oscilloscope and DMM?  My particular area of interest is 386/486.  I do have a 386 motherboard I'm working on which shows no signs of life and I have tried all the usual diagnosis steps that I know of, e.g. check for CLK2 signal reaching the CPU, coming from the two crystal oscillators, confirm jumpers set properly, confirm jumpers making contact, confirm PSU working properly, check all SMD solder points for loose contacts, check bottom of board for visible cold solder joints, run the multi-meter across all resistors and caps checking for shorts, ensured the BIOS is working in an identical board, tried new CMOS battery, tested the SRAM in an SRAM tester to confirm it is good, and replaced all socketed chips with know good ones.    The board has no electrolytic caps, and no MOSFETS.  No beep codes are emitted.  I have confirmed the board is setup correctly because I have an identical board which works to compare with.  The board basically has a QFP 206 DMA controller, and what looks like a QFP north bridge (UMC 481), a QFP south bridge (UMC 482), and various other TTL 74F DIP and QFP ICs. 

I'd like to start a new thread about how to troubleshoot this, but first I'd like to get a few recommendations from you experts about some good walk-me-through-it guides to early motherboard troubleshooting with an oscilloscope.  I do have a cheap 100 MHz Ebay-special type of ATTEN oscilloscope which has worked well enough for what designs I needed it for in the past.

Seems like I would need to know a typical 386, early 486-era start-up routine to even know where to begin probing.   Although UMC datasheets are often very hard to come by, the datasheets for the 206 and 481/482 have  been procured!
« Last Edit: November 13, 2017, 12:45:01 pm by feipoa »
 

Offline daybyter

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Re: Which Oscilloscope to buy for Computer repair
« Reply #26 on: November 13, 2017, 02:04:24 pm »
I have no repair experience with 386 boards. Only with older machines. I would focus on the CPU first. Has it ground, power, clock and reset signal? So it should start running then, trying to get data (code from ROM) via the bus.
 

Offline feipoa

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Re: Which Oscilloscope to buy for Computer repair
« Reply #27 on: November 13, 2017, 02:46:06 pm »
Well, the CPU is soldered to the motherboard.  it is an AMD 386DX in the QFP package.  According to the datasheet, revision C1 or later of this chip can be floated by soldering the FLT# to GND.  At present, the FLT# is connected to Vcc.  I was considering cutting the trace which connects the CPU to Vcc, and connecting FLT# to GND.  Once I do that, presumably I can insert any PGA-132 CPU into the adjacent PGA-132 socket (or I can just cut off the whole AMD 386DX). 

However, I did put into the PGA-132 socket a PGA AMD 386DX CPU of the same "D" revision (while the QFP AMD 386DX is still soldered and not floated) and I still did not get any signs of life.  While this test is not entirely conclusive in that the CPU is not the issue, it makes me want to take another direction FIRST before going back to the CPU.

I have 4 of these motherboards.  They all came in a "dead" state.  One one of the boards, one of the 206 QFP leads had separated from the pad.  Soldering it back fixed the board.  On the next board, the jumpers were too worn out and not making solid contact.  Fixing the jumper corrected the board.  Unfortunately, the solution for these remaining two boards isn't so straight forward and was hoping that someone with experience troubleshooting 386/486/socket 7 motherboards could guide me through the process.

I tried to attach a high res photo of board, but unfortunately, the 2 MB size limit of the forum won't allow for detailed viewing of the components.
 

Offline Neomys Sapiens

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Re: Which Oscilloscope to buy for Computer repair
« Reply #28 on: November 14, 2017, 10:29:49 am »
Whatever Scope you decide on, it should have X/Y mode, so that you can get or build a component tester attachment (sometimes called 'Octopus'), preferably one where you have multiple voltage and current ranges and frequencies. It is the biggest repair aid for boards, especially if you know the circuit only partially.
 

Online rhb

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Re: Which Oscilloscope to buy for Computer repair
« Reply #29 on: November 14, 2017, 11:53:50 am »
Take a look at the Good Will Instek website.  They have an India only sales promotion.  The UI may not be very good, but the hardware is quite nice.  Not familiar with these particular models.

http://www.gwinstek.com/en-global/Page/DGS_D_Promotion
 

Offline Neomys Sapiens

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Re: Which Oscilloscope to buy for Computer repair
« Reply #30 on: November 14, 2017, 12:15:50 pm »
Also, when looking at computer (and anything else microprocessor or -controller based) repair and diagnosis, it might be a good idea to look for a so called MSO (mixed signal oscilloscope), which has some logic channels as well.
They can be used (on those instruments I know) not only for display, but also for complex triggering.
 

Offline daybyter

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Re: Which Oscilloscope to buy for Computer repair
« Reply #31 on: November 14, 2017, 05:20:46 pm »
I don't think there is a special procedure to diagnose a socket7 board.
A 386 is a CPU like any other CPU. It needs power,gnd,clock. After a reset signal it comes into a defined state and starts running. It tries to find some code to process by putting addresses on the bus and reading code from there. You can see those signals with a scope or logic analyzer.
 

Offline feipoa

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Re: Which Oscilloscope to buy for Computer repair
« Reply #32 on: November 14, 2017, 09:34:01 pm »
I, personally, am  not looking for a scope and I have started another thread more pertinent to my current goals.   

https://www.eevblog.com/forum/repair/how-to-troubleshoot-your-defective-386486-motherboard-with-an-oscilloscope/
 

Online rhb

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Re: Which Oscilloscope to buy for Computer repair
« Reply #33 on: November 15, 2017, 01:51:09 am »
Something to make for your efforts is a "free run harness"  for the different CPUs.  This a device that can be inserted between the CPU and the MB and forces a NOP instruction on the databus.  This causes the CPU to cycle through all the addresses and will facilitate locating address line problems and bad ROM devices.

Long ago I made one for a 6502 using a socket and was able to locate a blown PROM using a 5 MHz recurrent sweep scope to probe the address lines.  Unfortunately, the replacement part cost so much I wound up buying a new computer instead.
 

Offline peteb2

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Re: Which Oscilloscope to buy for Computer repair
« Reply #34 on: November 15, 2017, 09:11:53 pm »
Apologies everyone but i might be going slightly off topic but if you are bored and have 5 minutes...  ;)


As a long served career repair tech specializing in Broadcasting equipment, i find it virtually amazing folks set about to repair mother boards from a PC. Agreed there have been times when i become involved in application-specific equipment which had been designed around a small generic 486 MoBo of the sort that would have been intended for a laptop. Here it was serving as a Master Camera Setup Controller Unit (the actual mother board and LCD served as part of the piece of equipment) which was at the time a very expensive piece of gear.

This is when the rules change i guess and it is WORTH repairing what is a mass-produced item that could so easily be completely replaced for benefit of reliability. That's where it's worth working on an aging MacBook too i guess, simply because they are currently of a value that says it is worthwhile to at least have a look...

I recall a 386CPU laptop with a terrible blue colored LCD display (no manufacture's name) that had been an extremely expensive purchase. To service it needed an equally expensive repair kit consisting of a batch of external programs (that ran on another PC and connected via a com serial port using some kind of inhouse serial protocol) and a special ROM chipset swapout and a bunch of floppy disks so i could begin to find the trouble! Using an oscilloscope would have been pointless.

In a similar case i had an audio-level/phasing indication metering unit from a studio sound control desk on my bench that was 486 CPU based that ran some kind of high level system ontop of fundamental DOS! The unit had been dropped and hit the floor hard. It now randomly crashed id program or would power itself down. Being extremely expensive to replace to the point it was unlikely the company would invest in such an item under current financial conditions i tried everything to make the unit become reliable. It was one thing to actually work through a bus looking at various blocks of data being passed using an oscilloscope but it wasn't until i plumbed in a my 16bit capable Logic Analyzer that i could capture blocks of activity that represented what the unit was calculating or processing i.e. actually doing. There was absolutely no possibility of a service manual so i was working blind... After the 5th day of doing so much it came down to the obvious fact that somewhere there was a crack or cracks internally of some tracks on the nine multi-layer board because of the fall so that meant it was pretty much the end.... I could have spent hours back engineering all the ASIC data sheets, the bus layouts for the 486 and it's ancillary chipsets find the breaks and try jumper even though they were probably internal vias but it simply wasn't worth it. I could not ensure reliably.

Another job was a PC built back when the 486CPU was the latest beast possible. For some reason the computer would randomly crash or simply not do something then lockup needing a reboot. It was used like that for years probably because it wasn't in a high use place did it ever get looked at.

Then the day came and it was rebuilt with a new and faster motherboard, larger RAM and something better than Win95... Out of interest i picked the old motherboard of the workshop trash a popped the old 486 from its socket after bashing off the heatsink.... I turned the chip over to see its pins and HELLO!... one pin in the central area folded over flat at 90 degrees.... It HAD to have been installed like that all those years ago and why it randomly caused the computer to do what it did...

So all i am saying is that chasing a fault on a PC motherboard could really be in actual fact a waste of time (unless you are doing it as a hobby) because today the things are so heavily loaded with such highly stressed components the biggest killer of all being heat and that starts the minute the dust gets in there and airflow cooling is compromised. Where i work a PC might be classed reliable for 2 yrs if that unless its a server crate or blade that's designed differently for even harsher work. The equipment has to be reliable so the minute there's a failure and brandnew unit usually ends up in its place with the benefit of fresh latest software... And if anyone showed me a 486 or 386 PC today i would probably laugh because the world has moved on i am sure unless it's in some very high value application equipment.  :blah:

« Last Edit: November 15, 2017, 09:18:10 pm by peteb2 »
 

Online rhb

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Re: Which Oscilloscope to buy for Computer repair
« Reply #35 on: November 16, 2017, 10:30:56 am »
@peteb2

Did you read the start of this thread?  The OP is in India and is a retired automotive engineer.  In India he stated that it is commonplace to make repairs to component level.  That's pretty much a lost art in the developed world, though TheSignalPath is trying hard to correct that.

But beyond that, if you have no money and no prospect of getting any other education, learning to repair things is a good start even if the repairs themselves are not very profitable.  When I was in graduate school, I repaired audio gear scavenged from the trash using a VOM and a soldering iron.  I didn't make a lot selling the stuff, but I *did* make money.

The fact that some things can't be repaired doesn't make determining the cause of the failure worthless.  Many times the failures are trivial to fix.  And troubleshooting is the same no matter what the technology is.  It's a *very* valuable skill which can only be acquired by practice.  And the more you know, the fewer tools you need.

Arguing that it is worthless to try reminds me of people who can't do math.  Why?  Because they won't try.  The people who are good at anything are the ones who don't give up.  It's taken me 40 years to learn to play guitar.  But I finally reached the point I can put a CD on and play along.  Some of my favorite stuff is from Clapton's "Unplugged" album.  I don't know what I'm going to do.  I just listen and my fingers do the talking.  I only screw up when I think about it.
 
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Offline PA4TIM

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Re: Which Oscilloscope to buy for Computer repair
« Reply #36 on: November 16, 2017, 07:44:20 pm »
I'm in the component level repair business, no computers or consumer stuff, at first only measurement and calibration gear but now also more and more industrial stuff (often pcb's that are part of something and do not work without the rest. The only way there is to test components.
But most gear has a lot of digital stuff inside. 90% of what I do has no documentation of schematics and also gear that is declared non-repairable by the official dealer/manufacturer. So a bit like what is common in India but rvery are in my country.

My most used gear are in order of most use:
-Very good soldering/desoldering gear
- several DMM's,
- a good real LCR meter,
- several scopes (350 MHz MSO, isolated 60 MHz scopemeter, 100MHz analog scope) I bought the scopemeter after some testing and for some speacial use but it now use it even more as my other scopes ( a Siglent see my review: http://www.pa4tim.nl/?p=5896 )
- special scope probes, I could not do without current probes so I have them in many flavours from a Tek 6042 upto a TTi iprober.
- component testers : curve tracer (tek 576), IC testers, a number of selfmade component testers.
-  function generator
- and a lot more that I need for very specialized things but not often.

A thing I almost never use and can live without is an ESR meter (however I do have several of them) But everyone has its own way of doing things. I could not do without a scope and  my Tek curve tracer.

I also play guitar (since 1982 or so) and agree with you on that
« Last Edit: November 16, 2017, 10:12:44 pm by PA4TIM »
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
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Offline feipoa

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Re: Which Oscilloscope to buy for Computer repair
« Reply #37 on: November 16, 2017, 08:34:38 pm »
Very odd that you mentioned this because for some reason I have had Eric Clapton's Unplugged "Layla" song going in my head at random times throughout the week, although these days, I don't actively listen to music.

Back on track - rhb and peteb2 - I really appreciate your comments.  I was kind of hoping to cease using this particular thread because I started a thread more specific to my needs, https://www.eevblog.com/forum/repair/how-to-troubleshoot-your-defective-386486-motherboard-with-an-oscilloscope/
 but it looks like I'll be reading on two fronts.  I was actually hoping that the OP would have updated us on his/her progress, but I guess he/she has moved on.

In response to some comments, I am doing this strictly as a hobby.  I used to to work as an engineer by profession and now have taken up collection of specific periods of computing history.  I also setup systems around such hardware as a hobby.  There is actually a fairly substantial following in this field of interest as of recent. e.g. you can check out the vintage computer forum, http://www.vcfed.org/forum/forum.php , or Vogons at http://www.vogons.org/ . The interest is mostly centred around vintage gaming on period-correct hardware, although there are others, like me, who don't game but are more into the hobby aspect of restoration and tinkering.  15-20 years ago, I could buy very high-end 1990's-era motherboards, CPUs, graphics cards, SCSI adapters, etc. on eBay for next to nothing.  These same items today, if you can even find them, now sell on eBay in the hundreds of dollars.  So aside from the hobby aspect of it, one may be able to reap substantial capital gains when selling.  By way of example, back in 2003, I could buy a rare Cyrix 5x86-133/4x for $25.  There was an eBay posting this year for this CPU, which only happens about every 5-10 years, and the bids were running north of $500 (although the reserve was never met).  Just 6 years ago, you could buy a Voodoo 5 graphics card on eBay for $30.  People are now paying $200+.

Another aspect of the hobby for me is that it brings me back to an age which I consider a golden era in computer history.  I am personally fond of the 386-486 era, but my interest does extend into Tualatins, though the passion for me diminishes substantially.

The two dead boards I'm trying to get working are not for me.  They are for a younger chap who seems to be developing a vintage computer fever.  They are actually his boards.  I have always enjoyed trying to repair old motherboards or computer hardware.  Sometimes I give up, and stick the board in a box for a decade or more; then at a later point, when I have slowly accumulated more knowledge, I am often able to get them running again, though not always.  This is a hobby and I enjoy learning and solving problems in the EE arena.  My main limitation now is time and sleep.  With 3 restless youngsters at home and a wife, my only time to tinker is the midnight hour and for a short duration.  Tonight, looks like I'll only have time to read posts.

peteb2 - very interesting stories.  Thank you for sharing. Sounds like that 486 pin was just barely making contact in its 90 degree bent position.  Perhaps some mild corrosion or oxidation over time made the contact intermittent. 

peteb2 - it is very likely that the boards of interest have been dropped.  They were sitting around some community college waiting to be scrapped.  Who knows how many static bodies rubbed all over them.  The fact that the other two boards (the ones I got working) were contact issues makes me lean in the direction that the 2 dead boards may have similar issues, and as per your story, could be inner-layer contact issues.
 


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