EEVblog 1418 - The Most EMBARRASSING Repair!

This "Repair" of a Keysight DSOX1102G oscilloscope was a tad embarrassing...

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#ElectronicsCreators #Repair #Hack

[DavePoo]

Dave exercises his right to repair after exercising his right to screw it up.

[AndyFletcherX]

Keysight have recently been a topic in the EEVBlog forums because they now appear to be refusing to provide supply, repair or calibration service for individuals and only providing service for companies. If they are not going to support hobbyists then I'm going to be avoiding them and will not be recommending their products to my clients. Seems like a bit of an own goal because hobbyists and students become equipment specifiers in the future.

[RaySan]

this is why it makes sense recording yourself disassembling something, even if you don't upload it anywhere....you can always go through your archive and watch why you have done something

[jasonbrindamour]

You should've soldered one side of the resistor to the board and left the other side flapping in the breeze so when you come back to it the original part is there :)

[funtechu]

If I had to guess, I would say that different devices that have different hardware may need to have their offsets compensated for in software, and so by changing it so there is a mismatch between the physical hardware and what the software thinks is present, those compensations end up producing what appears as an offset.

[briansmith]

Back in the 70, s I worked for Tektronix as a service engineer. The problem you saw used to be down to corrosion/ galvonics in the "Y" input select switching. DC offsets. Oh what fun. Clean those wafer switches. :)

[stevenm.]

Licensing... on a piece of equipment you bought.
That's like buying a calculator and having to pay a license to enable multiplication and division. Utterly ridiculous! Why do people put up with it?

[DanBowkley]

I dunno, if I were the engineer designing this thing I'd have to leave a couple idiot traps lying around. Like one of those video games where if you play a bootleg version it'll act like it's working but it absolutely won't let you beat level 4. If you manage to set R174 to 4.7k it thinks it's a Fisher Price My First DSO.

[andydelle]

Stereo amplifier repair 101: Use the good channel to trouble shoot the bad one. Have been doing that since my early teens. Of course at that age you often blow up the good channel trying to fix the bad one! My Dynaco 120 of the day is a good example. That was before I understood ultrasonic oscillation in baseband audio circuits

[OfflineSetup]

How embarrassing, but being naked behind the camera while filming reflective materials, did it not cross your mind this could happen?

[Gameboygenius]

Re: the question about different configurations: the most reasonable explanation to me is that the analog side of the DC offset generation circuitry differs between models, or even hardware revisions. Those set resistors are supposed to tell the firmware which hardware it's currently running on. So with this explanation it's not so much that the calibration data is ruined per se, but that the stimulus to the DC offset generation is ass backwards because it's for a different hardware configuration.

[bashkillszombies]

License code? Jesus, that's straight up evil.

[sefarkas]

Maybe the ID by voltage divider was a windowed range and you were out. Maybe your ID presented an ID for a product with a different hardware.

[mrmobodies]

1:52 That's why they call it Keysight needing a license key to use certain stuff.

[PatrickPoet]

A good visual inspection through a magnifier will find places where the solder has cracked around a through pin and even though it looks fine to a naked eye it isn't making electrical contact with the through component at _all_ anymore. Years of heating and cooling sometimes cracks the solder, especially if it was a little scant. My experience is old electrolytic caps and obvious things like this and solder balls account for a huge percentage of faults. Add in the occasional failed chip/diode (check the inputs they're all good, check the outputs, not so much), and you account for almost all. By the time you get that deep into it you'll be ready to find the occasional weird fault.

[OmarMekkawy]

At least Murphy didn't get you this time :D
When I do similar modifications like you did, I usually solder those original resistor from one leg ( Just to keep them in place and not electrically connected ). You also might use any sort of electrical tapes and glue them to the oscilloscope's chassis.

[Seegalgalguntijak]

"I didn't change anything about it!" It's always the same line users give when their stuff stops working...

[jusaca]

Actually the behaviour at the beginning seems to be just a setting in the menu!
Under Utility -> Options -> Preferences you can select between "Expand about Ground" or "Expand about Center". I think your scope was set to the second option, so when you changed vertical scale you also changed the position of ground on the screen.

[rsn]

When it is first calibrated it probably stores those initial resistor divider values as part of the calibration data and if the hardware no longer matches the stored value of the resistor divider it just assumes that the calibration data is faulty and something is wrong so never loads the rest of the calibration data.

[andymouse]

A Keysight BLT is gonna be delicious but very pricey ....cheers.