Keysight MSO7034B, Teardown and Repair [Success] - Page 1
Forum section: electronics / repair

author: HighVoltage
author_rank: Super Contributor
timestamp: June 18, 2016, 03:46:51 pm
content: I bought this Agilent / Keysight MSO7034B scope a while back in broken state really cheap.Symptoms: Does not turn on at all.So, I thought to make a teardown and repair attempt at the same time.I never opened one of these scopes before and I have not seen a tear down before of a 7000B series scope.To take the back cover off, remove the obvious screws, the handle and the feet.So far I took the back cover off and found a lot of dirt on the fan and in the housing.May be this was the killer for the PSU, although it looks pretty clean.Here are my first picturesInterestingly this PSU has lots of missing components.Usually when I have repaired some Agilent gear before, the PSU was fully populated.

author: joellinn
author_rank: Contributor
timestamp: June 18, 2016, 04:50:24 pm
content: Maybe someone salvaged itDid you try and measure voltages on the Header that goes into the scope? Are the fuses OK? What about the transformer?

author: nctnico
author_rank: Super Contributor
timestamp: June 18, 2016, 05:33:17 pm
content: It seems some outputs are not used so that would explain the 'missing' components. I'd start by checking the PSU's output voltages and go from there. Don't assume something is broken; always measure to determine something needs replacing or not.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 18, 2016, 05:37:59 pm
content: Thanks, yes, will test the PSU nextI took the main board out first to clean it all of the dust.Here are some pictures of the main board.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 18, 2016, 05:40:04 pm
content: And here are some pictures of the front end under the metal can.Anything else I should take close up pictures of?

author: SeanB
author_rank: Super Contributor
timestamp: June 18, 2016, 05:40:43 pm
content: Looks like a standard PSU board that produces multiple rails, and they only need 2 rails here ( likely 5V and 12V) so only populated those parts on the secondary side. My bets are the crinkled blue mains input cap upper left of the PSU by the mains input sent off the ceramic mains fuse as it failed short circuit. If not then suspect any high value resistors on the primary side, especially if the main transistor switch is not blown apart.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 18, 2016, 07:58:05 pm
content: The fuse is OK but the PSU is dead.So, probably a resistor failure in the PSU?I will continue the trouble shooting tomorrow...The schematics are probably not available for the PSU ?Just for completeness, here are some more pictures of the tear down.

author: nctnico
author_rank: Super Contributor
timestamp: June 18, 2016, 08:05:04 pm
content: Quote from: HighVoltage on June 18, 2016, 07:58:05 pmDon't guess but measure. First check all semiconductors. If those are OK apply power using a DC power supply to the low voltage part of the primary circuit (look up the datasheet for the required voltage) so you can check if the switching chip is doing something and the primary side MOSFET is switched correctly. Using a lab power supply makes this measurement safe to do. The next step is to apply power to the primary side capacitors using a different low voltage supply (30V to 40V and a low current limit setting). In this step you'll see some things happening on the secondary side as well.Edit: this seems like some kind of self oscillating resonant converter with a current feedback from the secondary side. Applying DC at the input should give some insight in where the path ends.

author: tautech
author_rank: Super Contributor
timestamp: June 18, 2016, 08:47:06 pm
content: Before you put a lot of time and effort into this is it not worth providing the voltages necessary from an external PSU to check the rest of the scope is functioning.

author: tautech
author_rank: Super Contributor
timestamp: June 18, 2016, 09:00:38 pm
content: Is that a dry joint on the inline fuse?

author: CJay
author_rank: Super Contributor
timestamp: June 18, 2016, 09:22:20 pm
content: There is absolutely nothing special about that supply, it's an off the shelf Artesyn device and is replaceable for a few tens of dollars.If you can't find the fault in a couple of hours, just buy a replacement or equivalent.Totally unworth the effort to repair unless you are doing it for the challenge.https://www.artesyn.com/power/assets/nfs110_ds_1213229025.pdf15V 110W, single rail supply.

author: tautech
author_rank: Super Contributor
timestamp: June 18, 2016, 10:06:30 pm
content: Quote from: CJay on June 18, 2016, 09:22:20 pmMTBF125,000 hours min.Yeah right.

author: gamalot
author_rank: Super Contributor
timestamp: June 18, 2016, 10:12:15 pm
content: Quote from: CJay on June 18, 2016, 09:22:20 pmTotally agree! I‘ve bought a Meanwell 12V PSU to replace the TDK-Lambda one in my Keithley 2306.

author: nctnico
author_rank: Super Contributor
timestamp: June 18, 2016, 10:31:21 pm
content: Quote from: tautech on June 18, 2016, 10:06:30 pmProbably at 25deg Celcius; at higher temperatures the MTBF drops considerably and even then it is just a theoretical number.It is quite interesting to find an off-the-shelve power supply in this kind of high end scope though.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 18, 2016, 10:40:19 pm
content: By far the most common failure in SMPSs is an electrolytic cap on the startup supply - look for a low-voltage cap on the primary side and replace it, regardless of what it might measure.Remember the main primary cap will stay charged quite a while on a PSU in this state so take care!

author: HighVoltage
author_rank: Super Contributor
timestamp: June 18, 2016, 10:54:34 pm
content: Quote from: nctnico on June 18, 2016, 10:31:21 pmYes, this is a big surprise to me as well.Although I think Keysight has stopped production, it is still available for sale in Germany for Euro 17.396 + VAT = Euro 20.701 (and that is without options)I would have expected a high end power supply.Thanks for all your suggestions, I think I will find the problem tomorrow.

author: tautech
author_rank: Super Contributor
timestamp: June 18, 2016, 11:05:31 pm
content: As Dave would say, you'll be on a winner, winner chicken dinner if it's an easy fix.Hope it is, good luck.

author: wraper
author_rank: Unknown
timestamp: June 19, 2016, 12:00:51 am
content: Quote from: tautech on June 18, 2016, 08:47:06 pmVery bad advise. Never do that unless you have a very good reason and triple check that you are doing this right. Little mistake and all the expensive hardware will be dead beyond repair.

author: nctnico
author_rank: Super Contributor
timestamp: June 19, 2016, 12:06:13 am
content: Quote from: wraper on June 19, 2016, 12:00:51 amI have to agree. I'm also reluctant to do this because it is easy to swap + with - and there usually isn't any reverse polarity protection on the boards. Secondly there can be requirements for rise-time, power good signals, etc.

author: tautech
author_rank: Super Contributor
timestamp: June 19, 2016, 01:35:04 am
content: Quote from: nctnico on June 19, 2016, 12:06:13 amOh really guys are we all novices or something.Oh wait isn't that what current adjustable bench PSU's are for?

author: tautech
author_rank: Super Contributor
timestamp: June 19, 2016, 03:37:12 am
content: Manuals for those following along at home.http://www.docs-library.com/pdf/1/6/agilent-7012.html#Hit the "Go to link" and another tab with the pdf will open and download.PSU checks are described on P77Basic as these PSU's are, anybody that has fixed scopes will know there'll be a Line frequency feed to the Mobo, possibly a mains gnd too and if it's a single rail supply there'll be multiple conductors to supply the current, hence the additional pins on the connector.

author: CJay
author_rank: Super Contributor
timestamp: June 19, 2016, 08:09:35 am
content: Quote from: nctnico on June 18, 2016, 10:31:21 pm~14 years MTBF continuous use, it'll be extrapolated from a series of 'torture' tests, high temperature, load etc. (Artesyn may well release data that shows how they derate MTBF for load and temperature and that will give a cllue as to how they test) but I do have PSUs that are considerably older and have been in use for at least ten years (on equipment like gas analysers) so for a quality part like an artesyn, I'd expect it to last a good number of yearsIt is a bit of a surprise to find an off the shelf part but the secret sauce on a lot of these 'scopes is the acquisition so it makes sense to have good quality off the shelf bits chosen for specification.

author: SeanB
author_rank: Super Contributor
timestamp: June 19, 2016, 08:32:41 am
content: Check R1, change the power transistor with the same type, change the low value resistor in the emitter, change all the little jellybean transistors and check all resistors are not open and it will work, providing the secondary side diodes or capacitors are not shorted. Also check the crowbar thyristor CR12 is not shorted and stopping the power supply.

author: nctnico
author_rank: Super Contributor
timestamp: June 19, 2016, 10:44:33 am
content: Quote from: tautech on June 19, 2016, 01:35:04 amNo, wisdom gained by experienceQuoteAt 110W you'll need a chunky bench PSU and also need to worry about power supply risetime and switch-on overshoots if the PSU is crappy enough.BTW: it seems line triggering isn't done through the PSU but there may be a small current transformer on the mains entry board.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 19, 2016, 04:30:11 pm
content: I think I found the culpritThe large high voltage DC capacitor was bad.This was a Nippon Chemi-Con 330uF 400VBut I only have a Rubicon 220uF 400V at hand.Installed the Rubicon and the power supply works.This power supply only has a single 15 V DC output.I will hook up a DC load and look at the ripple on the output.What do you all think.Should I get a new 330uF cap or should this 220uF cap do the job?

author: acbern
author_rank: Frequent Contributor
timestamp: June 19, 2016, 04:43:34 pm
content: Since this is probably a wide input range PSU (please check) the capacitor was selected for the lowest possible voltage (permissible input ripple voltage after rectifier). Since you are using it at 230V, it should work. I would still change it.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 19, 2016, 05:07:36 pm
content: Quote from: acbern on June 19, 2016, 04:43:34 pmHello acbernyes, it is 100 to 240 V AC PSUI pulled 2A out of the PSU and it seems tob e working perfectlyInstalled the PSU and the scope works !Look at this ... what a great Sunday it is !What an easy fix that was.Thank you all !I will measure now the current the scope is pulling from the PSU and the ripple voltage.

author: bingo600
author_rank: Super Contributor
timestamp: June 19, 2016, 05:20:05 pm
content: Great jobCongrats with your new scope/Bingo

author: TheSteve
author_rank: Unknown
timestamp: June 19, 2016, 05:41:38 pm
content: Awesome! This is one of those deals and repairs we all dream of!

author: HighVoltage
author_rank: Super Contributor
timestamp: June 19, 2016, 05:43:38 pm
content: Thanks,I measured the current from the PSU to the scope.Here are the results:I am surprised that it does take 2.7A from the PSU.The ripple voltage is about 10 mV AC (measured with 87V)

author: nctnico
author_rank: Super Contributor
timestamp: June 19, 2016, 05:57:31 pm
content: While you still have it open: can you identify where the scope get it's signal to trigger on the AC mains (line trigger source)?It's a great deal though! Now hack it into an MSO!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 19, 2016, 06:35:20 pm
content: I'd definitely get the correct cap to make sure everything is working within spec. Hardly a major cost compared to the value of the scope.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 19, 2016, 07:40:23 pm
content: Quote from: nctnico on June 19, 2016, 05:57:31 pmHmm, there is no other connection to the main board from AC, only the PSU +15V DCMay be the 50 /60 Hz is created on the main board, independent of the real AC ?QuoteYes, the hack will be nextQuote from: mikeselectricstuff on June 19, 2016, 06:35:20 pmYes, I already found an ordered the 330uF cap.I will take some more detailed measurements, before and after changing the the cap.Although I dont think it will make a big difference, you are correct to keep it in specs.I just measured the AC ripple on the output of the +15V DC and it is around 2 mV AC on the 87V Fluke Multimeter

author: tautech
author_rank: Super Contributor
timestamp: June 19, 2016, 08:09:50 pm
content: Quote from: HighVoltage on June 19, 2016, 05:43:38 pmHa, who would have expected the HV DC cap as the point of failure, not common for a SMPS.So 2.7A (40W) is roughly what you'd expect and could have easily been supplied by a bench PSU for checks too.Nice find HV and congrats on your cheap DSO.

author: nctnico
author_rank: Super Contributor
timestamp: June 19, 2016, 08:54:34 pm
content: To me it seems every repair technician has his (her) own list of common problems in switching power supplies but none of them apply to every SMPS out there.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 19, 2016, 09:05:03 pm
content: This is how the MSO6000 does it - I imagine the 7000 will be similarhttps://youtu.be/5lYbD9_eIko?t=366

author: nctnico
author_rank: Super Contributor
timestamp: June 19, 2016, 11:08:42 pm
content: Thanks for pointing to that video! Judging from the photos it wouldn't surprise me if the power entry board in the 7000 series is the same just like the power supply.

author: tautech
author_rank: Super Contributor
timestamp: June 19, 2016, 11:41:28 pm
content: Quote from: mikeselectricstuff on June 19, 2016, 09:05:03 pmYep, line frequency reference from another PCB, but it's often done directly from the PSU itself however when a cheap generic SMPS is used for these Keysights you have to provide another Line source.Does a single PCB with Line output configuration make for a more reliable setup or using 2 PCB's ?

author: HighVoltage
author_rank: Super Contributor
timestamp: June 20, 2016, 08:20:02 am
content: Thanks Mike for this explanation.I will have another look and make some detailed pictures, it looks it is the same setup in my 7034B

author: CJay
author_rank: Super Contributor
timestamp: June 20, 2016, 08:44:27 am
content: Quote from: nctnico on June 19, 2016, 08:54:34 pmWe do, but there's an awful lot of crossover and common faults, I think high value resistors on the primary, low value caps on the primary, leaky high value caps on the secondary and shorted secondary rectifiers would be the very first thing pretty much any tech who repairs these things will check for.Excellent news from the OP BTW, congratulations on such an awesome score, envious doesn't really cover it..

author: tautech
author_rank: Super Contributor
timestamp: June 20, 2016, 08:58:17 am
content: Quote from: CJay on June 20, 2016, 08:44:27 amAnd the HV DC primary side cap is low on the list ^^, right?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 20, 2016, 09:04:46 am
content: Quote from: tautech on June 20, 2016, 08:58:17 amDon't think I've ever seen it, but maybe because manufacturers realise it's a critical part and take more selecting it, as opposed to things like standby supply caps and resistors where a jellybean part is used despite it frequently be being exposed to significant heat or voltage stress respectively.

author: CJay
author_rank: Super Contributor
timestamp: June 20, 2016, 09:18:27 am
content: Quote from: tautech on June 20, 2016, 08:58:17 amIt really isn't a common fault in my experience, in the ten years or so I repaired PSUs as part of my job I can't remember replacing more than a handful of them that had failed in anything other than spectacular fashionIn my telly repair career, it was a different story, the multi value, single can capacitors were a bugger for failing in some sets (G11, duff rivets).For PSU repair work I found the component tester on the Hameg 'scopes makes the 'gross' fault finding really quick (we could turn around ~40 PSUs a day per tech if we got a large batch of the same types) so the primary reservoir would be picked up really quickly if it were faulty while testing the bridge/diodes and, depending on topology, the switching transistor(s) because it would look 'wrong'.

author: wraper
author_rank: Unknown
timestamp: June 20, 2016, 10:06:36 am
content: Quote from: tautech on June 19, 2016, 08:09:50 pmNot something PSUs are plagued with but is not something rare either.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 20, 2016, 11:23:26 am
content: Quote from: CJay on June 20, 2016, 09:18:27 amThis is still a feature on the small Rohde & Schwarz scopes.I never thought about using it "in circuit", interesting idea.

author: CJay
author_rank: Super Contributor
timestamp: June 20, 2016, 12:24:34 pm
content: Quote from: HighVoltage on June 20, 2016, 11:23:26 amI find it useful for things like power supplies, amplifiers, analogue power things, but I know other people aren't keen.I guess it's just personal taste and it really depends how often you repair things like that.It's useful for gross faults in circuit (shorted or open junctions, open circuit resistors, leaky, short or open caps), I can 'sweep' a board in a few seconds for those with a component tester and desolder parts that look suspicious to get in deeper with a meter or component analyser and confirm or disprove suspicious traces.They're not so great on 'subtle' things like high value resistors that have gone higher or nF caps but combined with a multimeter and some experience, they're really effective.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 20, 2016, 12:59:23 pm
content: Quote from: nctnico on June 19, 2016, 05:57:31 pmOk, here are some pictures of the AC board and the connection to the mains AC trigger.It looks like an optocoupler in between the AC and the wire to the main board.Even this little PCB is made by Agilent and looks great and much better than the PSC PCB.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 20, 2016, 01:11:24 pm
content: Quote from: nctnico on June 19, 2016, 05:57:31 pmAnd here are two pictures of the screen, before and after the hack.Thanks to some forum members for providing the 6.16 FW version. (No longer on the Keysight website available)The Hack is very simple, as long as the Firmware is 06.16.0001.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 20, 2016, 01:18:17 pm
content: Once the Service Menu is turned ON via telnet access, this new Menu is available under "License" in the "Utility" section.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 22, 2016, 03:00:28 pm
content: Quote from: mikeselectricstuff on June 19, 2016, 06:35:20 pmOK, to conclude this thread, I just installed the new 400V 330uF capacitor and all works great.Interestingly, the new cap is much largerOriginal Nippon Chemi-Con- 400V 330uF- 25 mm diameter- 40 mm tall- 29.8 GramsNew VishayBC- 400V 330uF- 35 mm diameter- 50.7 mm tall- 64 GramsThis new cap has an ESR of 0.07 OhmBut only measures 298 uFMay be this one is better, because it has a larger volume.But who knows, I have never used a Vishay electrolytic capacitor before.Thank you all for help and suggestions, it is really appreciated.

author: nctnico
author_rank: Super Contributor
timestamp: June 22, 2016, 04:26:07 pm
content: Hmm, normally replacement capacitors are smaller, not bigger!

author: Samogon
author_rank: Frequent Contributor
timestamp: June 25, 2016, 11:28:30 am
content: Quote from: HighVoltage on June 22, 2016, 03:00:28 pmIt is still in 20% tolerance.Again nice deal you made with this scope. Congratulations!

author: Greybeard
author_rank: Frequent Contributor
timestamp: November 13, 2020, 12:43:14 am
content: Can somebody help me to identify this diode in the front end of 7034A?The font ends of 6034A and 5034A seem to be nearly identical to 7034A.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 13, 2020, 09:52:10 am
content: Quote from: Greybeard on November 13, 2020, 12:43:14 amUnlikely to be anything exotic - just measure the one in another channel to determine how many diodes, shottky or not, zener or not.

author: Greybeard
author_rank: Frequent Contributor
timestamp: November 13, 2020, 10:52:18 am
content: QuoteI don't like the idea of unsoldering one of the working ones, that would be the last resort.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 13, 2020, 12:36:41 pm
content: Quote from: Greybeard on November 13, 2020, 10:52:18 amAt least you could try measuring it in-circuit

author: HighVoltage
author_rank: Super Contributor
timestamp: November 13, 2020, 01:25:26 pm
content: I still have the original high resolution pictures and cropped this area out againBut it is still not readable.I suggest like Mike said, try to measure the part in circuit and compare it to the other channels.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 13, 2020, 06:00:53 pm
content: Would also be worth looking to see if there are parts with the same marking elsewhere ( apart from other channels) - if there are this would indicate that it's probably a fairly general-purpose device rather than something exotic

author: Greybeard
author_rank: Frequent Contributor
timestamp: November 13, 2020, 08:20:14 pm
content: HV: I tried to process your photos, but no success.Mike: BTW, awsome homepage (tesla photos).

author: Greybeard
author_rank: Frequent Contributor
timestamp: November 13, 2020, 09:42:00 pm
content: Found a promising photo of the 1GHz frontend in this thread:https://www.eevblog.com/forum/repair/agilent-dso6054a-noise-on-two-channels/msg853423/#msg853423I think it is very probable same circuitry regarding this part:So CR202/302/402/502 should be a double PIN diodeHSMP3892(HP/Agilent/Broadcom, marking codeG2) = LXP1008‐23‐2 (Microsemi drop in equivilent).https://www.digchip.com/datasheets/download_datasheet.php?id=384631&part-number=HSMP-3892https://www.microsemi.com/document-portal/doc_download/9457-lxp1000-sot23-series-datasheetPS:Confirmed at 300MHz scope: MarkingG25Confirmed at 500MHz scope: MarkingG2F5 or F may be a maker or index mark.PPS:Case seems to be SOT-232 (smaller than SOT-23):So correct diode type should beHSMP389C(same G2 SMD code):