Keysight DSO-X 2004A dead - Page 1
Forum section: electronics / repair

author: Campus
author_rank: Contributor
timestamp: July 19, 2022, 08:39:24 am
content: Hi,my Keysight was in storage for about a year and now I wanted to start using it again but it's completely dead. No life sign whatsoever. Does it make sense to investigate this further or is this just too old to have any chance of being successful (especially for me without any power supply experience)?Kind Regards

author: Pinkus
author_rank: Frequent Contributor
timestamp: July 19, 2022, 09:52:57 am
content: Does the fan of the power supply start up (will be audible) and doesanyLED light up?

author: Campus
author_rank: Contributor
timestamp: July 19, 2022, 12:44:02 pm
content: Nothing, no fan no led, as if no power cable is connected.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 19, 2022, 01:04:32 pm
content: Likely to be an easy fix if it's the power supply. Most common fault on SMPSUs is startup supply cap - look for a small low-voltage electrolytic on the mains side of the supply and replace it.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 19, 2022, 01:31:19 pm
content: Yes, most likely the power supply.I had a different Keysight scope with a bad power supply and it turned out to be an overheated and open power resistor.You can power the scope with a lab power supply, to see if the rest of the scope is working.

author: Campus
author_rank: Contributor
timestamp: July 19, 2022, 01:38:49 pm
content: The caps look fine to me but I found a badly burned resistor (?) on the back:

author: Campus
author_rank: Contributor
timestamp: July 19, 2022, 01:42:53 pm
content: Quote from: HighVoltage on July 19, 2022, 01:31:19 pmCan you point me to a post where to connect it to a lab power supply? The mainboard seems to have quite a lot of connections to the power supply and I couldn't find any repair manual so far.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 19, 2022, 02:25:21 pm
content: Go to 10:00 in this video:

author: HighVoltage
author_rank: Super Contributor
timestamp: July 19, 2022, 02:30:23 pm
content: Quote from: Campus on July 19, 2022, 01:42:53 pmIt is a simple 2 wire hookup with a 12V power supply as you can see in the video above.Just make sure to connect the polarity correctly!!!!

author: Campus
author_rank: Contributor
timestamp: July 19, 2022, 06:04:09 pm
content: I have now successfully tested the device with just a plain 12V connection to the line board.Looks like the MOSFET mentioned in the video is also damaged in my case although it looks like new. The drain connected resistor is so damaged that I can not even recognize the print anymore. In my case it was colored in blue. Any idea what I need to be aware of when getting a replacement for this kind of resistor?

author: Bud
author_rank: Super Contributor
timestamp: July 19, 2022, 06:23:44 pm
content: Mosfets get damaged by storing the equipment in closet?Moisture ingression perhaps?

author: Campus
author_rank: Contributor
timestamp: July 19, 2022, 06:29:50 pm
content: I am confused about this as well. It was definitely working when I put the device into the original box and it was stored in a heated/dry office environment. It also made no sound when I tried to run it yesterday so I am a bit clueless what happened.

author: kripton2035
author_rank: Super Contributor
timestamp: July 19, 2022, 07:16:36 pm
content: main capacitor went dry during storage. at first power up, it caused inrush current that burned fuse, resistor and mosfet (and may be diode too)

author: Campus
author_rank: Contributor
timestamp: July 19, 2022, 08:43:02 pm
content: Thanks for the explanation. I will try to find replacements for these parts to replace them. I am still a bit puzzled why the cap looks perfectly fine and does not have slightest bulge or fluid around it. I also measured it to still have 85um capacity with my DMM.

author: kripton2035
author_rank: Super Contributor
timestamp: July 19, 2022, 08:55:40 pm
content: you must also measure the esr of the cap. a big cap can have too high esr and not bulging at all.it can also be another cap on the board that went high esr and made the current go too high in certain parts of the circuit.measuring the esr of all polarized caps on the board could be a good thing.

author: CapLeaker
author_rank: Regular Contributor
timestamp: July 21, 2022, 02:07:52 am
content: I ran into the same problem with my Agilent DSO-X 2012. I wrote about it in badcaps here:https://www.badcaps.net/forum/showthread.php?t=97854I even was able to come up with who made that PSU. It’s not made by Agilent. All it took to repair was a mini fuse and a new main filter cap that I got out of my parts bin.

author: Campus
author_rank: Contributor
timestamp: July 21, 2022, 06:47:36 am
content: I inspected the power supply under the microscope and several regions look quite bad. Even the metal housing of the supply has some burned areas. I am a bit afraid that I am not competent enough to measure all the components to make a good and solid (long-term) fix. So I will go for one of the available replacement power supplies which are mentioned in another thread for the same kind of issue on similar devices.

author: CapLeaker
author_rank: Regular Contributor
timestamp: July 21, 2022, 10:07:28 am
content: Check the pads of the main filter cap for a short. Take the 420V main filter cap out and measure it’s pads to see if there is still a short, if you don’t see any check the output for a short. Stick temporary a 420V 100 something uF in, replace the mini fuse and try it.Look at the bright side… I mean you can’t break stuff that’s already broken. I was kind of surprised to find that the actual PSU isn't made by Agilent at all. The only problem might be to find the correct size cap.In the other thread I posted the pdf for the replacement PSU. See it as a cheap learning opportunity.Btw… my scope is still working fine with the parts out of the junk bin.

author: Campus
author_rank: Contributor
timestamp: July 21, 2022, 10:12:41 am
content: Good ideaI will try to fix it just to learn a bit more how to do these kind of things. Thanks for the positive input.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 21, 2022, 10:12:45 am
content: Quote from: CapLeaker on July 21, 2022, 10:07:28 amPlease post the PDF here as well, since I can not look at it without an account there.

author: kripton2035
author_rank: Super Contributor
timestamp: July 21, 2022, 10:29:59 am
content: Quote from: HighVoltage on July 21, 2022, 10:12:45 am

author: voltsandjolts
author_rank: Unknown
timestamp: July 21, 2022, 12:02:25 pm
content: Hmm, note self: never design-in Cherokee International (China) Power Supply Ltd.

author: CapLeaker
author_rank: Regular Contributor
timestamp: July 22, 2022, 11:51:16 am
content: Quote from: kripton2035 on July 21, 2022, 10:29:59 amI've been over there for many years now, been lurking here for many years too, but never had made an account until the other day. Kripton2035 already copied the pdf here, thanks bud!I did notice that for some reason on 10 year old Agilent Oscilloscopes, the PSU goes poof.Just a shame to throw the whole thing out, because of a $1 cap and 50 cent fuse. I had bought some licenses for extra features on my scope. Agilent charged me a lot more than $1.50! Only to find out at the end that they are cost cutting by putting general available 3rd party PSU's in there. Made me think twice after that.

author: wraper
author_rank: Unknown
timestamp: July 22, 2022, 12:06:48 pm
content: Quote from: CapLeaker on July 22, 2022, 11:51:16 amWhat makes you think that custom made PSU would necessarily be any better? Also by it's looks its a decent PSU with good components used.QuoteDo you expect them fixing 10 yo oscilloscope for $1.5? Not to say nothing prevents you changing those parts yourself. Nor Keysight will repair that PSU, they will simply change it.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 22, 2022, 02:04:43 pm
content: Quote from: CapLeaker on July 22, 2022, 11:51:16 amActually this is how some of us get 10 year old scopes cheap and fix them easily.

author: CapLeaker
author_rank: Regular Contributor
timestamp: July 23, 2022, 01:13:00 am
content: Quote from: wraper on July 22, 2022, 12:06:48 pmuNo, Keysight does not sell / exchange or fix that PSU nor the unit itself. Once a unit is a few years old, Agilent / Keysight does not have any spare parts. Told me to buy a new one. However I was able to get the PDF what PSU is actually in there.The PSU isn't that bad, correct. BUT Agilent stuff isn't cheap. I've got older HP stuff and can't kill it. But 2 out 3 Agilent items I own, would have landed in the landfill as not repairable. The third Agilent item I bricked on a firmware update, but lucky me I was able to unbrick it.Not sure if it is just my luck or what.

author: wraper
author_rank: Unknown
timestamp: July 23, 2022, 09:25:52 am
content: Quote from: CapLeaker on July 23, 2022, 01:13:00 amHard to believe since this model is still in production. They probably won't sell you PSU but paid repair should be available. I won't be cheap though.

author: CapLeaker
author_rank: Regular Contributor
timestamp: July 24, 2022, 02:03:59 am
content: Quote from: wraper on July 23, 2022, 09:25:52 amI’ve tried and the only option was to purchase a new one. I guess the new ones must be different. Same thing as with the Agilent U1253B. The old ones from 10 years ago are different from the current ones, even so they share the same model number. Makes it really confusing.