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Electronics => Repair => Topic started by: enz on September 20, 2018, 11:51:24 am

Title: DSO-X 3024A Power Supply defect
Post by: enz on September 20, 2018, 11:51:24 am
Hi All,

bad luck today.

When I plugged in my DSO-X 3024A the circuit breaker tripped and I saw a light flash cominf out of the backside of the oscilloscope.
After opening the device and inspecting the power supply I noticed a burned part, see picture below:

I think the broken part was a varistor, but I am not 100% sure. Could also be a capacitor.
Can anyone identify the part?

Otherwise I would leave the part unpopulated.

Best regards,
Martin

Title: Re: DSO-X 3024A Power Supply defect
Post by: JFJ on September 20, 2018, 12:49:24 pm
The part might be a NTC thermister, like this:

https://www.yoycart.com/Product/571067033190/ (https://www.yoycart.com/Product/571067033190/)
Title: Re: DSO-X 3024A Power Supply defect
Post by: soesante on September 20, 2018, 01:24:34 pm
Believe its NTC Thermistor...

Sent from my SM-J730G using Tapatalk

Title: Re: DSO-X 3024A Power Supply defect
Post by: ArthurDent on September 20, 2018, 05:04:08 pm
The blown part is obviously a NTC thermistor as others have pointed out but the question is why did it blow? It is possible that it was just that part, it happens, but there may have been something more serious that caused it to blow. In the lower left there is F1 a 6.3A fuse, is that blown?

You say the problem caused a breaker to trip. That sounds more like a direct short from one of the A.C. input leads to ground (earth) or a line-to-line short. If it was just a problem within the power supply the 6.3A fuse would blow but not the breaker. What is the breaker capacity? It is probably several amps higher. There are 2 toroidal inductors on the left side of the power supply, probably one on each leg of the A.C.. If there was an arc-over in that area, that may have caused the problem.

It would be a good idea to carefully check the power supply out and not just replace that part and plug it back in to power.

Edit: I said fuse was 0.3A and it is actually 6.3A.  Thanks to PA0PBZ for pointing out my error.
Title: Re: DSO-X 3024A Power Supply defect
Post by: PA0PBZ on September 20, 2018, 06:02:16 pm
In the lower left there is F1 a 0.3A fuse, is that blown?

I think it says 6.3A so it could well be that the breaker was faster. When something like this happens the diodes are the first suspects. If you find one shorted replace them all!
Title: Re: DSO-X 3024A Power Supply defect
Post by: JFJ on September 20, 2018, 06:42:51 pm
The usual purpose of a thermistor, in this type of power supply, is to limit the inrush current to the main input filter capacitor. In normal operation, you wouldn't expect the thermistor to get hot enough to break apart. Presumably, something downstream of the thermistor went short circuit (e.g. the main switching MOSFET transistor). So, as ArthurDent suggests, it would be unwise to just replace that part and plug it back in to power.

A better way, would be to connect the oscilloscope to mains power via an incandescent lamp. A 60W light bulb, for example, would limit the current to around a quarter of an amp. If there isn't a short circuit, the lamp should, initially, glow brightly and then dim, but in the presence of a short circuit, it would continuously glow brightly.
Title: Re: DSO-X 3024A Power Supply defect
Post by: nctnico on September 20, 2018, 08:38:26 pm
The usual purpose of a thermistor, in this type of power supply, is to limit the inrush current to the main input filter capacitor. In normal operation, you wouldn't expect the thermistor to get hot enough to break apart. Presumably, something downstream of the thermistor went short circuit (e.g. the main switching MOSFET transistor). So, as ArthurDent suggests, it would be unwise to just replace that part and plug it back in to power.

A better way, would be to connect the oscilloscope to mains power via an incandescent lamp. A 60W light bulb, for example, would limit the current to around a quarter of an amp. If there isn't a short circuit, the lamp should, initially, glow brightly and then dim, but in the presence of a short circuit, it would continuously glow brightly.
I'd pull out a DMM first and check the rectifier and primary MOSFET for a short before attempting a repair or even power it.
Title: Re: DSO-X 3024A Power Supply defect
Post by: enz on September 27, 2018, 08:24:49 am
Hi All,

sorry for the late response, I was very busy.

Thanks for all the hints, very appriciated.

The defect part was indeed a 7Ohm Thermitor, thanks for pointing that out.

The 6.3A Fuse was not blown. This Fuse is only in Series to a varistor, so it only blows if the varistor goes defect.

The power supply is working fine now. Here is what happened:
The main capacitor (100uF/420V, Nichicon 105°C) was defect.
This caused the voltage to rise and the primary MosFET popped to a dead short.
This caused the Thermistor to overheat and blow (but maintain a low impedance connection). Due to the dead short of the MosFET the circuit breaker (16A) tripped.

I replaced the three parts and checked the rest of the power supply, but all other parts were fine.
Scope is back in business now.

The main problem seeems to be, that the supply is powered all the time. The scope is about 7 years old. Don't know why Agilent decided to put the switch on the secondary side.

Thanks again,
Martin
Title: Re: DSO-X 3024A Power Supply defect
Post by: HighVoltage on September 27, 2018, 11:10:13 am
I had it on a few Keysight and also Keithley instruments power supplies, that the NTC only broke.
Only exchanging the NTC solved the problem completely.
Funny: I bought a few extra NTC's and they are almost all gone by now.

I think they fail, when the instrument is turned ON/OFF multiple times, shortly after each other and the NTC is overloaded. I also noted that newer instruments have a much larger NTC installed ind the PSU.

Title: Re: DSO-X 3024A Power Supply defect
Post by: DEHiCKA on January 11, 2019, 03:20:56 pm
Got mine 3034A blown today exact the same way as OP.
Loud electric bang with smell of an electronic death and 16A circuit breaker tripped.
Last time it was powered more than 12 hours ago from the same outlet.

Clearly, PSU is not well designed: main cap heated so much for so long so the board on the other side is black and cracked.
One of the mosfets was blown to pieces (P12NM50). And there was an arc from the PSU backside to the scope's main shield.
The 6.3A Fuse was not blown. NTC has a small crack but still good. Probably something else is dead.
Here is another DSO-X blown the same way with some dead parts on the PSU ctrl board:
http://powersuppyrepair.blogspot.com/2018/02/lineage-power-cch0125f1-z03a.html (http://webcache.googleusercontent.com/search?q=cache:vKVaRSUmTC8J:powersuppyrepair.blogspot.com/2018/02/lineage-power-cch0125f1-z03a.html+&cd=1&hl=en&ct=clnk&gl=ru)

I do not really want to repair the PSU, but can not find where to buy a direct replacement yet.
It is 5"x 3" 12V 125W (https://www.eevblog.com/forum/repair/dso-x-3024a-power-supply-defect/?action=dlattach;attach=620551). DSO-X uses remote sense lines and remote on-off.

There are bunch of 5"x 3" 120W+ PSUs with sense and on/off (pull down), but I can not find one with the same pinout.


Title: Re: DSO-X 3024A Power Supply defect
Post by: DEHiCKA on January 18, 2019, 12:18:09 pm
Follow up on the repair.
The main 100uF/420V cap has degraded down to 9uF.
The PSU control board was also fried, so I did not bother to repair it.
Exchanged PSU for Meanwell RPS-400. Works fine now.

I'm glad the cirquit breaker was only 16A / 220V, not 32A or 40A!
Title: Re: DSO-X 3024A Power Supply defect
Post by: HighVoltage on January 18, 2019, 04:21:23 pm
Congratulations on the successful repair.

Nice that we can buy fitting power supplies for these scopes.
Title: Re: DSO-X 3024A Power Supply defect
Post by: frabre on February 13, 2019, 01:36:30 pm
Hi DEHiCKA,

I have the same problem of power supply.
I tried to repair but...
Which model of RPS-400: RPS-400-12 or RPS-400-12-C ?

If 400-12: no problem of shielding ?

If 400-12-C: no problem of height ?

Thanks in advance...


Title: Re: DSO-X 3024A Power Supply defect
Post by: DEHiCKA on March 20, 2019, 10:03:23 am
Hi, frabre
I have the cheapest RPS-400-12 without cage.
No problem with the shielding, it has a slight audible noise, but otherwise working just fine.
In/Out terminals are differ from original though, so you have to make some kinda adapter.
Title: Re: DSO-X 3024A Power Supply defect
Post by: Madmanguruman on February 03, 2020, 05:09:16 pm
Just chiming in about shielded vs. unshielded 3x5 power supplies. I recently replaced the same PSU from a DSOX3014A scope with a Murata PQC250-12 and a bit of Mylar to create some creepage between the cable bundles and power supply itself. So far so good, no discernable pick-up or noise issue. I would argue that if you are replacing with a non-caged PSU that you should carefully dress the cables to keep them away from hotspots or from touching any primary-side parts - this is why I added some Mylar under the cable assemblies as they cross the power supply.

Also, to sanity-check the scope before you get a new power supply, you can remove the PSU and connect a 12VDC 10A lab supply directly to the 12V rail (no need for enable or remote sense) - the scope will power-up and operate without these signals. My scope was drawing between 5.5 and 6.5A with a single scope probe connected and the scope capturing data.
Title: Re: DSO-X 3024A Power Supply defect
Post by: salvagedcircuitry on March 21, 2020, 04:10:39 pm
Hey Guys! I found a similar problem with my 3034a oscilloscope power supply. I made a repair video about fixing it. 

https://www.youtube.com/watch?v=fd1uQpH9Paw

Hats off to @DEHiCKA for posting the power supply blog repair link. My current mode controller was completely toast as well.

List of replacement parts:
Datasheet for look-a-like lineage branded power supply. CCH125 series:
http://apps.geindustrial.com/publibrary/checkout/CCH125?TNR=Data%20Sheets%7CCCH125%7CPDF&filename=CCH125.pdf (https://www.eevblog.com/forum/repair/dso-x-3024a-power-supply-defect/?action=dlattach;attach=620551)

Genuine Keysight PSU repair part: 0950-5277
https://www.keysight.com/my/partDetail/0950-5277 (https://www.keysight.com/my/partDetail/0950-5277)

Original mosfet:
https://www.digikey.com/product-detail/en/stmicroelectronics/STP12NM50/497-2666-5-ND/603691 (https://www.digikey.com/product-detail/en/stmicroelectronics/STP12NM50/497-2666-5-ND/603691)

Replacement mosfet:
https://www.digikey.com/product-detail/en/ixys/IXTP450P2/IXTP450P2-ND/2328313 (https://www.digikey.com/product-detail/en/ixys/IXTP450P2/IXTP450P2-ND/2328313)

Two pin Diode package near mosfet:
https://www.digikey.com/product-detail/en/on-semiconductor/MUR860G/MUR860GOS-ND/919926 (https://www.digikey.com/product-detail/en/on-semiconductor/MUR860G/MUR860GOS-ND/919926)

Current mode controller:
https://www.digikey.com/product-detail/en/on-semiconductor/UC3842BVD1R2G/UC3842BVD1R2GOSCT-ND/5802572 (https://www.digikey.com/product-detail/en/on-semiconductor/UC3842BVD1R2G/UC3842BVD1R2GOSCT-ND/5802572)

Replacement MOV:
https://www.arrow.com/en/products/v300la20ap/littelfuse (https://www.arrow.com/en/products/v300la20ap/littelfuse)

Replacement NTC Varistor:
https://www.arrow.com/en/products/b57237s709m/epcos-tdk (https://www.arrow.com/en/products/b57237s709m/epcos-tdk)

Replacement Fuse:
https://www.digikey.com/product-detail/en/bel-fuse-inc/MRT-6-3AMMO/507-1119-1-ND/4794478 (https://www.digikey.com/product-detail/en/bel-fuse-inc/MRT-6-3AMMO/507-1119-1-ND/4794478)

Replacement 1w 22k resistor under main filter capacitor:
https://www.arrow.com/en/products/erj-1tyj223u/panasonic (https://www.arrow.com/en/products/erj-1tyj223u/panasonic)

Tall cap I selected:
https://www.digikey.com/products/en?keywords=ucy2w101mhd (https://www.digikey.com/products/en?keywords=ucy2w101mhd)

Dimensionally compatible cap:
https://www.digikey.com/product-detail/en/rubycon/450VXH100MEFCSN22X25/1189-2028-ND/3564971 (https://www.digikey.com/product-detail/en/rubycon/450VXH100MEFCSN22X25/1189-2028-ND/3564971)

Power Supply Replacement Candidates:
Meanwell RPSG-160-12 (https://www.arrow.com/en/products/rpsg-160-12/mean-well-enterprises)
Meanwell RPS-300-12 (https://www.digikey.com/product-detail/en/mean-well-usa-inc/RPS-300-12/1866-4044-ND/7706051)
Meanwell RPS-400-12 (https://www.digikey.com/product-detail/en/mean-well-usa-inc/RPS-400-12/1866-4052-ND/7706061)
Meanwell EPP-300-12 (https://www.digikey.com/product-detail/en/mean-well-usa-inc/EPP-400-12/1866-1655-ND/7703132)
Murata PQC250-12 (https://www.digikey.com/product-detail/en/murata-power-solutions-inc/PQC250-12/811-3301-ND/6873845)
Bel Power ABC201-1012G (https://www.digikey.com/product-detail/en/bel-power-solutions/ABC201-1012G/179-2704-ND/4076488)
Title: Re: DSO-X 3024A Power Supply defect
Post by: mlloyd1 on May 07, 2020, 03:20:57 pm
so, is anybody seeing this issue on the 3000T models (yet)? :(

mlloyd1
Title: Re: DSO-X 3024A Power Supply defect
Post by: TheSteve on May 07, 2020, 04:33:22 pm
so, is anybody seeing this issue on the 3000T models (yet)? :(

mlloyd1

The 3000t series uses a different power supply that so far doesn't appear to have any issues.
Title: Re: DSO-X 3024A Power Supply defect
Post by: salvagedcircuitry on May 07, 2020, 04:57:59 pm
so, is anybody seeing this issue on the 3000T models (yet)? :(

mlloyd1

The 3000t series uses a different power supply that so far doesn't appear to have any issues.

Dave's early review shows the same lineage power supply @2:23
https://www.youtube.com/watch?v=H9QONLaitWU&t=2m23s (https://www.youtube.com/watch?v=H9QONLaitWU&t=2m23s)

Granted, they could have changed it out later on (I hope they did).
Title: Re: DSO-X 3024A Power Supply defect
Post by: TheSteve on May 07, 2020, 05:25:12 pm
Keysight has confirmed in the past that they have changed it. I know my 3024T has a different model supply. Perhaps it was after production had started.
Title: Re: DSO-X 3024A Power Supply defect
Post by: AndyC_772 on August 22, 2020, 11:10:54 am
Just to add another data point - this morning my MSO-X3104A died  :-BROKE

It was sitting on the bench, powered up but not actually connected to anything, when the display suddenly went blank without warning. I removed and reinserted the power cable, there was a loud bang, and the GFCI for the house tripped.

The main reservoir cap in the PSU has vented, and was very hot indeed. The current mode controller has blown the top off its package, and the gate resistor for the MOSFET Q1 is toast too.

Ordinarly I wouldn't even consider repairing an off-the-shelf PSU module, but this one appears to be a custom part that's not readily available, even though it looks like a standard item.

Has anyone replaced one of these with something else recently? Is there anything particularly special about the Lineage module that makes it hard to substitute for another unit?
Title: Re: DSO-X 3024A Power Supply defect
Post by: HighVoltage on August 22, 2020, 03:09:39 pm
I have always repaired the Keysight power supplies, because usually it is very simple.

What is different on the MSO-X3104A?
You have pictures?


Title: Re: DSO-X 3024A Power Supply defect
Post by: AndyC_772 on August 22, 2020, 05:08:48 pm
I don't think the MSO-X3104A has a different power supply. I've asked Keysight to quote for a replacement part, and there's always the option of fitting an alternative with a suitable wiring adapter, but since I have some spare time this weekend I figured it was probably worth seeing if the damage looks repairable.

I had a few different dead parts than others have seen; MOSFET Q1 has a series resistor which is 5.11 Ohms 0805, and R7 is 110mOhm 5% (probably 2W).

In my PSU both were open circuit; the gate resistor was blown to bits, and the larger one I suspect was damaged during extraction of C11. They're stuck together with white goop which made removing them to access the current mode controller (also blown to bits!) tricky.

The MOSFET Q1 had a big diagonal crack all the way across the package body, the main cap had vented, and the board was dark and discoloured around the 22k resistors on the underside. Part of me is curious to know what happened in what order. Another part of me is cursing a wasted day and just wants it back working again.

I was able to determine the values of the dead resistors by measuring them in a working PSU, which I borrowed out of my MSO-X3054A. Since I rely on my scope to make a living, having a spare on hand was never optional, and today my decision to keep two that are very similar has paid off. I've put the PSU from the spare scope into my 3104A which is now working fine.

Even the working PSU in the 3054A was very hot when I removed it, having been running for several hours since the 3104A died. I'm really not surprised they fail.

My MOV and NTC seemed OK, there's high impedance from L to N and about 7 Ohms across the NTC and chokes.

I should warn anyone else looking to work on one of these supplies, you'll need a powerful soldering iron and a good range of tips. The board is constructed with no thermal relief on any of the through-hole pads, and the copper draws heat out like no other board I ever remember working on. Desoldering the heat sinks and large components without damaging the board was exceptionally difficult even with my JBC, and you'll need to be both gentle and patient. The main cap C7 was especially reluctant to come out, and it's fortunate that the little copper pad on the top side of the board, negative terminal, wasn't actually connected to anything.

I wasn't able to find an exact replacement for the 110mOhm resistor, so I've ordered 100m + 10m to fit in series. All the other parts were available from stock at either RS or Farnell, including some parts which looked OK but which I had to remove to gain access to others. Given the cost of new components vs my time, I rarely re-fit used ones to anything.

Fingers crossed nothing else has failed, and when it's all reassembled I get a working PSU again. I'll be running it for some time out of the box on a decent load before I trust it with my scope.
Title: Re: DSO-X 3024A Power Supply defect
Post by: salvagedcircuitry on August 26, 2020, 08:15:12 pm
I don't think the MSO-X3104A has a different power supply. I've asked Keysight to quote for a replacement part, and there's always the option of fitting an alternative with a suitable wiring adapter, but since I have some spare time this weekend I figured it was probably worth seeing if the damage looks repairable.

I should warn anyone else looking to work on one of these supplies, you'll need a powerful soldering iron and a good range of tips. The board is constructed with no thermal relief on any of the through-hole pads, and the copper draws heat out like no other board I ever remember working on. Desoldering the heat sinks and large components without damaging the board was exceptionally difficult even with my JBC, and you'll need to be both gentle and patient. The main cap C7 was especially reluctant to come out, and it's fortunate that the little copper pad on the top side of the board, negative terminal, wasn't actually connected to anything.

I wasn't able to find an exact replacement for the 110mOhm resistor, so I've ordered 100m + 10m to fit in series. All the other parts were available from stock at either RS or Farnell, including some parts which looked OK but which I had to remove to gain access to others. Given the cost of new components vs my time, I rarely re-fit used ones to anything.

Fingers crossed nothing else has failed, and when it's all reassembled I get a working PSU again. I'll be running it for some time out of the box on a decent load before I trust it with my scope.

My PSU repair was rather painful, but successful. Overall, I'm not too fond of the repairability of the Lineage PSU design. It definitely took a lot of patience, flux and heat to get the aluminum heatsink off and not destroy the staking pads. I think I ended up having to super-glue a heatsink pad back on at the end of the repair process. I opted to leave the daughter PCB soldered in and just desoldered the failed soic-8 current mode controller on my unit. Since the lineage design does not instill confidence, I went with a meanwell RPSG-160-12 as a replacement power supply to have on hand in case the failure occurs again. Unfortunately, I goofed and ended up with the RPS-160-12 which does not have the remote-on feature which this oscilloscope needs as the power button is designed to switch the secondary side.
https://www.arrow.com/en/products/rpsg-160-12/mean-well-enterprises (https://www.arrow.com/en/products/rpsg-160-12/mean-well-enterprises)

If I could do the repair all over again, I would desolder the (4) series 22k 1w SMT resistors below the main filter cap and replace them with one ~88k (https://www.digikey.com/product-detail/en/te-connectivity-passive-product/ROX5SJ91K/A138105-ND/2385276) 4w or 5w through hole resistor and just leave the resistor spaced off the main pcb. This way the resistors can't directly heat up the back side of the filter cap. There is enough space between the bottom face of PSU PCB and the aluminum shell of the agilent oscilloscope to accommodate the resistor. Additionally I would add electrical tape on the back side of the oscilloscope casing where the resistor may come close. On closer look, It may be a set of 2 power resistors, I see a trace between the 3rd and 4th resistor on the back side.

Something like this:
(https://www.eevblog.com/forum/repair/dso-x-3024a-power-supply-defect/?action=dlattach;attach=1054730;image)
Title: Re: DSO-X 3024A Power Supply defect
Post by: AndyC_772 on August 27, 2020, 10:04:29 am
I'm a little hesitant to make a resistor modification like that because I'm not sure I can see a sufficiently robust way to mount a TH part off the PCB.

The SMT resistors may get very hot, but they are at least light weight and unlikely to detach and become dangerous if the scope takes a knock. I'm concerned that the added weight of a TH part could cause it to detach the already weakened pads from the PCB, and in the worst case this means a loose end at 400V flapping about.

As an aside, I was faced with a very similar problem here (https://www.eevblog.com/forum/repair/replacing-some-very-hot-resistors/). After I posted that thread, the equipment in question did actually fail again, and it was the resistor chain exactly as I'd predicted.

I've removed the resistors from my scope PSU just to check the condition of the board and solder joints. The board is blackened and the solder mask is cracked, but the pads are still firmly attached, and following a good clean with IPA, I'd put it in the "I've seen worse" category. I'll order some replacement resistors anyway, no sense refitting old ones.

Given that the failure is entirely predictable, I've also ordered a replacement main capacitor (this one (https://uk.farnell.com/rubycon/450vxh100mefcsn22x25/cap-100-f-450v-alu-elec-snap-in/dp/2102450)) for my other scope, by way of preventative maintenance. If I can spend half an hour swapping a single component, rather than waiting for a potentially catastrophic failure that will inevitably happen at the most inconvenient moment, that has to be time well spent, IMHO.

One thought I did have was to fill the space between the resistors and the internal aluminium chassis of the scope with a thermal gap filler pad material like this stuff (https://uk.farnell.com/t-global/l375-150-3-0a/gap-filler-3mm-sheet/dp/1372922[/url). This would conduct some of the heat out of the board and into the chassis, which in turn would keep the temperature of the capacitor down and help it last a bit longer.
Title: Re: DSO-X 3024A Power Supply defect
Post by: AndyC_772 on August 27, 2020, 10:05:34 am
ps. I also stumbled across an older thread containing some useful information - here (https://www.eevblog.com/forum/repair/resistor-of-a-keysight-ps-doubt!/).
Title: Re: DSO-X 3024A Power Supply defect
Post by: salvagedcircuitry on August 28, 2020, 05:48:03 am
I'm a little hesitant to make a resistor modification like that because I'm not sure I can see a sufficiently robust way to mount a TH part off the PCB.

The SMT resistors may get very hot, but they are at least light weight and unlikely to detach and become dangerous if the scope takes a knock. I'm concerned that the added weight of a TH part could cause it to detach the already weakened pads from the PCB, and in the worst case this means a loose end at 400V flapping about.

As an aside, I was faced with a very similar problem here (https://www.eevblog.com/forum/repair/replacing-some-very-hot-resistors/). After I posted that thread, the equipment in question did actually fail again, and it was the resistor chain exactly as I'd predicted.

I've removed the resistors from my scope PSU just to check the condition of the board and solder joints. The board is blackened and the solder mask is cracked, but the pads are still firmly attached, and following a good clean with IPA, I'd put it in the "I've seen worse" category. I'll order some replacement resistors anyway, no sense refitting old ones.

Given that the failure is entirely predictable, I've also ordered a replacement main capacitor (this one (https://uk.farnell.com/rubycon/450vxh100mefcsn22x25/cap-100-f-450v-alu-elec-snap-in/dp/2102450)) for my other scope, by way of preventative maintenance. If I can spend half an hour swapping a single component, rather than waiting for a potentially catastrophic failure that will inevitably happen at the most inconvenient moment, that has to be time well spent, IMHO.

One thought I did have was to fill the space between the resistors and the internal aluminium chassis of the scope with a thermal gap filler pad material like this stuff (https://uk.farnell.com/t-global/l375-150-3-0a/gap-filler-3mm-sheet/dp/1372922[/url). This would conduct some of the heat out of the board and into the chassis, which in turn would keep the temperature of the capacitor down and help it last a bit longer.

Yeah. I'm not under the impression that this was a decent quality power supply. The PCB material around the resistors was quite charred on my unit, which may indicate a low TG fiberglass board was used. I have not experienced many boards where neighboring soldermask cracks and flakes off after a desoldering procedure.
You have a very valid point, the weight of a THT resistor may be too much for whatever is left of the compromised pads that endured such elevated temperatures. That thermal pad looks like a promising solution. I'm guessing the pad would have to be around 6mm thick to sink the heat to the aluminum shell, but I think there are some noticeable diminishing returns with increased thermal pad z-height.

I'm glad you were able to get the scope back up and running!
Title: Re: DSO-X 3024A Power Supply defect
Post by: AndyC_772 on September 01, 2020, 10:20:30 am
Today the last few parts arrived to complete the PSU repair. I reassembled the unit and connected it to a 5R dummy load, to give it an opportunity to prove its reliability before being connected to my expensive scope.

It's as well that I ran the test. It lasted about 10 minutes before there was a bang and the fuse in my isolation transformer blew.

The damage was interesting - Q8 showed evidence of arcing from the tab to the heat sink, and it looked as though there may have been a tiny nick in the kapton tape which caused it to fail as an insulator.

I fitted my one spare Q8, and replaced the kapton tape under it with a proper thermal pad. This time it managed only 10 seconds before there was another bang and a visible puff of smoke.

I don't doubt it could be fixed again, but if there's a Mean Well that'll fit, then that has to be the better option now.
Title: Re: DSO-X 3024A Power Supply defect
Post by: AndyC_772 on September 04, 2020, 10:17:05 am
Today I installed a Mean Well RPS-160-12 into my 3054A, which had graciously agreed to donate its original power supply to keep the 3104A alive.

The MW has a different connector and pin-out, which requires a new wiring harness. It also requires a little filing of the mounting holes to make it fit, as they don't quite line up with the standoffs on the scope chassis. (Take care doing this, as a couple of them do make an important earth connection - and test for connectivity afterwards!)

There's an adjuster on the MW which can be used to set the output voltage. Noting that the silk screen on the scope's own dc-dc board refers to +13V from the PSU, I adjusted its output up to +12.9V.

Result? The scope turns on just fine, but the front panel power switch no longer does anything. The MW doesn't have the remote power-on feature that the original supply does, and there's nowhere to connect the REMOTE wire from the scope. It looks as though the RPS-400-12 does have remote power on/off, so with hindsight that could have been a better choice even though it's a more costly unit.
Title: Re: DSO-X 3024A Power Supply defect
Post by: HighVoltage on September 04, 2020, 02:58:10 pm
Nice that you got it partially working.

It might be a good idea to try the RPS-400-12 with remote control and see if you get it to work.

Title: Re: DSO-X 3024A Power Supply defect
Post by: georges80 on October 22, 2020, 03:32:08 am
Well, another lineage power supply bit the dust (in my msox2024a). Same old story, blew the transistor (and fuse) and the main cap has gone from 100uF to around 5uF.

Rather than try to repair, I followed the path of others and replaced with a Meanwell. In my case after a bunch of research/comparing, I went with an EPP-300-12 model. Mouser had it for $58. Bought some JST 4 pin females and pins to make the S+/S- and Power-on mate and then repurposed the existing AC plug to fit on 2 of the 3 pins (of the 5 pin connector) on the Meanwell. Cut the 3 GND and 3 +12V wires and crimped each set of 3 to a ring terminal.

It's a tight fit, but will fit and all go back together nicely. The Power-on signal of the EPP-300 talks properly with the scope's front panel button so all functions nicely.

Thanks to contributors of this thread to steer me down the right path to repair my scope. I did power it up with +12V from my powersupply first to verify nothing nasty had happened other than the crackle pop of the original powersupply. All was good so that was a relief and I knew I just need to replace the powersupply to be back in business.

cheers,
george.


Title: Re: DSO-X 3024A Power Supply defect
Post by: salvagedcircuitry on October 22, 2020, 05:46:25 am
You definitely made the right choice! I just don't think it's worth the hassle of repairing and troubleshooting the lineage power supply anymore, as it is really not a good design.

Suitable candidates I've come across so far:
Meanwell RPSG-160-12
Meanwell RPS-300-12
Meanwell RPS-400-12
Meanwell EPP-300-12
Murata PQC250-12
Bel Power ABC201-1012G
...

The original replacement unit I purchased, the Meanwell RPS-160-12, did not include the remote power-on option. I goofed and purchased the wrong version. The unit I meant to purchase was the Meanwell RPSG-160-12. What a difference one letter can make!

The replacement power supply needs to have a remote sense and remote power-on feature as the power switch on the oscilloscope switches the secondary side of the power supply and not the primary side. Without the remote-on feature, the oscilloscope power button does nothing. Plugging the oscilloscope in would be the on/off button, which is not ideal.

All these units seem pretty decent. I'm liking the fact that the Murata unit is higher efficiency and most importantly does not have a perpendicular daughter board, like the meanwells. This should make the murata unit easier to repair, but then again, none of these units should need any attention for a long time.

It doesn't look like the murata has fine adjustment on Vout, so from the datasheet it can't be set to 13v which is the output voltage of the lineage PSU. The meanwells have Vout fine adjustment. The bel power has minimal adjustment. This may not be a deal breaker as these are all 12v class power supplies and the original lineage PSU only had a +-5% voltage adjustment range and poor voltage regulation.

Glad to hear you got the msox2024a back up and running!
Title: Re: DSO-X 3024A Power Supply defect
Post by: rolkinas on December 03, 2020, 10:09:00 pm
After reading all this I took apart mine perfectly working DSO-X 2024A to check condition of smps. I use scope not that much and bought it used couple years ago.
Cap measures ok: 107uF.
But those baking resistors gets surprisingly hot. Precious preprogrammed obsolescence.
It seems that psu might survive longer with scope being powered on and fan running. While resistors still heats while unit is powered off. It's not funny having components near 100C in device being in standby...
Just curious if new SMPSs sold as spares by Keysight have such an issue?
Title: Re: DSO-X 3024A Power Supply defect
Post by: salvagedcircuitry on December 04, 2020, 04:21:29 am
After reading all this I took apart mine perfectly working DSO-X 2024A to check condition of smps. I use scope not that much and bought it used couple years ago.
Cap measures ok: 107uF.
But those baking resistors gets surprisingly hot. Precious preprogrammed obsolescence.
It seems that psu might survive longer with scope being powered on and fan running. While resistors still heats while unit is powered off. It's not funny having components near 100C in device being in standby...

This is excellent information. Thanks a bunch for adding the infrared images. Makes me want to pull the OEM PSU out of my other DSOx  :scared:
Title: Re: DSO-X 3024A Power Supply defect
Post by: Madmanguruman on December 04, 2020, 09:31:43 pm
I'm liking the fact that the Murata unit is higher efficiency and most importantly does not have a perpendicular daughter board, like the meanwells. This should make the murata unit easier to repair, but then again, none of these units should need any attention for a long time.

The Murata PQC250-12 works just fine with three DSOX3014As that I've repaired - the oldest repair has had close to 1 year of constant use with no issues so far.

Like with other units, the wiring harness needs to be modified to make it work but it does offer remote sense as well as remote on/off (possibly with inverted logic, but the button will still work.)

I must also admit that I'm biased - I work at the Murata power supply design center where the PQC250-12 was designed and qualified.

:-DD

Title: Re: DSO-X 3024A Power Supply defect
Post by: rernexy on December 23, 2020, 03:38:39 pm
Finally got around to dismantling my msox3054a after 8 or 9 years. Partly because of a high pitch hissing sound that always seemed to be present, and it's waaaaay out of warranty so now idgaf.

But lo and behold look what I've found on the power supply, the blackening around the 22K resistors under the big arse 420V cap.
The little black chunk to the left is what flaked away when I gently prodded between the leftmost 2 22K resistors, it's exposed a track.
Also you can see that on the underside of the shield it is starting to discolour/blacken in line with either the resistors or that mosfet (don't know).

Maybe time to throw the parts-cannon at it for pre-emptive maintenance.
Title: Re: DSO-X 3024A Power Supply defect
Post by: Jwalling on December 23, 2020, 05:05:28 pm
In years past, HP/Agilent would issue service notes on things like this.
Title: Re: DSO-X 3024A Power Supply defect
Post by: rolkinas on December 23, 2020, 06:29:29 pm
Hi, don't forget to check capacitance of 420V cap. It probably is semi-dry.
I am thinking about mounting something like power resistor on psu shield-heatsink in place of smd. something like ROX5SJ91K from Digikey.
Leaving these baking 22K where they are now is asking for trouble.
Title: Re: DSO-X 3024A Power Supply defect
Post by: rernexy on December 26, 2020, 08:09:55 am
Decided to desolder the 22K resistors.
They were hiding more blackening/carbonising/burning of the PCB. Pretty sure that wasn't my desoldering.
Title: Re: DSO-X 3024A Power Supply defect
Post by: rernexy on December 26, 2020, 12:36:03 pm
Different view of the pads (continuing previous post).
Shining a light from the opposite side, after removing the 420V cap, you can see cracks more easily on the inside of the resistor solder pads.
There is a faint crack at the upper right resistor, bottom pad.
Title: Re: DSO-X 3024A Power Supply defect
Post by: rernexy on January 04, 2021, 07:15:15 am
Parts I ordered arrived today. Bought 2 different models of the resistors and capacitor.

Measured the ESR of the cap from the supply and the new ones using an "ESR Meter Mk II" as seen in the photo.
1.4R for the old cap, 0.25R for the new ones.

Measured the capacitance of all of them with various multimeters, all read within 87uF to 95uF.
Then measured capacitance (not ESR) with the LCR45 at different frequencies, theres a few photos of that and a table below.

-OldNewNew (high ripple current)
1kHz  46uF87uF84uF
15kHz  1.08uF   cycled negative to ~110uF  cycled negative to ~110uF 
200kHz  282nF   6uF but cycled slowly between 5 and 8 uF  5.9uF but cycled slowly between 5 and 8 uF 


Here are specific parts I bought:

100uF cap:
LGW2W101MELA25 450V high ripple current https://www.nichicon.co.jp/english/products/pdfs/e-gw.pdf (https://www.nichicon.co.jp/english/products/pdfs/e-gw.pdf)
LGUW6101MELA same as on the supply https://www.nichicon.co.jp/english/products/pdfs/e-gu.pdf (https://www.nichicon.co.jp/english/products/pdfs/e-gu.pdf)

22K resistors:
CRGP2512F22K  https://www.te.com/global-en/product-4-2176331-1.html (https://www.te.com/global-en/product-4-2176331-1.html)
352122KFT  https://www.te.com/global-en/product-8-2176070-1.html (https://www.te.com/global-en/product-8-2176070-1.html)
Title: Re: DSO-X 3024A Power Supply defect
Post by: rernexy on January 04, 2021, 12:30:28 pm
Continuing from previous post, here are scope captures of 200kHz 1Vpp square wave fed into the old cap and the direct equivalent new cap (LGUW6101MELA). Just like what @w2aew demonstrates at https://youtu.be/115erzCCxgE

capture 1: old cap, scope DC coupled
capture 2: old cap, scope AC coupled
capture 3: new cap (LGUW6101MELA), scope DC coupled
capture 4: new cap (LGUW6101MELA), scope AC coupled
Title: Re: DSO-X 3024A Power Supply defect
Post by: Leo Bodnar on January 30, 2021, 07:57:23 pm
My MSO-X 3024A PSU blew up as well - just now. 
Nice consistency Agilent, or Shitsight or whatever you are called now.
Leo
Title: Re: DSO-X 3024A Power Supply defect
Post by: rernexy on January 31, 2021, 04:20:54 am
My MSO-X 3024A PSU blew up as well - just now. 

Do you have any photos of what specifically blew up?
How old was your 3024A?
Title: Re: DSO-X 3024A Power Supply defect
Post by: Leo Bodnar on January 31, 2021, 10:56:07 am
Looks like synchronous rectification MOSFET.
It's 7-8 years old - obsolete by iPhone standards.
Leo
Do you have any photos of what specifically blew up?
How old was your 3024A?
Title: Re: DSO-X 3024A Power Supply defect
Post by: rernexy on February 01, 2021, 11:57:31 am
Is the PCB blackened/burnt under the 22K resistors on the bottom of the PCB aswell (like others in this thread)?
Title: Re: DSO-X 3024A Power Supply defect
Post by: Leo Bodnar on February 01, 2021, 12:29:07 pm
It has discolouration and solder resist cracks.
Aren't these HV safety bleed resistors?  They can probably be increased in value in such case - but fixing it is polishing a turd.
It was probably designed and tested in 120V mains zone.
Leo
Is the PCB blackened/burnt under the 22K resistors on the bottom of the PCB aswell (like others in this thread)?
Title: Re: DSO-X 3024A Power Supply defect
Post by: 2N3055 on February 01, 2021, 12:47:58 pm
Looks like synchronous rectification MOSFET.
It's 7-8 years old - obsolete by iPhone standards.
Leo
Do you have any photos of what specifically blew up?
How old was your 3024A?

That must have been quite noticeable bang...
Is that a blob of ejected melted transistor metal on that mounting clamp ?

Stay safe,

Sinisa
Title: Re: DSO-X 3024A Power Supply defect
Post by: Leo Bodnar on February 01, 2021, 12:57:23 pm
Yes, it's a lava bomb ejected from inside the FET.  The explosion was very loud indeed.
Leo
That must have been quite noticeable bang...
Is that a blob of ejected melted transistor metal on that mounting clamp ?
Title: Re: DSO-X 3024A Power Supply defect
Post by: gman76 on February 16, 2021, 06:22:24 pm
Can you provide specifics on the harness re-wiring?  Is it just a matter of a couple wires?  Will it be obvious once I have the supply in hand?  I plan to use either the PQC250-12 or EPP-300-12.  Haven't purchased yet.
Title: Re: DSO-X 3024A Power Supply defect
Post by: georges80 on February 16, 2021, 07:07:59 pm
It's mostly self evident once you have the scope opened up and remove the dead PS. There's a few wires/connections.

Mains input, Front panel low voltage on/off control,  +12/0V main DC power and sense wires. If you are competent enough to use the scope then you can handle the re-wiring :)

Most of the work is getting the new supply to fit nicely (with the re-wiring) into the rather cramped space. Take your time.

cheers,
george.
Title: Re: DSO-X 3024A Power Supply defect
Post by: gman76 on February 22, 2021, 11:37:34 pm
Hi georges80, I'm buying the RPSG-160-12.  I took the original supply out and looked at the CCH125 pinouts. Everything looks obvious except the pin called REMOTE on the 1x6 header.  There are 3 wires coming from the main board into the CCH125, -S +S and REMOTE.

On the RPSG-160, I see two possibilities: PG and PS/ON.  I think its the PS/ON that I need to connect the REMOTE wire to, correct?  The pin called PG looks like an output.  If this is the case, then I'll need to remove the 3 wires from the orig connector and place the two sense wires in a new housing and the REMOTE wire into another housing since the RPSG has these split into two connectors.

Title: Re: DSO-X 3024A Power Supply defect
Post by: 2N3055 on February 22, 2021, 11:54:09 pm
Hi georges80, I'm buying the RPSG-160-12.  I took the original supply out and looked at the CCH125 pinouts. Everything looks obvious except the pin called REMOTE on the 1x6 header.  There are 3 wires coming from the main board into the CCH125, -S +S and REMOTE.

On the RPSG-160, I see two possibilities: PG and PS/ON.  I think its the PS/ON that I need to connect the REMOTE wire to, correct?  The pin called PG looks like an output.  If this is the case, then I'll need to remove the 3 wires from the orig connector and place the two sense wires in a new housing and the REMOTE wire into another housing since the RPSG has these split into two connectors.

PG is power good output. Remote is ON/OFF..
Title: Re: DSO-X 3024A Power Supply defect
Post by: rolkinas on February 25, 2021, 03:08:01 pm
Regarding original PSU.
I experimented with higher value resistors in place of cooking 4pcs 22K. AC voltage controlled by variac. Resistor values and coresponding psu start stop voltages below:

220k - start 80Vac , stop 75Vac
310k - start 98Vac , stop 75Vac
440k - start 135Vac , stop 75Vac
660k - start 190Vac , stop 75Vac
750k - start 217Vac , stop 75Vac

When psu starts, voltage drop on resistors becomes near 380V because PFC starts as well.
turn off voltage is determined by PFC

Even with 220k resistor stayed at about 70 degree C what is much more usable {hint to 110Vac grid fellas :) }
Title: Re: DSO-X 3024A Power Supply defect
Post by: gman76 on March 01, 2021, 08:19:44 pm
Received the Meanwell RSPG160 supply, expanded holes to get the screw holes lined up, re-arranged wiring on connector.  Plugged it into 120VAC, not sure if it would go bang, but quietly powered up.  Scope is now back up and running.

Worked fine at 12.0V., but adjusted Vout up to 12.6V. 

The only issue now is that the front power button doesn't work.  I probed the REMOTE signal (PS/ON) and it's always low.  Pushing the power switch doesn't change the DMM reading, just slightly.  Maybe need a GND return?  Or is this the wrong signal?

EDIT:  It was indeed the ground connection of the 1x4 header (CN901).  I made a wire with a crimp on each end.  Front power button works great.
Title: Re: DSO-X 3024A Power Supply defect
Post by: tapelu on March 15, 2021, 10:09:13 am
I'm liking the fact that the Murata unit is higher efficiency and most importantly does not have a perpendicular daughter board, like the meanwells. This should make the murata unit easier to repair, but then again, none of these units should need any attention for a long time.

The Murata PQC250-12 works just fine with three DSOX3014As that I've repaired - the oldest repair has had close to 1 year of constant use with no issues so far.

Like with other units, the wiring harness needs to be modified to make it work but it does offer remote sense as well as remote on/off (possibly with inverted logic, but the button will still work.)

I must also admit that I'm biased - I work at the Murata power supply design center where the PQC250-12 was designed and qualified.

Hi, how do I have to modify the wiring harness so that the power supply starts with the power switch? If I connect pin 1 to pin 8, the oscilloscope starts directly, but I want the power switch to be able to be used?

:-DD
Title: Re: DSO-X 3024A Power Supply defect
Post by: Madmanguruman on March 16, 2021, 12:50:44 am
I'll share my reverse-engineering below.

The pinout of the Molex header (on the DSO-X side) is as follows:

(https://i.imgur.com/ee7KvIw.png)

1: +12V
2: +12V
3: +12V
4: +12V return
5: +12V return
6: +12V return
7: Return sense
8: +12V sense
9: Remote on/off

For the PQC250-12:

- Run 3 wires from the DSO-X Molex header pins 1-2-3 to +12V (any of J2 pins 1-6)
- Run 2 wires from the DSO-X Molex header pins 4-5 to +12V return (any of J2 pins 7-12)
- Run 1 wire from the DSO-X Molex header pin 6 to J3 pin 8 - this is the return for the remote on/off signal
- Run 1 wire from the DSO-X Molex header pin 7 to J3 pin 6 - this is the low-side remote sense
- Run 1 wire from the DSO-X Molex header pin 8 to J3 pin 5 - this is the high-side remote sense
- Run 1 wire from the DSO-X Molex header pin 9 to J3 pin 4 - this is the remote on/off signal
- The AC cable assembly will plug in directly without modifications.

(https://i.imgur.com/jAQGFNR.png)

Because the PQC250-12 is open-frame I usually put a thin insulating sheet behind the wiring harnesses / in front of the power supply.

(https://i.imgur.com/FemdyDa.png)

Three DSOs with PQC250-12 are deployed in my lab, and all have passed their annual traceable calibration tests (done by an external accredited laboratory).

(Depending on the remote enable logic, you may find that the pushbutton is reversed: in=off, out=on - this can be changed via a few resistor pops/no-pops but why bother?)
Title: Re: DSO-X 3024A Power Supply defect
Post by: tapelu on March 16, 2021, 06:02:32 am
 :-+
Perfect ! Many, many thanks for your effort !
Title: Re: DSO-X 3024A Power Supply defect
Post by: ketch on April 21, 2021, 08:26:21 am
Hello. I need to know the value of the resistor from the photo.