Oscilloscope Fluke PM3082 powersupply problem?
in [Repair]
|
From: powerampfreak on 14 Jun 2010 07:23 On 14 Juni, 12:08, JW <n...(a)dev.null> wrote: > On Sun, 13 Jun 2010 14:16:36 -0700 (PDT) powerampfreak > <powerampfr...(a)hotmail.com> wrote in Message id: > <9d66d54d-7f21-418f-ac7e-78c950fd2...(a)z8g2000yqz.googlegroups.com>: > > > > >I was given an oscilloscope, a Fluke PM3082 from a retired industrial > >electronics engineer. > >He said that during a measurement, the oscilloscope's powersupply just > >bang and a flame came out of the rear panel. After this, the scope was > >left for several years...until I got it. > >The mains fuse has really exploded. Shattered glass in the fuse > >holder. A brief examination of the primary side of the smps reveals no > >shorts. The smps is an ordinary flyback supply. Mains rectifier ok, > >switch ok, snubber, line filters all ok. Really don't know why the > >mains fuse went. > >I just don't want to put a new fuse in and try again, not before I > >investigate the cause. > >Could an incorrect measurement setup cause the mains fuse to explode? > >Anyone familiar with these scopes or perhaps has a service manual for > >it? > >Best regards > >PAF > > IF you are sure there's nothing wrong on the primary, check for shorted > diodes and caps on the secondary side of the switching transformer. You > mention that you checked the "switch". Do you mean the power transistor(s) > that drives the primary side of the switching transformer? > > As Jeff said, isolate the power supply from the rest of the scope if > possible. You should be able to use a lower rated fuse at this point to > help minimize any damage if you don't have any way to current limit the AC > input. > > http://www.jetecnet.com/claims to have a service manual for $10. > > Might also want to search for free manuals for PM3084, PM3092, or PM3094. > They may share the same power supply. I've examined the primary side of the powersupply very carefully. Absolutely NO signs of damage anywhere. The Y caps measures correct 2nF (2pcs of 1nF) also X cap ok at 0.22uF. A NTC inruch limiter measures 15ohm, correct according to the text on it, primary switch transistor ok, mains rectifier diodes ok all of them... But the curiousity took control over me. I cleaned up after the blown fuse. Put a new one (1.6AT) - connected it to mains - and it works! All channels and functions seems to operate just fine. There are really no sign of flames anywhere. One thing which I haven't paid any attention yet, is the mains filter which is an integrated block of some coil and filtercaps encapsulated. I will change the Y and X caps to make sure they're ok. I've never seen a shorted secondary side make the mains fuse explode. Just primary shorts has the power to do this, in my opinion based on hundreds of smps repairs. Anyway, it appears that I've got another nice looking four channel oscilloscope on my bench! :-)
From: N_Cook on 14 Jun 2010 07:37 powerampfreak <powerampfreak(a)hotmail.com> wrote in message news:23ba5952-2509-45b2-b3ce-d0a18e4321d6(a)z8g2000yqz.googlegroups.com... > On 14 Juni, 12:08, JW <n...(a)dev.null> wrote: > > On Sun, 13 Jun 2010 14:16:36 -0700 (PDT) powerampfreak > > <powerampfr...(a)hotmail.com> wrote in Message id: > > <9d66d54d-7f21-418f-ac7e-78c950fd2...(a)z8g2000yqz.googlegroups.com>: > > > > > > > > >I was given an oscilloscope, a Fluke PM3082 from a retired industrial > > >electronics engineer. > > >He said that during a measurement, the oscilloscope's powersupply just > > >bang and a flame came out of the rear panel. After this, the scope was > > >left for several years...until I got it. > > >The mains fuse has really exploded. Shattered glass in the fuse > > >holder. A brief examination of the primary side of the smps reveals no > > >shorts. The smps is an ordinary flyback supply. Mains rectifier ok, > > >switch ok, snubber, line filters all ok. Really don't know why the > > >mains fuse went. > > >I just don't want to put a new fuse in and try again, not before I > > >investigate the cause. > > >Could an incorrect measurement setup cause the mains fuse to explode? > > >Anyone familiar with these scopes or perhaps has a service manual for > > >it? > > >Best regards > > >PAF > > > > IF you are sure there's nothing wrong on the primary, check for shorted > > diodes and caps on the secondary side of the switching transformer. You > > mention that you checked the "switch". Do you mean the power transistor(s) > > that drives the primary side of the switching transformer? > > > > As Jeff said, isolate the power supply from the rest of the scope if > > possible. You should be able to use a lower rated fuse at this point to > > help minimize any damage if you don't have any way to current limit the AC > > input. > > > > http://www.jetecnet.com/claims to have a service manual for $10. > > > > Might also want to search for free manuals for PM3084, PM3092, or PM3094. > > They may share the same power supply. > > > I've examined the primary side of the powersupply very carefully. > Absolutely NO signs of damage anywhere. > The Y caps measures correct 2nF (2pcs of 1nF) also X cap ok at 0.22uF. > A NTC inruch limiter measures 15ohm, correct according to the text on > it, primary switch transistor ok, mains rectifier diodes ok all of > them... > But the curiousity took control over me. I cleaned up after the blown > fuse. Put a new one (1.6AT) - connected it to mains - and it works! > All channels and functions seems to operate just fine. > There are really no sign of flames anywhere. One thing which I haven't > paid any attention yet, is the mains filter which is an integrated > block of some coil and filtercaps encapsulated. > I will change the Y and X caps to make sure they're ok. > I've never seen a shorted secondary side make the mains fuse explode. > Just primary shorts has the power to do this, in my opinion based on > hundreds of smps repairs. > Anyway, it appears that I've got another nice looking four channel > oscilloscope on my bench! :-) > > > > > > > What are the primary side HV caps like? I would replace or at least remove and inspect underneath.
From: JW on 14 Jun 2010 08:45 On Mon, 14 Jun 2010 04:23:13 -0700 (PDT) powerampfreak <powerampfreak(a)hotmail.com> wrote in Message id: <23ba5952-2509-45b2-b3ce-d0a18e4321d6(a)z8g2000yqz.googlegroups.com>: >One thing which I haven't >paid any attention yet, is the mains filter which is an integrated >block of some coil and filtercaps encapsulated. I've been doing repair work for over 25 years, but until a few months ago I had never seen one of those fail. Was repairing a Lecroy 9374 scope that would run for a few hours, then blow the line fuse. Turned out to be the chassis mount input filter. You could actually feel it running quite warm. Glad to hear you got your scope up and running. If you don't already have a operators manual, you can download one from Fluke.
From: Jeff Liebermann on 14 Jun 2010 11:57 On Mon, 14 Jun 2010 04:23:13 -0700 (PDT), powerampfreak <powerampfreak(a)hotmail.com> wrote: >But the curiousity took control over me. I cleaned up after the blown >fuse. Put a new one (1.6AT) - connected it to mains - and it works! >All channels and functions seems to operate just fine. Congrats. I would have used an isolation xformer and variac, but if you have a supply of fuses, that works. >There are really no sign of flames anywhere. One thing which I haven't >paid any attention yet, is the mains filter which is an integrated >block of some coil and filtercaps encapsulated. Probably made by Corcom. <http://www.corcom.com> They can be blown by a lightning hit, but not much else. >I will change the Y and X caps to make sure they're ok. Are there any MOV disks around the AC power jack? If yes, look for a tiny hole where the flames exited. >I've never seen a shorted secondary side make the mains fuse explode. >Just primary shorts has the power to do this, in my opinion based on >hundreds of smps repairs. Now that you mention it, you're right. Secondary shorts usually just cause the switcher to shut down. If there are big fat capacitors on the output lines (not commonly found on PC switchers), they could store enough energy to blow the primary. I've seen secondary shorts blow the primary fuse in "brick" type switching power supplies, but not resulting in the blackened smoking mess you described. That would require a short on the primary side. >Anyway, it appears that I've got another nice looking four channel >oscilloscope on my bench! :-) However, this begs the question of what caused the flames and smoke? If the fuse was intact, it's unlikely. If it was an AC power line fault of some sort (lightning hit, lost neutral, hi-v distribution line falls on power line drop), it would have destroyed other pieces of test equipment in the lab. Pardon my suspicious nature, but methinks you should run it with the covers off and keep an eye on this scope for a while. -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
From: William Sommerwerck on 14 Jun 2010 12:20 > However, this begs the question of what caused the flames and > smoke? If the fuse was intact, it's unlikely. If it was an AC power > line fault of some sort (lightning hit, lost neutral, hi-v distribution > line falls on power line drop), it would have destroyed other pieces > of test equipment in the lab. Pardon my suspicious nature, but > methinks you should run it with the covers off and keep an eye > on this scope for a while. Though Jeff is almost certainly correct, it's possible that the original "blast" was caused by a screwed-up ground. I haven't used my scope in a long time because I'm paranoid (probably without reason) about connecting it to a DUT that is also connected to the power line. (Go ahead, start throwing garbage at me for my ignorance/stupidity.)
First
|
Prev
|
Next
|
Last
Pages: 1 2 3 4 Prev: Horizontal sync problem with Sony E500 monitor Next: GE Cordless Phone Speaker Problem |