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Smoke und fire after switching on old electronics TEK DSA 602
Posted by
Physikfan
on 08 Aug, 2017 19:31
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Hello friends of electronics
A dealer for used electronics supplied me two Tektronix 11000 oscilloscope frames, DSA 602 and DSA 602A.
I was of the opinion that the devices were checked at least once before delivery.
I switched on the devices in a large exhibition hall to test the frames and some 11000`s like 11A72 etc.
That was not very smart.
After approximately 5 to 10 minutes after switching on, one of the devices worked electrically initially faultlessly, biting smoke came out from both devices, which greatly influenced the air quality in the exhibition hall.
Even one of these devices started to burn inside.
After extinguishing the fire, the dealer agreed not to have checked the equipment before loading.
However, every experienced electronics engineer should know that one should deal very carefully with a very long time of unused HP and Tektronix devices.
You should first connect these devices to a variable mains supply and the full mains voltage should applied step by step only after 2-5 minutes, in order to re-form various capacitors and to avoid potential explosions etc.
I would be interested in whether someone has already had similar experiences with smoke and fire when switching on old electronics.
The only positive thing followed this action was a corresponding price reduction.
I will present some pictures of the damaged parts soon.
I hope I get from you also some hints how to repair these devices.
The documentation of the Tek devices is unfortunately not sufficient in the 11000 series, in contrast to the 7000 series.
Best regards
Physikfan
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#1 Reply
Posted by
bd139
on 08 Aug, 2017 19:36
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Sounds like mains filters. Many a time have I filled up my living room with the guts of them. They make a right mess inside the kit.
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#2 Reply
Posted by
alm
on 08 Aug, 2017 19:54
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However, every experienced electronics engineer should know that one should deal very carefully with a very long time of unused HP and Tektronix devices.
You should first connect these devices to a variable mains supply and the full mains voltage should applied step by step only after 2-5 minutes, in order to re-form various capacitors and to avoid potential explosions etc.
This was recently discussed on the TekScopes Yahoo! group. A variac does not do much for capacitor reforming, since it will not limit the current, and can kill some switching power supplies without a good under voltage lockout. It also defeats any time delay that old power supplies may have. If you want to reform caps, take them out and feed them from a power supply limited to a low current. I would do good visual inspection for loose wires, burnt parts or loose screws/foreign bodies. Also check any voltage selection (internal jumpers or external switches) and correct fuse ratings (check if some idiot found a suitably sized bolt that fit the fuse holder). Apart from that, just turn it on and hope for the best.
I would be interested in whether someone has already had similar experiences with smoke and fire when switching on old electronics.
My first suspicion would be X-caps (Rifa?) in the power supply input filter. Assuming these scopes have them.
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#3 Reply
Posted by
bd139
on 08 Aug, 2017 20:10
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Every time I hear RIFA or Schaffner I dive under the table and don the gas mask
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#4 Reply
Posted by
bitseeker
on 08 Aug, 2017 22:50
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Every time I hear RIFA or Schaffner I dive under the table and don the gas mask
Yes! Beware of the excessively dynamic duo.
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#5 Reply
Posted by
amyk
on 09 Aug, 2017 02:10
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Those mains filter caps are more likely to turn into smoke bombs than other regular caps, which either silently dry out to the point of being useless or go out with a short pop.
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#6 Reply
Posted by
GreyWoolfe
on 10 Aug, 2017 00:47
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Oh, yes. A couple of years ago, someone gave me a Tektronix tube scope, I can't remember model. I didn't have a variac then so, foolishly, I plugged it in and turned it on. Almost immediately, something popped, smoke and a tendril of flame erupted. The smell was memorable and it lingered for a day or so. SWMBO wasn't happy with me, she made me put it on the curb for pickup.
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#7 Reply
Posted by
bd139
on 10 Aug, 2017 07:20
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SWMBO at this location casually walks over to the window now, opens it, sticks her head out and carries on with her business as usual until the smoke has cleared
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#8 Reply
Posted by
GreyWoolfe
on 10 Aug, 2017 12:26
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SWMBO at this location casually walks over to the window now, opens it, sticks her head out and carries on with her business as usual until the smoke has cleared
My office is an extension on the back of the house that the original owners built. She doesn't like coming out into the office, she says it's intimidating out here. I can't understand why. Just because there is my company laptop with dual displays, my personal computer with dual displays, my workbench with all kinds of electronics devices on it with a 32" TV as a monitor, all the network equipment and everything else (storage shelves), I don't see what is intimidating about it.
She usually just closes the sliding glass door. However, that day the door was open and she wasn't home at the time of the incident. Add to the fact that she is practically allergic to air and almost any smell aggravates her sinuses, it explains why I got into trouble.
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#9 Reply
Posted by
Kjelt
on 10 Aug, 2017 13:05
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Yup one of the mainsfilter capacitor of my old Philips scope also turned itself into a lot of toxic smoke and I used it around 8 months or so before, so this failure can just happen when the capacitor thinks its his time.
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#10 Reply
Posted by
bd139
on 10 Aug, 2017 13:11
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My last two explosions were Philips scopes. The thing that gets me is you crank the things up on the mains and let them bed in for a few minutes and just as the worrying dies down and you have some confidence in it. Just when you're relaxing it is followed by pssssssssssssssssssssssssssss phut!
SWMBO at this location casually walks over to the window now, opens it, sticks her head out and carries on with her business as usual until the smoke has cleared
My office is an extension on the back of the house that the original owners built. She doesn't like coming out into the office, she says it's intimidating out here. I can't understand why. Just because there is my company laptop with dual displays, my personal computer with dual displays, my workbench with all kinds of electronics devices on it with a 32" TV as a monitor, all the network equipment and everything else (storage shelves), I don't see what is intimidating about it. She usually just closes the sliding glass door. However, that day the door was open and she wasn't home at the time of the incident. Add to the fact that she is practically allergic to air and almost any smell aggravates her sinuses, it explains why I got into trouble.
You should buy her a gas mask
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#11 Reply
Posted by
Kjelt
on 10 Aug, 2017 13:15
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My last two explosions were Philips scopes. The thing that gets me is you crank the things up on the mains and let them bed in for a few minutes and just as the worrying dies down and you have some confidence in it. Just when you're relaxing it is followed by pssssssssssssssssssssssssssss phut!
the worst thing actually which I am quite
to say, a friend of mine warned me a year ago to preventively replace that capacitor..... yeah postponing is not always the smartest thing to do.
All old Philips scope owners: I warned you
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In the old days, with iron powerline transformers, it was customary for one to use a Variac and turn it up s--l--o--w--l--y.
Nowadays, if the units have a SMPS, then slowly ramping the supply will cause it to "hiccup"...depending on the design it could cause it to become damaged.
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#13 Reply
Posted by
alm
on 10 Aug, 2017 13:29
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How well did Variacs work with time-delay circuits used in old tube equipment to allow the tubes to warm-up before applying power to the resit of the circuit?
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#14 Reply
Posted by
bd139
on 10 Aug, 2017 13:36
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Variacs were only really very good for doing line voltage regulation tests if you ask me. Stuff still explodes when you ramp the voltage and there's something wrong either way. My variac can handle 8A without blowing up as an example! That's going to kill anything you connect to it. I've seen a lot of people sticking an incandescent lamp in series with a device. That makes more sense as the thing will light up if there's something wrong before the magic smoke comes out of the DUT.
Really though; knowledge of this issue, inspection, measurement, safety goggles. Most modern devices you can spot explosions risks i.e. cracked and leaky caps and anything with the word Schaffner on it.
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#15 Reply
Posted by
Rbastler
on 10 Aug, 2017 13:46
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None of my tube gear does have a time delay after it switches the rest on. Or more correct would be to say, that for those with a rectifier tube that time delay is already included, by working when heatet up, like the rest.
This is actually the only time I used a variac, so I woudnt shock the tubes filament. Didn't bother for semiconductor gear. Wy would you do it ?
I too had a mains filter cap in my PE1540 dying with a pffffff-tsch, while performing a load test.
Edit: I used a incandeshend lamp as a short detection, when I repaired tube radios. Works like a charm.
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#16 Reply
Posted by
nanofrog
on 10 Aug, 2017 14:09
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#17 Reply
Posted by
alm
on 10 Aug, 2017 14:26
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How would a mains-rated bulb blow from being put in series with a short?
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#18 Reply
Posted by
Rbastler
on 10 Aug, 2017 14:28
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It woudnt. Just limit the current. Comes with free short/too much current indicator
Sent from my A0001 using Tapatalk
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#19 Reply
Posted by
nanofrog
on 10 Aug, 2017 14:58
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How would a mains-rated bulb blow from being put in series with a short?
Bulb filament acts as a fuse (too much current, and it pops/vaporizes as it's over-heated). The bulb brightness also acts as an indicator; the brighter the bulb, the more severe the problem.
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#20 Reply
Posted by
Gyro
on 10 Aug, 2017 15:36
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It doesn't act as a fuse, it acts as a PTC thermistor. It won't pop because worst case it will see normal mains voltage.
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#21 Reply
Posted by
GreyWoolfe
on 11 Aug, 2017 11:53
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#22 Reply
Posted by
Physikfan
on 11 Aug, 2017 14:38
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Pictures of the damaged DSA602:
DSA602
Power supply from the side
Power supply from the rear
Rear of rear cover plate
smoked components
I am looking forward to your comments
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#23 Reply
Posted by
bd139
on 11 Aug, 2017 15:05
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That's definitely mains filter. You can tell by the brown stains. Quite a lot of damage. Write off IMHO.
It'll probably be fine if you can get a replacement supply and clean up the chassis though.
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#24 Reply
Posted by
Physikfan
on 11 Aug, 2017 19:27
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Images of parts of the smoking and burning DSA602A:
Power supply board with defective filter X2
Filter X2 in detail, this component burned.
This board looks better than the non-firing board of the DSA402.
I am looking forward to your comments.
Works like a charm for me. If she won't take it, do like giving a pill to a dog; put it in her food. 
