Smoke und fire after switching on old electronics TEK DSA 602 / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Smoke und fire after switching on old electronics TEK DSA 602

1 2 next

Move Thread

LAN_403

Physikfan

Tue Aug 01 2017, 11:51AM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

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.

You will get some pictures of the burned 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

Sulaiman

Tue Aug 01 2017, 12:16PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Variacs are excellent tools but I prefer putting a high wattage mains voltage filament lamp in series, (especially for smps, which does not apply here)
I expect to see a brief flash from the lamp at power-on due to caps charging etc.
then a dull or no glow for normal operation, and fully bright if things go wrong.
The current limiting provided by the lamp usually protects from fire etc.
A switch contact across the lamp allows full power operation once you feel comfortable.

When we see what was damaged other ideas may come.

johnf

Tue Aug 01 2017, 07:05PM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

usually it is the electrolytic capacitors depolarising---acting like short circuits this takes out the rectifiers and they go short circuit and now the ac on the DC rail kills at random.
the other failure mechanism is a shorted turn in the mains transformer due to green spot

DerAlbi

Tue Aug 01 2017, 09:40PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Reforming old capacitors is perfectly possible, but i dont see how this can be done in a working device. Once you supply enough power for the operation of a device there is no way to limit the heat of the capacitor leakage current. So its a well meant thought having a light bulb in series, but it simply does not work like that.It only works if you put in a 50k resistor and dont turn the sucker on. But most poer supplies have some StBy power drainage so there is also no use.

Conundrum

Fri Aug 11 2017, 05:18AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

Same here. I think the correct method is to use a variac in series with load.

Physikfan

Fri Aug 11 2017, 02:34PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Pictures of the damaged DSA602:

MG 0001400x270

DSA602

Power supply from the side

MG 0011400x313

Power supply from the rear

MG 0013400x543

Rear of rear cover plate

MG 0015400x305

smoked components

I am looking forward to your comments

Hazmatt_(The Underdog)

Fri Aug 11 2017, 04:05PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Yea that's one of those clear WIMA mylar caps. Boy they sure do go up in flames don't they.

I had a couple do that, made a real mess of things. It's just the line input filter though. You can see the surge clamp tube under the char.

Just start rinsing the soot off with IPA, assess any actual damage, and replace the cap with a .01uF 600V PP type WIMA.

The smoke however, has permeated every nook and cranny of the scope though, you will probably need to rinse every part of that guy.

You ought to replace that clear one next to the inductor in the upper right corner as well for good measure (even though it never sees any AC)

I don't envy you having to deal with the smell, but it will eventually dissipate, that scope is going to stink for a while though.

Hydron

Fri Aug 11 2017, 06:08PM

Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208

If it's the line input filter then wouldn't an X or Y cap (depending on location) be a better idea than just a standard 600V PP cap?

And yes, those damn caps are terrible, have seen bad ones a number of times myself (though nothing with dramatic flames!)

Physikfan

Fri Aug 11 2017, 07:28PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Images of parts of the smoking and burning DSA602A:

MG 0089400x295

Power supply board with defective filter X2

MG 0098400x190

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.

Hazmatt_(The Underdog)

Sat Aug 12 2017, 04:45AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Can you make out the value on the top of the cap?

Keep up the good work.. you should be able to salvage this one.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob