Tektronix Oscilloscope problem

[sido]

Will do so WM6....But it will have to be tomorrow as now its dark and cold here and i dont want the house power going off if problem continues. I have a isolation transformer which i could use but it is in storage. Thanks for the advise and will keep you posted.

Cheers Sido

[WM6]

I think if i break the connection it might give me a quick test. What do you think? What possible damage can be done? Maybe the other identical capacitor might burn?

Yes, you can break the upper pin of damaged capacitor for quick test without tragic outcome.

Other capacitor might burn if it is in same bad condition as first, otherwise not.

But if you wish, you can replace bad C for test with more lover voltage capacitor in series too. Maybe you have 7 capacitor of 68nF suitable for 500V=. If you put those 7 capacitors (or at least 6) in series, you can get approximate C replacement for test. Be careful to not to make some new shortage with those chain of capacitors.

[sido]

Hi WM6, thanks for the reply.

I was thinking of breaking the connection of the Capacitor after seeing the schematic. You are possibly right that it is a smoothing capacitor that may have shorted.

There is another 2 identical Capacitor's that a connected in-line and also go to ground.

See schematic below.

I dont have an identical or equivalent at hand now, but will see if i can source one out of a old CRT computer screen in the shed.

There is no other visible burnt marks on other components or the under side of the PCB that i can see.

I think if i break the connection it might give me a quick test. What do you think? What possible damage can be done? Maybe the other identical capacitor might burn? If so then i might have some other issues other than that bad looking capacitor. (Waiting for all replies before attempting the above)

Oh BTW i have a portable safety switch that i will plug the mains power cable too for extra safety.

Cheers Sido

[WM6]

In old devices mostly electrolyte C are problem.

Here we have high voltage which can be dangerous too to (foliar) C which lost their dielectric properties.

If your HV C is heating, then it is short-circuited inside. If all other part around are OK (take a look at bottom side of PCB too), you can try to broke visible C pin and put in series with broken capacitor new C with the same value as on picture:



If yo do not have such HV capacitor in your stock, you can try even without this new C, only with broken pin of existing C (seems smoothing C for HV) without some fatal outcome. If burning bad smell appear again there must additional error somewhere.

[sido]

Hi all, must be the time of Oscilloscope failures. Just read Tinkerers thread as he is having faults with his. Mine seam more serious though.

Took out my Tek 2215A 60Mhz Oscilloscope from storage to use on projects here. Was working a year ago since being in storage. Well.......

Powered it up today, unit ran perfect for about 5 minutes, then i noticed the square wave signal on the CRT i was viewing began to shrink slowly towards the center on the screen, then followed a burning bad smell beginning to emerge from the case. (similar to a bad cap).

I quickly switched unit off from the power switch on the unit.

Note: The unit's fuse did not blow while this happened at all.

Interesting thing happened though......Upon switching unit off, 3 seconds later my house safety switch tripped and i lost AC 240 Volt to my power points.....HOW Can that be?

Any way, i removed the covers to inspect the unit and this is what i have discovered so far. I suspect the power supply has given up, considering the unit is 28 years old and looks like it has not been refurbished since being built from factory. Original factory caps noted.

The Pics's below show the suspected faulty visible part. Its a 0.01 mf Capacitor which is connected to ground. Not sure what other damaged parts could be there.

I have the Full Service manual for this scope, but not familiar with SMPS, apart from the obvious warnings of high voltage's floating around this area and the anode lead that goes to the CRT from the flyback transformer. I have discharged that lead to ground but have not done the SMPS caps so far.

I have signed up with the Tektronix forum, but i am waiting for moderator approval for now.

In the meantime any opinions or suggestions are welcome as to how to go about fixing this problem, Thanks

Cheers Sido