Products > Test Equipment
Blew Up My First Oscilloscope!!!
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james_s:
Well I'm not arguing that they're the best or anything but they're still old. It's unknown whether the currently manufactured ones will exhibit the same fault, one can hope they've been improved.
duak:
Some 2200 series scopes also have problems with some 470K or so 1/4 W resistors in the focus circuit.  If the the scope is apart, look for a group of  resistors with a bit of space around them.  The PCB itself might also look a bit stressed.  If I remember correctly, Tek used 5 or so of them in series to handle a 1 KV or so potential.

Cheers,
tooki:

--- Quote from: james_s on February 28, 2019, 06:03:14 am ---
--- Quote from: tooki on February 28, 2019, 04:47:02 am ---What amazes me is that Kemet is still manufacturing those awful things. (Kemet bought up Evox-Rifa years ago.)

For example, here’s the datasheet for the exact series shown in the preview of Dave’s video above: http://www.kemet.com/Lists/ProductCatalog/Attachments/322/KEM_F3011_PME271M_X2_275.pdf

Like... ugh.

--- End quote ---

Perhaps they have been improved?

Also it's worth noting that the ones that are failing now are mostly more than 20 years old, while not ideal I have a hard time being upset over 20+ year old components failing. I had one burn up in the power supply of an Apple IIe years ago, it made a bunch of stinky smoke but it didn't really cause any collateral damage.

--- End quote ---
Valid points to be sure, and I did consider that (somewhat) without mentioning it before.

My hunch, though, is that they haven't been changed, or else they'd have changed the part number.



--- Quote from: Zenith on February 28, 2019, 01:21:36 pm ---Here are two Rifa 2200pF Y class capacitors which are probably over 20 years old, but are unused and have been kept in reasonable conditions.  Both are cracked in the same place. The crack underlines the Rifa logo and goes up just short of the corners and there's a similar crack on the back. It looks to be an age related thing.

There are loads of X and Y rated capacitors of the same age which don't have this class fault.

--- End quote ---
The local mom-and-pop electronics store/living museum has bins of Rifa caps that are cracked, for sale. o_O
JohnPen:
High value Resistors with high voltages across them used to be a problem with the old CRT TV years ago.  The focus potential used a chain of high value carbon resistors, often in the Megohm range, and they used to shift dramatically in value as they aged.  Sometimes down by several Megs other times similarly upwards.  High voltages across resistors, particularly the carbon based ones,  are definitely not very good for them. :(
Zenith:

--- Quote from: tooki on February 28, 2019, 06:33:21 pm ---[]Valid points to be sure, and I did consider that (somewhat) without mentioning it before.

My hunch, though, is that they haven't been changed, or else they'd have changed the part number.


--- End quote ---

They caused no problems whatsoever for the OEM or the first owner.

The manufacturer didn't find they caused production rework or warranty claims.

The first owner wasn't likely to keep the unit for more than ten years, and there weren't many post warranty problems, which the maker wouldn't particularly want.

Rifa had a successful product which they'd had to pay to have certified with UL and the rest.

No one, who mattered, cared what was going to happen 12 years plus down the line, and probably still doesn't.
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