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capacitor exploded on mid 80s ultrasonic

William D

New Member
Is it possible to determine an appropriate replacement based on these pics? and would it be prudent to replace the other 2 next to it?
I have contacted the manufacturer but don't expect any help from there. L&R T28B ultrasonic. Any help would be, well, helpful, and appreciated.
IMG_1298.jpgIMG_1323.jpgIMG_1311.jpg
 

rjenkinsgb

Active Member
A common noise suppression configuration uses an X class capacitor across supply live and neutral, plus two Y class capacitors between live & earth / neutral and earth.
eg. https://www.electronicproducts.com/uploadedImages/Passive_Components/Capacitors/FAJH_Kemet_1S_Nov2014.jpg?n=8113
The two blocks on the left will represent fuses.


I suspect the blown part is an X class cap. If it is, tracing the connections should show it connected directly across the mains input (after the fuse).

The 250 still visible is presumably the voltage rating; many are now 275V rated, just go on physical dimensions to find the largest value that will fit in the existing space with 250V or higher rating.

Some examples:
https://uk.rs-online.com/web/c/passive-components/capacitors/polyester-film-capacitors/?applied-dimensions=4294459177,4294466083
 

William D

New Member
Thanks for your help. I ordered the type below. So just for my general knowlege the farad capacity isn't real critical as long as it is enough, too big is no problem as long as there is room on the board. are there different applications where too much capacity would be bad?
Safety Capacitor;Dielectric Material : Polypropylene;Model : MKP
Series : X2;Capacitance : 1uF;Tolerance : 10%
Withstand Voltage : 275V AC;Rating Voltage : 250V AC;
 

rjenkinsgb

Active Member
are there different applications where too much capacity would be bad?
Yes, absolutely, in many applications the capacitor ratings can be critical.

It just happens that the one you need is purely a suppression part, rather than being interconnected directly with any other electronics.
In that case, the only critical things are the "X" class and the voltage rating.
The value is just whatever you can fit in, it could be massive not do any harm.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I presume you've checked that it all still works OK?, it's not a functional part, so the unit should work perfectly without it. It's only there to reduce interference IN and OUT.
 

tvtech

Well-Known Member
Most Helpful Member
Years ago, Wima had blue X2 caps that Telefunken used on 715 sets here. Genuine Wima and genuine Telefunken chassis. The caps liked to catch on fire...smoke and acrid smell everywhere. We (techs) simply cut them out. In those days, Wima was the only manufaturer doing the X2 thing (80's). SMPS noise suppression was new ground.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Years ago, Wima had blue X2 caps that Telefunken used on 715 sets here. Genuine Wima and genuine Telefunken chassis. The caps liked to catch on fire...smoke and acrid smell everywhere. We (techs) simply cut them out. In those days, Wima was the only manufaturer doing the X2 thing (80's). SMPS noise suppression was new ground.
Historically Wima made the most unreliable capacitors of their day, they were abysmally unreliable - standard repair technique was to replace any and all Wima capacitors before you even started fault finding, often you would find it all worked after that.
 

tvtech

Well-Known Member
Most Helpful Member
Historically Wima made the most unreliable capacitors of their day, they were abysmally unreliable - standard repair technique was to replace any and all Wima capacitors before you even started fault finding, often you would find it all worked after that.
So lets see....anything Wima was replaced....lol.

hahaha.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
So lets see....anything Wima was replaced....lol.

hahaha.
It worked - and as they were all the same age, they were all likely to be faulty, or going to be very shortly.

I once went through a long series of swaps - I started with an old Philips cassette recorder (EL3301 or similar), which I got for free, repaired and swapped for something else, repaired that - and so on - ended up with a motorbike :D (and never spent a penny!)

Anyway, one of the items I got was a Philips reel to reel valve tape recorder, which had an electrical fault (rather than the more usual mechanical - belts etc. problems). So I took the bottom off, it was pre-pcb, so wires and components EVERYWHERE, looked round - oh look, there's a Wima (just one) - cut it out, soldered a new capcitor in, job done, on to the next swap.
 

tvtech

Well-Known Member
Most Helpful Member
The ONLY issues ive ever seen with Wima Caps is their early blue X2...noone other. Otherwise, they would not still be in bussiness.
 

William D

New Member
Thanks a lot for all your feedback. I didn't want to plug it back in until I replaced the capacitor but I will remove the capacitor and try it.
Would I need to run a jumper across where the capacitor was? I have to say with electronics, a lot of the time what I think makes sense is completely wrong.
 

William D

New Member
I removed the exploded capacitor, and here are the 2 adjacent. Are the cracks an indication that they are on their way to failure as well?
Or could they go on indefinitely. They don't appear swollen, (possibly just very slightly). I will reinstall this board tomorrow and see how it goes without. On a side note would this be the appropriate forum to discuss spark suppression on a late 19th century electric clock? The main problem with this clock is carbon buildup on the contacts (Hipp toggle system)

IMG_1343.jpg
 

JimB

Super Moderator
Most Helpful Member
Would I need to run a jumper across where the capacitor was?
Do NOT replace any capacitor with a shorting link.
In this case that would result in a dead short across the mains supply.

Are the cracks an indication that they are on their way to failure as well?
Or could they go on indefinitely.
Those capacitors should be replaced.
The replacements should be " Y rated ".

On a side note would this be the appropriate forum to discuss spark suppression on a late 19th century electric clock?
Yes why not.

JimB
 

Nigel Goodwin

Super Moderator
Most Helpful Member
The ONLY issues ive ever seen with Wima Caps is their early blue X2...noone other. Otherwise, they would not still be in bussiness.
You're obviously FAR too young, and don't repair equipment from that era :D

Although I suppose all such capacitors will have failed decades ago, so unless you get an item for repair that's been sat in a cupboard for 40 years you're unlikely to see any.

But still in business, despite making extremely unreliable capacitors 'back in the day'.
 

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