wiring capacitor on speaker crossover

[jamman1125]

Hi there,
I'm undertaking repairing a crossover for my pair of JBL control 5 speakers, however upon de soldering the old capacitor expecting to find + - marks on the PCB there is nothing. The old capacitor is also not marked so that couldn't help me.

This is an electrolytic capacitor so it needs to be wired the right way, I'm just not sure which way that is. As the schematics I found online don't divulge much. (Below is the link to the schematic)

https://www.google.co.uk/url?q=http...PDFYQFggRMAI&usg=AOvVaw2DX6P3igl0DipxSfq4_Zn_

Here are some pictures, any help would be greatly appreciated.
Thanks!

 

[Harald Kapp]

Lacking markings, this may be an unpolarized electrolytic capacitor or a film capacitor which is available as 4 µF. The schematic symbol does not indicate an electrolytic capacitor.

If you cannot get hold of such a capacitor for replacement, you can use two polarized capacitors of twice the required capacity back to back.
A picture of the capacitor would be useful, too.

 

[jamman1125]

Lacking markings, this may be an unpolarized electrolytic capacitor or a film capacitor which is available as 4 µF. The schematic symbol does not indicate an electrolytic capacitor.

If you cannot get hold of such a capacitor for replacement, you can use two polarized capacitors of twice the required capacity back to back.
A picture of the capacitor would be useful, too.

Hey, thanks for the reply.

Ok I see, I was unaware that unpolarized electrolytic capacitors existed. Here is a picture of the original capacitor:

The values on it are 4.7 MFD, 100v, +- 10%

and here is a link to the new capacitor purchased:

http://uk.rs-online.com/web/p/alumi...74D504438267374613D55425432413452374D50443826

 

[Harald Kapp]

Sure looks like an electrolytic capacitor without polarity markings. For teh back-to-back technique you'd have to use two 10 µF capacitors. Using two 4.7 µF capacitors will result in 2.3 µF effectively which will not match the filter design. If you have to buy another capacitor anyway, get an unpolarized type directly and save the effort of building the back-to-back combination.

Note that the schematic calls for 4 µF, not 4.7 µF.

 

[73's de Edd]

Here's the way I am seeing it . . . . . and I can't believe that I saw the whole thing . . .

That missing capacitors hole set is probably one of a set of TWO electrolytics that are being twice the capacitance needed, so that there will be an effective halving in value when being used in series. PLUS you now have created a non polarized equivalent unit.

Confirm that on the present top cap . . . that I have assigned markings to . . . . also fathom the situation in your mind, via the " mortified " side schematics mark-up.
You can see the companion little .01 HF shunting cap as the brownish-red poly cap.

Also some times in its history, it seems to have taken out the rather hefty current SK3 incandescent lamp that is in series with the woofer to protect it in case of SUSTAINED power input by increased resistance as its filamant heats. UNLESS you hit it with some music material that has just critically spaced out bass thumps and it pops the lamps filament.
In replacement, to avoid the yellow pookie covered up wire leads they just cut out the old lamp and left wire snippets to butt solder to . . . . big solder blobs and all . . . ..

A PROPER replacement would have been to expose/scrape copper side pads ( at the BLUE areas ) and solder tin their then clean bare copper surfaces.
Then you bend right angle L's to the ends of the lamps wire leads and tin those leads and position on top of the pre tinned, newly created pads, and re-flow solder.

ADDENDA . . . you had added on while I was poking up so I did not have the benefit of seeing the old cap.
So confirm to see if that top cap is present or of they were solely using a non polarised cap instead, at your vacated pads at the bottom.



MARKUPS . . . . .

73's de Edd

 

[jamman1125]

The component is one single capacitor, but I think an important bit of info on the old cap that I missed was the two letters NP which i have just noticed on the other functioning crossover. Im assuming this mean Non Polarized? Also does non polar, and bi polar mean the same thing? As this is what they are also being advertised as online.

Edd, you are also correct on the shoddy SK3 replacement, which is much neater in the other crossover, I can happily say I did not carry out that repair.

As suggested by Harald, I can just buy a non polarized cap rather than creating one from two. Does it matter if the capacitor I buy has its prongs on one side, or both sides?


Thanks for your very helpful reply

 

[73's de Edd]

Yes, all of those descriptions are being relevant to a bipolar electrolytic capacitor.

Is there an electrolytic being at those rear mark ups that I have shown.. . . . or just other parts connections ?

As it is . . . . .your bipolar electrolytic and its shunting .01 are being complete and at the front of the board.

I am seeing the central horizontal foil divisional line as being the separation of the tweeters voice coil connections, being made at the extreme right solder connections just at those corners.

Does it matter if the capacitor I buy has its prongs on one side, or both sides?

one side = Radial leads
both sides = Axial leads

Preferrably with radial leads like you previously had . . . .but . . .
In a pinch you can make a radial from an axial by folding a top lead over and routing against the case to form a side by side radial configuration at their ends . . .HOWEVER . . . usually that folded over lead is not long enough, so you have to make a lead lengthening splice, central to that lead, then cover it with spaghetti insulative tubing.


Thassssittt . . . .

 

[jamman1125]

Yes, all of those descriptions are being relevant to a bipolar electrolytic capacitor.

Is there an electrolytic being at those rear mark ups that I have shown.. . . . or just other parts connections ?

As it is . . . . .your bipolar electrolytic and its shunting .01 are being complete and at the front of the board.

I am seeing the central horizontal foil divisional line as being the separation of the tweeters voice coil connections, being made at the extreme right solder connections just at those corners.

Does it matter if the capacitor I buy has its prongs on one side, or both sides?

one side = Radial leads
both sides = Axial leads

Preferrably with radial leads like you previously had . . . .but . . .
In a pinch you can make a radial from an axial by folding a top lead over and routing against the case to form a side by side radial configuration at their ends . . .HOWEVER . . . usually that folded over lead is not long enough, so you have to make a lead lengthening splice, central to that lead, then cover it with spaghetti insulative tubing.


Thassssittt . . . .

Hi Edd, no the only other capacitor on the circuit was the ceramic 0.1uf. I believe your mark up pointed to a solder point for the coil winding and to either the tweeter or woofer.

Great thanks for that very useful info, I shall try to find a RADIAL cap then =)

All the best to you and Harald