AVI CD player - circa 1998

[TNC]

A recent house move meant that my Hi-Fi separates have had over a year and a half's rest in dry store.
Finally I have the time to put it all together and the first switch-on results in a strong smell and a little puff of smoke
from the AVI cd player!
A look inside confirms a small cap has "let go"!

Would just welcome confirmation of the fact that despite the pcb signage, it is not polarised and
is straightforward 4.7mf cap?

Many thanks  Trevor    
   

[Mark Hennessy]

That's a tantalum jobby. Definitely polarised.

However, you'd probably be OK to replace it with a good quality aluminium electrolytic.

[ppppenguin]

That is a 4.7uF tantalum. Nasty little things. It is polarised. Suggest replacing with an ordinary 4.7uF electrolytic. You may want to replace any others of the same type at the same time.

PS: Mark replied while I was writing.

[Refugee]

That is a custard tant. They are most commonly blue and do have a smoking habit.
They are indeed polarised.
A good quality electrolytic will work fine in all locations with those in them.

[Terry]

Would just welcome confirmation of the fact that despite the pcb signage, it is not polarised and
is straightforward 4.7mf cap?

A 4.7millifarad cap, Trevor?

Good luck with finding a non polarised one of those!

It is clearly marked 4µ7, as Jeffrey and Mark have pointed out, so why would you want to replace it with a (physically very large) non polarised cap? Or are you thinking of it as 4n7 because you were reading it upside down?

I also agree with Jeffrey's suggestion to replace all of these horrible things.

[TNC]

Thanks Guys...note to self...I must use my glasses more often!
I have no schematic but assume they are part of the power section
...only problem is the amount of dismantling required to get behind...unless
I just remove them leaving the tails to solder on the surface.  

I guess you would consider that a bodge??  

Trevor

[Refugee]

It is not a bodge if you intend to make a dry joint

[Mark Hennessy]

It's most likely connected to the output of the adjacent 5V voltage regulator, and so it's worth checking if the IC survived the ordeal. It might be fine, or it might give no output voltage (hopefully), or it might simply pass the input voltage straight through to the output, which could cause further damage.

Of course, you might already know the answer to this - have you powered the player up yet? If not, it might be wise to use a variac and if the output voltage from the regulator rises above 5V. In my experience, they usually fail safely to 0V when they've been abused, but not all the time.

In my experience those modern yellow tants are actually very reliable. It's unfortunate (but understandable) that they often end up being them across supply rails, because when they do go short, the results are often dramatic. But I've had regular electros do exactly the same. On balance, I'm not wholly convinced they are much less reliable, it's just that their failures are more memorable.

In this case, you might as well do them all because of the difficulties of getting the PCB out, but that mechanical issue is the only reason to change them IMHO. I doubt the others are likely to fail any time soon - you've just been unlucky.

No doubt others will be along to tell me how wrong I am, but I'm young enough to not have been bothered by the earlier ones ("beware the blue tants"), and I've always used them conservatively and sparingly. I can only recall one failure (it was a dramatic, smoky one) in the last 20 years, but couldn't begin to guess at the number of electrolytics that I've replaced in that time.

Today, modern electrolytic caps are much better than they used to be, and will work as well as a tant does in most (though not all) situations, so there's less reason to fit them now. And at least most modern electrolytic types fail with a bit less smoke and drama than tants. However, leaking electros wreck PCBs - especially the infamous SMT types that were so popular back in the '90s. I've spent hours working on a bit of Tek gear (a bit of a monster, frankly) with countless faults caused by those, and I know that the repairs are only temporary because before much longer some other fault will emerge as the result of corrosion silently taking place under an IC or similar. I wish they had used tants, frankly. The very thin PCB tracks from the vias from the inner power plane layers to the top to make contact with the pads are so very thin that they would have act as fuses!

[Refugee]

The Japanese used to crank the leads on small electrolytic capacitors to allow a bit of air space under them so that any leakage would dry out before it damaged the board.
Tants are better in signal paths on transistor gear as they fail short circuit if there is any surges in voltage or current on power rails.
There was a fad for them in professional gear in the late 1970s and any that were on power rails when there was any kind of surge would go off like fire crackers.
A little bit of contact bounce on the mains switch on kit with a transformer in it was the worst.

[TNC]

Well the replacement went ahead without problem...but it looks like the voltage regulator may have been brought down too.
....machine display lights, remote acknowledged and CD sled all power up - and a CD can be loaded.....but play does not initiate.

Trevor