Leaking Mullard capacitors?

Started by VintageGear, April 12, 2014, 01:17:08 PM

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VintageGear

So I got this MXR phase 100, the earliest version with the beautiful Mullard 'tropical fish' caps. Problem is, the damn thing didnt work anymore after pulling it out of the drawer where it has been for many years. I noticed there is some 'glue'-ish, transparant stuff visible at the legs of the caps. Given the fact these tropical fish caps are hard to come by, I do not wanna try to replace em straight away. I'm familiar with radial electrolyte caps which leak a nasty green stuff, but I've never seen the hotglue appearance on caps. Anyone has experience with possible leaking Mullard caps?
I dont have a picture right now but I can make some later this week if any of you want.

duck_arse

hello and welcome, vintage.

it is unlikely anything has leaked from your tropical fish. it is more likely hot-melt or similar, like you said, used to provide some mechanical support, because of the sheer size of these caps. if the ends around the leads are still intact, they should be orrlright.

we love pictures. sometimes we can fixxe pedals just by asking to see them.
You hold the small basket while I strain the gnat.

R.G.

Caps that are not (1) electrolytic or (2) fluid-oil-containing cannot leak. There is no fluid inside them to leak.

"Tropical Fish" caps are simply mylar film caps from an era when they marked the values by stripes of colored epoxy rather than printing letters and numbers on them. No magic inside.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

newperson

#3
plus they tend to rot and fall apart.  at least in every ARP.  i do not like them.  

Much more likely one of the 8 ICs, a transistor, the LDRs, loose wire, switch, jack, etc.  

VintageGear

Thanks for the replies and the welcome!
Here are the promised pictures.
The first one shows the 'stuff' on the capacitor between the IC and the resistor, above the LDR.
I wonder how the IC/transistor go bad if the effect just lays in the drawer, unused, and ceases to work. Cosmic radiation? :icon_rolleyes:

Guess I'll probe around a bit if the fishies aint fishy!




R.G.

Just out of curiousity, why do you say that those are Mullard caps? That style of labeling values was not limited to Mullard.

I'm guessing that the grak on top of the caps is the remains of the foam insulating sheets - is that right?

Have you replaced the electros on the board, if any?

Finally, approach it as suggested in "what to do when it doesn't work".
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

VintageGear

Quote from: R.G. on April 13, 2014, 10:11:51 AM
Just out of curiousity, why do you say that those are Mullard caps? That style of labeling values was not limited to Mullard.
I assumed. Thought all MXR phase 100 pedals were fitted with Mullards, but judging from your reply I might be wrong?

Quote from: R.G. on April 13, 2014, 10:11:51 AM
I'm guessing that the grak on top of the caps is the remains of the foam insulating sheets - is that right?
Yeps. Already cleaned a whole lot off, that stuff is everywhere. Yuck. Degrades quite badly.

Quote from: R.G. on April 13, 2014, 10:11:51 AM
Have you replaced the electros on the board, if any?
Haven't touched my soldering iron yet; went for visual inspection first. Perhaps I could reheat every connection on the board to rule out any dry solder cracks?

Quote from: R.G. on April 13, 2014, 10:11:51 AM
Finally, approach it as suggested in "what to do when it doesn't work".
Will do. Keep ya'll posted if you want to.

R.G.

Quote from: VintageGear on April 13, 2014, 10:40:13 AM
I assumed. Thought all MXR phase 100 pedals were fitted with Mullards, but judging from your reply I might be wrong?
I have no clue if all MXR [whatever] pedals were fitted with Mullards or whatever. But I do know that Mullard had no monopoly on the color striping for presenting values. Mullard may have made "tropical fish", but tropical fish does not mean Mullard, necessarily.

It seems unlikely from what I have read and seen of the insides of MXR pedals that MXR would go for only Mullard parts. But I'd appreciate any real info references you have.

Quote from: R.G. on April 13, 2014, 10:11:51 AM
Haven't touched my soldering iron yet; went for visual inspection first. Perhaps I could reheat every connection on the board to rule out any dry solder cracks?
Actually, if it were me, I'd probably put power on it and go directly to voltage measurements on all the ICs before soldering. That would likely tell you directly about any faiing caps.

If you find multiple problems, then do the scattergun resoldering.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

Jdansti

Looks like your caps have Saprolegnia. (fish fungus)  ;)

Seriously, good luck with it! :)
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R.G. Keene: EXPECT there to be errors, and defeat them...

Gus

I "Repaired" a phase 100 by turning the the rotary switch from setting to setting. 
I did this a few times to clean the contacts.

wavley

Quote from: R.G. on April 13, 2014, 10:11:51 AM

I'm guessing that the grak on top of the caps is the remains of the foam insulating sheets - is that right?


Yep, that's what I would say, looks like every vintage MXR I've ever opened.
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VintageGear

Okay. I feel retarded. Why you might ask? Well...
I found the original schematics for the MXR online. Using these I measured the voltages and stuff and nothing peculiar happened; I could wrap my head around any broken component. Carefully actually tracing the signal path I got confused. The schematic, which had the annotations of wire colors, didnt match with mine. And yes, in retrospect (why did u guys miss it, huh, huh ;)) the input and output are swapped inside the case. I fed the sine to the output, and the input I plugged into my amp. Swapping both plugs, boom, awesome phasing audible. 1 hour well spend on a lifelong lesson: Start at the beginning instead of the first OpAmp. Derp.
Thanks for all the input guys, I'll be around!

armdnrdy

Quote from: VintageGear on April 14, 2014, 03:05:59 PM
And yes, in retrospect (why did u guys miss it, huh, huh ;)) the input and output are swapped inside the case.

Looking back in retrospect....your statement from your first post seemed to imply that the effect worked before you "put it in the drawer for many years"

Problem is, the damn thing didnt work anymore after pulling it out of the drawer where it has been for many years."

I think that the key word is "anymore".  :icon_wink:

Anyway....good to see you got it going! and thanks for the gut shots.
I just designed a new fuzz circuit! It almost sounds a little different than the last fifty fuzz circuits I designed! ;)