• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Repairing surface-mount components

Thunderscreech

Thunderscreech

Jun 4, 2008
6,707
270
Fredericksburg, Virginia
#1
The Diode on my Metal Muff blew out during a ground short a whie ago ([rant]WHY DOES EHX MAKE BRUSHED BARE-METAL CASES! A LAYER OF CLEAR LACQUER IS ALL YOU NEED! ONE COAT![/rant]) trouble is, the diode is a surface mount. Or, at least i think it is. We'll assume that it is since it's the only one up next to the power jack. it works, provided you hook it up to another pedal. Solo, it's a no-go.
provided a diode is actually the problem here. I have not tested it at all, I'm just going with what I know

My question is how do I replace the surface mount diode? and what tools do I need to perform that replacement? I'm figuring a soldering iron with a small tip, and a steady hand (and a replacement diode of a similar type from mouser. The XO EHX pedals use the 1N4000x family of diodes, so it seems)
:help:
 
#2
A really fine tip and a really steady hand. :) And some tweezers and a desoldering braid. It helps if your iron has adjustable heat as well. The component is just sitting on top of the solder pads. I would apply the desoldering braid and the iron, and then tweezer away the old component when enough of the solder has been removed. Then use one hand to apply the new diode in place with the tweezers, your second hand to apply the tip of the iron, and your third hand to feed in the solder.

They make special SMT soldering irons which make it unnecessary to have three hands, but it's not cheap or practical for most people to buy an SMT iron for only occasional repairs.
 
#3
If it only serves to save the device when you insert the plug backwards, it is possible to solder over the diode.

It will not work if it is a rectifier diode (check if the power going in is DC or AC)

I did this on an old peddle and it worked fine. Keep in mind that you are removing a safety device from the circuit and if you ever install a plug or battery backwards- poof.

I do not recommend you do this as I have never seen your circuit, but if you are going to junk the thing, why not.

Attempt at your own risk. I assume no liability.

Also, you can substitute a normal diode in that place by soldering 24 awg wire to the board and soldering your component to the wire (had to do this to an opamp in a mixer once)... because GOOD LUCK getting the right SMT component. Also keep in mind that a diode must be installed in the proper direction. Consult a schematic or charred remains to find the direction. It will be marked with a white dot or band. The board may be marked as well.
 
#5
Thunderscreech said:
This seems to be what it is. Current going in is "humped" DC (^-^-^-^-^-^-^ for want of a better description).
Click to expand...

Sounds like badly filtered DC. Is it a quality plugpack you're using?

Back to the topic at hand, don't be afraid to mangle the old SMD diode - melt it with an iron until you can push it away in a smelly little blob! (but be careful not to damage the tracks around it) If there's enough room, you could bend the legs on a regular diode (a 1N4148 will probably do - about 5¢ worth) to meet with the solder pads. A "Ω" shape usually works.
 
#8
Ba55Man1ac said:
...don't be afraid to mangle the old SMD diode - melt it with an iron until you can push it away in a smelly little blob! (but be careful not to damage the tracks around it)
Click to expand...
Oh lordy! Do this at your own risk and don't be surprised when you munch the pads off the board. It's surprisingly easy to do!

Lets take it back a step shall we?

Plugged in by itself it's a no go. But with the signal cables plugged into another pedal, it works. Right?

This means nothing more than that the ground connection to the DC jack is interrupted - the signal cables provide a current path to the power supplies ground via another pedal.

If the diode you speak of is a reverse polarity protection diode, and it has gone open circuit, then you shouldn't notice any problem. After all, the diode is normally reverse biased which means it looks like an open circuit as far as the power supply is concerned. If it has blown short, then it will be shorting out your power supply meaning nothing will work. The latter is much more likely IMO.

Now, what have you done to test your theory? We could be barking up the wrong tree here.
 
#10
niftydog said:
Oh lordy! Do this at your own risk and don't be surprised when you munch the pads off the board. It's surprisingly easy to do!

Lets take it back a step shall we?

Plugged in by itself it's a no go. But with the signal cables plugged into another pedal, it works. Right?
Click to expand...

Yes.

niftydog said:
This means nothing more than that the ground connection to the DC jack is interrupted - the signal cables provide a current path to the power supplies ground via another pedal.

If the diode you speak of is a reverse polarity protection diode, and it has gone open circuit, then you shouldn't notice any problem. After all, the diode is normally reverse biased which means it looks like an open circuit as far as the power supply is concerned. If it has blown short, then it will be shorting out your power supply meaning nothing will work. The latter is much more likely IMO.

Now, what have you done to test your theory? We could be barking up the wrong tree here.
Click to expand...


Other then plugging it in and not getting anything while it was by itself, that's all I've done. I guessed it was the diode was because I've had similar things happen to my Little Big Muffs (both cases the diode shorted out and had to be replaced).


So I guess now I need to find where the ground doesn't work? The Metal Muff has a ground spring which bumps up against the case. Would that being dirty cuase an interrupted ground?
 
#11
Thunderscreech said:
So I guess now I need to find where the ground doesn't work? The Metal Muff has a ground spring which bumps up against the case. Would that being dirty cause an interrupted ground?
Click to expand...
Forgot to ask, are you using the same daisy chain to power the muff and the other pedals? Do you have the ability to try a separate power supply for the muff?

Where is this ground spring? Are you sure it's supposed to touch the case? Do you have a multimeter?

Is the weather nice where you are? :smug:


Gaaaahh, so frustrating! The metal muff schem was on photobucket not too long ago.
 
#12
niftydog said:
Forgot to ask, are you using the same daisy chain to power the muff and the other pedals? Do you have the ability to try a separate power supply for the muff?

Where is this ground spring? Are you sure it's supposed to touch the case? Do you have a multimeter?

Is the weather nice where you are? :smug:


Gaaaahh, so frustrating! The metal muff schem was on photobucket not too long ago.
Click to expand...

Good thing is, I can answer yes to most of this :D.

The Metal Muff is residing at a compadre's house, so tomorrow evening I will make a call and go get it.

When I got the muff, it was in a chain with other pedals. Always was, until the day I decided to try it on it's own with bass(after a couple years. and then it sat for a while with no use, too), that's when the trouble happened. Currently, it is daisy-chained with a Dunlop Jimi hendrix Wah (the JH-1), and works fine in daisy chain.

I will take some pics and post them tomorrow.

Multimeters are not a problem in my house. my dad being an electrician, I ask for a meter, he says "which one?"
 
#14
Iron Butterfly on turntable: Check

Test Meter: Check

Sorry for the bizarre photo layout, but there was no easy way to take a good enough picture of it all...

Here's the whole beast:
DSC_0988.jpg


and the beast in quarters:
DSC_0989.jpg


DSC_0990.jpg


DSC_0991.jpg


DSC_0992.jpg
 
#15
Ok, so is D2 the one you were suspecting? It looks fried to me. They even helpfully give you the part number - mmbd4148se - which is effectively used as a diode/fuse!

This seems like something different to just a diode across the DC jack hence why it's not reacting as I might have expected.

That ground spring arrangement is a new one on me. Bizarro.
 
#17
niftydog said:
Ok, so is D2 the one you were suspecting? It looks fried to me. They even helpfully give you the part number - mmbd4148se - which is effectively used as a diode/fuse!

This seems like something different to just a diode across the DC jack hence why it's not reacting as I might have expected.

That ground spring arrangement is a new one on me. Bizarro.
Click to expand...


I will agree. D2 was the first thing that caught my eye before I read any of the text. She looks a little bloated. And she looks like she is right in the power path. Hence if she is open there would be no power right?

What happens when you check continuity over it (in both directions)? If you get nothing, either way, she is for sure blown. (you can check using those two convienent test points next to the diode) Have you tried calling New Sensor and asking for a new diode? A schematic? I would bet mouser would have that diode in stock for you.

Also what happens if you use a 9 volt battery?
 
#19
bassmodder said:
I will agree. D2 was the first thing that caught my eye before I read any of the text. She looks a little bloated. And she looks like she is right in the power path. Hence if she is open there would be no power right?

What happens when you check continuity over it (in both directions)? If you get nothing, either way, she is for sure blown. (you can check using those two convienent test points next to the diode) Have you tried calling New Sensor and asking for a new diode? A schematic? I would bet mouser would have that diode in stock for you.

Also what happens if you use a 9 volt battery?
Click to expand...

haven't tried a nine volt battery, but based on my previous experience with these pedals, it seems like it will work with one.

Of course, D2 will get tested to make absolutely sure, but the bigges thing now is replacing it. :atoz:

EDIT: Well Lookie here: Invalid Link Removed
 
#20
Yay, someone give me a gold star for guessing it was a 4148! Not sure if it looks blown, could be just some flux on top. Does it scratch off with your fingernail? The option is still there to get a non-SM 1N4148 from your local & whack it in - even just to confirm that's the problem. Obviously using the diode test on your multimeter will give you a good idea.
 

Latest posts

Top Bottom
Back