Fried pedal with incorrect adapter: Fixable?

[MatthewC]

Hey guys. First post here, long time reader.

I have a MarkBass Compressore pedal that I love to death. But over the course of many gigs, AC adapters have come and gone. The factory adapter was rated at 12V, 550mA. I recently did something I have come to regard as stupid. I attempted to power it up with a 12V 1500mA adapter. The pedal immediately lodged a complaint in the form of an unsettling burnt electronics smell.

When I took the pedal apart, I can clearly see the first capacitor (or whatever its called) after the AC jack has some burn around it. Now, when I plug the pedal in with the correct adapter, it just cycles on and off.

I'm going to have to either replace the pedal or service it.

My question is: is this serviceable? And if so; would a novice with electronics, such as my self, be advised to attempt it, or should I bring it to a professional. And my second question then would be can any one give me a diagnosis of what exactly I may have fried. For the price of repair, should I just spring for a new one?

Cheers guys!

[ManuelJG]

If the factory adapter is 12v-550mA, it should work just fine with a 12v-1500mA adapter...

[Dr Greenthumb]

I'm no electrician but I always thought you could use a power supply rated for more mA than what the device needs, as it will only draw what it needs.

Are you sure the power supply you used instead of the stock one was the right polarity??

[MatthewC]

The reason I even attempted to power it on with the 1500mA is because I had read that it would be fine; the pedal will pull the current it needs.

I have tried every variable with polarity. I bought one of those Wal Mart adapters that has the replaceable ends. When plugged in, this adapter just causes the pedal to power cycle on and off.

So if the 1500mA shouldn't have fried it, then I wonder what happened. Like I said, I noticed a smell straight away and I can see some burn on the PCB when I open it up.

[DannDubblewe]

It was most likely reversed polarity.


Snap a shot if what's fried and we'll all go from there!

[rratajski]

Re-check your pedal requirements and the specs on the adaptor.
Perhaps the adaptor is just ac and my an adaptor.

Read this: http://stinkfoot.se/archives/528

[delta7fred]

The protection diode* is usually 1A (1000mA) so if your 1500mA supply was the wrong polarity it has probably fried the diode and then taken out sensitive devices further down stream.

Not a job for a novice. Everything is fixable but it may come with a high price tag, it depends what has blown (plus time).

*There are 2 ways of protecting a pedal, a series diode that blocks all reverse voltage but also drops the supply by a small amount amount, or a parallel diode that shorts out an incorrect polarity power supply and does not cause any loss of voltage, yours sounds like it had the latter.

[MatthewC]

Ok, this is starting to make sense then. The 1500mA may have been the wrong polarity. I will take a picture as soon as I can, but the pedal is at my practice space at the moment.

They run $200 new. For the price of repair, would it be just the same to purchase a new one?

[rratajski]

You won't know until you contact the company for repair...

[--Vissinger --]

Even if it's repaired, there's still the possibility some of the electronics have been degraded and will fail or become noisy before long. Considering the likely repair cost, together with the long-term risk, you're better off replacing it.

[MatthewC]

Let me ask you guys this, what accounts for the power cycling of the pedal? If the diode and other things are fried, wouldn't it simply not turn on?

[rratajski]

9v power (and ground) can still move through portions of the PCB.
By on do you mean working or that the LED is on?

[icecycle66]

I second getting a pic up here.

Make sure you get a good shot of the area around the power source and any capacitors.

[MatthewC]

I'll get a picture up later tonight.

By 'on' I mean the power indicator LED lights up and I can hear the unit 'click' on like it does under normal operating circumstances. Well, to be more accurate, I hear it click on and off, on and off, etc..

[rratajski]

You're hearing the footswitch click over...
The LED is receiving 9v power and ground. It's not indicative of whether the pedal works or not.

[Skrogh]

The clicking is probably from the relay in there taking care of bypassing the effect. The thing is made with smd components, so changing burnt out things wont be easy, but defiantly doable. Give us some gutshots and helping will be a lot easier.

[megafiddle]

Was the 1500mA adaptor a linear supply?
(linears are relatively heavy whereas the newer switching suplies are pretty light)

A linear supply often supplies an open circuit voltage that is quite a bit higher than
the voltage at rated output. That supply should be 12V at 1500 mA, but it might be
significantly more at lower currents.

I have a small 9V adaptor that measures about 13V with no load (0 current). It only
drops down to 9V at rated output.

As everyone already said, reverse polarity was likely cause. If not though, excess
voltage, if it's a linear supply, could be cause. Least likely because they are less
common, is that the supply was a 12V AC supply.

[delta7fred]

Ok, I've done a bit of netsearch and I would forget about trying to repair it yourself.

It is surface mount with about 8 chips (big problem). On the plus side it is analogue and well spaced out so if you find someone who is capable of changing surface mount chips and likes a challenge then you could probably get it fixed. How much it would cost (how long it would take) is anyone's guess.

I recently got a chorus/echo/delay pedal in for repair that had been plugged to an incorrect polarity supply. I took one look inside and saw it was surface mount, with custom chips, with 3 or 4 components that had let out the magic smoke so I put it back together and stuck a "beyond economic repair" label on it. Had it been my own I would have had a go at fixing it but I could have spent a week on it and still had electronic scrap.