Visual Sound One Spot dead? [behavior explained + pictures]

[Cortexturizer]

Hi folks, I am having a problem with my One Spot which I love btw! Yeah, it's cheap and if I could I would just buy a new one [not available in my country] so I am trying to get this one salvaged if it's even possible...

It was extremly hard to open this thing without damaging it even more











nothing seems to be burned. Anyone seeing something I cant?

The unit behaves strange, when I measure voltage it's oscillating from 9.5V to about 7.8V and all the values in between. I don't think it's some sort of broken contact or something, though once I managed to get a steady 9.5V on it without changing at all, but as soon as I moved the device slightly it started behaving like described. Strange.
Is this salvagable or should I throw it away?

Thanks!

[Scruffie]

Go on DIY Stompboxes and contact R.G Keen, as the designer he always takes a look at failures to work out what happened.

[Cortexturizer]

Did that just a couple of minutes ago, he responded and told me I was out of my mind opening this :-D

Still I thought it would be nice posting pictures here just to see how complex the unit is, and I haven't seen a picture of the guts anywhere on the internet.

[jkokura]

You were nuts opening that thing!

Seriously, with the price of these things, I'd just get a new one, or find another used one.

Jacob

[GermanCdn]

Just out of curiousity, which country are you in that you can't get another one?  It looks like an EU plug, and if you are in the EU and you can't get another one in country, go to www.thomann.de, they'll ship anywhere for cheap (or free) in the EU, and you can get more than just the Visual Sound stuff, in fact, you could get their isolated Harley Benton (Joyo rebranded) power supply for about the same price.

[jimilee]

They're on eBay uk also

[Cortexturizer]

I'm in Serbia, we are not in EU, and I cannot buy lots of nice stuff like the rest of mankind can. We are somewhat like Sudan, just with less sun and more buildings. Though even Sudan must have better laws and regulations, customs, and healthcare than Serbia...ahhh I am boring you with this.

Yeah, the reason I tore this apart was because I wanted to look inside and I couldn't find pictures on the internet. It's such a complex power supply, here's what R.G. has to say about it:

"They are good pics. A couple of things that aren't obvious:
- The gap with no traces in it on the bottom side, with the blue epoxy dipped device in the routed-out gap beside it. That gap is a bit more than 8mm, as required by safety regulations for minimum creepage and clearance distances for withstanding 4000V transients on the AC line
- The routed-out gap is for keeping the same thing for the transformer pins, not giving high voltage transients a path to short between primary and secondary.
- The yellow tape surrounding the power transformer on the top side serves much the same purpose, because the transformer body bridges the PCB trace gap.
- The windings inside the transformer have multiple insulation layers and creepage/clearance distances of 8mm from primary to secondary **inside** the transformer.
- The bright yellow box-style capacitor on the component side is rated for several thousand volts, and for self-clearing in case it punctures, and for not burning if it's shorted, being rated for across-the-AC-line use.
- The tiny transformer-looking thing beside the cap is a common mode inductor to keep RF switching noise from being broadcast back out using the AC power lines as an antenna. It has to be oriented so its magnetic field does not re-radiate this noise into the power transformer or the secondary outputs.
- There are two L-shaped aluminum heat sinks. The one closest to the yellow across-the-line cap has a high voltage MOSFET attached. If it's not a full epoxy-dipped MOSFET, that heat sink has 400Vdc on it if the power supply is being quiet, and around 600-800V peaks when it's working.
- The big black electro cap beside the main power transformer has 150-400Vdc on whenever the thing is plugged in. There's enough energy there to stop your heart, and this is a tiny, tiny power supply.
- That same cap has the word "vent" on it. This indicates the position of the weak spot in the cap that is designed as a safety valve so the cap's insides will spew out there instead of everywhere, and instead of exploding. It has to be oriented a certain way to maintain this safety provision.
- The exact positions of the traces on the bottom of the PCB (and on the top side, where they're not visible) matters to both performance, low noise, and safety. There are a couple of those that will raise output noise by 10-100x if they're moved a millimeter or two, even if they still connect to the same places.
- The component choices matter. There are often contradictory requirements for component choices and trace placement, so that making something better makes something else worse, and so getting a good design can be a several-dimensional optimization."

Crazy stuff.

I'm gonna order one asap. I need it for the gig that's on 28th of August. Just enough time for it to arrive.
I usually order through Banzai Music from Berlin, Germany. They are not the cheapest but have much better components than Tayda for example, very high quality stuff and some really unexpected caps and brands that I haven't found elsewhere. Try em.

[gordo]

I seem to recall R.G. mentioning that you could be killed to death opening one of those things.  Musta been that little heart stopper...

[hoodoo]

Killed to Death, that sounds dangerous

[jimilee]

I seem to recall R.G. mentioning that you could be killed to death opening one of those things.  Musta been that little heart stopper...

There's your band name right there, "\m/ Killed To Death \m/ " You are welcome! 

[gordo]

It's an old Bugs Bunny reference: "I coulda been killed to death!" and the first time I got zapped working on an amplifier it was the first thing that popped into my head.  Unfortunately that was followed by a string of expletives that would have made a hooker blush...