Making A Current Blasting Power Supply With Old ATX Power Supplies

what is Current Blasting? I hear you ask..
Well sometimes when you have a fault with a piece of equipment it's not always easy to track down the issue - it usually comes down to a failed component that has shorted internally - a single failed component of possibly thousands so one method of tracking it down is blasting it with high current (at a low voltage)
It is quite a fun method of trouble shooting because most of the time the failed component explodes off the board, starts smoking or gets very hot.
so what's the best method of doing this? well get a high amp power supply which costs loads of money OR make one out of an old computer power supply.
You have probably seen people make power supplies out of these before for powering their projects which I don't personally think is that great of an idea because of the high current involved but you can use it for that if you wish.

The reason why these things are great for current blasting purposes is because the junked one I have (which is from a very cheap case that had a power supply on it) has a 5volt rail of 27 amps, a 12 volt rail of 13 amps and a 3.3volt rail of 25 amps. which as you can imagine is more than enough.

now for the usual "danger" crap...
I'm sure by now you're used to reading disclaimers and warnings to the point of being desensitized by it and it is easy to ignore these things.
but these things can be very dangerous so you need to take a lot of care when building/hacking these things. They have a lot of capacitors which may retain high energy even when the unit is unplugged. you NEED to make sure they are discharged before you start handling it - that goes for the filter capacitor on the IEC mains input - sometimes they don't have a bleed resistor and can discharge 240 volts (or whatever your local voltage is) into you which I can assure you bloody hurts.

2 Things you must be aware of to use these things

1. in order to switch it on you need to solder the Green wire to Ground (black wire) I suggest
doing this by means of a switch. The green wire will be labelled "PS" or "PSON" on the main PCB

2. some ATX power supplies need a minimum load to function which is around 200mA
to achieve this you must bridge the 5 volt and Ground terminal with a 22Ω resistor.

if you're interested in how this was worked out you can use ohms law
R(resistance)=V(voltage)/I(current) so you type into your Calculator
5 / .200 = 25 so you have the answer 25Ω and you round down to your nearest value which was 22Ω in my case


Anyway here are some pictures, if you have any questions don't hesitate to ask. 

Bare ATX PCB

very cheap supply I found in my shed

I found this on the net some time ago, I'm not sure who it belongs to so if it's yours let me know and I will credit you and your site

Signal Injector / Tracer Stripboard Veroboard Layout

A quick but very useful project. I "designed" (I say designed, it's just a simple astable multivibrator with a basic transistor amplifier) 10 minutes last night and built it this morning basically to help fault find because I'm sick of having to fire up the function generator/scope when I just need a quick tester.
so as usual I will share it with you people.

Maxon OD-880 Overdrive Stripboard Veroboard Layout

Another guitar overdrive (groan) but it's a good type of thing to build when you can't think of original ideas and I am abit stuck at the moment so I thought I would find a schematic of this particular Overdrive and lash up a layout, build it and then post on here for all you people.

The original unit used 3 LM741 op-amps and I was very very tempted to just use a dual and a single op-amp instead but I know people get a bit funny about using alternative IC's and stuff even though it would sound no different, however I specifically laid it out in a way that I could make a little daughter board to use a dual op-amp rather than 2 singles to get better battery life out of the thing.

If you want to experiment some choice component values to alter would be C4, R6, R7, the signal diodes (1N4148) and R9

How To Work Out Parallel Resistance (If You're Completely New To Theory And Don't Get Maths)

First of all you need a Scientific calculator to "play along" I know the one in windows is adequate if you don't have one, I'm not sure what the Mac one is like but I'm sure it will be fine. I personally use a Casio Fx-7000G - it's from the 80's and it's ace - go on eBay and try and find one. I'll put a picture of it below.

Hope this helps anyone who has struggled with it.

Once you Have grasped it you can go test your skills HERE

Ignore the Numbers That's Nothing To Do With This Article

6 Tact Switch Debounce Veroboard Stripboard Layout

This is one of those boring circuits which you need to know when dealing with CMOS circuits and I imagine it would come in useful for those of you using microcontrollers like Arduino/PIC etc.

using this circuit you get a nice clean switch signal from a mechanical switch avoiding miss-switching

2 channels of the switches in action

Guitar FX Regulated Power Supply Stripboard Veroboard Layout

My store bought Effects power supply has been annoying me lately, it's buzzing both from the box and in the guitar signal,it's bad tempered and cuts out and generally just puking up it's entrails, I've been fixing it over and over for years and I finally thought "bugger it I will make a new one" so I did.

It is a very simple build however it is not one to be taken lightly as it involves the mains so you need to take all due care and attention.
Use a metal enclosure and Earth the Chassis, this both adds safety and cuts any stray noise.
Make sure you use a fuse - in my case I used a connector that had a fuse compartment built into it

You will notice that I used a uncommon type of regulator, you can of course substitute this with a LM7809 Regulator, they are pin compatible though I suggest you try and find the ones noted on the stripboard layout.

Be Careful