Can a 470uF or 100uF Capacitor Cause a Short Circuit in 7805 Regulator Circuit?

Hello all...
Having recently finished  a small project, I'm having a small dilemma with a short circuit.
The power side, comprises small components.  The input is AC(6-9v), which goes through 4x IN4007, then with a 470uf cap, onto a 7805 regulator, and again a 100uf capacitor. When switched on the regulator got very hot, to much to handle. I examine the board, before inspecting components. This was fine, as it was a home made PCB, this check was previously done.
I removed the 7805 as it may of been faulty, putting a new one in, same results. At this point again I inspected the board under a magnifier light, and doing a continuity test across the power lines, this came back as a short circuit. I removed the IC and LCD, same result.
I gave up as it was late, but still thinking about it, i was wondering if a capacitor can go short circuit ?
Ive included an image of the power side of the circuit.
Many thanks
Rich

Rich, I had exactly this problem with a small power supply I built.  I had a 22uF tantalum on the output of the 7805 and it went short.  So it can happen.  Electrolytics are more likely to go dry and high resistance, but it's not unknown for them to go short.  The acid test is to remove it and see if the problem goes away.A couple of observations- 100UF is a bit large for the output side of a 7805 - 10uF should be quite adequate (if you're using small components and space is limited, this will be good).- In cases like this it is good practice to make the working voltage of your cap at least double the maximum it will encounter in normal use.  Since this is 5V regulated, a 10uF 10V would be adequate.- I presume you have a multimeter - measure the voltage across your cap and see if it is 0.0 or some intermediate value - a volt or so.  This may give you a clue based on what the regulator is driving.- it is always good practice to construct and test the power supply section of a project before connecting the rest of the components.  It may avoid letting the smoke out of more expensive parts :-)Let us know how you go

Hi Rich-To add to David's comments; Looking at the schematic, there appears to be a short between the input and output pins of the 7805.  I guess that's probably just an error on the schematic, but it wouldn't hurt to inspect the hardware just to make sure.If the 7805 is in a TO-220 package, make sure the input is on the lef-hand pin, ground is in the middle, and output is on the right.Don't throw away the 7805 you pulled off of hte board.  It's really hard to kill those.  They are protected against overcurrent and overtemperature.If you're using tantalum capacitors, double-check the polarity. They tend to do bad things if connected in reverse.While the power is off, poke around with an ohmmeter. If the capacitors measure below a few hundred ohms, don't turn the power back on until you find the problem.-Rick 

Nice call on the shorted 7805, Rick.  I assumed that was just the way it was drawn.  But Rule No. 1 is: Never Assume

Thanks for the replies.@David - I will reduce as you advised down to a 10uf.I did not think of a cap going short, until i thought of it later on after.
@rick - The short you mentioned on the 7805, i think that's a simple error on the authors part. I'm not using tantalum capacitor, just the basic electrolytic. I do have a couple of cap meters, so i will test them as i go along. 

I have to say though, its my own fault, due to not using new capacitors. Ive a box of new electrolytic caps, but being a tight ass, i used old ones which i took from some old boards. I will put new ones in..
To give you an insight to what this board is, its a simple timer for my PCB tank. Having set the temperature and placing the board in the tank, I go off to do other things and forget its in there, and at times Ive killed boards. So I wanted a simple timer for turning off say after 4 minutes. Its based on a 16F877A chip, passive components + relay and 16x2 LCD.  I can't remember the authors name, only 'Ken'. I made it up last year, but the board was a rush job, and looked nasty, so Ive redone it.Thanks again for the replies, and I will get back to you David with the outcome of putting new capacitors in.
Rich

Rich - always test reclaimed components before using them.  I do a lot of this myself:

http://www.eetimes.com/author.asp?section_id=36&doc_id=1320904 A capaciatance meter is great to have, I built one myself and also have an LCR meter now, only about 50 bucks but worth that many times over. Electrolytic capacitors have a finite lifespan so are not really worth recovering unless they are known to be fairly new or are big power supply smoothing types which cost a lot new.   Good luck and thanks for the feedback...and please let us know what the problem finally turns out to be, it's nice not to be left hanging.... Cheers // David

Hi David
Here is the the outcome..I put in the new caps and still nothing, so after an hour of tearing some hair Ive left out, i  inspected again with the mag light, this time, i noticed something between tracks.Using a scalpel, i scraped away, what i don't know, and it worked. The only conclusion is that a very  minute soldering bridge or whatever shorted out at this point. (I nearly gave up and was going to make another board)

I read your post with interest.  I can sit in the kitchen happily removing usable  components with my heat gun, and then the wife comes out with a face like a bull  -  happy days....
Thanks for the help along the way
Rich

Rich - glad you found it.  I was suspicous that an electrolytic would cause your problems,  Solder bridges are a pain when they are small.  but well done. When you say Mag light are you referring to those torches, or to a magnifying light?  If the torch, invest in an anglepoise or hand held lighted magnifier - they are worth their weight in gold for this sort of stuff.  Even a cheap USB microscope - you can pick up one with a 1.3 or 2.0 MP image that plugs into your PC for about 50 bucks these days.  
My wife would not let me near the kitchen with the heat gun.  I used to do it in the garage and she'd still complain.  Now I sneak it in at work and she still says I stink when I get home.   You can't win.  But some types of PCB do smell pretty foul when they get hot, I steer clear of them, you don't know what you are breathing.Anyway, been a pleasure.  Till next time / Cheers / David

Hi DavidSorry for late reply.
The 'Mag light',  is have a magnifier lamp, i think i bought from the Range store, very nice magnification, with nice bright light, worth its weight in tea any day. Also Ive a 4 inch colour  screen with camera which also records/snapshot to SD card, which i bought from Banggood, and as you said a USB microscope .
Nice talking to you.Rich

Rich...right, seems you're pretty fixed up for finding shorts on boards then!  Do use these tools when you need to, I've messed around for an hour once with simple magnifying glass (my magnifying lamp wasn't working) but found the short in 30 seconds with the USB microscope.It sounds like you are having fun, which is the main thing!