Q: Why Does Wal-Mart Stay Open Late?

u turned em

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A:  So a novice can go back to Wal-mart and buy another MS20(this time WM2) when he fries the first board!  FIRST TIMERS TAKE NOTE....this is what happened when I hooked up a test battery with the (+) and (-) reversed!  Mine started smokin!.....and I knew it was fried! Oh well, I'll call this one a learning experience.  I actually had it working and firing the camera.........but I just could not leave it alone.  Fortunately, I had the camera disconnected when I smoked it.  On a better note, Wal-Mart has the WM2's on sale for $7.88 and they have plenty of them!

A REAL HELP QUESTION:  I'm going to swap the R26 resistor for a 220K resistor.  I got the 220K's from Radio Shack today, but they are bigger in size.  The package says "220K-ohm, 1/2 watt, 5% tolerance, part number 271-1132".  Is this the correct resistor?  Any help will be appreciated.  Thanks.....and meanwhile I'll start over!Text
 



Hill Hopper

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As long as they are 1/4 watt, they are ok. DO NOT GO TO 1/2 WATT. What's on the board are normally 1/8 watt if I'm not mistaken.
 

u turned em

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Thanks ******!  I'll go back and look for the 1/4 watt resistors.  Have you made this modification (the 220K) yourself and did it give you the delay/closed relay time you were looking for?  My relay is holding about 3 to 4 seconds.  I'm assuming that too long of an added delay may cause problems with some cameras?.....didn't I read that somewhere?  
 

Tinhorn

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Uh-Oh, ****** made his 1st mistake of the day,  he he

The wattage of a resistor don't matter as long as it's the same wattage or LARGER.  Larger wattage takes up more physical space, that's all, and if there's room to get it in there, it'll work.  HH is not alone, a lot of people think a bigger wattage resistor is a no-no!

I don't know what cam u're using but I like to see a shutter hold down time of 10 seconds on the Canan Owl PF just to be sure it'll snap a pix.   Some Owl's have to have the shutter held down several seconds after setting over night or longer before it'll fire or you might get a No Fire or Blooper Flash.....  (the flash circuitry has to have time to charge up is why)

Tinhorn
 

Hill Hopper

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Maybe so, but I have had problems with 1/2 watt resistors from Radio Shack. This mainly occured with Radio Shack 220k 1/2 Watt.
 

coyotebandit

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I found this on a search.

there are two simple ways of working out the power dissipation of a resistor,
the first is to measure the Voltage across it, then use the following P = V * V /R (v squared divided by R).

the second, less easy is to measure the current through the resisitor, this requires inserting the ammeter so is less elegant, however the equation is P = I * I * R (I squared R).

This will give you the dissipation of the Resistor, now to select an appropriate value, I would suggest means that you have to select a resistor with at least twice the dissipation, ie. if you calculate that the resistor will dissipate one watt, pick a 2 watt or higher one.

Actual resistor dissipation chosen also depends on where it is, ie. if it is next to something hot, use a higher rated R again.
 

u turned em

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Tin, Hill, and Coyote, and all,

Thanks for the clarification and education.  I went back to RS and had no luck in finding 1/4 watt 220K's in an individual five-pack, but lo-and-behold they had a double-lifetime supply (500 piece) resistor assortment(....anybody need a resistor?) that has the 220k's plus 270k's,330k's, and so on.  That's generally my luck.....having to buy the whole store to get a 20 cent part!  

So far, I can say that everything is working as it should.  The new 1/4 watt 220K is still slightly larger than the other resistors on the board, and so the 1/2 watt would have been a real jumbo!  As it should, the new 220K closed the relay for 10-11 seconds.  I just finished quickly reviewing Jon5ja's "MS20 Power Reduction Post", and I have re-asserted myself that I am no electrical engineer!  Some of you guys must do this type of stuff for a living, because y'all know more about it than a proctologist knows about hemorrhoids!!!!  And thanks to y'all, the rest of us electronically challenged folks can have fun working on this project.  Now it's time to start thinking about mounting this thing in the box.  Thanks again.
 

Hill Hopper

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Inside. I built quite a few with sensors on the outside, and they are a real pain in the butt to open up if you have a problem, or what to make any modifications, like adding a timer. Much easier inside.
 


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