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proscan pi problems

A

Anonymous

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hi can any body give me some advice i have built proscan pi with eric fosters recomendations ive checked for shorts every thing seems ok but dont work the output transistor to coil gets red hot
and pin 6 of the 709 (mc1709)which is supose to go to zero with adjustment of p1 does not seem to do anthing thats taking a voltage reading from ground to pin 6 the voltage is always the same as the input voltage ie 10.5 v or 9v if a 9v input is used i do have a scope but not sure what reading to look for off what pins still learning im afraid any help would be gratefully accepted
 
Hi Ian,
There are others here who are probably sharper than me and could give better advice but I'll try to help until they respond <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT=":)"> I believe that your coil switching transistor (T2) is not being pulsed but is staying on. First, I would remove the coil from the circuit so as not to damage the switching transistor. Then check the output (pin3 of U1) of the 555 timer and verify you are getting a square wave or pulse. If not there is a wiring error in the area of that chip. If you are getting a pulse then check the base of T1 and verify you have it there. If not, make sure the wiring is correct surrounding that transistor including that its inserted (connected) properly. If you do see it there, check the base of T2 and its wiring. If everything looks correct until T2, then the problem is in that transistor and its components. I wouldn't be concerned with what you are seeing at the 709 until you get the current switching through the coil. Also, remember that the on time of the pulse should be much less than the off time (pulse rather than square wave). My first attempt at building my own unit had the same overheating problem. The coil and MOSFET switching transistor got extremely hot. I had a problem in my code in the PIC. I was turning it off and on with a 50% duty cycle (squarewave) and the on time was too long. I corrected my pulse routine to a pulse out put of overall period of 2mS (500pps) with an on time of 200uS. The circuit worked great after that and the coil and MOSFET ran cool.
Good luck and let us know how you make out.
Charles
 
Hi Ian,
I saw your post on the Geotechnology page and the point of my post was really not that your circuit might pulsing improperly but that it probably wasn't pulsing at all somewhere down the line. If your 555 is pulsing at pin 3 then as long as you used the resistors called for in the plans it is probably correct (duty cycle). Use your scope to check that the pulse is switching the transistors on and off.
Good luck,
Charles
 
hi charles i did email you with my findings on what you suggested but having afew problems sending and recieving mail at the moment so my apologies anyway pin 3 is pulsing and the bc560 is inverting it to the coil driving transistor
but hard to read on scope anyway i changed the
resistors r1 and r2 round and got a good square wave which did seem a little better but still ran hot after a while whats starting to bother me now is there doesnt seem to be anybody who has built the proscan and it actually worked check back to the geotech forum anyway it dont look good any more advice greatly acepted especially about what
pulse i should get out of output transistor
ian
 
Hi Ian,
You mention changing R1 and R2 around to get a good square wave. As Charles mentioned, you should have a much longer off time than on time. If you are driving the output transistor with a square wave, then it will certainly get hot.
Eric.
 
hi eric
i am begining to think that my output transistor is short circuit when i put it on the scope it just reads the input voltage yet when icheck the base its definetly being pulsed from the inverted bc560 output when i changed the resistors round imiscalculated the on off periods i think
ian
 
hi all
the problem on proscan is the output transistor
is bd911 to220 which makes the pcb for proscan wrong the pin out is wrong if you use to220 which is what i was sent when i ordered mine and i didnt realise it, it wasnt getting pulsed
ian
 
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