Just started MPP project

[Chet]

At step 3, I am not receiving an audible signal between TP1 and 0K. I replaced U4 NE555 and powered up. IRF740 began to overheat. I removed the coil, which returned the Mosfet to normal temperature. I have the coil wires hooked up centre cable to middle connector PL2, and shielded cable (coil has copper shield connected to negative lead) to outer PL2. Centre connectors (PL2 & PL4) are connected beneath the board. Any suggestions as to what may be the problem? Could the Mosfet be defective? What voltages should I expect from the three mosfet legs?

Hi multieagle

"TP1 and 0K" Is "0K" the same as TP10? The MOSFET will over heat if the pulse is not correct at TP1. TP1 should look like your previous oscilloscope display in Post #14 or Figure 5 of the build manual. If not leave the coil disconnected and look for a problem around U4. Do not reconnect the coil until you have the pulse correct on TP1.

Regards,
Chet

[Qiaozhi]

At step 3, I am not receiving an audible signal between TP1 and 0K. I replaced U4 NE555 and powered up. IRF740 began to overheat. I removed the coil, which returned the Mosfet to normal temperature. I have the coil wires hooked up centre cable to middle connector PL2, and shielded cable (coil has copper shield connected to negative lead) to outer PL2. Centre connectors (PL2 & PL4) are connected beneath the board. Any suggestions as to what may be the problem? Could the Mosfet be defective? What voltages should I expect from the three mosfet legs?

If you don't have a signal at TP1, then the TX oscillator is not running. If U4 pin3 is stuck high, the MOSFET will be hard on, and connecting the coil will definitely make it get hot. You need to fix the TX oscillator problem before proceeding any further.

[multieagle]

At step 3, I am not receiving an audible signal between TP1 and 0K. I replaced U4 NE555 and powered up. IRF740 began to overheat. I removed the coil, which returned the Mosfet to normal temperature. I have the coil wires hooked up centre cable to middle connector PL2, and shielded cable (coil has copper shield connected to negative lead) to outer PL2. Centre connectors (PL2 & PL4) are connected beneath the board. Any suggestions as to what may be the problem? Could the Mosfet be defective? What voltages should I expect from the three mosfet legs?

[Chet]

I have finished to Step 5, and must now wait for missing parts. I had some problems with terminology and processes. For one thing, did not realize a coil must be attached at Step 4. I am using two coils made for the Surf PI, both are copper tape shielded and work well on the Surf. 3 coils are around 300uH, 1 coil 278uH and 1.2 - 1.6Ω. However, I'm getting a reading of 1.5v at TP3 on my multimeter and that does not change with popcan or other metal. On my osiloscope, I'm getting an average 1.10v and that also does not change in the presence of metal. I may have to construct another unshielded coil for test purposes?? See attached image.

Hi multieagle

Attached are a couple of sample oscilloscope displays for TP3.

Scope_9 is with no target.
Scope_13 is with a large metal object near the coil.

Chet

[multieagle]

Images to Step 5.

[multieagle]

I have finished to Step 5, and must now wait for missing parts. I had some problems with terminology and processes. For one thing, did not realize a coil must be attached at Step 4. I am using two coils made for the Surf PI, both are copper tape shielded and work well on the Surf. 3 coils are around 300uH, 1 coil 278uH and 1.2 - 1.6Ω. However, I'm getting a reading of 1.5v at TP3 on my multimeter and that does not change with popcan or other metal. On my osiloscope, I'm getting an average 1.10v and that also does not change in the presence of metal. I may have to construct another unshielded coil for test purposes?? See attached image.

[multieagle]

Finished Step 3 and tested okay.

[multieagle]

Okay, just found the answer: http://www.geotech1.com/forums/attac...5&d=1413800548

[multieagle]

In step 3 it states a 100pf capacitor should be placed under the board between Q2 collector and U2 pin 7. I understand where it is to go, but to which Q2 leg does it connect? Is it the outside leg attached to the trace?

TIA

[Silver Dollar]

Well I have to finish it up tonight.

[Qiaozhi]

I built a Davor GEB PCB for my mini;
[ATTACH]32178[/ATTACH]

They plug in via 5 pins so can be swapped out easily;
[ATTACH]32179[/ATTACH]

Did it work as advertised? If so, how well did it perform?

[Silver Dollar]

Also, how do the resistors on your board act across the IC holders?

? Not sure the question. I soldered the SMT IC's to an adapter board and soldered the parts to pads on those boards.
A few parts are "flying" I solidify those with Tack Pac so they do not break during handling.

Small components can be just as reliable but if you are experimenting a lot they are a bit more fragile. Everything is made with
tiny parts these days. Flying parts are susceptible to breaking if you grab the board wrong. Flexing the pcb can crack components.
But build it and pop it in a case and it's just as reliable as anything out there...

[multieagle]

I note the kit uF capacitors are mini-sized (except for the 1000uF). Does size matter (smile)? I had read on another forum that smaller components may not be as durable, more suscepable to failure?

[multieagle]

I built a Davor GEB PCB for my mini;
[ATTACH]32178[/ATTACH]

What is a Davor GEB?

They plug in via 5 pins so can be swapped out easily;
[ATTACH]32179[/ATTACH]

Also, how do the resistors on your board act across the IC holders?

TIA

[Silver Dollar]

I built a Davor GEB PCB for my mini;


They plug in via 5 pins so can be swapped out easily;