Just started MPP project

[green]

Chet, maybe I just have no clue as to how an osilloscope works! Here is an interesting shot.

Some suggestions. Like Chet has said, make sure the probe is on x10 when looking at coil volts. I wasn't used to looking at high voltage circuits and learned the hard way. When posting screen shots have the scope attenuator setting match the probe setting (x1 x1 or x10 x10). Try using 1,2,5 and 10 usec/div. You should get a better display of flyback. Looking at the scope specs it looks like it should do whats needed. Vertical scale 50 volts full scale, x10 500 volts full scale.

[Chet]

Testing Step 5. Images showing TP1 & TP3 Scope results

NOTE: Does not appear to recognize coil target. No change in voltage. I am getting 3.26v at TP3.

TP3 readouts (last image CH1)
Frequency 1.05KHz
Duty Cycle: 99 - 100%
Pulse: Between 944us - 4.7mS
Fall Time: 1.00uS
Rise Time: between 917uS - 2.8mS

Hi multieagle


The scope display has low signal levels in millivolts. It should be swinging plus and minus 3-4v.


The voltage at TP3 should be around +0.9v to +1.0v. Measure for +4.75v on pin8 and -4.75v on pin 4 of U5. If they are off by more than 0.25v check the 5v power supply checks in step 1 and 2 of the build procedures.


Your scope has reached its limits on viewing fast pulses. The flyback pulse is 1 to 2 us in width. Your scope samples at 1 MHz which is a 1 us rate. You need at least a 10 MHz sample rate to resolve much fidelity on fast signals. You can still gleam some useful information but TP3 will be choppy and will lack some accuracy.


Does your scope probe have a voltage rating of 600v or higher? If not you could burn out the input circuit of your computer/oscilloscope by connecting to the damping resistor that has 450v present.


Regards,
Chet

[multieagle]

Step 5 Images

Testing Step 5. Images showing TP1 & TP3 Scope results

NOTE: Does not appear to recognize coil target. No change in voltage. I am getting 3.26v at TP3.

TP3 readouts (last image CH1)
Frequency 1.05KHz
Duty Cycle: 99 - 100%
Pulse: Between 944us - 4.7mS
Fall Time: 1.00uS
Rise Time: between 917uS - 2.8mS

[multieagle]

Step 4, with coil attached, oscilliscope attached to damping resistor. Coil 354uH 1.3Ω Image attached.

[multieagle]

I reinstalled the MOSFET and R1 resistor. TP1 remains the same. I have tried to get a larger sample rate. The directions state the Max real time sample rate is 48MS/s. Guess that means you have no control, the system displays real time, no exceptions???? It is a very simple, $89 computer based program. Hantek 6022BE version 1.0.4


Taking a rough measurement with cursor between pulses:

Cursor Time=922uB Frequency=108.5khz
Cursor Time=899uB Frequency=1.113khz

uB or u8 or ?

What do these figures indicate?

[Chet]

YAHOOOOOOOO!!! Whatever we did, am now getting a high pitch signal.

Thank you, thank you, thank you.

Image attached: 500uS 2.0v

Hi multieagle

That's great news!

Be careful to make sure your coil is ok before you proceed on with the checkout of the transmitter. Do not touch the 740 MOSFET while the power is on! If it is pulsing correctly there is 450 volts present.

Have a great day,
Chet

[multieagle]

The -12v and -6.5v across C6 indicates that C6 is not shorted. It might be open which is rare but can happen.

TP1 at -11.11v is reasonable.

Perhaps since you are having problems with your oscilloscope try a speaker connected between TP1 and TP10 as stated in step 3 of the build procedures.

Regards,
Chet

YAHOOOOOOOO!!! Whatever we did, am now getting a high pitch signal.

Thank you, thank you, thank you.

Image attached: 500uS 2.0v

[Chet]

Thanks for the instant electrical 101. <smile> No wonder no one understands me!
C6 Pins: -12 & -6.25

TP1 returns -11.11v

The -12v and -6.5v across C6 indicates that C6 is not shorted. It might be open which is rare but can happen.

TP1 at -11.11v is reasonable.

Perhaps since you are having problems with your oscilloscope try a speaker connected between TP1 and TP10 as stated in step 3 of the build procedures.

Regards,
Chet

[multieagle]

Thanks for the instant electrical 101. <smile> No wonder no one understands me!
C6 Pins: -12 & -6.25

TP1 returns -11.11v

[Chet]

I am getting only 0.031v at TP2

U4 is all screwed up

1....-12...................5...0
2....-6.25................6..-12
3....-11...................7..-6.25
4....0......................8..-3.9

If I understand correctly: 2 & 6 should be the same 4 & 8 s/b same values.
Strange that 2 & 7 are same values. What could cause that? Bad socket?

Hi multieagle

The pins are numbered from the top counterclockwise from the top left; go down 1, 2, 3, 4, then across the bottom to 5, then up to 6, 7, 8. 8 is across from 1 at the top.

So;
1.....-12v........8....0v
2.....-6.5v.......7....-12v
3.....-11v........6....-6.5v
4.....0v...........5....-3.9v

Pins 2 and 6 at -6.5v are ok

Pins 4 and 8 at 0v are ok

Pin 1 is -12v for power is ok

Pins 5 and 7 are floating; not used in this circuit so the voltages are probably not important.

Pin 3 is close but should be pulsing

If D3 is still good and the 555 chip is still good then it might be that C6 is bad. There is another capacitor in the build package for C16.

Regards,
Chet

[multieagle]

I am getting only 0.031v at TP2

U4 is all screwed up

1....-12...................5...0
2....-6.25................6..-12
3....-11...................7..-6.25
4....0......................8..-3.9

Negative 5v at U8 pin 4

If I understand correctly: 2 & 6 should be the same 4 & 8 s/b same values.

[Qiaozhi]

Yes, between TP1 & 10, black (neg) lead to TP10. Images attached.

Are the +5V and -5V supplies OK?

[multieagle]

Can you post a clear (not out-of-focus) photo of your PCB?
Looking at your most recent scope shot, it looks like you have the timebase set to 50us/div. If the marks on the horizontal are the divisions, it appears the pulse rate is only 100Hz. You haven't stated where you're taking the measurement. Is it between TP1 and TP10?

Yes, between TP1 & 10, black (neg) lead to TP10. Images attached.

[Qiaozhi]

Did that and used my last 555 chip. I'm still getting different readings 2-4 & 6-8. I have resoldered everything to no avail. There are no bridges or bad solder points. So, not the 555. Probably something close by. Perhaps a faulty socket? I'm not up to removing sockets at the moment, so will shelve it for a while. Thanks to all who contributed.

Can you post a clear (not out-of-focus) photo of your PCB?
Looking at your most recent scope shot, it looks like you have the timebase set to 50us/div. If the marks on the horizontal are the divisions, it appears the pulse rate is only 100Hz. You haven't stated where you're taking the measurement. Is it between TP1 and TP10?

[multieagle]

Its hard to read your display, but it looks like very low level voltages which may just be noise from the chopper in the 5 volt power supply. It looks like U4 is still not oscillating.

Try resoldering the connections and try another 555 chip if you have one.

Regards,
Chet

Did that and used my last 555 chip. I'm still getting different readings 2-4 & 6-8. I have resoldered everything to no avail. There are no bridges or bad solder points. So, not the 555. Probably something close by. Perhaps a faulty socket? I'm not up to removing sockets at the moment, so will shelve it for a while. Thanks to all who contributed.