Just started MPP project

[Chet]

Removed the MOSFET and R1. Am again getting a pulse. See image. Will pick up the 470 tomorrow and do a temporary install, along with a new 740. Fingers crossed.

Hi multieeagle

It may be that your oscilloscope isn't triggered properly but the display should be like the one you previously posted in post 14 of this thread.
The signal should go positive for 50 usec then negative for 950 usec then positive again for 50 usec.

Regards,
Chet

[multieagle]

Hi multieeagle

It may be that your oscilloscope isn't triggered properly but the display should be like the one you previously posted in post 14 of this thread.
The signal should go positive for 50 usec then negative for 950 usec then positive again for 50 usec.

Regards,
Chet

Back to the drawing board! As good as it gets (attached). Regular pulse. I have the 740 and R3 removed, but that should not be in play.

[multieagle]

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

[Chet]

Back to the drawing board! As good as it gets (attached). Regular pulse. I have the 740 and R3 removed, but that should not be in play.

Hi multieagle

Did you check to see if you have 0 ohms between pin 2 and pin 6 of U4? And check for 0 ohms between pin 4 and pin 8. There may be a cold solder joint on one or more of the pins. It would be worth a try to sweat a little more solder into all of the U4 connections.

The wave shape you have now will have the 740 MOSFET turned on 50% of the time. It will still run hot. When the pulse is right it will only be on 50 usec every 950 usec.

Regards,
Chet

[Chet]

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

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

[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.

[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]

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]

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

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

[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.

[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]

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

TP1 returns -11.11v

[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]

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]

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