Hammerhead Rev. D Finish, but little problem...

[Sebastos34]

Hi,
I've just finish my hammerhead, with the rev.D pcb from silverdog's shop,with opt.1. (thanks to him for the great quality pcb, and his help!)
All seems to be right during 10 minutes (I haven't tested all pots and autotrack)
But after a moment the sound will be reverse[IMG][/IMG]d (a big treble sound when no target, and the sound stops whet I put a target... )
I've shorted resistors R7, R8 and R15 as noticed by carl on his article, maybe it's not good for the rev. D ?
Q10 and Q12 were replaced by C337, and Q13 is a C327. I've turned them from 180° to have good pin correspondance.
This is a pic of my pcb.

this is a pic of my board...


Do you see anything wrong?
Thanks

[maca404]

I have had this before and I think it has to do with the gain it goes quiet because it is overloading when a signal comes through try adjusting r35 down a bit.

[Sebastos34]

Thanks four tour answer maka404.
I tried to move all pots, but it's the same...
Impossible to change that... I think that something is wrong, on my board. Maybe a bad component?
I don't know where is the problem...
Do you think that changing the damper resistor value could change something? Actually, I've dont set it to good value, just for testing.

[Sebastos34]

On autotrack mode, detection is good, but I always have a treble sound on speaker, and I can't get it quiet while moving pots. All was ok during 10 first minutes of use!

[Sebastos34]

I don't understand...
I replaced IRF740 headsinked it, made a new coil with bigger wire, moved some resistors who was mounted on sockets, and now, all is ok during 5 seconds, and irf740 is burning!!! With smoke.
Somebody have an idea of my problem?
Please!!! I'm going to be crazy...

[Thomas]

what is the Ohms of the damper resistor?

[Sebastos34]

Hi,
My new coil is 490uH and the damper resistor is 680ohm.
Thanks

[Qiaozhi]

Hi,
My new coil is 490uH and the damper resistor is 680ohm.
Thanks

Do you have access to an oscilloscope?
If so, you should monitor the TX oscillator output to see if the pulse width is too wide and/or the pulse repetition rate (freq) is too high.

[Sebastos34]

Yes, I have a old oscilloscope, and I have monitored tx output, but I have a big problem...
Yesterday I had oscillations, but inverted, and now, I have a continuous +15V, and no detection. I can't see where is the problem, and I don't know if I need to wire jumpers or not.
Thanks

[Thomas]

TP1 OK? TP2?

[Sebastos34]

Hi, TP1 have the same look as carl's photo, but I think that my frequency is too high.
TP2 is really not good...

[porkluvr]

... Yesterday I had oscillations, but inverted, and now, I have a continuous +15V, and no detection...

Your picture is fuzzy, and between your camera and my PC the color rendering is not accurate, but in your photo, R4 looks like 10kΩ, 5% (brown black orange gold). It should be 1.5k. A 10k resistor would cause pulse-width to be wider than normal.

Also check R1. The picture is so fuzzy that I don't want to hazard a guess what those color bands are but don't like what I see. Should be 56kΩ or ther'bouts.

If either or both resistors are wrong it could make your power consumption skyrocket.
Like I said, color rendering is imperfect so I can't tell for sure. I'm just calling it the way it looks.

And...
Do you really have a 15V power input? If you used the ICL7660 your hammerhead may be living on borrowed time. ICL7660 is only rated for 10.5V input Absolute Maximum. Absolute Maximum. I did not make that up.

Even with 12V input, I think that ICL7660 is inadequate for the job (ICL7660A would be a safer choice)... but that is not my horse to beat.

[Sebastos34]

Hi,
Thanks for your reply.
I've verified R1 and R4 but they are ok.
And effectively I'm using a 12V battery pack with 8 AA.
Maybe it's too high... I'm going to test that with 9V.

[porkluvr]

Don't panic, using 9V is not going to solve anything (but it wont hurt for testing). Who knows, your ICL7660 might last forever.

You have an oscilloscope?! Disconnect your coil and run tests without the coil.

IF you still have problem with IRF740 getting hot, you should remove it and make sure everything looks OK before installing another one. You can check timing and power without the IRF. You have Carl's original 15 page article, right?? Look at fig.21 on page 15. You should have an inverted waveform (and swinging from 0 to -12V) at the emitter of Q2.

Judging from what you wrote earlier, you started with what sounded like a minor problem. Then you developed another bigger problem by either:
1) replacing the coil,
2) replacing the IRF740,
3) moving things around.

You need to figure out what caused that second problem. Work backwards.

[Sebastos34]

Hi porkluvr, and tanks for your useful help!
I moved some components, I've replaced the coil, and now I Can detect a medium object during 5 seconds. After that, I've a lot of noise on tp8, that is covering good signal.(it's the same without coil)
On TP2, I've a waveform that is oscillating between 0 and -20mV. I don't know why IRF740 is cold now.(maybe dead)
I'm on the good way. I think that a component is bad. The question is: what component must be replaced? On Tp1, I've oscillations that vary from 0 to -5v, and at the enter of Q2, oscillations are between 0 and -10V.