Minipulse build

[petere]

Hi
Received my Minipulse Rev D board today, thank you Silverdog. Very nice.
Completed step 1 and have -4.96v

[petere]

Finished step 2, all good with 4.92v

Finished step 3, all good, replaced R8 with a 50k trimpot to allow adjustable frequency. Will put a trimmer on R7 as well.

Planning on implementing KRinAZ modifications so I will hopefully be able to use it in the goldfields here in Victoria.

Cheers

[petere]

Completed steps 4 & 5

Step 4 not sure if the voltage is as it should be, I make it about 180v.
Oscope Volts set at 5 x 10 & time set at 2us

Step 5 looks OK to my untrained eye.
Oscope volts set at 0.1 x 10 & Time set at 5us

Wired the coil plug up to suit (in my mind anyway, correct me if I'm wrong) my commercial NF mono coil which is around 340uH & 0.4 ohms.
Don't have a DD coil to test but hope this will work.

Will press on anyway
Cheers

[petere]

Step 6 complete. All looks OK to me.

First photo is TP1 & TP5 showing pulse width on top and main sample delay below.
Was a bit confused with the sample delay trace thinking it was the width I was looking at.
Oscope settings of 50us and 0.5v x 10 for all photos.

Second photo is TP5 & TP6 showing main sample delay and secondary sample delay.

Third photo is TP7 & TP8 showing main sample pulse width & secondary sample pulse width.

[petere]

Step 7
Looks OK. Video shows trace as I pass a pair of pliers over the coil.
Scope set at 50ms x 10
Video at link below

https://youtu.be/wq05ak8SIRw

[petere]

I now have a working minipulse.
The video shows a quick clip of me testing the detector with a small gold nugget.
The scope time setting is 5us.
The damping resistor is around 1630 ohms.
I still need to finish off a couple of temporary items and bundle the whole thing up.
Planning on making an aluminium enclosure.

Thank you Qiaozhi for your comprehensive and easy to follow build document.
Thank you KRinAZ for sharing your mods.

https://youtu.be/aLQBeCWTCjg

[petere]

I just charged the batteries and reconnected them to the detector, there was a bang and flash coming from the area of R3-D10, I think R3 is cooked. Bugger.
Hooked it up again, there was a low growl from the speaker then smoke started coming out of U2.
Can anyone suggest what may have happened. The battery voltage is around 12.3v
Cheers

[Qiaozhi]

I just charged the batteries and reconnected them to the detector, there was a bang and flash coming from the area of R3-D10, I think R3 is cooked. Bugger.
Hooked it up again, there was a low growl from the speaker then smoke started coming out of U2.
Can anyone suggest what may have happened. The battery voltage is around 12.3v
Cheers

Don't you just hate it when that happens.

At first I thought it sounded like Q1 was stuck on, causing R3 and D10 to overheat. But then you said that U2 released the magic smoke, and U2 is the LT1054 voltage converter. The battery voltage is well within range, assuming you actually have an LT1054, and not an LT1054L. The L stands for low voltage, and that particular version is only rated to 7V.

Analyzing a problem remotely is always difficult. Could it be something as simple as a small length of wire or solder had fallen onto the board and caused a short? It doesn't really sound like a component failure caused the flash/bang.

[petere]

I think I will replace a few parts and then work my way back through the steps. R3 is definitely brownish tinge. Might replace Q1 as well. not sure about D10
Just checked pin4 U8 at around 7.7v
Need to order some parts now so might take a while.
U2 is LT1054CP
Thanks for your Help

[petere]

Ok back in business.
I made a mistake with U4, put in a TLC555, instead of NE555, that is where the bang and flash came from judging by the split in the side. Am getting new glasses next week.
Raided some parts from my not very successful hammerhead build.
Replaced R3, U1 & U3 & am temporarily using a 7660 in place of the LT1054 for U2, seems to work OK.

[Teleno]

Ok back in business.
I made a mistake with U4, put in a TLC555, instead of NE555, that is where the bang and flash came from judging by the split in the side.

If that's the true cause then Silverdog has to stop delivering the kits with TLC555, as was my case.

[petere]

Not silverdogs fault.
I sourced the parts myself.

[Qiaozhi]

As far as I'm aware, all 555s can tolerate an absolute supply voltage of 18V. This seems to have been the case from at least 1973.
For a flash/bang event to occur, I would suspect there was unintended short-circuit on the PCB.

[CAS]

As far as I'm aware, all 555s can tolerate an absolute supply voltage of 18V. This seems to have been the case from at least 1973.
For a flash/bang event to occur, I would suspect there was unintended short-circuit on the PCB.

Unfortunately the TLC555 can only sink up to 150mA max and source up to 15mA max whereas the NE555 can sink or source up to 225mA max. Have come across this issue before in a few other circuits where I havent really taken notice of what 555 I put in.

[Qiaozhi]

Unfortunately the TLC555 can only sink up to 150mA max and source up to 15mA max whereas the NE555 can sink or source up to 225mA max. Have come across this issue before in a few other circuits where I havent really taken notice of what 555 I put in.

The specified part is NE555, but I would expect a TLC555 to work just fine. The current source/sink requirements in this application are much lower than the limits quoted above.

Petere - In the image -> P1020687.jpg, I can see the battery pack is connected by flying wires. I assume you didn't accidentally connect the battery pack in reverse?