Baracuda broken

[BKY1337]

I measured the transistors instead of the voltage converters.

I got -7.8V for the 79L05 and 18.8Volts from the Output of the 78L05 with my 12V Battery.

[Andi68]

Something is wrong

[waltr]

I have only a DSO150 , i fear that i can damge it with too high voltages.

Then use a couple of resistor to create a Voltage divider to ensure the DSO is safe. Use high enough resistor values to ensure current limiting.
I use a 79k and a 1k to divide Coil fly-back to lower level.

Something is wrong

Sure sounds that way.

[homefire]

Your DSO 150 will work fine anyplace but the coil it's self with a 10 X Probe. Without the 10X you can still look at the output of the first Amp.

[BKY1337]

Can i use such a 10x Probe with my DSO? https://www.ebay.de/itm/Tastkopf-Pru...8AAOSwnNBXXSm1

Is it better than two resistors?

[waltr]

A good 10x probe would be better than a resistor divider due to capacitance but only if the circuit to be measured can be loaded, and thus change characteristics like when measuring the Self Resonant frequency of a coil.

A 10X probe divides the Voltage by 10 so you must READ the scope's manual, or what is printed near the inputs, for what the MAXIMUM Voltage allowed. Then multiple the MAX Voltage by 10 and ensure this is greater than the maximum Voltage in the circuit to be tested.

But as homefire stated: in a PI detector the only place where the Voltage will be high is directly on the coil right after it is switched off. It then 'flies-back' to a few hundred Voltage.
This is where I use a resistor divider as I described to ensure the Voltage the scope sees if safe.

[kt315]

A good 10x probe would be better than a resistor divider due to capacitance but only if the circuit to be measured can be loaded, and thus change characteristics like when measuring the Self Resonant frequency of a coil.
--
self resonant freq is 500-600kHz while a range of his pocket oscope is 200k.

[BKY1337]

Yes maximum is 200khz and 50Vpp.

I think i found the faulty part. I can measure 7.8Volts at the Output of the +5V Voltage regulator with 9Volt battery.
I have 11.2V there with my 12V battery.

I think the circuit works ok because 7.8 is still in the range where the other part of the circuit works but 11.2 is too much.
I dont think that 11.2V can destroy anything.

I need to wait until i have a new one.

[waltr]

Sounds like the problem.
Do double check the pin out of the +5V regulator you are using. Not all regulators of similar part number have the same pin-out. Different manufactures can and do have different pin-outs.
Also, ensure you are looking at the pin-out diagram correctly, some show from top of reg others show from bottom.
Guess how I know this!!!

[BKY1337]

I already tried to use it in the other direction without success it didn't work in the wrong Direction.

[BKY1337]

I replaced the 78L05 and now i have +5V and -5V. But the problem is still present.

The Mosfet gets hot. I get a signal when i touch it without connected coil.

I think i should replace the ICs and the Mosfet.

I also have a signal now when i connect the coil and 12V Battery and i set the treshold pot a little bit over threshold.
This wasnt before. I hope the Mod was not the cause of this.

[kt315]

give pic on U4 pin8.

[BKY1337]

Can you tell me the settings which i need to use on my DSO?
It seems like i can not measure anything.

With or without coil? I can not use a coil with 12V because of the Mosfet.

[BKY1337]

This is TP2 (at the left from U4):

I cant get a signal from Pin8. Or im too stupid to measure it.

Measured without Coil and 12V.

EDIT: I just saw that i measured Pin14 , not Pin8 :-D

[BKY1337]

I completely pulled out two through hole platings where the mosfet is.
Was not a good Idea to desolder the mosfet.

Here is the Signal from the gate of the Mosfet, with desoldered Mosfet.



I can not measure anything at pin8.