Hantek DSO2xxx schematics

[DavidAlfa]

AFAIK it's 2-layer only, then it's a little layout bug made by the trainees at hantek 

[DavidAlfa]

Is it me, or the AWG output protection diode D5 placement was a VERY bad idea?
External peaks will go right away into the +-5V analog voltage without any limitation, potentially killing a lot of stuff.
The diode and/or traces/pcb will burn in no time, and if the diode opens the voltage will reach the amplifier anyways.

Such stupid design. Should be placed at the pin 6 of the amplifier, so R9, R11, R143 limit the current, yet protecting the amp.
In the worst case, the damage will be just a burnt resistor.

[pcprogrammer]

Yep would have been better. Always think twice before connecting something to this input/output.

[gnuarm]

Is it me, or the AWG output protection diode D5 placement was a VERY bad idea?
External peaks will go right away into the +-5V analog voltage without any limitation, potentially killing a lot of stuff.
The diode and/or traces/pcb will burn in no time, and if the diode opens the voltage will reach the amplifier anyways.

I'm confused.  There are resistors totaling 50 ohms in either path.  That's 100 mA if you apply 10V when using the AWG.  If using the external trigger, it's 100 mA at 8.3V. 

Such stupid design. Should be placed at the pin 6 of the amplifier, so R9, R11, R143 limit the current, yet protecting the amp.
In the worst case, the damage will be just a burnt resistor.

Am I looking at a modified schematic?  What you think it should be?  If so, I agree. 

Although, I have done exactly this on designs before.  If there is no option for series resistance, this is still an effective way to deal with static. 

Hmmm, you are making me rethink this.  The design I'm referring to runs the signals through an analog switch for isolation.  The diodes are to ±12V on the connector side.  The 12V supply is on the motherboard and is supplying 8 of these circuits plus the motherboard circuitry.  The -12V is very light.  The idea of sinking the excess voltage into the supply, is that the normal supply current is greater than the surge current.  The -12V rail likely has almost no current.  So that's not good.  I thought the switches were ESD protected internally, but I only find this for one of the part numbers used.  I guess that's why I added the diodes. 

This is to a connector used for serial ports of different standards (RS-232, 422, 449, etc), and audio.  Not likely to be driven by anything beyond ±12V other than static.  Are networking equipment rooms anti-static protected? 

I'm redesigning this card to replace EOL components.  I will need to take better notes this time.  They've asked me to use parts that are expected to be in production for 10 years.  Not sure how that's going to happen.  They have a service that evaluates parts for them.  It will be interesting to see what they come up with.

[pcprogrammer]

Am I looking at a modified schematic?  What you think it should be?  If so, I agree. 

Yep that is a modified schematic. The original is here: https://github.com/pecostm32/Hantek_DSO2000/blob/main/Schematics/Mainboard/Waveform%20Generator.png

[gnuarm]

Am I looking at a modified schematic?  What you think it should be?  If so, I agree. 

Yep that is a modified schematic. The original is here: https://github.com/pecostm32/Hantek_DSO2000/blob/main/Schematics/Mainboard/Waveform%20Generator.png

Ok, but 50 ohms is not going to make much diference really.  If the input is connected to +12V that's going to be 240 mA.  I use the diode clamp to prevent an ESD surge from reaching the chip inputs.  Fed into the power line means the capacitance of the power bus will absorb most of the surge.  The devices themselves typically have ESD diodes into the power rails, so in reality, the added diodes are just protecting the on chip diodes. 

[pcprogrammer]

And that is why the manual of the scope states that the allowed voltage on the trigger input is 0 - 3.3V only.

External: External trigger input, it is on the front panel of the oscilloscope. The external trigger signal must be a 0-3.3V [CMOS] waveform.

[DavidAlfa]

but 50 ohms is not going to make much diference really

Really? The +-5V supplies have a load of about +600, -250mA.
Without resistor, a wire moves, the clip snaps, briefly touching 12V, but you have very low impedance path to +5V through the diode, being such small diode it'll will blow apart, and pray nothing else gets damaged.
With 50R in series, you'll have (12-5)/50=140mA max, the resistor will survive a quick "touch" instead destroying your frontend.
And if you hold the connection for longer, the resistor will dissipate ~1W, will act as a fuse, limiting the damage.

[gnuarm]

destroying your frontend

Thank you for making my case.

[enot]

I drew a diagram of the power supply (new type, Batch202207)

[eurotips]

The TR signal in power supply adapter is the synchronization with the AC network.  I would like to power scope from a LiPo battery. Is it necessary ?

[morgan_flint]

The TR signal in power supply adapter is the synchronization with the AC network.  I would like to power scope from a LiPo battery. Is it necessary ?

Probably not, but read here