1.) Elev Servo Pos H Input Pin# 95 is at 0.049 VAC , the output of U37 pin#6 is 0.011 VDC
2.) Elev Servo Pos H Input Pin# 95 is at 0.063 VAC, the output of U37 pin#6 is 0.030 VDC
3.) Elev Servo Pos H Input Pin# 95 is at 0.080 VAC, the output of U37 pin#6 is 0.050 VDC

 

To troubleshoot the techs next to me use a 2K ohm resistor that is grounded , they ground each node/junction using the 2K ohm resistor to ground to find out where the DC offset/noise is coming from

The output of U37 pin#6 is the Sum of noise and DC offsets of all the stages before it and in parallel to it

How would you guys troubleshoot these types of problems?

You have to make the Pitch servo Sums output null out at Zero volts, Not at .011 , .063, .050 VDC

 

Here is other schematics of the same type of troubleshooting problems when troubleshooting noise, dc offset voltage with NO signal is applied to the inputs

The output needs to be at Zero volts VDC , not 0.011 vdc or 0.030 vdc etc.

How would you guys troubleshooting this?

 

You have to separate the circuit to some parts from the left input to the right output, and measure it by O'scope for each stage of op amp or bjt, and in parallel a 1K resistor to Gnd with input of each stage, and not in parallel the 1K, to measure two different input.

 

If hard to separate the circuit, then you just in parallel and not in parallel the 1K(or 2K) resistor with each input of stage to try.

 

You have to separate the circuit to some parts from the left input to the right output

I have tried this, but when I separate the circuit or Parallel circuits that are being summed, it will RAISE the output noise/dc offset voltage on the output

It goes from 0.011 vdc to 0.080vdc

I'm guessing when you separate the stages it changes the LOADing effect
for this type of noise/dc offset voltage troubleshooting

If hard to separate the circuit, then you just in parallel and not in parallel the 1K(or 2K) resistor with each input of stage to try.

If i go direct to ground , shorting out the input or output of a stage, without a 1K or 2K resistor to ground

The 2K resistor to ground when shorting out an input or output of a state helps protect the In rush current right?

Shorting out an input or output of a stage direct to ground can damage the input or output of an transistor or op amp right?

 

He/they said it over at ETO before they were banned. Look at the schematics he posts, words like flap, elevator, etc, are on them.

Don't know about Malaysia airline, that was a joke.

Wow, ETO banning before AAC. I guess our mod's hands are tied since AAC TOS only references auto. <sarcasm>

 

Hey guys stop hijacking my thread

Stay on the subject please

 

I saw the reference to Malaysia airline but let it go.

Just be warned that it isn't a joke and very inappropriate for AAC.

 

I have tried this, but when I separate the circuit or Parallel circuits that are being summed, it will RAISE the output noise/dc offset voltage on the output

It goes from 0.011 vdc to 0.080vdc

I'm guessing when you separate the stages it changes the LOADing effect
for this type of noise/dc offset voltage troubleshooting

Assuming that the all inputs are independent of the inverting adder, then when you connecting all the inputs to GND or +5V or some other voltage, the output should be the sum of all inputs, the adder should be including the resistors that they already there.

If i go direct to ground , shorting out the input or output of a stage, without a 1K or 2K resistor to ground

The 2K resistor to ground when shorting out an input or output of a state helps protect the In rush current right?

Shorting out an input or output of a stage direct to ground can damage the input or output of an transistor or op amp right?

When we don't know the input/output connecting to any circuit or device, using a resistor connecting to GND is a more safe way to do, normally the input can be connecting to GND directly, but we can't guarantee that, so using a resistor is a better way, but the output can't connecting to GND directly that's for sure, as you know that it could be damage the bjt, mosfet or op amp, so the output should connect a resistor for Load.

 

so using a resistor is a better way, but the output can't connecting to GND directly that's for sure, as you know that it could be damage the bjt, mosfet or op amp, so the output should connect a resistor for Load.

Yes it will overload the bjt,mosfet, op amp if you connect it direct to ground right? raises the current very high on the output pin

the output should be the sum of all inputs

Right, its the SUM of all the noise voltages and DC offsets when there is NO input signals

How do you guys troubleshoot circuits like this?

When you want the output of the last stage of the circuit to be zero volts, but it's generating noise/dc offset voltages

So how would you troubleshoot it please?

 

Yes it will overload the bjt,mosfet, op amp if you connect it direct to ground right? raises the current very high on the output pin

Yes.

Right, its the SUM of all the noise voltages and DC offsets when there is NO input signals

How do you guys troubleshoot circuits like this?

When you want the output of the last stage of the circuit to be zero volts, but it's generating noise/dc offset voltages

So how would you troubleshoot it please?

1. The middle point of R263,R264 connecting to Gnd
2. The middle point of R266,R267 connecting to Gnd
3. The middle point of R269,R270 connecting to Gnd
4. Pin 13 of CD4053 connecting to Gnd
And measure the Pin 6 of U37.

The points that I chosen still has the resistors to isolated, so don't worry they won't damage anything.

 

1. The middle point of R263,R264 connecting to Gnd
2. The middle point of R266,R267 connecting to Gnd
3. The middle point of R269,R270 connecting to Gnd

U37 pin#6 is outputting 0.030 Millivolts

4. Pin 13 of CD4053 connecting to Gnd
And measure the Pin 6 of U37.

U37 pin#6 is output ZERO

It does fix the problem, but like i said , it's an AC voltage going into the CD4053

the output of U37 pin#6 is a DC voltage millivolts

The points that I chosen still has the resistors to isolated, so don't worry they won't damage anything.

When looking at a schematic , how do you know when the resistors are isolated so your can do a direct ground short?

What are some rule of thumbs

 

U37 pin#6 is outputting 0.030 Millivolts
...
It does fix the problem, but like i said , it's an AC voltage going into the CD4053
the output of U37 pin#6 is a DC voltage millivolts

Unsolder the C37(0.1uf) and measure the Pin 6 of U37 again.

When looking at a schematic , how do you know when the resistors are isolated so your can do a direct ground short?

What are some rule of thumbs

Through the mux pic#4,#3, you can see the resistors as :

1. The middle point of R263,R264 connecting to R219(4.99K), calculating how much current will flows through it, it just an approximate values, all the details on the circuit as attached.

2. The middle point of R266,R267 connecting to R227(4.99K), calculating how much current will flows through it, it just an approximate values, all the details on the circuit as attached.

3. The middle point of R269,R270 connecting to R219(4.99K), calculating how much current will flows through it, it just an approximate values, all the details on circuit as attached.

4. Pin 13 of CD4053 connecting to R203(88.7K),R204(100K), calculating how much current will flows through it, it just an approximate values.

 

Ok thanks

The transistors are switches that are tied to a buss or what?

When transistor switches that are tied to a buss like this, what is it called?

Transistor switches Q27, Q22, Q26
Transistor switches Q18, Q21, Q25

They use PNP transistors

Plus they ground the collector to make the transistor into a switch

But other circuits i have seen ground the emitter to make the transistor into a switch

What is the difference between grounding the emitter VS ground the collector to make a transistor in to a switch

Is it Sink and Sourcing?

 

Also on another revision they added 2 diodes and a resistor on the output of the OP amp U37

What does these 2 diodes do to the output of the output

Here is the schematic

 

Because the op amp will output a voltage from -V,0,+V, but the next stage only need the 0,+V, so it used diodes to cut off the negative voltage, and protecting the parts of next stage, why it used two diodes, what i thought was to get more protection, when anyone of diode was damaged, but another one still can be work, it means that the parts of the next stage are very important .

 

Because the op amp will output a voltage from -V,0,+V, but the next stage only need the 0,+V, so it used diodes to cut off the negative voltage, and protecting the parts of next stage,

Is this called Rectifying the output? is it called something else? because you're cutting of the negative cycle

 

Ok thanks
The transistors are switches that are tied to a buss or what?
When transistor switches that are tied to a buss like this, what is it called?

It a common output point, you can google "R2R DAC", "R2R DAC LM358" to get some ideas.

Transistor switches Q27, Q22, Q26
Transistor switches Q18, Q21, Q25

They use PNP transistors
Plus they ground the collector to make the transistor into a switch
But other circuits i have seen ground the emitter to make the transistor into a switch
What is the difference between grounding the emitter VS ground the collector to make a transistor in to a switch

Is it Sink and Sourcing?

Normally the PNP using in the high side and NPN using in the low side, why they used PNP in the low side, because the op amp in the last stage could offer the -V, that's the point that if can't provide a -V, then the PNP in the low side that when it turn on the Vce could be too high as 0.9V~1.1V, and that is not a good voltage level for a switch, specially when the next stage is using with a logic level circuit.

If a PNP using in the high side, that is a sourcing, but in low side still as a sink.

Those circuits using the different resistors and bjts to do the switches, and to be a voltage divider, so they look like some kinds of binary DAC, and I wonder is there a resistor missing in the E of Q19.

 

If a PNP using in the high side, that is a sourcing, but in low side still as a sink.

PNP using in the Low side = sinking?

Because the op amp will output a voltage from -V,0,+V, but the next stage only need the 0,+V, so it used diodes to cut off the negative voltage, and protecting the parts of next stage,

When the Diode cut off the negative voltage or negative cycle, is this rectifying?

What kind of inputs don't like a negative voltage?

What kinds of IC chips , Gates, Digital IC chips , don't like a negative voltage