Help me troubleshoot this simple design

Hi

i have built the ESR meter from this page

http://members.shaw.ca/swstuff/esrmeter.html

and unfortunately it doesn't work at all... i tryed to reflow the joints
but nothing... the PCB has two minor defects two rails wasn't ok after
the developemnt of the PCB so i used a piece of wire. As far as i can see
everything else is fine.

here's some photos of my build, please tell me what to check or measure on it.

P.S i'm using a 6V DC tranformer to power this thing....

please see the comment at the end of the article under concern., and I quote below-

"........... I used the PCB layout as a guide for placing and wiring the components (printed and glued to proto board).................... "

1. Please check whether the circuit is wired properly as the layout has not been used/checked by designer himself. He has just used it as a placement guide.

2. I find from the photo you have posted that at lease three of the 3 nos of 680E appear 270E--please check the top three.

3. I also fear whether the 2N2222 is placed properly (if any other substitute is used, please ensure proper mounting-- plastic 2N2222 follows EBC pinout, thus I expect flat surface downwards on the top layer photo .

Resistors are fine...it's just that the three first are placed backwards than the rest two and look like their values are different. The transistor is a 2n2222emitter is placed down (where the white resistor is)

also the joints in the back side look awful...they aren't that awful the photos i uploaded are bad quality that's why they look like oxidized...

it would be much of a help if someone can tell me what to measure and what to expect...

specificaly about the transistor, i measure nothing between base-emitter... (it is possible i might not be able
to measure the transistor, because i'm not sure if my digital multimeter can deal with so small values of AC)

Use part of the circuit as a test probe and probe the connection marked with a red dot.

You should get deflection on the meter if the oscillator is working.

whiz115 said:

Resistors are fine...it's just that the three first are placed backwards than the rest two and look like their values are different. The transistor is a 2n2222emitter is placed down (where the white resistor is)

also the joints in the back side look awful...they aren't that awful the photos i uploaded are bad quality that's why they look like oxidized...

it would be much of a help if someone can tell me what to measure and what to expect...

specificaly about the transistor, i measure nothing between base-emitter... (it is possible i might not be able
to measure the transistor, because i'm not sure if my digital multimeter can deal with so small values of AC)

Click to expand...

The component overlay modded file is attached for plastic 2N2222

Last para , thanks to Elebek1388, has resolved a way to test .
regarding resistors still i have a doubt and better have a check, as reverse sequence is not matching -- actually legibility is poor). Also ensure that the IC is placed properly( don't mind)

Assuming that you have a voltmeter, the way to proceed is to first check that you have good connections for power supply and ground. For example, you put your meter's black probe to circuit ground, put your red probe on your +5 input to the board and check for 5 volts DC. Then move your red probe to various points on the board that should have 5V and see if it gets to those points. If not, then trace back and find why not.

Next, check DC bias to discrete stages and interstage connections. For example, the base of Q1 should have about 1 V DC on it. The emitter should have about 0.3 volts DC.

Next, start checking AC signals from the left to the right. First, see if the IC1D is oscillating as it should by using a high frequency AC probe (a diode and a meter?) You can use your own circuit starting at C3, as an AC meter, but you must disconnect C3 on the left side and use this as your probe input. Touch this probe to IC1D pin 2 (not pin 1!) and see if you get any reading. You can also try using your regular voltmeter on its AC volts setting, but you may not read anything since the frequency of the oscillator may be too high for your meter.

If you see no AC, then find out why. Try substituting another meter to see if it is your meter that is a problem. Don't proceed with further AC tracing until you are sure that the oscillator is working as this is essential to all the rest of the circuit.

Please substitute the esrmod.png, I suggested, with this one --

i had the following results

VCC=5.70V

base-emitter: 610mV DC and when i turned the multimeter at 200VAC range
it shows "00.7". If i probe base and (-) of power source i see 770mV DC

Where the 680ohm resistors are if i probe between resistor-IC pin and the (-) of my power source i measure 5.50V DC but when i turned the multimeter to 200VAC then i see 11.2 (probably mV) resistors #2 from the top shows nothing.

probably first time i did a check to the transistor i did something wrong that's why i didn't had any results.

now what else should i do?

P.S i didn't understood very well what RadioRon says about checking the IC for AC signal.

guys thanks for the help you're offering me...i really apreciate this because for me it's a bit important to troubleshoot it.

some more details to add...

it draws ~30mA from the source...
from the output i can measure ~260mV/2uA

any opinions?

This would be so easy if you had an oscilloscope that you could borrow, but without that, we can try some more things. Let's follow a logical approach to the debugging process. First we want to be certain that the meter is not faulty. The meter is easy to test if it is a DC current meter. You just attach a series resistor of value about 270K ohms to the meter then apply 5.5 VDC to this series circuit. The meter should move and indicate about 20 uA. Be careful to use the right resistor and not use one that is a much lower value like 27K or 2.7K because many meters are easily damaged if you put too much current through them.

If the meter passes this test, then we can re-attach it to your circuit board. Next, we can follow the advice of eblc1388 in his post where he shows how to use the meter plus the rectifier bridge circuit to create an AC voltage probe. I recommend that you follow his diagram, and then use this probe to measure the AC voltage at the output of the oscillator.

whiz115 said:

i had the following results

VCC=5.70V

base-emitter: 610mV DC and when i turned the multimeter at 200VAC range
it shows "00.7". If i probe base and (-) of power source i see 770mV DC

Where the 680ohm resistors are if i probe between resistor-IC pin and the (-) of my power source i measure 5.50V DC but when i turned the multimeter to 200VAC then i see 11.2 (probably mV) resistors #2 from the top shows nothing.

Click to expand...

I think that the DC voltages at the transistor are approximately correct so it seems that the transistor bias is good enough. But I am wondering why you measure AC voltage using the 200VAC range on your meter? Why don't you measure with a lower range, like 10VAC for example? The measurement of "00.7" is encouraging and may indicate this is working OK.

The reading of 11.2 on the 200VAC range for your resistor-IC connection point doesn't make any sense to me. Again, why don't you use a more sensitive VAC range than 200? I don't trust this reading of 11.2. If your meter is an auto-ranging type, then perhaps you are seeing 11.2 mV reading but if it is not an autoranging type, then this would mean 11.2V which is impossible.

I checked my own two meters to see how they respond to 150KHz signals. I put a 5V clipped sinewave signal into the meter at 150KHz, with a scope across the leads to check that signal is there, and the meter indicated 0.00 VAC. Then I check my Radio Shack meter (autoranging, model ?) and it did exactly the same thing. I conclude from this that you cannot accept any measurement of 150 KHz from simple digital voltmeters. So, the only method you have of measuring AC voltage for this is to use your rectifier circuit as mentioned to feed a DC voltmeter or sensitive microammeter. Those rectifiers plus the capacitor change the AC to DC to make it easier to measure.

I also want to add this comment: do not despair. With patience and knowledge we will find your circuit fault.

RadioRon said:

This would be so easy if you had an oscilloscope that you could borrow, but without that, we can try some more things.

Click to expand...

yes i know... but i can't buy or borrow one but i'm thinking to buy a multimeter which is able to measure frequency up to 10MHz

RadioRon said:

Let's follow a logical approach to the debugging process. First we want to be certain that the meter is not faulty.

Click to expand...

with VCC=6.53V
resistor=467K
the current is 13,8uA

RadioRon said:

If the meter passes this test, then we can re-attach it to your circuit board. Next, we can follow the advice of eblc1388 in his post where he shows how to use the meter plus the rectifier bridge circuit to create an AC voltage probe. I recommend that you follow his diagram, and then use this probe to measure the AC voltage at the output of the oscillator.

Click to expand...

The diagram is not 100% clear to me.. i understand that the dots are the places which i should measure, but the "X" is what? it's the steady point?! and why he shows the circuit broken next to the "X"?

also explain a bit what exactly you mean by saying AC voltage probe? you want me to use a diode in one of the multimeter's probe so i can make half rectification of the AC signal?

RadioRon said:

But I am wondering why you measure AC voltage using the 200VAC range on your meter? Why don't you measure with a lower range, like 10VAC for example?

Click to expand...

because the lowest range is 200VAC and the highest 600VAC... it's not auto-ranging and i don't know if it can pickup frequencies of 150KHz.

this is my multimeter...
**broken link removed**

RadioRon said:

I also want to add this comment: do not despair. With patience and knowledge we will find your circuit fault.

Click to expand...

i'm not! yet... btw i have one more 74HC14N spare if we need it...

whiz115 said:

some more details to add...

it draws ~30mA from the source...
from the output i can measure ~260mV/2uA

Click to expand...

Using the schematic, I estimate that it should take about 28 mA (+/- 4 mA) if it is working OK.

whiz115 said:

with VCC=6.53V
resistor=467K
the current is 13,8uA
...

Click to expand...

This seems good, so the meter is OK.

whiz115 said:

The diagram is not 100% clear to me.. i understand that the dots are the places which i should measure, but the "X" is what? it's the steady point?! and why he shows the circuit broken next to the "X"?

also explain a bit what exactly you mean by saying AC voltage probe? you want me to use a diode in one of the multimeter's probe so i can make half rectification of the AC signal?
...

Click to expand...

The X is a point where you need to break open the circuit. This would be done by unsoldering the left hand lead of C3 and letting it float in space. Then you would connect a piece of wire to this floating lead of C3 and the other end of the wire becomes your test probe. By doing this, you create an AC voltmeter out of your 50uA meter plus R17, C6, D1-4 and C3. We will use this AC voltmeter to check the rest of the circuit. However, we must add one more component to make it work. We must add some resistance in series with the 10K resistor R17. This is because the meter I assume you are using is a 50uA meter but with only a 10K ohm value at R17 we will have too much current flowing into the meter during our probing so we need to reduce the circuit sensitivity. We do this by adding your 467K resistor (even better would be a value between 75K and 270K, like 100K would be very good) in series with R17. This is temporary. Once we get everything working this will be removed.

An AC voltage probe is what we have just created and it is just another name for an AC voltmeter. It is simply an "envelope detector" followed by a DC meter. Our envelope detector is made up of the bridge rectifiers D1 to D4 plus C6. This turns AC into DC and works at your high frequency of 160 KHz.

whiz115 said:

because the lowest range is 200VAC and the highest 600VAC... it's not auto-ranging and i don't know if it can pickup frequencies of 150KHz.

this is my multimeter...
**broken link removed**

Click to expand...

OK, now I understand about the range. This meter cannot pickup frequencies of 150 KHz. That is why we must use the AC voltmeter discussed above to probe your circuit.

When you have modified your circuit to create the AC voltmeter then you can touch the probe wire to IC1D pin 2 and report what current you see on the meter. Also tell us exactly what resistance you added in series with R17.

RadioRon said:

AC voltmeter out of your 50uA meter plus R17, C6, D1-4 and C3. We will use this AC voltmeter to check the rest of the circuit. However, we must add one more component to make it work. We must add some resistance in series with the 10K resistor R17. This is because the meter I assume you are using is a 50uA meter but with only a 10K ohm value at R17 we will have too much current flowing into the meter during our probing so we need to reduce the circuit sensitivity.

An AC voltage probe is what we have just created and it is just another name for an AC voltmeter. It is simply an "envelope detector" followed by a DC meter. Our envelope detector is made up of the bridge rectifiers D1 to D4 plus C6. This turns AC into DC and works at your high frequency of 160 KHz.

Click to expand...

i haven't used any resistors or anything else because the output of the esr meter is connected to an analog multimeter and i have choosed the smallest range...

pin #2: 5mA

R2: ~4.3mA
R3:
R4: ~4.3mA
R5: ~4.3mA
R6: ~4.3mA
R7:
R8:
transistor collector: ~3mA

whiz115 said:

i haven't used any resistors or anything else because the output of the esr meter is connected to an analog multimeter and i have choosed the smallest range...

pin #2: 5mA

R2: ~4.3mA
R3:
R4: ~4.3mA
R5: ~4.3mA
R6: ~4.3mA
R7:
R8:
transistor collector: ~3mA

Click to expand...

It seems that you are making a serious error in your measurements. It is not appropriate to probe these various points using your multimeter on any current range. In other words, you should not be using a mA meter to probe this way. A mA meter should only be used in series connections, not parallel probing as you are doing. You must use a voltage scale to probe. Using a mA scale can damage your circuit or the meter. The reason for this is because a mA meter is a very low resistance device, so it puts an extremely small load resistance on your circuit if you probe with it. On the other hand, a volt meter has a very high resistance, so it usually doesn't affect the circuit you are probing.

It is OK to put an analog multimeter at the output of this ESR meter but if you don't use a resistor, then you must select a volt range, not a current range on the meter.

Further discussion from me will be delayed as I am going out for dinner.

lol.... i hope i didn't burned anything!

pin #2: ~3.08V

R2: ~2.88V
R3:
R4: ~2.88V
R5: ~2.88V
R6: ~2.88V
R7:
R8:
transistor collector: ~2.15V

P.S note that my power supply is not stabillized and as you understand values aren't exact...
have a good dinner!

Remove R3 and rest of circuit functions. go for functional tests of ESR measurement .

whiz115 said:

lol.... i hope i didn't burned anything!

pin #2: ~3.08V

R2: ~2.88V
R3:
R4: ~2.88V
R5: ~2.88V
R6: ~2.88V
R7:
R8:
transistor collector: ~2.15V

P.S note that my power supply is not stabillized and as you understand values aren't exact...
have a good dinner!

Click to expand...

There is one other thing that might cause error in your measurement. That is that since the analog multimeter is probably a very high resistance, the time required for voltage to bleed off of C6 may be too large. You can check this by making a measurement (any measurement), for example, probing Pin #2 and noting how long it takes for the voltage reading to die back to zero after you stop touching pin 2 with your probe. If the reading goes down to zero very quickly (like in a couple of seconds or less), then we don't have a problem, but if the reading takes a long time to go back down to zero (like greater than 10 seconds), then we should add a parallel resistor across C6, with value 470K ohms to 2 Mohms. This is simply to ensure that a reading that you make is not affected by residual voltage on C6 left over from your previous reading.

If this isn't a problem, then lets look at your measurements. 3.08 Volts at pin 2 is very good, and indicates that the oscillator is working. 2.88 volts at pins 4, 6, 8, 10, and 12 are also very good and indicate that the buffer amps are working. If you have no voltage at pin 6, you can choose to remove R3 and forget about it (this one buffer isn't critical and you can leave it disconnected) or we can find out why there is no AC voltage there by examining and possibly repairing the solder connection at pin 5 or at pin 6.

The value of 2.15 V at the transistor collector also seems to be good. However, this assumes that you have a capacitor across the test terminals TP1 and TP2. If you don't then this voltage is not correct. I will assume that you have a good capacitor there.

So, if all these voltages are correct, then your circuit is working. When you probed the collector of Q1, you essentially reconnected the original circuit back together, and now you are getting a reading on your meter. So does this not mean the circuit is working? Perhaps the problem was simply your use of mA scale instead of voltage scale while not having anything at R17?