jay diddy 5 transistor esr meter

[pete g]

hi all, greetings from s. florida. I just completed the 5 transistor esr meter project. need some help to determine if its working right. at turn on the meter goes all the way to the right. when I short the probes the meter does not go all the way to the left. when I scope the output, I get a square wave at 94khz, vpp of 90mv. has anyone else built this project? should the meter go to the right without shorting the output? I posted this in test equiptment by mistake.

[EntropyWizard]

Something went wrong. The meter should hold near the left origin. You can use the zero adjust on the meter face to calibrate the left mark (open circuit). When you short the terminals, it should move all the way to the right-most mark. You can calibrate the right zero (0 ohms) with the pot that is specified in the circuit.

[pete g]

hi, thanks for your response. I made the smd version, I checked the board, looks ok, the problem must be in the meter circuit? any ideas?

[Bryan]

Well other than the obvious, shorts, opens, defective components. I assume the PCB design has been tested by others and is correct by the schematic.

[pete g]

hi bryan, to answer your question, I don't know. i'am curious as to whether this design has been proven out by someone. from what I can see, it appears the osc signal is always present at the meter, thus the full scale deflection. I verified this by scoping the signal.

[dannyf]

at turn on the meter goes all the way to the right. when I short the probes the meter does not go all the way to the left.

With the probes open, the meter should not move at all, at its left most position.

With the probes shorted, the meter should go to the right.

[pete g]

hi dannyf, thanks for the info. is it possible for you to trace the osc sig with the probes open and shorted?  then I might have a shot at fixing this project. since its smd, knowing exactly whats wrong will spare the pcb. thanks.

[dannyf]

is it possible for you to trace the osc sig with the probes open and shorted?

I don't know what that means.

If I were to debug it, I would make sure that a) the oscillator is working, and b) the dc working points make sense. and go from there.

[pete g]

hi danny, in my first post I stated that the osc is indeed working. i'am getting a 94khz square wave at vpp of 90mv, this at the probes. the dc is a rock solid 5v. whats not working is the metering half of the ciecuit. i'am not asking you to debug, only to provide some assistance.

[pete g]

as far as the tracing of the signal, I meant a verbal explanation of the sig flo.

[dannyf]

I meant a verbal explanation of the sig flo.

It is fairly simple: an oscillator, through a driver stage, drives a resistor in serial with ESR. The signal over the ESR is amplified by a differential amplifier and the rectified portion goes through the meter.

It is fairly complicated for what it does.

[dannyf]

i'am getting a 94khz square wave at vpp of 90mv, this at the probes.

So the oscillator + the driver are working.

the dc is a rock solid 5v. whats not working is the metering half of the ciecuit.

You should establish that the DC working points are correct first. Otherwise, you get nothing to work with.

[pete g]

hi dannyf, I think I found an error on the picture that shows the parts on the board. there is a resistor marked RB that should be R8 the value on the schematic shows this resistor value as 150 ohms. it should be 1500 ohms. is this correct?

[dannyf]

I don't know what/which schematic you are referring to.

If you suspect its value is incorrect, parallel a 150ohm resistor to it and see if it works.

[pete g]

false alarm, although the value of that resistor has an effect, its not the problem. I misread the resistor (smd) 1500 is 150 ohm. rats!

[Jay_Diddy_B]

pete g and the group,

I know a thing or two about this circuit. I have been away from my a laptop for a few days, but I am back now. I will post some waveforms, which should help with the troubleshooting.

Several people have built this circuit successfully.

Regards,

Jay_Diddy_B

[dannyf]

its not the problem.

I obviously don't know what the problem(s) here are. But the issue with the design is that the rectifier is open loop. As such, if there is too much attenuation of the oscillator signal, the meter reading is quite non responsive - a sharp drop off.

the way it is attacked here is to use more gain. A better solution is to get the rectifier into the feedback loop.

[pete g]

checked some voltages. with the leads open q4 & q5 are conducting. .6 forward bias, collectors at 1/2 b plus (2.5v) if I turn off q4 the meter goes all the way to the left.

[dannyf]

'checked some voltages. with the leads open q4 & q5 are conducting. .6 forward bias, collectors at 1/2 b plus (2.5v) if I turn off q4 the meter goes all the way to the left.'

I think you can benefit greatly by being concise. Without a schematic, no one knows what q4 or q5 is. Telling tour readers what vbe is tells them far less than if you told them what VB is and what ve is....

Right now,you are saying a lot without being informative. It helps if it is the other way around. Posting a schematic with the DC working points in it will tell your readers far more than all you have said so far.

Hope it helps.

[pete g]

well the problem is. is that there are no voltages on the schematic. i'am really surprised you don"t remember this project as you were a fairly prolific contributor to the thread. I think the schematic can be had the same way I got it and that is search on this website for the 5 transistor jay diddy b esr meter. I thought that would be fairly obvious.

[Bryan]

well the problem is. is that there are no voltages on the schematic. i'am really surprised you don"t remember this project as you were a fairly prolific contributor to the thread. I think the schematic can be had the same way I got it and that is search on this website for the 5 transistor jay diddy b esr meter. I thought that would be fairly obvious.

Yes, but there was a number of revisions and different schematics, PCB designs posted, some tested some not. Which one did YOU use.

[Jay_Diddy_B]

Hi group,

I have had some time to take some measurements in the lab.

These measurements were taken from the unit described in this thread:

https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/msg171364/#msg171364

The schematic is reproduced here:



I have added the dc voltages. These voltages were measured with a Fluke 187.

The input terminals were open circuit for all measurements and scope waveforms.

Waveforms


Q3 collector voltage:



This waveform should swing from rail to rail. The average voltage should be approximately half of the supply, 2.5V. The frequency is nominally 100kHz.


TP1 Waveform



This waveform should be the voltage on Q3 collector time 3 / (150 +3) = 98mV p-p


Q4 Base Voltage



The average voltage should be 5v(10K/(10K +27K) = 1.35V


Q4 Collector Voltage




Q5 Base Voltage



Q5 Base voltage is the same as Q4 Base voltage


Q5 Collector



The voltage on Q5 Collector is the same as the voltage on Q4 collector when the input is open.

Q4 Base (AC Coupled)


Q4 Collector AC coupled




These waveforms and voltages should help you troubleshoot the circuit.

Regards,

Jay_Diddy_B

[dannyf]

The driver should output a near 5vpp square wave. So the probe, when open, should show about 90mvpp.

The bases of the two amplifiers sit at 1.4v, and their emitters at 0.7v, and their collectors at 2.2v. All vs. Ground.

Anything materially different from that suggests troubles.

[pete g]

wow!! this is great. my question is, if the signal is getting to the meter with the probes open circuited, what keeps the meter from deflecting?

[dannyf]

It is a bridge configuration. One arm of the bridge has fixed attenuation and another has its attenuation varying based on the duts ESR.

If the proves are open, the same unattenuated signal will show up on the meter - it is not going to move at all.

The biggest meter movements come when the difference between attenuation is the biggest - when the probe is shorted.