hi all, working on a project that is titled ESR METER WITH TONE. unfortunately, I can't get it to work. the link below is the project i'am working on. I had trouble trying to source a KIA75558P so I used a lm1458 instead. the circuit works up to the cathode of D3. no dc voltage is present? I have replaced D3 and C6. IF I SUPPLY AN EXTERNAL VOLTAGE TO THE CATHODE(D3), the meter responds by deflecting as it should, otherwise no meter deflection takes place(with output leads shorted). can't figure why no dc is being produced.

http://www.qsl.net/kh6grt/page4/esrmeter/esrmeter.htm

 

Why do you think the LM1458 is a suitable replacement for the KIA75558P? Do they have the same pinouts?

 

Hello,

You can compare the pinout in the attached PDFs.

Bertus

 

...the circuit works up to the cathode of D3. no dc voltage is present?

I'm not sure what you mean by that. Is the oscillator signal appearing at C5?
You may like this thread, particularly towards the end where I had success using my DIY meter.

 

the circuit works up to the cathode of D3

Is there an AC voltage on the anode of D3?
Are the +/- supply voltages correct?

 

Is there an AC voltage on the anode of D3?
Are the +/- supply voltages correct?

yes, there is a 2-3vpp signal at the anode of d3. the power supply voltages are correct. I think the lm1458 should work in this circuit. the signal at the anode of d3 is moving up and down slighty, don't know if this is normal.

 

yes, there is a 2-3vpp signal at the anode of d3 ...

Do you mean the cathode, or do you mean anode with C6 disconnected?

 

there is a 2-3vpp signal at the anode of d3

Is that measured with a voltmeter or an oscilloscope? If with a 'scope, what are the voltages at the positive and negative peak of that waveform. If not with a 'scope, can you get access to one?
[edit] And is that waveform a 100kHZ squarewave?

 

I had trouble trying to source a KIA75558P so I used a lm1458 instead. the circuit works up to the cathode of D3. no dc voltage is present?

Doesn't seem to be anything special about kia75558. So lm1458 should work.

I would first check power, making sure that you are getting good Rail voltages.

Then make sure u1a is producing the right oscillatiib, the trace that waveform through the transistors base, collector, and bridges output, ....

For what it does, the meter is overly complicated, and doesn't perform as well.

 

Doesn't seem to be anything special about kia75558. So lm1458 should work.

I would first check power, making sure that you are getting good Rail voltages.

Then make sure u1a is producing the right oscillatiib, the trace that waveform through the transistors base, collector, and bridges output, ....

For what it does, the meter is overly complicated, and doesn't perform as well.

hi guys, thanks so much for responding. the sig is present at the anode of d3 with d3 connected. i'am using an o scope the sig at the anode of d3 is approx. 2vpp at 100kc.the rail voltages are plus and minus 4.6v. the output sig at j&k is 150mv @ 100kc.

 

What are voltages of the top and bottom of the signal at D3 anode?
Like this image shows a square wave going from -1V to +1V.

 

if theres no voltage at the k of d3 that means theres no feedback volt at pin2 of u2a. what is the result of that?

hi albert, the scope i'am using automatically shows the pp voltage. which is a sine wave at plus and minus 1volt.

sorry, plus and minus 2vpp.

 

approx. 2vpp at 100kc.

That statement provides far less information than "the peak is at X volt and the trought is at Y volt, vs. ground.". A perfectly working circuit should swing 2-3Vpp without getting the diode to start to conduct.

the output sig at j&k is 150mv @ 100kc.

No idea what "j&k" is so cannot help you there.

In general, it is helpful to others trying to help you if you post a schematic and be precise in your description of issues / measurements.

 

hi albert, the scope i'am using automatically shows the pp voltage. which is a sine wave at plus and minus 1volt.

Please ask your scope very nicely to show you the actual voltages relative to ground not relative to each other.

The circuit around U2A is a peak rectifier. The voltage across C6 should be equal to the positive peak of the voltage at U2A pin 3. Because the signal is capacitor coupled to pin 3 it should swing positive and negative of ground and it is the positive peak of that waveform which should be stored on C6.

There is a reasonable description of how this works here:
https://en.wikipedia.org/wiki/Precision_rectifier

 

No idea what "j&k" is so cannot help you there.

In general, it is helpful to others trying to help you if you post a schematic and be precise in your description of issues / measurements.

There is a link to the project, which includes a schematic in the original post.

 

Please ask your scope very nicely to show you the actual voltages relative to ground not relative to each other.

The circuit around U2A is a peak rectifier. The voltage across C6 should be equal to the positive peak of the voltage at U2A pin 3. Because the signal is capacitor coupled to pin 3 it should swing positive and negative of ground and it is the positive peak of that waveform which should be stored on C6.

There is a reasonable description of how this works here:
https://en.wikipedia.org/wiki/Precision_rectifier

dannyf I posted a link to the schematic in my opening post.

albert I asked my scope very nicely, my scope said kiss my ass!!!

albert I asked my scope very nicely, my scope said kiss my ass!!!

seriously, how do I make the meas you requested, al?

 

albert I asked my scope very nicely, my scope said kiss my ass!!!

I would trade such a rude scope in on a better one!

 

I would trade such a rude scope in on a better one!

your right papa, but I don't sweat the small stuff.