Inexpensive curve tracer - Page 1
Forum section: electronics / testgear

author: caius
author_rank: Regular Contributor
timestamp: May 02, 2015, 08:40:22 pm
content: Hi all,some days ago I built the Alan 'w2aew' inexpensive curve tracer following his schematics, I used a 220VAC to 6VAC trasformer (I actually can measure 6.7 VAC on secondary) and 47 KOhm 1 Watt resistor.But I have some strange results.Here are some pictures for a better understanding.First one is about testing a 1N4004 diode, you can see that the horizontal line forks, this happen when I adiust clockwise the VOLT/DIV of CH2 (Y) channelSecond picture is a 330uF 50V capacitor testing, I got a vertical line like it was shorted.This happens with all capacitors I tested (ceramic, electrolytic, etc...)My scope is a Goldstar OS-9100P used few times.I triple-checked the curve tracer circuit (very simple) and it's OK, no mistake done.Do you think my issue depends from a faulty or not calibrated scope?Besides, I can measure 5.8V across probes so I presume this curve tracer in not the ideal for testing TTL or CMOS IC ( I repair mostly digital circuits).Anyway I could easily observe bad junctions on known faulty TTL by putting positive probe on GND of IC (which is like the base of an NPN transistor) and negative one on inputs(collectors) and outputs(emitters) of the logical gates and comparing patterns with a good reference IC.This, obviously, with both ICs out-of-circuit.So, this curve tracer is not suitale for in-circuit testing because components can be affected by connections with other parts of circuit.I conclusion : is there an effective way to properly test component in-circuit?A friend of mine suggested me a Scopemate rather than an Huntron (he says the latter can damage ICs):http://www.ebay.co.uk/itm/WAVETEK-SCOPEMATE-2-IC-and-Component-Tester-/310701153192Thanks in advance if someone will answer me and sorry for long thread!

author: kripton2035
author_rank: Super Contributor
timestamp: May 02, 2015, 08:57:37 pm
content: to test in circuit, you must jhave a probe signal that does not exceed 250mV, so that semiconductors does not start to work.most of the time, you can go to 500mV if you don"t have shottky diodes in the circuit for example.some huntron can inject 50V, and so can damage components if you dont take care about that featurealso, most of the huntron dont have a 200mV signal test, only the last models have this featureI dont know about the scopemate, but it seems to inject 5V test signal ? so it will not destroy 5v tolerant circuit (but it will destroy 3v circuits...)

author: caius
author_rank: Regular Contributor
timestamp: May 02, 2015, 09:04:00 pm
content: Hi and thanks or reply.Yes, with Scopemate 2 the device under test receives approx 5v AC 300 microamps.

author: Wim_L
author_rank: Regular Contributor
timestamp: May 02, 2015, 10:09:13 pm
content: Quote from: caius on May 02, 2015, 08:40:22 pmI see this part hasn't been answered yet, so I'll give the quick answer: Yes, this is normal and expected. The impedance of a capacitor of this size at 50 Hz is going to be -9.6 i ohms, plus whatever ESR it may have. This is very small compared to your series resistance (47k), so that capacitor will look almost like a short circuit.

author: caius
author_rank: Regular Contributor
timestamp: May 02, 2015, 10:18:47 pm
content: Did you mean capacitive reactance?

author: Wim_L
author_rank: Regular Contributor
timestamp: May 03, 2015, 01:26:15 am
content: Yes. I wrote it as a complex impedance, but it's essentially the same.

author: caius
author_rank: Regular Contributor
timestamp: May 03, 2015, 08:45:20 am
content: I find this variant of circuit, it seems to be suitable for in-circuit testing as the current and voltage are limited to safe values for most devices (less than 1 VAC and than 1 mA):What are the safest and effective signal characteristics for in-circuit testing of most components including TTL and CMOS?

author: Fraser
author_rank: Super Contributor
timestamp: May 03, 2015, 11:17:54 am
content: Huntron spent a lot of time and money on testing to prove that their design of curve tracer did not cause harm to any TTL or CMOS chips. It was in their interest to say such however. I have yet to hear of damage caused to a TTL or CMOS IC by such a unit (when used correctly) however.http://www.huntron.com/sales-support/pdf/independent-study.pdfI believe that there were risks when using an older version Huntron 1005 on more modern IC's such as 3V3 and lower voltage technology.I bought a later TR210 I-V analyser that is equipped with specific low voltage ranges for modern applications. It works well.Aurora

author: nbritton
author_rank: Frequent Contributor
timestamp: October 09, 2015, 08:45:34 pm
content: Are the curve tracer kits I see on eBay worth it? i.g.http://www.ebay.com/itm/Transistor-Diode-Curve-Tracer-Component-Tester-With-Probes-Connection-Cables-/161294643173I don't know much about curve tracers, I saw a few videos on youtube of people using them and through it would be cool to have one too. What kind of budget do you need to get a decent curve tracer for hobby use?

author: GreyWoolfe
author_rank: Unknown
timestamp: October 09, 2015, 10:51:49 pm
content: Quote from: nbritton on October 09, 2015, 08:45:34 pmSee caius' post, that is a very simple circuit that can be built on a piece of veroboard. I have built the same circuit and it does the job. How much you spend depends on how fancy you want. I drew out and etched a small pcb because I had the supplies to do it at the time. The resistors and hook up wire I already had. The BNC connectors and banana jacks were purchased cheap from a hamfest. I had a pair of multimeter test leads laying around and I used an old 2 position printer switch enclosure that someone gave me. The most expensive part for me was the transformer. Mine sits right on top of the o-scope, so I made some short BNC cables from RG-58 coax I have. The cable may not be the best choice, but I get the wave form patterns I expect so it works for me.I have no doubt that you can order all the parts and pick up a plastic enclosure off of eBay much cheaper as you won't pay for someone else to put it together.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 10, 2015, 02:53:25 am
content: Quote from: GreyWoolfe on October 09, 2015, 10:51:49 pmYou can do stepped transistor measurements with that? And negative resistance, such as what is show here?:

author: Shock
author_rank: Super Contributor
timestamp: October 10, 2015, 12:44:47 pm
content: Quote from: caius on May 03, 2015, 08:45:20 amhttp://www.americanradiohistory.com/Archive-Poptronics/70s/1975/Poptronics-1975-08.pdf

author: GreyWoolfe
author_rank: Unknown
timestamp: October 10, 2015, 03:35:24 pm
content: nbritton, it doesn't do stepped transistor measurements. In fact, there are only 2 leads so you are checking from base to emitter, emitter to collector and base to collector separately. I don't know if it will do negative resistance. I've really only checked components outside of a circuit.

author: PA4TIM
author_rank: Super Contributor
timestamp: October 10, 2015, 11:45:26 pm
content: http://www.pa4tim.nl/?p=1437The schematic for a stepped transistor curvetracer.I made some octopussies too. Besides that I have a Tek 576 and a VU-data tracker.