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Hantek CC-65 AC/DC Current Probe Teardown and Testing

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Glowas:
Hi Guys,

I've decided to find all components and upgrade my CC-65 current probe. I have problem to get OPA1652AIDGK. Is anybody have proposal for direct substitute for this part ?
I thought about OPA1642AIDGKT but Im not sure  :-\ Many thanks for any advice.

Best regards,
Pawel

apirltag:
OPA1678 is a fully compatible replacement.

dcac:
I just noticed member MikePie had drawn in the differences between cc65 and the Peaktech 4250 clamp, found here: https://www.eevblog.com/forum/testgear/peaktech-4250-acdc-current-clamp-teardown-and-repair/msg4565725/#msg4565725

And as I always thought the circuit for the zero button on cc65 was a bit odd and not really configured as a regular “sample and hold" like the Peaktech 4250 seems to be. I tried to implement the same circuit on cc65 by removing the 10M resistor and but in a 220n filmcapacitor instead of the bulky 470uF electrolyte.

But this just resulted in a huge drift and the clamp could not hold zero for more than a couple of seconds. I’d already checked the U1-1 272C op amp datasheets from a few different manufactures and they suggested input bias to be something like 2 to 6 pico-amp. So 220n capacitor should be able to withstand this for quite some time without much change to the “sampled” voltage level. But when I measured the output on U1-1 the voltage was dropping very quickly. So ruling out possible faulty capacitor and measuring the resistance on U1-1 input to ‘infinity’. The only thing left was the 272C being faulty - but with the original circuit configuration with the 470uF cap it worked as it should.

So removing the cap again and measured the input bias, and yeah.. about 1800 pico-amp. So I’m thinking these 272C are fake or very bad quality. Anyhow... this can explain why the cc65 is prone to drift - more than it should - and why they used this huge 470u electrolytic capacitor, that has problems like leakage and dielectric absorption. The Peaktech zero circuit is probably much more stable using a filmcapacitor and probably genuine 272C op amps.

 
           

Fraser:
An interesting discovery. Thank you  :-+

Are you intending to fit genuine/correct quality 272C op-amps in your unit now, or just leave it as manufactured, with the large electrolytic capacitor ?

Fraser

dcac:
Yes, I think I have a couple of tlc2272 laying around, somewhere. They should not only be a direct replacement but also a noticeable improvement to the 272. Both lower noise and lower input bias current, only 1pA, so they would be worth a try when I find them.

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