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

--- Quote from: jrf on July 07, 2020, 02:36:52 pm ---Agreed R34 is actually R24, Typo. Thanks! Good to see others interested enough to check & let me know.
R269 is on the bottom of the board & clearly marked on the photos I have.
Colours Brown-black-black-green---brown(I think).  Looks like 1-2W.  2 other schematics here show it but one says 100M.
(will not dismantle again, now, as the power switch can be a pain if the wipers fall off!)
Not sure why it is there, under the board as well as in the circuit, or the size!??
Often large capacitors have dischage resistors to make them safe to work on some time after the power is removed or for ballancing but neither apply in this circuit.

I agree adding 100nF after the reg is actually in parrallel with C9, so is unlikely to do much. Missed that!. C1 has nothing to do with the regulator ripple & C7 is large already.
By putting a capacitor on the input to the reg it implies a resistance in the battery supply circuit. ie dirty switch contacts? or poor battery, but that is often why capacitors are put there! ie my second new 100nF. May be undersized!. Did you put it to battery -ve or circuit gnd? Not impressed with the power/selector switch at all! Designed to give problems!.

Cheers,
John.

Cheers,
John.

--- End quote ---

Hi John,
I am sorry I missed that through hole resistor. I do have seen those pictures but I forgot it is on the other side of the board.
As I mentioned before my current probe is Peaktech 4250. It does not have any component on the other side of the board except for two LEDs, the physical Zero switch and on/off switch contacts. I have attached pictures here borrowed from the other thread (https://www.eevblog.com/forum/testgear/peaktech-4250-acdc-current-clamp-teardown-and-repair/).

What I am calling ripple is actually oscillations due to lack of a capacitor at the regulator input terminals. The one that is in Peaktech seems to be unstable without the input capacitor. I tried 100n first, then 1uF but these didn't make much difference. The next up with me was 6.8uF and it did the trick.
I added the capacitor at the input of U5 and circuit ground. And it removed all the oscillations and regulator started giving clean output.

Regards,
Qasim.
mqsaharan:

--- Quote from: Martin72 on July 07, 2020, 03:06:57 pm ---Here is the schematic I´ve drawn from my owon cp-05+ (200Khz, 4/40/400A, appx 170€):

https://www.eevblog.com/forum/testgear/pintek-pa622-current-probe-crap-or-just-cheap/msg2220903/#msg2220903

It seems, it´s nearly the same design regardless of the price.

--- End quote ---

Hi Martin,
Thanks for the review of CP05. Some pictures from your forum thread are not showing up.
Did you happen to test the probe with increased supply voltage? Did it perform any better?
You are right. MC33078 does need 5 volts minimum dual supply. I don't know why the designer couldn't find any other part that can work at 3v like other op amps used in this clamp. Or why didn't he made sure of the proper supply voltage for this particular part.

Regards,
Qasim.
Martin72:
Hi Qasim,

No, increasing the supply didn´t take any effect  - Except that I´d burned out the hall sensors... :(
Fortunately they´ve send me a second one without any questions...


--- Quote ---Some pictures from your forum thread are not showing up.
--- End quote ---

Hm, I still can se all of them (Browser: Edge)....

Martin
mqsaharan:

--- Quote from: Martin72 on July 07, 2020, 06:40:07 pm ---Hi Quasim,

No, increasing the supply didn´t take any effect  - Except that I´d burned out the hall sensors... :(
Fortunately they´ve send me a second one without any questions...


--- Quote ---Some pictures from your forum thread are not showing up.
--- End quote ---

Hm, I still can se all of them (Browser: Edge)....

Martin

--- End quote ---

My bad. Never mind. I forgot to check the rest of the pages of your thread.
Pictures on page 1 where you announced that you've received the CP-05 are missing as well as in the post after the next post. But its all right.
I am using Firefox on Ubuntu.

I just read that you have already checked with higher voltages with no difference in performance. This begs the question, have the designer made some arrangement to make up for the supply of MC33078 or what trick he used to make this op amp work at lower voltages. Or perhaps this op amp can work at lower voltages with minor decrease in performance.

Anyway, good luck with your current probe project.

Qasim.
jrf:
Martin72,
If you want to test at 5v then you need to modify the voltage regulation circuit feeding the halls. This is normally temperature compensated at about 0.8v. ie maintain -3v at R11-10k or change the 10k to maintain the same voltage at the halls. Can't see any temp comp in that circuit. Any noise on that 3V will be reflected to a degree in the readings. Although your halls supply is +/- the same voltage. A bit of common mode rejection? C4 may cause a low frequency ripple, depending on size, if any noise on -3v there. Cap is required as all circuits have it.
Yes most of these circuits using 4 pin halls only will be very similar. Looks like yours also has a auto zero at power on?
I also would like to have a spec on the halls used!!!
How is yours affected by large DC currents? ie magnetized? Zero shift?

Qasim,
Thanks. Will look at that cap as low dropout regs are known for needing low impedance supplies & oscillation is common. Better to have & not need than have random issues. More testing rqd...

Cheers,
John
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