Products > Test Equipment

Peaktech 4250 AC/DC current clamp teardown and repair.

<< < (3/4) > >>

technogeeky:

--- Quote from: schmitt trigger on February 03, 2018, 07:44:06 pm ---Mystery solved!
Finally on this weekend I had some spare time to open my probe.

I found that those empty capacitor holes are in parallel with the SMT tantalums nearby.

As a fact, one can read C7 and C7A, C1 and C1A.............meaning that you could fit either a SMT or TH component on the board depending on availability.

--- End quote ---

To me, that really begs the question of why they don't include more capacitance. So the through hole electrolytic capacitor spots are just alternates for the tantalums they included. But surely if they included larger tantalums, the noise would be lower as this modification suggests.

I really don't understand.

SeanB:
Larger value tantalums would be expensive, and possibly not usable in the PNP process they have due to size or mass, so they used either ones on the machine already or the largest value they could reliably place instead. Going for the TH part and hand soldering would be more expensive as well, and using SM electrolytics would probably not work either as they would have the same mass and height limits that were there for the other caps already. In any case 22uF added to the existing 10uf and 22uf ones would be a good improvement.

The Soulman:

--- Quote from: schmitt trigger on February 03, 2018, 07:44:06 pm ---Mystery solved!
Finally on this weekend I had some spare time to open my probe.

I found that those empty capacitor holes are in parallel with the SMT tantalums nearby.

As a fact, one can read C7 and C7A, C1 and C1A.............meaning that you could fit either a SMT or TH component on the board depending on availability.

--- End quote ---

Looking at the pics it is actually quite obvious,  :-[  when time comes I will try to draw a schematic of this thing, gotta know what each of those pots do..

mqsaharan:
I replaced the caps C1A, C7A and C9A with double values as suggested in this thread without checking or even thinking what I was doing. The power supply ripple remained there. I didn't bother to actually measure it but it was substantial. Then I soldered a 6.8uF capacitor at the input of voltage regulator U5 and all the ripple was gone. This was the only small value capacitor I had at hand that did the trick. The inputs of U5 in this circuit are the negative pad of C7A or pin 1 of U5 and the tab or middle pin of the U5 is the positive input.
I would suggest to install around 10uF cap before replacing or adding to the suggested (C1A, C7A and C9A) capacitors in order to get rid of the ripple in the power supply. I didn't replace the caps again and left these double value caps installed.
I haven't used this probe too much. But the little testing that I have done, it is good enough for my hobby work.

Edit: I forgot to mention that the schematic, forum member jrf, posted in that Hantek CC-65 thread (also attached here) is almost the same for this probe with difference in some components values.

Edit2: Added the picture and schematic.

grumpee:
Old thread, but thank you.  I added a 10uF electrolytic capacitor in parallel with a 12nF ceramic on the input of regulator U5 as described above and it completely got rid of the low frequency ripple on the output.  The attached images show the output ripple before and after the mod.  I'm sorry I didn't record it, but when I measured the voltage on the input of that regulator, the ripple was quite high (several hundred mV I think) and was definitely causing the output to ripple at the same frequency (~590Hz).

Cheers!

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod