I'm Hacking a Resistor! Rant - Page 1
Forum section: electronics / general

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 12, 2012, 09:40:58 am
content: damn you! you make me look like a fool! you took my precious time with my wife yet you dont feel good? i thought there's an easy way cheap for this very simple thing! i hate you! and i'm going to hack you! damn you ee! damn it!

author: PeterG
author_rank: Frequent Contributor
timestamp: April 12, 2012, 09:55:22 am
content: Sooooo........... Bad day at the office?Regards

author: Excavatoree
author_rank: Frequent Contributor
timestamp: April 12, 2012, 12:38:59 pm
content: Widlarize a resistor?

author: Time
author_rank: Frequent Contributor
timestamp: April 12, 2012, 02:17:31 pm
content: the hell?

author: olsenn
author_rank: Frequent Contributor
timestamp: April 12, 2012, 02:27:47 pm
content: If I was on Salvia Divinorum, I might just understand what the hell this post is about!

author: Excavatoree
author_rank: Frequent Contributor
timestamp: April 12, 2012, 04:09:26 pm
content: It seems as if Mechatrommer has been vexed by a bad resistor - costing much time. (Or that's my guess. If I'm wrong, then read no further.)If so, then I suggested he was discussing Widlarizing the resistor. For those unfamiliar with the term, I post this excerpt from Mr. Bob Pease's book: Troubleshooting Analog Circuits. (However, I suspect I'm preaching to a choir that sings better than I......)"But there were times when Bob  would discover he had wasted a day or two, just because one bad part had screwed up his circuit. He would bring this bad part -- a capacitor, a pot, a transistor, an IC, or whatever -- over to the vise and lay it on the anvil part. Then he would calmly, methodically beat it with a hammer until the smallest remaining part was indistinguishable from the dust on the floor. Then he would go back to work and get the right answer. He explained that it makes you feel much better if you do this, and, you know that bad part will never come around again and goof you up. He was right."

author: BBQdChips
author_rank: Contributor
timestamp: April 12, 2012, 05:07:29 pm
content: I had one of those days last week. Had a 2 minute change for a board. Bridged a couple pads on a pcb and spent 2 hours tracking down what had happened to brick the thing...Ya have those days,and yer almost always in a hurry when you do.

author: Ajahn Lambda
author_rank: Regular Contributor
timestamp: April 12, 2012, 07:06:09 pm
content: Just drink yourself happy like a normal person.

author: slateraptor
author_rank: Frequent Contributor
timestamp: April 12, 2012, 07:15:02 pm
content: eBay Asia 1 : 0 Shafri

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 13, 2012, 12:04:14 am
content: ever have time where you expect a resistor to be a resistor? not transforming into another thing like... inductor? or resonant filter? yeah maybe "widlarizing" is the right term, i've done the hammering few days earlier. but then hit by another problem again few hours ago. frustrated!

author: amspire
author_rank: Super Contributor
timestamp: April 13, 2012, 01:03:52 am
content: I went back and looked at your Ringy Voltage Divider post, and it is possible the problem is not the capacitor.You were getting ringing at 200MHz.F = 1/(2*pi*L*C)-2, so L = 1/(F2*2*pi*C) = 39nH. 39nH is not much. It could be the capacitor or it could be the circuit board.To tell, add a series SMD resistor of about 47 ohms to the capacitor. If it still rings at 200MHz, it is the capacitor. If it doesn't ring, then the inductance is in the board layout and your problem was the capacitor was just too good. Do you have a solid copped layer on the back? If so, how many feedthrough links from front to back of the board do you have? If you look at a lot of HF designs, they go a bit beserk with the number of feedthroughs to the ground layer just so they do not accidentally make an inductor.Richard.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 13, 2012, 01:40:16 am
content: yes these threads come together:https://www.eevblog.com/forum/beginners/ringy-voltage-divider-at-10mhz-and-higher/msg103789/#msg103789https://www.eevblog.com/forum/buysellwanted/where-to-buy-low-inductance-resistor-and-capacitor/msg103942/#msg103942i know i may have nonclean psu and fg, my pcb is not optimum, but i've tried put gnd barrier as much as i can (saving the pcb echant planet). but this is not the excuse for this resonant effect. by right, the circuit should not exagerate this, it should damp it. people swear by "lab quality" psu and fg to do a design. but what if the proven product comes out of market exposed with all the nasty noise and abuse. should it withstand this? without resonating? my divider certainly not. and this is just a divider, not a fancy 100+ pin fpga.i know now i've been following doug ford's path. i saw his HV divider, i just dont get it! i did exactly what he did, and what i got is ringing! i'm fucking dont get it. i tried circuiting on air, i tried on pcb with and without gnd plane, i tried another pcb, use buffer amp and without. it still there ringing. will buying and waiting order for expensive resistor will save it? i dont know. if yes good, if not, i may cut all my hair into baldnessi swear by "skill matters" not "tools" but i dont have the necessary skill! oh shoot!Quoteexactly an advice that i need, will see what i can do.Quoteyes i have. feedthrough not sure, random, maybe 4 maybe 5 here and there linked by sma connectors etc, how many do i need? i can see the effect of having gnd plane and not, i can see the coupling between my circuit and it. maybe i havent tried hard enough.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 13, 2012, 01:49:36 am
content: Quote from: amspire on April 13, 2012, 01:03:52 amyeah maybe not the capacitor. without it, everything's fine, but who knows that bastard stray inductance is just waiting for his friendly capacitance to make a resonant party.

author: amspire
author_rank: Super Contributor
timestamp: April 13, 2012, 02:13:04 am
content: Quote from: Mechatrommer on April 13, 2012, 01:49:36 amJust decrease your bandwidth down from 200MHz to 200Hz, and the world will be totally sane again.I do not know your amplifier, but just a warning - sometimes a capacitor directly across a high speed amplifier input can do things you do not expect. You may need to add a small series resistor (like 100 ohms) between the capacitor and the amplifier input as well, after you sort out your ringing capacitor problem.Richard.

author: amspire
author_rank: Super Contributor
timestamp: April 13, 2012, 02:21:17 am
content: By the way, if you look at that 200MHz ringing, if it is still there without any active circuit connected, then there is very little damping. For that to happen, the ESR of the capacitor has to be less then 1 ohm - perhaps 0.1 ohms. That is impressive for 100pF cap. That's what I mean about the capacitor being too good. If you got a lousy one, it probably would have worked perfectly.Richard.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 13, 2012, 02:52:40 am
content: as this is still not absolute, so there's no way of telling what actually happened. too good caps may indicate that its not the problem at all, maybe something else, more delusive and dark. or maybe i was looking at aliasing of higher freq order on my 50-100mhz scope. w2aew bjt oscillator thread comes to mind now.ps: please note thats a -60db voltage divider. so the ringing is -60db from the main input signal. probably as well resistor noise creeping in?

author: amspire
author_rank: Super Contributor
timestamp: April 13, 2012, 03:09:49 am
content: Quote from: Mechatrommer on April 13, 2012, 02:52:40 amThen put your scope in equivalent sampling mode. That gives you an effective sampling rate of probably well over 20Ghz, depending on our scope.I suspect you capacitor has a lead inductance of around 1nH, so it is probably not the problem. Inductance in resistance tends to make the response curve bad, but does not usually cause ringing due to the dissipation of the resistance.As far as your board is concerned, putting feedthroughs from the ground track to the bottom layer every 1cm should really help. Or even adding links around the edge of the board.When you see a beautiful ringing like you have, either an active circuit is oscillating, or you have a LC circuit without much damping resistance in the L/C circuit. It is something real, and if you can add some resistance at the right point, the ringing has to disappear.If you do find your capacitor is ringing internally, you can solve this by replacing it with smaller capacitors in parallel - preferably several different values. Say a 68pF and a 27pF in parallel.Richard.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 13, 2012, 05:07:47 am
content: thanks richard. you gave some food for thought to keep me going (i'm already thinking revising my circuit specification to compromise with lesser voltage division). about the oscillating active circuit. i also captured the fg output in yellow trace but looked clean, but blue trace oscillating so bad, so i suspect its not the active/driving circuit. is it possible the opamp is oscilating but it produces cleaner output? here one of capture in that thread. cleaner yellow trace (fg/board output) but very bad voltage divider output (blue trace)edit: i've made report in another thread on putting resistance (47ohm) in series of compensating 100pF caps. result: more attenuated ringing, but its still there at higher freq.sim indicating putting resistance in series creating another "pole" in freq respond, trying different caps values to no success to get flatter respond

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 13, 2012, 07:34:12 am
content: ok ok wait. i may have put the title wrongfully. instead of "hacking a resistor", it should be "hacking the ground".https://www.eevblog.com/forum/beginners/ringy-voltage-divider-at-10mhz-and-higher/msg104203/#msg104203now what? that big flat copper plate? how i'm going to hack that?this got worst, even a simpler thing turned out to be more complicated. i finally hit my face back to the ground.

author: free_electron
author_rank: Super Contributor
timestamp: April 13, 2012, 08:57:40 pm
content: widlarizing is for beginners... here's my favorite solution :Set on fire , grind ashes or other remains down to fine dust, pour dust in a cubic foot of concrete , bury block 6 feet down , plant an oak or some other long living tree on top of it..Guaranteed that part will never vex you again , and you did nature a service by planting a tree.