How to inject voltage with AAA battery to Xstal - help - Page 1
Forum section: electronics / beginners

author: Nexxen
author_rank: Regular Contributor
timestamp: June 27, 2023, 06:56:50 pm
content: Hello!!I have a problem with low voltage on a motherboard's 32.768KHz crystal.0.02VI'd like to try injecting voltage to the xstal as in the past V was higher and probing it made the board power on.My idea, but I suck at electronics, is to use a 1.2V battery adding a resistor to the positive lead that'll touch the xstal.I can't figure out if it is indeed correct to use a resistor and what its value should be.I thought 0.5V to be enough to do this test. 0.7 is a steep reduction, before I end up killing the board I prefer to have a more experienced user's opinion and help.Thanks!

author: wraper
author_rank: Unknown
timestamp: June 27, 2023, 07:20:42 pm
content: Please don't. If there is no oscillation and no DC voltage on crystal, there is zero chance injecting voltage will help. The only thing it can do is causing more damage.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 27, 2023, 07:39:33 pm
content: A crystal produces an approximate square wave riding on a DC bias.If you are no longer seeing that DC bias which previously you were reading, it means that the IC driving it could be damaged.How did you measure the crystal? With a DMM set for DC volts?What device is this crystal connected to?

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 27, 2023, 07:42:25 pm
content: If just probing it before would turn it on, perhaps there is an open point on the board? Bad Solder connection??

author: Nexxen
author_rank: Regular Contributor
timestamp: June 27, 2023, 08:22:39 pm
content: Multimeter on DC.It is connected to the southbridge, ICH7 (intel).The board has since stopped doing anything, no power on at all. But with the little that came to the crystal it did power on.It's a last resort thing, just give some more juic than the multimeter and see if it is still alive.Otherwise it's spare bin.I need closure tooThanks!

author: Nexxen
author_rank: Regular Contributor
timestamp: June 27, 2023, 08:29:02 pm
content: I thought of that but it's too time consuming, I looked around and spent 10hrs on it and I'll buy a known working next time."powers on more often than not" ain't my level of un-expertiseI just ordered an oscilloscope, I'm a beginner for sure.

author: Benta
author_rank: Super Contributor
timestamp: June 27, 2023, 10:55:05 pm
content: Dunno where you got your initial idea from, but it's a surefire way to destroy a 32 kHz crystal.On motherboards, the rechargable button cell is the problem, and prodding that with 3 V usually gets the clock and the CMOS storage running again. Replacing the cell is the solution.

author: Nexxen
author_rank: Regular Contributor
timestamp: June 27, 2023, 11:20:23 pm
content: Nope, it's not the cr2032 battery. That works.I looked all that's RTC and last one is southbridge dying or dead.I need to know how to inject voltage this way. What is the value I should use for a resistor.It's a 1.2V, 800mah AAA. I need 0.5V or 0.4V output.

author: Benta
author_rank: Super Contributor
timestamp: June 28, 2023, 12:02:42 am
content: A typical 32 kHz crystal needs at maximum 1 uW of driving power (yes, that's microwatt). Forget your 3 V prodding, something else is wrong.

author: wraper
author_rank: Unknown
timestamp: June 28, 2023, 01:10:11 am
content: Again, injecting voltage onto crystal is an utter nonsense. If there is VCCRTC voltage but no oscillation, then either chipset of crystal is dead.Quote from: Nexxen on June 27, 2023, 11:20:23 pmI need to shoot my foot to cure painful joint, please suggest what gun should I use.

author: Terry Bites
author_rank: Super Contributor
timestamp: June 28, 2023, 12:23:29 pm
content: The crystal element flexes with a voltage applied and just might snap with DC.Check the caps and parallel resistor are ok and it’s all correctly wired.Try a new xtal, those RTC one’s cost $0.05.Even a 10x probe is enough to stop it oscillating, so you might see nothing. It's capacitance may shift the frequency as well.What RTC ic are you using? One of the pins will be driving the XTAL, its that one you want to probe.

author: wraper
author_rank: Unknown
timestamp: June 28, 2023, 12:43:18 pm
content: Quote from: Terry Bites on June 28, 2023, 12:23:29 pmCrystal won't snap at DC. However applying DC may damage the chipset, there is no separate RTC IC. I do not understand logic behind this and what applying DC bias is supposed to achieve to begin with.

author: Nexxen
author_rank: Regular Contributor
timestamp: June 28, 2023, 02:51:00 pm
content: I tested, with a ICH7 schematic at hand:- new crystal and old crystal on different board: old works 100%, new: still no pwr on (2x6 and 3x8)- pF caps: 12.5 / 15 / 20 /22 /30 values: no go- resistance in between: reading ok, replaced, no go- 1117 Vsb 3.45 (yes, it's the correct voltage selection, cleared by other users)- power connector, shorts: nothing- Vsb to SB: checked as far as I could- +5VSB Ok- no super hot componetnsall basic have been done, only thing left is dc on xstal/ SIO reads okOn other motherboards, with ICH7 southbridge, V to xstal can go as high as 1.4V, but others were mostly 0.54/0.47, just one with 0.74.I'm getting 0.09 on Rx1 and 0.02 on Rx2If I put some load as high as 0.5 or maybe 0.4, it won't toast anything. Worst case I do an "electro DC fatality" on this board... I put too much effort and time for a 15$ board second hand.I learnt the crap out of this one and I'm absolutely happy with that but this board already came with other issues I had to rapair.If by "stimulating" the xstal I had a power on, why not. Replacing the SB is costly, difficult and basically useless ($ and t wise).I found a 0.56V Cr2032 and I'll try this tonight.If the SB is toasted and can't provide a V to xstal, maybe it can work again this way with some ext V....If you have a technical explanation to teach me something I'm all ears and I'm even gonna take notes.Next step is taking some online classes to at least have true basics udner my hood.I replied in haste, don't read me as pi$$ed.

author: wraper
author_rank: Unknown
timestamp: June 28, 2023, 03:06:19 pm
content: Quote from: Nexxen on June 28, 2023, 02:51:00 pmDon't you get that the problem is not about the lack of oscillation at all? Some DC bias is due to how oscillator circuit works. Applying DC bias externally won't magically start oscillation. If there is no DC bias at all, as I said, either there is no VCCRTC arriving to the chipset or chipset is dead. The only reasonable thing you can do by injecting something, is applying 32kHz signal to RTCX1 from external source.

author: Nexxen
author_rank: Regular Contributor
timestamp: June 28, 2023, 11:43:40 pm
content: Could you tone down your enthusiasm, thanks.---Instead of -- on post card I get 00. Don't know if it is just a signal with no real sense, just picked up and output so.At this point it's way beyond anything I know and I'll buy another one.-- The End --

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 28, 2023, 11:57:23 pm
content: https://youtu.be/b9434BoGkNQ

author: vk6zgo
author_rank: Super Contributor
timestamp: June 30, 2023, 03:21:13 am
content: Quote from: Nexxen on June 27, 2023, 06:56:50 pmWhen you are saying "crystal", do you mean the actual piezoelectric device which is normally used with active devices like BJT transistors or FETs to produce a "crystal oscillator", or the "crystal oscillator module" which contains just such a "crystal oscillator", consisting of an active device, the crystal itself, & some other passive device, all encapsulated in some form or the other?Such a devicedoesrequire DC supply voltages to work, whilst the actual "crystal" should not be subjected to DC.The second illustration in the following link shows the difference in appearance of the two things.https://en.wikipedia.org/wiki/Crystal_oscillator

author: radiolistener
author_rank: Super Contributor
timestamp: June 30, 2023, 04:25:32 am
content: Quote from: Nexxen on June 27, 2023, 08:22:39 pmI think this is not DC offset, but average voltage of AC signal on the crystal. This is how DMM works in DC mode - it shows average voltage for AC signal. Since there is no oscillations, this is why you don't see that "bias offset" anymore.If you try to inject DC at crystal pin it will not help, it just can lead to damage of IC which is connected to the crystal.Note that a quartz crystal doesn't require DC voltage for working. It works like LC circuit, it has some resonant frequency. But the difference with LC circuit is that quartz crystal has more stable resonant frequency.Here is equivalent circuit of a quartz crystal, as you can see, it doesn't require any power supply, and don't require any DC bias:

author: MK14
author_rank: Super Contributor
timestamp: June 30, 2023, 05:42:03 am
content: I'm guessing, so a suspicion only. I've fairly rapidly read or skimmed both threads, so could easily have missed things or misunderstood.In another thread of the OP's, which seems to talk about this 'voltage injection' fix, what really seems to have happened, is the probe(s) which injected the voltage, were really changing the stray capacitance, which started/stopped the crystal oscillator.It was almost certainly NOTHING to do with any voltage, just the stray capacitance changes.The capacitance was mentioned in another thread. But, instead of taking the advise of a presumably far more experienced engineer. They decided to walk away, and start a new thread, with their 'voltage injection' will fix it approach.OP, feel feel to correct me as necessary.Also, they apparently seem to be saying they changed the original 12pF crystal capacitor, for a 22pF one. Which may be why it has stopped working, as I don't think they understand that those values can be rather critical.Also, it could be why a probes stray capacitance could make it work again, as it could influence the circuit enough to get it working again (temporarily).Thread in question:https://www.eevblog.com/forum/beginners/rtc-via-32-768khz-crystal-voltage-and-pf-values/msg4870406/#msg4870406