Replace internal 10MHz crystal with external frequency standard? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 10, 2019, 05:32:33 am
content: I have looked around after some article about replacing internal crystal with external frequency standard, but have found nothing.First I do presume that you can't just unsolder the crystal and solder some coaxial cable in place of that and direct to an external 10MHz frequency standard. :-)I presume there have to be some sort of circuit?

author: MosherIV
author_rank: Super Contributor
timestamp: October 10, 2019, 06:45:55 am
content: Depends on the piece of equipment.Some equipment allow it by having an external input for alternate clock source.If not, then you have to understand the circuit around the xtal, it may be easier to tap into the xtal circuit output.No articles !?! There are several posts around the subject on this forum!

author: magic
author_rank: Super Contributor
timestamp: October 10, 2019, 10:15:55 am
content: Most crystal oscillators are inverters with an input and output pin and you can simply feed external clock into the input if you figure out which one it is. Need to take care of voltage levels and amplitude and overload/ESD protection if it's to be robust.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 10, 2019, 06:58:18 pm
content: Quote from: MosherIV on October 10, 2019, 06:45:55 amOne candidate for that modification would be the Rigol MSO5000, I know that Dave talks about the MSO5000 and the MSO7000 circuit board, being wary similar. The MSO700 has, on it's cabinet, an external connector for a 10MHz frequency standard, while the MSO5000 don't have any holes made in the case for that. Great if the MSO5000 already has place to that on the circuit board.Great to here that there is articles already on this forum, it's just shows that I have used the wrong search terms, what word did you use?Quote from: magic on October 10, 2019, 10:15:55 amWery interesting and nice to here, then I just have to find out, how to proceed:-)

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 11, 2019, 06:15:09 am
content: I have tried to look at Daves great pictures of both the MSO5000 and 7000 but I can't seem to find out if the MSO5000 do have possibility for external frequency standard, could anyone please take a look and maybe point me in the right direction?MSO7000:https://www.flickr.com/photos/eevblog/43924619101/in/album-72157698340312471/At both images can I see the AUX OUT and the same components right above, near the LAN connectionRigol MSO7000 Oscilloscope TeardownbyDave Jones, on FlickrMSO5000:https://www.flickr.com/photos/eevblog/44893167325/in/album-72157701904033821/And right beside the AUX OUT on this picture, but no space for the EXT IN on this:Rigol MSO5000 Oscilloscope TeardownbyDave Jones, on Flickr

author: magic
author_rank: Super Contributor
timestamp: October 11, 2019, 07:11:32 pm
content: Now you need to find the oscillator you want to modify, simple as thatIt may be a passive crystal connected to some chip with two traces or perhaps an integrated clock generator with GND, VCC and OUT. Both look like a tiny rectangular metal can if they are SMD.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 11, 2019, 08:43:01 pm
content: Quote from: magic on October 11, 2019, 07:11:32 pmGreat way to guide me, I think I have found it:-)It looks to mee as a passive crystal, right?

author: james_s
author_rank: Super Contributor
timestamp: October 11, 2019, 11:50:58 pm
content: Looks like a self contained oscillator to me, although I've been told that plain crystals come in the same package so it's hard to say for sure. Looks to me like that capacitor below it is a decoupling capacitor connected between the ground plane and what would normally be the Vcc pin of a 4 pin oscillator.

author: james_s
author_rank: Super Contributor
timestamp: October 11, 2019, 11:52:38 pm
content: The LMX2582 is a commodity part, datasheet is available, since that's what the crystal is feeding I'd start by looking over the datasheet for that.http://www.ti.com/product/LMX2582

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 12, 2019, 02:00:32 am
content: Quote from: james_s on October 11, 2019, 11:50:58 pmQuote from: james_s on October 11, 2019, 11:52:38 pmThanks wary much, I have never understood how one can look at a part and then just know what it is:-) If I do not have a number or if it is not a standard part like a resistor, I am totally lost:-)I''ll read the datasheet, but do you think it is doable for a noob like mee to replace that crystal with a signal from the HP Z3805A? :-)

author: james_s
author_rank: Super Contributor
timestamp: October 12, 2019, 03:03:17 am
content: The number is printed right on it, all I did was google LMX2582.I'm not familiar with the particular frequency standard so I can't really say without knowing more. I'm sure it would be possible to do without too much effort but I don't think I'd be trying to modify an instrument like that unless there was a really good reason, there is always risk of damage and of course you will void the warranty and probably greatly reduce any resale value. What's wrong with the factory oscillator?I don't mean this as an insult, but it seems like one of those tasks where if you have to ask how to do it, you probably don't need it.

author: radioactive
author_rank: Regular Contributor
timestamp: October 12, 2019, 04:42:50 am
content: Quote from: FriedMule on October 11, 2019, 08:43:01 pmThe LMX2582 has a differential reference input. In the image you posted, you can see one side of the differential input ac-coupled to a resistor tied to ground and the other side of the ref input being fed by the 10 MHz single-ended oscillator output. At least that is what it looks like from the image.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 12, 2019, 05:29:46 am
content: Quote from: radioactive on October 12, 2019, 04:42:50 amYes it is propperly how it is, but can first be sure after desoldering:-)Quote from: james_s on October 12, 2019, 03:03:17 amLOL yes my comment was because I thought you had told the name on the crystal, but did wary fast find out that you meant the chip, but I kept the comment because it is still true:-)The reason for me to replace the crystal is that it wanders all over the place and do in no way agree with my frequency standard. So I thought that why not get the scope to use the same standard as the rest of my gear and thereby let it all be in sync.I had / do hope I could build a small circuit that could be "dumped" in the place where the crystal is now, without having to do much other then desolder the crystal and solder my contraption. :-)EDIT: If I desolder the gray plate under the crystal, I think I can be less harch against the crystal and there are some space to use, maybe I could use some sort of soldi wire to act as "legs" pointing at the original soldering spots?

author: magic
author_rank: Super Contributor
timestamp: October 12, 2019, 07:34:57 am
content: You will not desolder this 4-pad sub-PCB easily without a hot air gun. Maybe with ChipQuik.And using hot air, you will melt the whole assembly and risk having it fall apart if you aren't careful.You will greatly increase patient's chance of survival if you leave the generator alone and remove the coupling capacitor instead.And really start with scoping the circuit to know what kind of voltage levels it uses and make sure you can generate a proper signal for it before taking anything apart.Maybe see how it's done in the version with factory-made clock input.