Crystal raised from PCB. Is that normal? - Page 1
Forum section: electronics / projects

author: TinkeringTomas
author_rank: Newbie
timestamp: November 13, 2021, 10:02:26 pm
content: Hey everyone!After opening up a cheap VGA to HDMI adapter, I noticed the 24.567MHz crystal was raised from the PCB. I've never seen this before, and doubt it's a great idea...Do you peeps know if this is done for a particular reason or did they just go "nah, it's good enough for Aus....AliExpress"?

author: wraper
author_rank: Unknown
timestamp: November 13, 2021, 10:05:21 pm
content: The strange part is that its terminals are flat. Looks like SMD crystal with plastic part removed and terminals straightened. Probably they don't even fit into the holes and thus don't even go thru them.

author: ataradov
author_rank: Super Contributor
timestamp: November 13, 2021, 10:21:12 pm
content: Yep, they did not have though hole version, so they improvised. Now, flat pins provide more rigidity compared to round ones (at least in one direction).At the same time, in my experience when you do this, metal weakens that you can realistically only un-bend them one time, after that they just break.If you are bothered by it, find a crystal with the same frequency and replace it.And it is strange that they even bothered to remove the plastic part. It is possible that they got the crystals from production line before the plastic was applied. Possibly even scraps that did not pass the test. Look under the package where the pins are attached. Are there any signs of bending?

author: TinkeringTomas
author_rank: Newbie
timestamp: November 13, 2021, 11:15:30 pm
content: Good points! I too noticed that the pins weren't flat, but I somehow assumed there were just flat-pinned versions for some reason.I've pulled out the little microscope and looked under the crystal. I haven't looked at the bottom of SMD crystals much and certainly not up their skirt (is this going to flag something now?) but it looks like a normal through-hole package to me. If you look closely, it appears the pins come out of the package round but are shoved into a tube that's flattened?Would these type of pin lengths affect the signal much, you think? The output of the device is somewhat unstable and blurry (not usable for any length of time). It might have to do with the converter chip (just a single IC doing all the work) not syncing to the source properly, or just crappy components in general.

author: ataradov
author_rank: Super Contributor
timestamp: November 13, 2021, 11:31:45 pm
content: This is a fresh crystal that is supposed to be SMD, but never was. I would assume this is a reject or a line pull, I see no reason to make this device as a standalone unit.The length itself is irrelevant, it would not cause any issues. But the questionable origin of this crystal probably warrants a replacement. It is not likely to help with your issue, but who knows. It is worth a try.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 14, 2021, 12:44:51 am
content: If the adapter work, just leave it that way

author: magic
author_rank: Super Contributor
timestamp: November 14, 2021, 07:40:18 am
content: They ran out of THT crystals or got a deal on SMD crystals fraction of a penny cheaperI have seen a similar thing: the footprint was for a cylindrical can crystal but they bodged HC49 in there, flying 2cm above the board on the full length of its leads because it wouldn't fit normally.

author: Zero999
author_rank: Super Contributor
timestamp: November 14, 2021, 09:25:38 am
content: Perhaps they selected the wrong PCB footprint, or accidentally ordered surface mount crystals?

author: ataradov
author_rank: Super Contributor
timestamp: November 14, 2021, 05:46:54 pm
content: But this crystal was never fully SMD - the legs were not bent at any point. If they were, there would be a noticeable bend near the case. Those are half made crystals.

author: Monkeh
author_rank: Super Contributor
timestamp: November 14, 2021, 07:09:17 pm
content: Quote from: ataradov on November 14, 2021, 05:46:54 pmShenzhen market extra good price for you, good crystal, very high quality!

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 14, 2021, 07:12:09 pm
content: From a reliability standpoint, it looks pretty bad. =)