Replacing SMD Electrolytic caps with SMD ceramic caps on Sega CD's main board? - Page 1
Forum section: electronics / beginners

author: ReeseRiverson
author_rank: Newbie
timestamp: July 10, 2017, 02:55:45 pm
content: Upon research, I've seen where these Sega Genesis/Mega Drive attachments definitely need the surface mount electrolytic capacitors replaced, because of the corrosion they can cause from leakage. From what I've seen, a lot of folks simply replace them with through-hole electrolytic capacitors. Which was what I originally was going to do until I seen GameTechUS' video on a Turbo Grafx Duo with replacing its capacitors with the SMD ceramic capacitors. While at the same time, someone kindly pointed out Dave's video on ceramic capacitors and their voltage dependency.()While it was very informational, I'm still left a bit confused since I'm still a beginner on electronics. Though I've replaced capacitors quite a few times with more direct replacements or someone already enlightening me on what to replace them with. So I'd like to ask a few questions on this topic to see if these will still be pretty ideal for my Sega CD or if there's a better route to go.So basically I want to start off with was the mention of DC bias offset in the video. Is this basically the same as a just hooking it up to say a 5v DC power source or a battery? Is it that any DC voltage at all will reduce the capacitance of a ceramic capacitor at all?There are ten 10uf 16v electrolytic surface mount capacitors on the main board that are leaking that need to be replaced. (I'm assuming 91% Isopropyl alcohol is ideal for cleaning it all up?) I thought the idea of using ceramic capacitors will be easier and a lot cleaner than trying to use through-hole electrolytics, especially long-term.https://www.dropbox.com/s/dgohlexn6k23va9/Mega%20CD%202%20of%202%20A3.pdf- Here are the schematics on the console.Based on what I seen it uses an NEC 2405 voltage regulator so there's 5 volts DC within the system. If I'm understanding correctly, based on what Dave has said and resource like this:http://www.murata.com/en-us/support/faqs/products/capacitor/mlcc/char/0005there is a 40% decrease in capacitance? So say a 10uF cap would be more or less a 6uF on 5V DC? If that's the case wouldn't a 15uF capacitor be more ideal to bring the necessary value closer to what it needs to be? Like any of these caps?https://www.digikey.com/products/en/capacitors/ceramic-capacitors/60?k=&pkeyword=&pv13=93&FV=380009%2C440005%2Cffe0003c%2C1c0002&mnonly=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25I'd like to do what's best for the console since I want it to last as long as I can possibly make it can.Also the capacitor placement numbers are: C41, C42, C43, C44, C45, C46, C47, C48, C49, and C50.With the caliper I measured 3.5mm on the width of the base on the existing capacitors, the soldered sides.Pictures:

author: schmitt trigger
author_rank: Super Contributor
timestamp: July 10, 2017, 03:07:28 pm
content: Class-II ceramic capacitors do have voltage dependency. The X7R ceramic is not so bad, so if you decide to replace them, choose that particular ceramic type.

author: ReeseRiverson
author_rank: Newbie
timestamp: July 10, 2017, 03:17:00 pm
content: Quote from: schmitt trigger on July 10, 2017, 03:07:28 pmSo with the X7R caps, would I be fine with going with 10uF then, or will I need to consider 15uF with the 5V DC supply voltage in the system?-Edit-So something like this?https://www.digikey.com/product-detail/en/avx-corporation/1206YC106KAT2A/478-5725-1-ND/2136333

author: suicidaleggroll
author_rank: Super Contributor
timestamp: July 10, 2017, 03:22:41 pm
content: The drop in capacitance with bias voltage that is a problem with MLCC depends mostly on package size. 10uF in a 1206 package should show very little drop in capacitance with a 5V bias, I wouldn't worry about it. It mostly becomes a problem when you start trying to cram a lot of capacitance into 0402 and 0603 packages.

author: ReeseRiverson
author_rank: Newbie
timestamp: July 10, 2017, 03:29:16 pm
content: Quote from: suicidaleggroll on July 10, 2017, 03:22:41 pmAlright cool! That helps me a lot, and if the AVX brand I linked above will suffice, then I'll likely placing my order soon then.