Repairing the FIC 4386-VC-HD Hybrid 486/386 Motherboard!
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- Опубликовано: 24 июл 2024
- Is it a 486 or a 386 board? It's both! Today I'll be repairing a damaged 486/386 hybrid board. This is the FIC 4386-VC-HD motherboard that I bought as-is on eBay. After a repair attempt gone wrong by the previous owner, several components will need to be replaced.
Necroware's open source Benchmarq RTC modules:
github.com/necroware/nwX287
Here's my video on RTC modules and my experience constructing the nwX287:
• Next-level RTC module ...
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00:00 Introduction
01:05 A Look at the Board
03:25 The Damage
05:44 A Special Mention
06:30 The Plan and the Tools
10:21 Desoldering the DS1287
11:28 Desoldering the Capacitor
12:31 Replacing the Capacitor
14:05 Installing the Socket and RTC
15:57 The Moment of Truth
16:30 Troubleshooting
17:43 Success and Conclusion 
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I think it's mad that a system can be rendered completely unresponsive by a missing or faulty RTC module. I've encountered this a couple of times now but the first time was maddening! Chased all sorts of shadows until I worked out what it was. Great work on this board - I wish all my repairs were this simple.
Remember that the RTC module not only handles the clock, but also the system configuration (CMOS Setup, as it was called). However, the very first steps of the BIOS POST ignore the configuration and just test the basic functionality of the system, and this shouldn't be affected by the RTC. On the other hand, if a misbehaving RTC interferes with the bus, it can prevent proper BIOS reads and hang the system on startup, I think. Over all, it's just another device hanging on the ISA bus.
Desoldering with the wrong tools is no fun. I agree 100 percent. The hakko desolder gun is definitely on my list.
U gotta remember too with a board like this, there was a point in time it could easily be replaced for next to nothing. Changes the amount of effort worth putting into a repair job.
Great video!
This motherborad was in my first ever pc about 30 years back!!
I still have the MB, framed on the wall as decoration in my gaming room! :)
Now I know what to do if I ever want to get it running again.
A trick I learned when resoldering caps or sockets is to spread the legs after they go through the holes, or end legs on the ziff sockets, and the tension will keep it in place. Then solder and snip as always.
Part of the reason a working RTC is required for the system to post is because generally the BIOS settings are stored in the Battery Backed RAM in the RTC module itself.
Exactly. Those thing aren't JUST a "clock generator"
A board like this was the first motherboard I purchased (upgrading from a 286 a friend gave me, that also has 4x 256k sims).
After getting the system up and running, the first addition I made was 4x 1M sims, for a whopping total of 5M!
Later, I found a AM486-40 at the same store I got the board from.
Lots of fun learning about DOS and Windows 3.1!
That dallas module can be easily disassembled. Just use solder with flat ti (about 2mm wide), heat it about 180-200C, and pry small peaces of epoxy. Ventilation strongly recommended.
After removing epoxy you will have clean a chip and can remove soldered battery. Solder battery holder to you taste (I just use laying around holders for CR2032), and you repair Dallas 😁
Thanks for the comment! That's very interesting, I don't think I've ever seen that style of mod done before. I have several flat DS1287/DS12887 modules that I may try to modify at some point.
Love seeing old boards come alive, thanks for this.
Great job as usual ;)
Also desoldering with that gun seems like a dream, I really need one too
Nice! I have about 3 or 4 systems that need a simple repair of the Dallas battery but I don't have a desoldering gun or the skills to do the dremel fix.
just discovered your channel ! great videos ! I just love the good cap/bad cap thingy 😂
Thanks very much! 🙂👍
my dad opted for that option back in the day too because those boards cost a lot of money
The other thing that special socket allows, is running a 487SX "alone". The 487SX was really a fully featured 486DX with an extra pin to keep someone from sticking it in the normal socket. This board could run a 487SX with the special socket.
Thanks for your comment! Indeed! I noticed mention of the 487SX in the board's manual too. I hope to buy one for my collection one of these days.
@@vswitchzero If I remember correctly, the 486 SX chips were like the 386 chips in that they had no math co-processor, hence the 487SX was made.
The 486 DX chip, of course HAD the Math CO.
@@mstover2809yes, apparently the first batch of them were fully fledged 486DX with the math coprocessor disabled.
But the weirdest value proposition was to upgrade it with a full 486DX, expensive as one, branded as the 487SX, leaving in a another socket socket that 486SX in an OFF state. 😅
I had a presumed dead board rotting around for years until i did a last inspection before throwing it away. It turned out to be a broken leg of the 3v battery holder that prevented the board from even powering on...
Very cool board!
Hey just to let you know. The video shows 360p as the only resolution available. Cheers!
Yeah sorry about that! RUclips is taking a very long time to process the HD version for some reason. Hopefully it'll be done soon. 👍
Happy ending.
The few PCs I built over the years, I won't believe it after putting together everything inside the case and if it won't post.
I've got an at&t computer with a Pentium 90. It also will not work at all without a working Dallas clock chip. It also won't work if the new Dallas chip is good but has an invalid date and time...that part was hard to figure out and fix.
Would you mind uploading the AMI BIOS to retroweb? I believe they only have Award BIOS versions for this board. Great video, hope to see a follow up with an upgraded CPU!
Thanks! I didn't realize the AMI BIOS was missing, will definitely do that the next time I dig out the board.
that Dallas realtime clock chip - those are still made, I believe. And still used in new product designs. You don't need a homemade replacement.
Indeed! I've bought a few brand new DS12887A+ modules from DigiKey and they work great too. I use them when I'm trying to maintain the original look of the board. The custom ones do have the benefit of being able to easily replace the battery, but I'm sure the DS12887s last a long time with a fresh battery anyway :)
its better to have a socketed battery...but yes...
Nice video. Can i ask where you source your cache chips for 386/486 boards. Thanks
It’s becoming very difficult to find them at reputable sellers (or they are very expensive). I’ve taken a chance with overseas NOS chips on eBay a few times and have had success. It’s best to avoid the “really fast” spec’d 10/12ns stuff because a lot of it is fake relabeled stuff, unfortunately. The 15ns is very plentiful out there and safer 👍
looks like first necroware rtc board was hanging down i2c bus, so pc won`t boot.
Definetly not the works job I have seen someone do. It looks like they were pretty careful, but their tool slipped. I can almost hear the "awww" when it happened.
Great video, looking forward to the follow up with 386/387 and 486 benchmarks!
Thanks! Definitely still on my list to do. Just need to find the time 🙂
Lucky man... I've got one of these... but mine only has a socket for a 387 Co-Processor... and mine has a Award Bios, not AMI BIOS
Hey, thanks for great repairing tutorial! I have identical mobo with 386dx 40 (soldered) and 486dx2 66 (in socket) unfortunately when I try to enable 386 i just get black screen. Could this be, because oscillator installed on the board is 33 Mhz (for the 486dx2 66)? Do I need to replace the oscillator for 80 MHz one to be able to enable the 386 cpu? I like this mobo very much and would really like to get the 386 working. By the way where could I get those oscillators from?
Thanks! Yeah that's quite possible. 386s generally need a 2x crystal (so 80MHz for the DX-40). I haven't tried putting a 486 in this board yet, but I believe there are two crystal sockets (one for the upgrade socket and one for the onboard CPU). If the optional crystal isn't installed, I think it uses the primary one for both sockets. I'm not sure if this type of crystal is a part still available new from places like Mouser/Digikey. I remember looking a while back and couldn't find them except for on eBay and the second hand market. Perhaps someone else could chime in if they have some ideas.
11:01 Wow. I'm impressed. Is this Hako that good?
I don’t have any other desoldering tools to compare it against but I’ve been really impressed by it so far. It is very expensive though, unfortunately. I was really torn about spending that much on a tool like this but the quality is top notch and I have no regrets 👍
Good day. Could you tell me the nominal value of the resistor assembly on this motherboard under the number RN50. Thank you.
Sorry for the slow reply on this. Looks like RN50 is very low-impedance. Just 0.25ohms or so. With those low values, I assume it just operates like a bunch of jumpers. Most of the other RP/RNs on the board I checked are 22 ohms. Hope this helps.
Hello, I have a question. I have a 4386-vc-v motherboard with 3 ram memories, 256k not 4! only 3. 486DX2 and 486SX processor and one isa video. But when I turn it on, it doesn't turn on. Will it be necessary to install complete memory bank?
Thanks for the comment! Yes, my understanding is that with 30-pin SIMMs you need to fully populate the bank with four sticks. I believe it has to do with the data bus width. With 386 and 486 platforms, the 32-bit external bus requires four 32-pin (or one 72-pin SIMM) to work.
Hello, do you know if these motherboards do not turn on when they do not have the Dallas battery? Because I don't know, my Dallas 12887 is broken.
I have a question sorry not related to this board it's related to your socket 7motherboard build. I have a board made by PC chips or ECS and it also requires that vrm in order to do the split voltage CPUs does anybody know where I can buy one of those voltage regulators because it plugs in the same way as your Socket 7 board in that build video.
Hi Clint, check out Necroware's VRM modules in this video: ruclips.net/video/CMiGVQbMC5U/видео.html - I responded in more detail to your comment in the socket 7 video as well. Cheers!
Don't you use flux core solder?
I see so many of these repair videos using excessive amounts of flux prior to getting an iron near it, would be cheaper and a lot less cleaning (which isn't even strictly neccessary).
I wonder if a Pentium Overdrive would work on a board like this?
Thanks for your comment! It’s not an overdrive socket with the extra row of pins required, unfortunately. The extra pins are just for power delivery if I’m not mistaken. That said it could be possible to create a socket adapter for it, which would be an interesting project 🙂
The tin you use already has flux in it. You don't need to use more.
Shipping cost was like four times the cost of the component? Why wouldn't you purchase other components you may need in the future for stock to negate the shipping cost? then you benefit, not them!