386 DX/40 Motherboard repair

[@rickchagouri-brindle6520]

I know this is one of your older videos, but I was really pleased to stumble across it because quite apart from it being very entertaining and informative, I was struggling with restoring one of these exact motherboards! Thanks again!

[@tony359]

One of my "cringing" videos, yes :) But I'm glad you enjoyed it and you found it useful! I can't even remember what the fault was on that motherboard! :) Thanks again!

[@e1woqf]

First thing to do is to clean up the corrosion from the leaked battery and to look how far the electrolyte has spread. In this whole region look for interrupted traces and damaged solder joints. After repairing the damage it's time to start the troubleshooting. Otherwise you're wasting a lot of time.

[@tony359]

I don’t disagree! Thanks for watching!

[@Inject0r]

cool video! The difference between the 15ns and the set of 4x 20ns SRAM cache chips are that the single IC is for tag RAM. Essentially, it's a buffer between the SRAM and CPU, with a register to determine if the cache lookup by the CPU was either a hit or a miss. It needs to be at least as fast as the rest of the SRAM IC's, so the fact that the installed SRAM IC for tag RAM is faster, is great! A side note: The tag RAM IC gets stressed the most, so if you would have any caching issues, you'll probably be wise to diagnose that one first.

[@tony359]

Thank you Tom! It’s very interesting indeed. I didn’t know about that. It’s a very cool system. I wonder what would have been the performance price to pay if the TAG RAM wasn’t there and the buffer was on the cache memory itself - besides the space used by the buffer itself. Thanks again for watching!

[@magnum333]

Congratulations on the repair! I had one 386SX that suffered a similar problem. If you bent it sometimes it booted... at first I thought it was related to the ram sockets, since I noticed that when I pushed the ram down it booted. I replaced the ram sockets many times (a true test of patience), convinced the sockets were the culprits... Finally, I gave up and tried to "reflow it" and I think I cooked it xD Some IC leaked a black gunk on the underside of the board, very weird. Still haven't gotten back to it. I think the poor thing has suffered enough ✝

[@tony359]

You made the famous "Motherboard Lasagna" :) It could have been a bit of everything to be honest, sorry to hear it did not survive! And thanks for watching one of my earliest videos, not the best in terms of audio and editing :)

[@magnum333]

@@tony359 LOL! That's very appropriate, since it's brown/orange. I'll watch more of your videos since I'm also fond of repairing old stuff. The nice thing about these old motherboards is that almost everything can be repaired. They don't have a lot of ICs. The only unrepairable thing is a damaged chipset. Everything else can be tracked down and replaced/fixed. Maybe even the lasagna can come back to life some day. Anyway, great channel! Watch you later. Have a nice day.

[@tony359]

@@magnum333 it's one of the reasons I like old stuff: you can follow traces, probe things, fix things and most importantly learn things. Ove the course of many years I was able to use my tools to see how a bus works - I'm not sure I could do that on modern stuff, or at least it would be much more difficult and would require a massive microscope! Have a great day too and thanks again for your kind words!

[@radionicretrofit]

Nice video again! I like repair videos like this. Also a post card would be very useful in repair videos. Regarding 5th sram cache chip its tag chip. No difference from others.Keep it up mate!

[@tony359]

Thanks a lot! More videos coming for sure! Interesting about the TAG ram chip, basically an index of the content of the cache. From Vogons :) "As for the purpose of TAG ram, in a nutshell, instead of storing data (banks 0 and 1 are your DATA STORE), it holds identifiers (pointers) to say what data is in those data stores and what location from RAM it came from. When a program points the CPU to a memory location in RAM, the TAG chip should say whether or not (Hit or Miss) that data has been cached for faster access. This is called a Cache Lookup" Been thinking about a post card indeed. It may be useful.

[@aliencray7269]

It was a power good line all that time but you found this in a hard way 😂 Any way it is interesting result because I expect reset line to sticks high when no p.g., not just no pulse at all 😮

[@tony359]

For the life of me I cannot remember what was wrong with that board - too much time ago! But I'm glad you enjoyed it despite being a very old video!

[@hawksights]

I guess the jumpers JP7,8,11 are setting the timing frequency of the varialbe timing ic (which sometimes is governed by a crystal oscillator) so it is always double the processor clock speed

[@tony359]

I wasn’t aware that it’s supposed to be twice the CPU clock speed - eventually realised after fiddling with more boards! Thanks for watching and sorry for the quality of the video (early days!)

[@yorgle11]

Are those power connectors in AT motherboards unique to PCs? I suspect they are generic connectors, but I don't know what they're called. If we knew their name it probably wouldn't be hard to get new replacements. It just seems whoever started using those connectors (IBM?) would have picked an off the shelf part - no need to reinvent the wheel. I looked close at pictures of Molex KK connectors, but I think they're different. The Molex pins are square, the pins on motherboard connectors are rectangular. The design of the plastic shroud is also different.

[@tony359]

I had to watch the video again as I could not remember what the fault was with that MB! First, sorry for the very poor Audio/Video/Editing quality of that video, it's very old! :) Yes, I am sure that that connector is standard. It's not easy to search as "AT" is seen as the preposition :) It's like when I'm searching for old Apple Macintosh stuff and Google ALWAYS point me to the modern stuff :) Thanks for watching, I hope you can also enjoy some of my latest videos, should be a bit easier to watch! :)

[@yorgle11]

@@tony359 No problem with the quality IMO, but I'm sure it keeps getting better. I saw some of your other repair videos and enjoyed them, so I decided to go back to the older motherboard videos and watch them in order. I haven't watched the C64 videos yet but I'll probably go back to those when I'm in the mood for the 8-bit era. :)

[@tony359]

Let me know what you think! The latest C64 video has been largely ignored but I thought it was an interesting repair - and the videos are not too long!

[@raresp7218]

Hi. Good video. Where can we find the checkitpro dos app?

[@tony359]

Hi - thank you and sorry, this is a very old video and editing and sound were... well, improvable! :) can you try this link for Checkit Pro 1.1? (Assuming KZbin won't remove the link...) dosdays.co.uk/topics/Software/diag_utilities.php

[@devonandersson300]

Did you ever find out what causes the keyboard problem in Doom?

[@tony359]

I haven’t yet. I have not given up and I hope I can publish a part 2 at some point - but I haven’t fixed it yet! Thanks for watching!

[@twiterMatt]

Hi, quick question, is it possible to replace existing cpu on motherboards like this one?

[@tony359]

Hi - good question. I think so but you might need to change the crystal to a different speed if the CPU is different. Obviously you'll have to desolder and solder a new one which is not for the faint of heart! :) Are you trying to replace a broken one or is that an upgrade?

[@sotikmaster]

tomato 4DPS , не могу починить , не работают ide , отпаял все микросхемы sn74.….. ,проверил в программаторе - тесты проходят, биос пробовал даже 4.01 , даже с флоппи не грузит, процессор a486dx2*66

[@tony359]

it's difficult to diagnose from over here... All I can suggest is to watch my videos and try to follow my steps (which won't be the only ones of course and others might have better ideas). Good luck!

[@sotikmaster]

@@tony359 Спасибо , не знаю точно ли переведется, оказалось был перебит проводник на этой старой плате, в микроскоп увидел, позже сниму видео на канал

[@tony359]

@@sotikmaster that's good news then!! Amazing!

[@roki977]

that was my 1st pc

[@Telee_Pawt]

You're impressed? What about me?

[@tedvicarri6153]

I thinks its time to chuck it in the bin, and get with the 21st century….who in their right mind would bother repairing a 386!

[@tony359]

Being in the 'right mind' is so boring though! Thanks for your comment!

[@tedvicarri6153]

@@tony359 no disrespect intended, and as interesting as fault finding a 386 MB might be, maybe a more current MB might be more useful…..perhaps?

[@tony359]

@@tedvicarri6153 maybe one day! I’ve repaired some newer boards but not on video. Old ones are good for learning, components are larger and they’re cheap to buy. Also there’s the ‘nostalgia’ factor 🙂

[@frizzlefry1921]

@@tony359 And anything that can be kept alive and out of a 3rd world country burn pile is great.

[@tony359]

@@frizzlefry1921 That is a very good point! Those "burn pile" are giving me goosebumps... :(

[@vinczejani]

why you did not use diag card?

[@tony359]

I didn’t have it back then 🙂