Repair Marathon 21.04: #1 Soyo SY-015G Am386DX

[Music] hello and welcome just as promised today i'm going to take care of this 386 main board was heavily damaged by leaking battery and i'm quite confident that it is dead i didn't try to turn it on because it is very oxidized and electrical current could make it even worse so first i will have to neutralize and clean all the green gunk from the traces the battery was already removed now let's desolder everything around the battery mount holes what is in the way and potentially hiding oxidized traces underneath the keyboard connector is pretty much ready for the trash i will replace it by a new one this is how it looks so far the oxidized traces are very fragile so i never tend to remove all the parts and try to leave some of them which in my opinion could be still okay and are not necessary to remove if such parts will make troubles later i still will be able to remove them some traces were already completely rotten away as i remove the isoslot i also saw this broken trace this one goes from here to all of the isoslots below so overlooking this would mean that all the isoslots would be dead that's why it is important to look under every suspicious part this broken trace and pad was not visible under the iso slot from above at all okay time for some white vinegar if you don't know why i'm doing this watch my other video about battery electrolyte neutralization as you can see the oxidation is on the backside just as bad so to keep vinegar directly on the pcb from both sides i use a thick paper towel wrapped around the board this way the spilled white vinegar will drain through the holes on the pcb and will be soaked by the paper towel from the other side left like this wrapped into drained paper towel for about 20 minutes vinegar should have enough time to get into all the small holes and neutralize the electrolyte after that the main board must be washed with soap and water doing this don't forget to wash it properly with a lot of clean water afterwards and let the board dry in the warm dry place for about 24 hours so now the traces can be cleaned from the oxide i'm using a dremel with some fine polishing tools i found it to be the most efficient and gentle way of doing this fiberglass pencil is definitely worse for the pcb as well as for your fingers doing such work please never forget to wear a mask the fine dust is for sure not very healthy to breathe in unfortunately some traces were damaged too much by the electrolyte some parts vanished completely and must be restored i am using some wire and a lot of solder along all the traces this will not only give back the continuity but also restore the thickness needed to stand the required [Music] current [Music] [Music] the corroded traces were already very weakened so soldered wires on top could be easily ripped from the board again give it some additional strength and protection i'll cover them with multiple layers of nail polish which i've stolen from my wife so should i stop doing videos one day and vanish without any trace that's probably because she found it out okay time to put all the parts back the at power connector was partially corroded i have no replacement but i have another corroded connector where i could take two pins out you see two of them look slightly silvery where all the other are golden that's [Music] why [Music] so [Music] i replace the corroded keyboard connector by a new one [Music] yeah and this is the result so far looks quite good if you ask me i left the jumper wire on the back side since i don't know what this is for but i guess the one who made it knew why this was needed now let's check the continuity on the second pin of the isobus which was restored previously [Music] this looks very well we have continuity to the chipset i already tested the board for shorts and it looks good so time for the first run and as you hopefully can see some numbers are running on the postcard analyzer this means at least that the board seems to be alive at least to some extent let's add some memory and add a pc speaker yay one long and eight short beeps that means that everything is initialized but the graphics card is missing let's add one [Music] the main board still complains about missing video card let's test another one i will try this 8-bit cga card can you hear the memory check ticks means the card was detected let's try another 16-bit card tank et4000 this one seems also not to work okay next try this card can work as 16 as well as 8-bit with autodetect let's see if this one works and it does indeed i have a feeling that it has something to do with the 16 versus 8bit okay since the 8-bit cards do work let's concentrate on the 16-bit part of the iso slot what can we use to test it well you don't always need an expensive oscilloscope sometimes such a logic probe for a couple of euros is more than enough it lights up red when there is a logical one in the pin you are touching or it lights up green if there is a logical zero if there is a pulsation of signals between logical one and 0 the yellow led lights up so let's test the signals let's start with data pins data 15 14 13 12 11 10 9 8 pulsing everywhere this pin is memory write signal which is low active so logical one is perfectly fine this is memory read is pulsing which means it is trying to read something all the time this is address line 17 pulsing 18 pulsing 19 pulsing 20 pulsing 21 pulsing 22 pulsing 23 look at that it is high all the time this one should actually pulse as well the data and address lines are usually connected to the cpu through a bus transceiver 74ls245 see it is a signal amplifier with an ability to detach the pass anyway let's search the related bastron silver this can be easily done using a multimeter by switching into continuation mode and touching one of the related address lines with one end and going over the legs of suspicious boss transceiver with another end of the multimeter and as you see this one down here is the related 74 ls245 as you can see the address line 22 goes directly to the transceiver as well as our problematic address line 23. okay this is definitely the transceiver we are searching for let's desolder and test it the traces here are very tightly packed so to avoid too much damage always add some fresh solder also using a heat gun a little bit can help let's see what tl 866 says about this ic [Music] and it seems to be good okay how does a transceiver work simplified it just puts to the output what it has on the input so let's check the inputs [Music] and would you look at that during all the other inputs are pulsing the one which is actually the address line 23 is neither zero nor one it is dead it is disconnected from any circuits if you want so actually this pin should be directly connected to the cpu so either the cpu is damaged or the trace somewhere between this pin and the cpu okay i looked into the datasheets for the 386dx cpu and found that this pin is our address line 23. the socket has one-to-one connection to the onboard cpu up there i checked the connection with multimeter and it is connected also if i turn on the system you can see the address line 23 pulsing here so the connection somewhere between the cpu or cpu socket and the transceiver got lost after some careful looking with magnifying glass i found this corroded trace here far away from the battery i have no clue why it got corroded here but let's polish it down to the copper and take a better look yeah and as you see there is connection from the named pin of the cpu socket to this point on the trace but there is a tiny almost invisible crack which cuts the trace in two i think the transceiver can be put back in its place to solder the trace i'll put a lot of flux first and then team the copper as good as i can without shorting anything around then just add a thin piece of wire and solder it to the trace if you have enough flux and solder then the wire will be pulled straightly by the tension well if the wire is tiny enough i'm using this method all the time to fix physically damaged traces let's do the continuation test and we have contact also to the cpu as you can hear very nice and again i add some nail polish to protect this fix let's give it another try i'm using a 16 bit et4000 graphics card again and here you go the card was detected and we have an image i will add an ide controller with a compact flash card and microsoft dos in it a small setup in the bios the compact flash card i'm using is 500 max and there is no floppy connected [Music] [Music] and here you go the main board seems to be back to life it's but it does just fine let's see what's is in 4 says 3d6 dx40 16 megabytes of ram seems to be true what about the benchmark 43.2 points is quite high for a 40 megahertz 386 dx that is actually impressive by the way in the introduction videos to this repair marathon i told that this main board has no cash ics and therefore no cash well in the comments i was pointed to the fact that the micronics chipset used on this mainboard actually has some built-in cash and indeed this main board has 8 kilobytes of level 1 cash which is obviously working at about 30 megabytes per second speeds usual to level 2 cash it is not too much but obviously combined with quite fast chipset it seems to be enough to make all the heavy lifting well i would call it a success this main board is completely working i didn't spend too much time testing it yet but so far i didn't notice any issues the main words were unstable and surprisingly fast i enjoyed this repair very much and i hope you did as well please don't forget to mention your impressions below and i would be glad to have you on my channel again when i continue this repair marathon and so far this is it for today and i say thank you and goodbye wait wait wait and before you switch off i would once again point to the amazing community driven ultimate hardware 2019 project a huge database of retro main boards where you can find manuals photos rom images and more there you can search and identify your main boards now as easy as never before and if not already included the boards i am repairing in this repair marathon will eventually all land in the database as well also this soyo sy-015g is in the database and i already uploaded the photos and the bios rom image there a group of people working hard on this project and improve it daily adding new features improving cleaning and extending the databases please support the guys however you can in the name of the whole retro community thank you very much for your support you

Channel: Necroware

Views: 8,463

Keywords: retro, hardware, soldering, repair, review, nerd

Id: CrD6hALcbkc

Length: 15min 28sec (928 seconds)

Published: Sun Apr 18 2021