Repairing a 486 motherboard Soyo Sy 025

Discussion in 'Retro & Arcade Worklogs' started by RogerWiIco, Mar 28, 2021.

  1. RogerWiIco

    RogerWiIco Member

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    I Picked up a faulty 486 motherboard here not long ago after starting a wtb thread, thank you BiggusDickus
    The board came originally from ebay and was listed with the fault of not detecting a keyboard and having some scratches on the back. This is a type of project I was looking for.

    I had some time in the last few days to make a start, mainly taking photos and inspecting it.
    So far my findings are:
    - 2 of the scratches on the back are for communication between the 2 72pin ram slots to external cache so not very likely related to the keyboard error
    - the 3rd scratch is over only 2 traces going to the last isa slot from what looks like a memory buffer, however both the traces show continuity with a multimeter - definately not a issue here
    I will be leaving the scratched traces on the back of the board to the very last.
    - The external battery has been removed, it looks like it was removed as it started to spill so there is not a massive amount of visible corrosion upon a quick glance but I did locate some corrosion damage.
    - The corrosion from a mild battery spill is in the usual spot right next to the keyboard plug, which is usually the most common problem when a battery spills - non working keyboard.
    - I identified 1 trace so far that does not have continuity and some corrosion. I will be removing all the through hole and smd components in the affected area and test more traces when there is better access.
    So far I have about ~20 components to remove, clean and reassemble. There might/will probably be more as corrosion travels and spreads up and down traces so more might be identified as this progresses.

    So far that is the main plan. I am doing this as a hobby project and plan to spend about 1 hour per session, with 1 or 2 sessions per week. I will also be doing it outdoors in natural light, I just don't enjoy sitting in a cramped garage with led lighting and flux fumes, its supposed to be a hobby so also weather dependant.

    The tools that I will use are:
    - Weller soldering station
    - De-soldering gun station - some ebay brand
    - Hot tweezers - some ebay brand
    - Microscope - Radiant (No idea about microscope brands got it years ago used on gumtree)
    - Cheap usb microscope for taking pictures
    - Iso alcohol, pcb cleaner, tweezers, sandpaper, solder mask, solder, flux and some other misc small tools I can't think of now

    Ok and now for some pictures:
    [​IMG]

    A beatiful 486 motherboard, vlb slots, 30 pin and 72pin ram slots. A nice clean example.

    [​IMG]
    And from the back, I highlighted both the areas with the scratches, for general refrence as zoomed pictures don't show where the area is located.
    [​IMG]
    The area so far that is affected by the battery acid and will need removal of components and cleaning. The first isa slot has a few pins that are going green but I don't think I will be removing the whole slot just for those few pins.
    [​IMG]
    Where the external battery used to be, upon close inspection can see corrosion has started the attack on the legs of the filter (F1) and eating away a via on the L3 line which has lost continuity.
    [​IMG]
    Corrosion is attacking the keyboard plug and under it.
    [​IMG]
    Further down the right corrosion has spread to some of the smd components which I will be removing.
    [​IMG]
    The 2 scratches on the back between external cache and the 2 72pin ram slots, they look to be ok but for the sport and consistency I will re-tin them with solder and put some solder mask on top at the very end.

    So this is it, I am sure there will be some surprises along the way. To make a start I put in a quick session today.

    [​IMG]
    Removed the following through hole components:
    1 x line filter
    1 x keyboard connector
    3 x electrolytic capacitors (next to the psu power plug)
    1 x 4 pin selector, for external battery operation I think?
    1 x tantalum capacitor
    [​IMG]
    The above mentioned components pictured
    [​IMG]
    4 pin battery selector, line filter and keyboard connector plug taking a bath in vinegar.

    Thats all for now time to pack up
     
  2. Pierre32

    Pierre32 Member

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    Great photo presentation to illustrate the issues :thumbup: Good luck with it - look forward to the next chapters.
     
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  3. adz

    adz Member

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    This thread needs a NSFW tag, pure mobo repair pr0n right there :lol: Looking forward to seeing more :thumbup:
     
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  4. Mistikal

    Mistikal Member

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    Cute little board, I can see why you're saving it :)
     
  5. Draxx

    Draxx Member

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    Wow, I had one of these boards MANY MANY moons ago - was one of my first forays into the PC world, coming from Amiga. I think it would have been around 1997, just prior to the release of Win98
     
  6. Flamin Joe

    Flamin Joe Member

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    FYI you can still buy right angle 5 pin DIN connectors such as these from Jaycar.

    https://www.jaycar.com.au/5-pin-right-angle-pcb-mount-din-socket/p/PS0350

    A brought a handful of ones similiar to these years ago for jobs like this. You can only clean so much on these connectors so figured it's better to just replace the lot with a brand new one.

    They don't have the same look as they are lacking the metal shield but in my case I was using them to replace keyboard headers on XT motherboards so they were a perfect match.
     
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  7. OP
    OP
    RogerWiIco

    RogerWiIco Member

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    Thanks for the tip, I will actually grab one and might play with trying to move the metal bracket over, otherwise ill solder it as is, always nice to have a brand new part replacement drop in
     
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    RogerWiIco

    RogerWiIco Member

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    I wasn't planning on doing any work on it today but was a really nice day in Melbourne, sunny not too hot not too cold no wind etc so I did a quick session outside of course.
    [​IMG]
    I got some hot tweezers 2 or 3 years ago and never ended up using them since hot air or simply a soldering iron is the quick way. So had some fun trying them out for the first time, can't say I was too impressed but they did the job fine, some of the more corroded smd components were a bit tough so had to scratch the corrosion off the solder and reflux on a few attempts. But everything came off.
    [​IMG]
    Wicked all the pads and prepped them with new solder.
    [​IMG]
    On a microscope view quiet happy with the new solder on the pads, the caps will glide like on butter with a slight touch of the soldering tip.
    [​IMG]
    All the components are off now, gave them a dip in vinegar 1 by 1 so I don't lose the order. Ready to be reassembled at the end of the project

    Next I am looking to take off the solder mask from the traces that were connecting the corroded components, hopefully nothing is eating them up from the inside. Will lay a layer of solder anyway on top of the suspect traces.
     
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  9. OP
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    RogerWiIco

    RogerWiIco Member

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    Last 2 weeks being school holidays I hardly had any time, I'm usually time poor anyway + lots of rain in Melb.

    Nothing at all really happened.

    Minimal work and update:
    I saw some corrosion made its way to the back of the pcb and onto some of the pins, naturally it travelled to the back through the vias and traces.

    I was going to do it systematically front then back but maybe its actually better this way, do a few scrubs on the back and let it dry and cure while working on the front.

    I attacked it a few times with vinegar and a antistatic brush, pretty much a few minutes then leave it in the garage for a few days to dry.

    Still had some residue so today I gave it a nice clean/scrub with "kleanium" multi-purpose pcb cleaner I got from Jaycar.

    I will let it dry, clean with water, dry again and see if any of the corrosion is visible. In the meantime I should fit in a session or 2 to strip those traces on the front.

    [​IMG]

    [​IMG]

    bare minimum to keep thread alive
     
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  10. pfrcom

    pfrcom Member

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    F1 in your pics possibly fuse for keyboard

    If it fails continuity test, probably why keyboard's not being detected
     
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  11. OP
    OP
    RogerWiIco

    RogerWiIco Member

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    Good point, F1 filter is the first thing that came to me but F for fuse also works. I guess filter or fuse if it blows circuit fails. I never bothered to check continuity as visually it passed, usually blown fuses or filters have some indication. But yeah I had to check it out now.
    Luckily it does have a low resistance, low enough to pass continuity.

    Good tip tho, saves me trouble later if it was blown trying to determine a replacement

    [​IMG]
     
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  12. OP
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    RogerWiIco

    RogerWiIco Member

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    I stripped the traces, kind of disappointed they were nice and clean but at least they haven't been damaged, strange how the corrosion seems to have travelled through some of them to arrived at the other end, perhaps it's not visually seen yet and/or I took off a layer of corrosion with the solder mask.

    Anyway since I stripped the mask from the top I cleaned the bare traces, vinegar again followed by iso.

    After cleaned up I flowed them all with solder, I guess if there is any corrosion hiding this process will help burn it off and also strengthen them.

    To finish up I covered them with some green solder mask I have, followed by some uv light to cure it.

    [​IMG]
    Stripped traces look ok, I guess if there was any corrosion it came off with the solder mask

    [​IMG]
    Flowed them all with solder on top, any corrision should be burnt off if it survived the cleaning beforehand. Everything shows continuity also
    [​IMG]
    And painted my own solder mask, only had green. Not as pretty as I hoped but has consistency at least.

    Next I will be reattaching all the through hole and surface mount items.

    After that I will go over the scratched traces on the back.

    After after that I did notice a few other solder points that look a bit greenish, just mixing new solder should do the trick to burn off any junk
     
  13. Pierre32

    Pierre32 Member

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    Impressive stuff. The green solder mask is almost a tribute to the fallen corrosion.
     
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  14. OP
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    RogerWiIco

    RogerWiIco Member

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    Didn't think of that but ironically makes perfect sense
     
  15. pfrcom

    pfrcom Member

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  16. OP
    OP
    RogerWiIco

    RogerWiIco Member

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    I did some work on removing more corrosion on the right bottom edge of the board today, front + back and got to those scratches on the back of the pcb.

    The solder points on this section look very faded to the naked eye and I could just make out some green, so looking under magnification I could see the corrosion also spread here.
    [​IMG]

    [​IMG]
    Front view a bit closer
    [​IMG]
    Back view - at this stage for a 20-30 year old board this is normal can't expect to have shiny new solder, however...
    [​IMG]
    Under the microscope I couldn't let it go. Plan is to simply remelt the old solder and mix with new burning away the corrosion which hopefully has been mostly neutralised with the previous vinegar, pcb cleaner and iso scrubs.
    [​IMG]
    Basically same procedure as the left hand side, scratch off any visible corrosion, take off the traces that look affected and flux + solder until all the gunk is burnt off.
    [​IMG]
    Same thing on the back, also tinned the 2 traces that had a scratch over them. No time to solder mask today.
    [​IMG]
    Before and after picture which unfortunately my cheap usb microscope struggled with the after picture.
    [​IMG]
    And finally the 2 sets of scratches on the back of the board. As I said previously the scratches weren't deep enough to cut the traces and they showed continuity I still decided to do a fix for the visual aspect. Will apply solder mask on next session.

    This project is progressing slowly to near the end, but still a few things to do
    - Solder mask to everything that has been re-tinned
    - Attach all the smd and through hole components that are off. (I got a new keyboard connector from jaycar as was tipped off previously here)
    Give the board a nice overall scrub and clean.
    - Visually inspect for anything I may have missed

    Also I checked my AT psu which I haven't used in 1-2 years and there is leaking caps inside. I have ordered some new caps for the psu so that will also be part of the project.
     
    Last edited: May 12, 2021
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  17. Mistikal

    Mistikal Member

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    Really enjoying the progress being made here, nice work.
     
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  18. OP
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    RogerWiIco

    RogerWiIco Member

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    Looks like I am on the home stretch from here, today all the components are back in their places.
    [​IMG]
    Top view
    [​IMG]
    A much clearer view of the components back at their homes.
    [​IMG]
    Keyboard connector is back in, actually its a new connector with the old plate, more detail on that later on.
    [​IMG]
    Filter... sorry fuse is in
    [​IMG]
    So it turns out the metal backing does clip out form the keyboard plug. I took it off the old plug (left) and installed on the new plug (right) from jaycar, thanx Flamin joe for the tip.
    I also sanded down the metal with high grit sandpaper since it looked pretty worn and gave it a shot of automotive clear coat, to protect the exposed metal I guess.

    Few close ups of the components reinstalled:
    [​IMG]
    [​IMG]
    [​IMG]
    Its only under the microscope you realise how hard it is to fully clean up all the left over flux when things look micky mouse to the naked eye
    [​IMG]
    Traces on the back of the board were not forgotten
    [​IMG]
    The back of the board where keyboard connector is and few of the through hole caps that were removed live.

    So from here I think this is it, ready to be fired up. My final thoughts are I am about 90-95% happy with this, some of the soldering on the smd caps diodes and resistors doesn't look as smooth as I would like it to due to the old solder still being on the components after removal but this is just cosmetical.

    As I mentioned my psu does not look healthy and after spending some time on the motherboard its not a risk im willing to take, so a psu partial recap is next.

    [​IMG]
    This is a AT psu so 15-20 years old? Looks not bad overall
    [​IMG]
    They are not swallen or cracked, it does look like one leaked, I can't figure it out perhaps its some factory glue of some sort, but why there hmmm not worth the risk I think
    [​IMG]
    Same residue here, I will replace this cluster of small caps and the 2 big
    ones
    [​IMG]
    The same or similar residue is here under the coil which is strange, coils don't leak, so something from factory I guess. Still seeing it under the caps got me spooked, might as well change them out.
    [​IMG]
    Got 2 rubycons to replace the 2 200v caps and got some cheaper brands for the smaller caps.

    So this is nearly it
     
    Last edited: May 29, 2021
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  19. badmofo

    badmofo Member

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    Lovely work, something to be proud of Looking forward to seeing it roar into life.
     
  20. Gibbon

    Gibbon grumpy old man

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    Great work - really enjoying this thread. Thanks for posting it!
     

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