Hi everyone, I wonder if you could help me with repairing a old 486 pc that this year started giving 3 beeps at startup. 3 beeps i understand is a ram error. I checked everything and was about to scrap it when I remember at one time its cmos battery leaked over the pcb. I was wondering if maybe there was still some acid under the ram slots so I took them off and I found a tiny bit and so far found one bad contact between a pcb track and a smd component. I also found smd components had fallen off. Trouble is they are missing but wonder could you tell me what they are. There are others on the board that are identical if you can identify them in the 1st pic if you look between where the ran slots were you will see BC4. What is it? In the other picture you will see some bits with labels starting TC1 TC2 etc what are these too?
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Microstar 486 motherboard repair
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Re: Microstar 486 motherboard repair
Looking at https://en.wikipedia.org/wiki/Reference_designator I don't see "BC" listed. I would assume being in between RAM slots is a capacitor ("C"). Measure it and try replacing the missing spots with those.
TC is listed as "thermocouple", I would assume it's part of the temperature sensors on the board to prevent overheatingLast edited by SluggerB; 02-03-2021, 12:26 PM.
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Re: Microstar 486 motherboard repair
Originally posted by SluggerB View PostI would assume it's part of the temperature sensors on the board to prevent overheatingASRock B550 PG Velocita
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Re: Microstar 486 motherboard repair
How the hell did you get the memory slots out of that board in one piece?!<--- Badcaps.net Founder
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Re: Microstar 486 motherboard repair
Originally posted by Topcat View PostHow the hell did you get the memory slots out of that board in one piece?!
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Re: Microstar 486 motherboard repair
Originally posted by stj View Postelectric desoldering pump can do that - i'v salvaged pci slots that way
Ive not been able to get a capacitor readings from my meter and had to use my multimeter x1k diode scale to get a reading from any of the smd components. For example BC4 gives 352k one way and with probes reversed i get 432k. One of the other parts i thought was a resistor also gave different readings both was ie: TC1 also gave 432k & 353k. This makes me think these are either diodes or maybe electro caps. C21 also gives dual readings of 755k & 866k. These are just examples and all the smd components are either grey or brown coloured with no markings or green coloured with a value marked on them which I gather are resistors.
So how do i find the value of say BC4 which is the same as the one between the momory slots that had fsllen off and gone missing. Ive ordered myself a dedicated capacitor and ESR meter to see if that can get a better reading. Here is a pic of BC4.
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Re: Microstar 486 motherboard repair
I think both BC and TC are capacitors.
The "B" and "T" pre-fix in front of the "C" is probably just for specifying its use in the circuit diagram for whoever designed this. I've seen a similar scheme on LCD monitor boards and video cards, where sometimes caps would be referenced with "CE" or just "C"... and sometimes, there would be a pre-fix to the "C" like this case. I don't know if I have any pictures that show it, but I'll dig around in my collection, if I can even remember which monitor board had these kind of weird designator naming.
In any case, just replace these with ceramic caps. 0.1 uF might work, but 1 uF should work too for the power filtering ones.
Originally posted by Topcat View PostHow the hell did you get the memory slots out of that board in one piece?!
I've pulled PCI slots out (that AMD Kadoka motherboard in a Gateway Select PC I found a while back, if you remember), but memory slots... never. Perhaps because this is an old motherboard, it doesn't have such thick ground and power planes as newer motherboards. Now I'd like to see someone remove a memory slot on a current gen mobo without damage. Probably still possible, but likely will be much much harder.
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Re: Microstar 486 motherboard repair
Originally posted by momaka View PostI think both BC and TC are capacitors.
The "B" and "T" pre-fix in front of the "C" is probably just for specifying its use in the circuit diagram for whoever designed this. I've seen a similar scheme on LCD monitor boards and video cards, where sometimes caps would be referenced with "CE" or just "C"... and sometimes, there would be a pre-fix to the "C" like this case. I don't know if I have any pictures that show it, but I'll dig around in my collection, if I can even remember which monitor board had these kind of weird designator naming.
In any case, just replace these with ceramic caps. 0.1 uF might work, but 1 uF should work too for the power filtering ones.
I know, right!
I've pulled PCI slots out (that AMD Kadoka motherboard in a Gateway Select PC I found a while back, if you remember), but memory slots... never. Perhaps because this is an old motherboard, it doesn't have such thick ground and power planes as newer motherboards. Now I'd like to see someone remove a memory slot on a current gen mobo without damage. Probably still possible, but likely will be much much harder.Originally posted by stj View PostBC are caps - probably .1uf given the age.
TC may be inductors
I was wondering, I thoght I saw 2 little bits fall of and its obvious BC1 was one but if there were 2 bits what was the other? All the other pads dont look like they have been used except TC5 which is strange as it has no pads for anything to solder to. Its possible it might have completely fallen off in one lump I suppose. So what do you think should i replace it? Checking with meter it seems the stud (if thats what its called) next to where the pad was has contact to the memery slot hole closest to it and just below to the right. Is this a part I should also replace or is it not nessesary or can be left out without any effect? See photo.
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Re: Microstar 486 motherboard repair
I hate the dreaded beep beep beep ... reminds me of this old 286 board I had. Was really intermittent, sometimes it'd work, frequently not. Was a RAM issue but since it was intermittent, it probably was a broken trace somewhere... finding where is the question.
The board ended up finding the round file.Last edited by eccerr0r; 02-06-2021, 11:28 AM.
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Re: Microstar 486 motherboard repair
Originally posted by eccerr0r View PostI hate the dreaded beep beep beep ... reminds me of this old 286 board I had. Was really intermittent, sometimes it'd work, frequently not. Was a RAM issue but since it was intermittent, it probably was a broken trace somewhere... finding where is the question.
The board ended up finding the round file.ASRock B550 PG Velocita
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"¡Me encanta "Me Encanta o Enlistarlo con Hilary Farr!" -Mí mismo
"There's nothing more unattractive than a chick smoking a cigarette" -Topcat
"Today's lesson in pissivity comes in the form of a ziplock baggie full of GPU extension brackets & hardware that for the last ~3 years have been on my bench, always in my way, getting moved around constantly....and yesterday I found myself in need of them....and the bastards are now nowhere to be found! Motherfracker!!" -Topcat
"did I see a chair fly? I think I did! Time for popcorn!" -ratdude747
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Re: Microstar 486 motherboard repair
Originally posted by stj View Poston those old boards, you need to make sure the plating on the ram matches the sockets.
gold on gold, or tin on tin.
if you mix them you get a galvanic reaction and you have to clean the black coating off your simms every month or 3.
I converted it to a 3x AAA battery pack instead of the pcb battery so wont happen again if I can fix the 3 beeps.
Its a good motherboard a d has ISA and PCI slots and takes the x586 cyrix processor.
If any of these capacitors are missing does affect the ram modules by letting in noise etc. Would these caps falling of cause the 3 beeps?
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Re: Microstar 486 motherboard repair
Originally posted by stj View Postunless your overclocking, you probably dont need all the .1uf caps.
they only add stability anyway.
Again, I'd just go with something more standard, like 1-4.7 uF 16-25V ceramic caps and call it a day. If you have any spare broken GPUs or laptop motherboards you can use for parts, just grab some of the ceramic caps from there.
Also, even if you happen to replace an SMD inductor with an SMD ceramic cap, the worst that could happen is th board will not POST or work. But on the other hand, if you replace an SMD ceramic cap with SMD inductor by mistake, you'll likely create a short-circuit from a power rail to ground, and that can burn traces. So when it doubt, just use a ceramic cap for everything... that is, if you don't feel like doing it the more proper way and checking where each trace goes to determine what the part should be.
Originally posted by stj View Poston those old boards, you need to make sure the plating on the ram matches the sockets.
gold on gold, or tin on tin.
if you mix them you get a galvanic reaction and you have to clean the black coating off your simms every month or 3.
Originally posted by stj View Postthe problem with AAA is if you use anything other than eneloops they will probably leak when you arent looking!
Unless he keeps them with long wires away from the board. Then they can leak (and they will) all they want.
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Re: Microstar 486 motherboard repair
Unless he keeps them with long wires away from the board. Then they can leak (and they will) all they want.
Done a few of these.
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