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PS/2 55SX - is this a 486SLC upgrade?

thisisamigaspeaking

thisisamigaspeaking

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Feb 13, 2024
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Can't find any pictures of something like this, I am guessing it is a 486SLC upgrade? System isn't working right now, needs a good cleaning and Dallas replacement at the least.

upgrade.jpeg
 
I’m pretty sure it is, yes. (Assuming you’re talking about the thing under the green heatsink.) I would recommend caution if you’re thinking of removing it for cleaning unless you think it’s the cause of the system not working, I don’t know how well its retention clip system would survive it.
 
Eudimorphodon said:
I’m pretty sure it is, yes. (Assuming you’re talking about the thing under the green heatsink.) I would recommend caution if you’re thinking of removing it for cleaning unless you think it’s the cause of the system not working, I don’t know how well its retention clip system would survive it.
Click to expand...
It's black screen right now, powers up, drive spins up (drive's caps have leaked though), no output, no beep, nothing. I understand a bad Dallas can sometimes cause that.

Obviously filthy inside so I am going to take it apart and drench it in Deoxit and/or CRC QD. Maybe I should even go for a distilled water and soap bath of the boards?
 
I mean, we can't rule out it's the problem; those things work by grounding a pin on the soldered-down 386sx CPU which tells it it to "go to sleep" (switch all pins to a high impedance tristate mode), thus allowing the parasite CPU to take over. If there's a bad connection or something there (which certainly could be due to oxidation or whatever) it could be putting the CPU to sleep but failing to take over. But... yeah, I'd check other possibilities first. If it were oxidation on its pins I kind of wonder if you could get away with squirting some deoxit or similar around it without removing it and letting it air dry thoroughly before powering up.
 
Eudimorphodon said:
I mean, we can't rule out it's the problem; those things work by grounding a pin on the soldered-down 386sx CPU which tells it it to "go to sleep" (switch all pins to a high impedance tristate mode), thus allowing the parasite CPU to take over. If there's a bad connection or something there (which certainly could be due to oxidation or whatever) it could be putting the CPU to sleep but failing to take over. But... yeah, I'd check other possibilities first. If it were oxidation on its pins I kind of wonder if you could get away with squirting some deoxit or similar around it without removing it and letting it air dry thoroughly before powering up.
Click to expand...
I cleaned the board (only removed the riser and HDD cable) and put a new Dallas in (12887). Still no luck. This is what I'm getting on infrared so it looks like the 486SLC is running. Still stuck at blank screen. One thing I noticed was that the 486 (or its heat sink?) was a bit loose and I pushed it back down. But it looks like it is running...

55SX.jpeg
 
That's a Cyrix 486SRx², which was designed to clip on top of a 386SX CPU. It's a clock-doubled 486SLC with a 1 kB internal cache.

L_Cyrix-Cx486SRx2-25-50MP (install).jpg


But note the disclaimer: "386-SX16 MHz computers manufactured before 1991 are not electrically compatible with Cyrix's 486SRx² upgrade":

 
Anyone have any input on how to go about removing the 486SLC without destroying the clips? Someone else might want it.

edit: Got it off, comes off very easily. I don't think it got damaged but it seems possible to disassemble it further and work on the pins if necessary. System now beeps at least and caps lock works on the keyboard.

It's a 20/40, I had only seen the 25/50 mentioned.

I'm going to offer it for sale if anyone is interested. I don't need it since it won't work with this system.
 

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I have a 55sx that also needed a new Dallas chip. I had tried some modern alternatives but they did not work. Ended up having to file down the Dallas chip that was in the system and wired a battery to it. I cannot remember if I got a post without doing this. Worth a shot if you still cant get an image on screen.
 
mbliss11 said:
I have a 55sx that also needed a new Dallas chip. I had tried some modern alternatives but they did not work. Ended up having to file down the Dallas chip that was in the system and wired a battery to it. I cannot remember if I got a post without doing this. Worth a shot if you still cant get an image on screen.
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Since it is giving me the two short error beeps I'm expecting, I'm not sure what to make of it. It didn't error out on the display adapter in POST. What I have read for the most part says a 12887 (but not necessarily variants) should work instead of a 1287.

I'm actually a bit worried my VGA cable is bad, I was having trouble with my NuXT as well. Going to order as high a quality of a cable as I can find, tired of cheap ones breaking pins etc.
 
hello
Application is mentioned " Test your system using SXCHK.EXE if it yours is compatible with this upgrade." here : 386 CPU Upgrade
perhaps it can tell if your system will work with 486sx..
/cimonvg
 
thisisamigaspeaking said:
Anyone have any input on how to go about removing the 486SLC without destroying the clips? Someone else might want it.

edit: Got it off, comes off very easily. I don't think it got damaged but it seems possible to disassemble it further and work on the pins if necessary. System now beeps at least and caps lock works on the keyboard.

It's a 20/40, I had only seen the 25/50 mentioned.

I'm going to offer it for sale if anyone is interested. I don't need it since it won't work with this system.
Click to expand...
Interested 😁
 
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