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486 lock up issues

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New2vtgpc

Experienced Member
Joined
Oct 22, 2019
Messages
122
Location
Iowa
So...been working on a 486 pure dos build for a while and finally got it ready to assemble...but ran into snag. The pc will lock up at random times (mid dos install, game booting, memmaker, sb card install etc. Even if it sits a bit too long, keyboard stops responding, but the cursor blinks like it ready.
Any ideas what I'm missing? Ive rechecked jumpers tried 2 different vid cards (1mb western digital and 512k Trent), 2 diff io controllers (one standard hmc 16 bit isa and 1 goldstar vlb) tried no cache, 64k, 128k, 256k cache, all different ram config, jumper settings to adjust the cpu speed....nothing. Just randomly freezes with blinking cursor after the c prompt.
 
Pull your cards and clean the contacts with an eraser then re-seat, but be careful not to jamb them back into the slots. Download and run "MEMTEST86" https://www.memtest86.com/download.htm
If you have another AT power supply you may want to swap it just to eliminate a possible cause. Need more info on your setup; ie mobo type, RAM, CPU, DOS, etc.
 
Just curious, but what speed of CPU are we talking about? Pretty much any 486 with a speed over 33Mhz needs at least a heatsink and anything above 66Mhz would likely benefit from a fan as well...
 
NeXT said:
To possibly narrow it further. What version of DOS and what drivers/TSR's are running?
Click to expand...

Dos 6.22, and currently...no other drivers or tsr. I had the supplemental floppy and the starter floppy from Phil's but eliminated them early on
 
Agent Orange said:
Pull your cards and clean the contacts with an eraser then re-seat, but be careful not to jamb them back into the slots. Download and run "MEMTEST86" https://www.memtest86.com/download.htm
If you have another AT power supply you may want to swap it just to eliminate a possible cause. Need more info on your setup; ie mobo type, RAM, CPU, DOS, etc.
Click to expand...

Mobo is Lx400 a/p vlb, 8mb of parity ram, 486dx2 66mhz, dos 6.22.
The psu is the only thing i havent tried yet. I have two others, but one im sketchy about since it popped a nreaker on the bench (there was nothing plugged into it, juat bare on counter but still)
 
T-R-A said:
Just curious, but what speed of CPU are we talking about? Pretty much any 486 with a speed over 33Mhz needs at least a heatsink and anything above 66Mhz would likely benefit from a fan as well...
Click to expand...

486dx2 66mhz. The board came with an 486sx2 50mhz, but the board supports the dx2 so I swap cpus and reset jumpers. I put a small heat sink but I did notice the cpu gets very hot to the touch even with heatsink
 
New2vtgpc said:
486dx2 66mhz. The board came with an 486sx2 50mhz, but the board supports the dx2 so I swap cpus and reset jumpers. I put a small heat sink but I did notice the cpu gets very hot to the touch even with heatsink
Click to expand...

Like T-R-A said, you should definitely at least be using a heatsink. In this case, having one will definitely help to increase the lifespan of the chip. If you want, you can also install a CPU fan.
While I'm not certain this is the issue in your case, I've had computers that would lock up or shut down when the CPU overheats. Do you have any other boards to test the 486DX2-66 in, to see if the same thing happens? Does the board also lock up when using the original 486SX-50 chip?
 
TH2002 said:
Like T-R-A said, you should definitely at least be using a heatsink. In this case, having one will definitely help to increase the lifespan of the chip. If you want, you can also install a CPU fan.
While I'm not certain this is the issue in your case, I've had computers that would lock up or shut down when the CPU overheats. Do you have any other boards to test the 486DX2-66 in, to see if the same thing happens? Does the board also lock up when using the original 486SX-50 chip?
Click to expand...

Ya know....i never tested the sx ..ill try that next. I just swap psu and still does at random. But yea the dx2 even with heat sink feels super hot.. Like cant touch it hot. I'll test the sx2 and report back
 
Ok so update...and list of attempted fixes
I removed all cards, cables, chips and jumpers. Cleaned edge connectors...cleaned and reseated bios, ram, cache chips...reset all jumpers. Tried 2 diff video cards, 2 diff io cards...3 cf cards, 2 cf2ide adapters, a 400mb hdd, and both a 486sx2 and 486dx2. Still did locked up at random...but now the lock up doesnt freeze pc, but makes keyboard not responsive...i noticed this durind jazz jackrabbit (the screen and music kept moving).
Hard reset and same thing when it froze mid typing...so tried different keyboard but no change. Redid the edge connector cleaning and tried a ps/2 keyboard with 5pin din adapter, and redid bios settings....and havent locked up since.
Was it my keyboard? I find it hard to believe 3 5pin at keyboars would all become nonrepsonsive mid typing...but so far so good. I'll try it again tomorrow night and see but its stable at the moment
 
New2vtgpc said:
Ok so update...and list of attempted fixes
I removed all cards, cables, chips and jumpers. Cleaned edge connectors...cleaned and reseated bios, ram, cache chips...reset all jumpers. Tried 2 diff video cards, 2 diff io cards...3 cf cards, 2 cf2ide adapters, a 400mb hdd, and both a 486sx2 and 486dx2. Still did locked up at random...but now the lock up doesnt freeze pc, but makes keyboard not responsive...i noticed this durind jazz jackrabbit (the screen and music kept moving).
Hard reset and same thing when it froze mid typing...so tried different keyboard but no change. Redid the edge connector cleaning and tried a ps/2 keyboard with 5pin din adapter, and redid bios settings....and havent locked up since.
Was it my keyboard? I find it hard to believe 3 5pin at keyboars would all become nonrepsonsive mid typing...but so far so good. I'll try it again tomorrow night and see but its stable at the moment
Click to expand...

This is just a wild guess, but I suppose it's possible the keyboard or the connector itself was shorting something out, causing the computer to lock up. That being said, glad you've finally been able to get the computer running stable.
 
TH2002 said:
This is just a wild guess, but I suppose it's possible the keyboard or the connector itself was shorting something out, causing the computer to lock up. That being said, glad you've finally been able to get the computer running stable.
Click to expand...

Thanks. And yea its weird, I tried that same ps/2 keyboard before and it became unresponsive as well previously but now its works fine with rhe ps/2. Idk I'll dig in my storage and find another 5pin and see if it locks up as well....
But for now...im having fun...and surprised duke 3d actually runs well with this setup
 
New2vtgpc said:
Ya know....i never tested the sx ..ill try that next. I just swap psu and still does at random. But yea the dx2 even with heat sink feels super hot.. Like cant touch it hot. I'll test the sx2 and report back
Click to expand...

You need a fan on there or the CPU is going to die from thermal death.
 
New2vtgpc said:
I know....trying to find one. I have several socket 7 fans but none that will work with a 486 socket 3.
Click to expand...

Any fan/heatsink is better than none. Just set a fan up to blow across the heatsink. Even a fan blowing on the bare CPU itself is better than nothing since the ceramic package tends to spread the heat out.
 
GiGaBiTe said:
Any fan/heatsink is better than none. Just set a fan up to blow across the heatsink. Even a fan blowing on the bare CPU itself is better than nothing since the ceramic package tends to spread the heat out.
Click to expand...

Ive got a small heat sink on it currently, but find are only maybe a 1/4 tall. one of the socket 7 coolers does look like if I tske the fan off...i can swap the socket 7 clip for the clip holding the heatsink on the 486.
But yea I need fan in this build, just running a level jazz jackrabbit got stuff little warm....duke3d was punishing this heat-wise.
 
Agent Orange said:
That's a new one on me. I've been using pencil erasers on various card edges and contacts for over 50 years with a great deal of success.
Click to expand...

Using an orange pencil eraser is something like a drug addiction. The more you use it the more you need to use it. First, they are made with rubber. To make rubber what it is, they add sulfur. Every time you use it, you leave some sulfur film on the connector. These are also abrasive. Continued use wears through the the gold plating.
Technically a clean gold to gold contact should never need recleaning. Of course, our old computers suffer many indignities. Some people still smoke, even knowing the death that awaits them. Moisture from poor storage locations is another. Then there are rodents that seem to think a computer is a great place to make a nest.
I find that cleaning the contacts with alconox, then vinegar followed by a rinse in DI water works quite well. I then use a suitable thin layer of dielectric grease. I used to use DC4 but I've has good luck with various automotive dielectric greases.
To give an example of how well it works. How many have had a ZX80 with the RAM expansion module. Sometimes, just carefully typing in the program result in a crash requiring a reboot. I'd put a little DC4 on the leads. To show how well it worked. I'd pick the ZX80 up a foot off a hard table and drop it while running a program. To show that it wasn't a fluke, I'd repeat several times. I'll admit that the program would sometimes crash when the module was knocked off but there are limits to everything. It never crashed as long as it stayed on.
An no, DC4 is not a conductor. In fact is is often used as a packing grease on high voltage connectors. It works by keep air from the connection.
Dwight
 
Dwight Elvey said:
Using an orange pencil eraser is something like a drug addiction. The more you use it the more you need to use it. First, they are made with rubber. To make rubber what it is, they add sulfur. Every time you use it, you leave some sulfur film on the connector. These are also abrasive. Continued use wears through the the gold plating.
Technically a clean gold to gold contact should never need recleaning. Of course, our old computers suffer many indignities. Some people still smoke, even knowing the death that awaits them. Moisture from poor storage locations is another. Then there are rodents that seem to think a computer is a great place to make a nest.
I find that cleaning the contacts with alconox, then vinegar followed by a rinse in DI water works quite well. I then use a suitable thin layer of dielectric grease. I used to use DC4 but I've has good luck with various automotive dielectric greases.
To give an example of how well it works. How many have had a ZX80 with the RAM expansion module. Sometimes, just carefully typing in the program result in a crash requiring a reboot. I'd put a little DC4 on the leads. To show how well it worked. I'd pick the ZX80 up a foot off a hard table and drop it while running a program. To show that it wasn't a fluke, I'd repeat several times. I'll admit that the program would sometimes crash when the module was knocked off but there are limits to everything. It never crashed as long as it stayed on.
An no, DC4 is not a conductor. In fact is is often used as a packing grease on high voltage connectors. It works by keep air from the connection.
Dwight
Click to expand...

I understand the concern. However, it's not like you're setting on the back porch and going at it all day on a few cards. Maybe the card gets 'erased' once in its lifetime.
 
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