Bad motherboard?

[MrRedHat]

I have an Asus VL/I-486SV2G rev 2.0 motherboard which I think is bad. The machine runs fine for hours with the turbo off, but when I turn it on, I start to get random errors. For example, if the machine has been powered down for a while and I turn it on, it’ll work ok for about 10 to 15 minutes. Then the machine starts to randomly lock up and get worse the longer it stays on, to the point where it won’t even boot MS-DOS.

I’ve tried with only the video card and IDE controller plugged in. I tried a different memory, video card, IDE controller, (VLB and ISA), hard drive, CPU, and new Power Supply. I don't see any caps that look bad either.

I was wondering if anyone else had any ideas that I could try. It seems like a sweet MB and I'd hate to toss it.

 

[RJBJR]

Could be memory. Try switching the memory chips or go to minimum memory and switch chips when it locks up.

As you mentioned capacitors, you usually can't tell a bad cap just by looking at it.

 

[MrRedHat]

Oops, I forgot to mention I tried different memory too, sorry. I edited the post.

Is there a way to tell if a capacitor is bad or not?

 

[arrow_runner]

If the caps are bulging, leaking, or 'lifted',they probably need replaced. Look up blown capacitors and leaking capacitors on google images.

What CPUs are you trying? It really sounds like something's overheating.

 

[MrRedHat]

What CPUs are you trying? It really sounds like something's overheating.

I was thinking something could be over heating too, but the system is set pretty basic. I'm trying a 486DX2/66 CPU. I have this heatsink and CPU fan on it. The heatsink and fan seems to work fine in another 486 system.

 

[GottaLottaStuff]

If it works fine with the Turbo off, and overheats with the Turbo on, then something is getting overclocked when it's in Turbo mode. check the settings to see what the Turbo button is actually doing.

 

[Stone]

If the caps are bulging, leaking, or 'lifted',they probably need replaced.

If they are bulging, leaking or lifted they definitely need to be replaced. It's the ones that aren't bulging, leaking or lifted that are bad but not visibly so and need to be replaced that are the real problem.

 

[RJBJR]

Oops, I forgot to mention I tried different memory too, sorry. I edited the post.

Is there a way to tell if a capacitor is bad or not?

You can test for a dead shorted cap with a multimeter. That is not the problem as a dead shorted cap would probably keep the board from booting.
There is special test equipment to test failing caps.

Have you tried putting the BIOS in fail safe mode? Disabled the L1 cache? (if you disable L2 the board might not boot but you can move a jumper to enable less of the L2 cache, would let you check some of it or all if you switch chips around). Reseat the BIOS chip and any other socketed chips. Look closely at the MB traces. Check the ports for dirt/debris. Double check the jumpers.

Disconnect the turbo switch and switch it to turbo by adding/removing a jumper, or by making momentary contact between the pins ( depends how the board senses turbo mode ) the turbo switch could be messing up.

Make sure CPU voltage setting is correct.

Like Arrow_Runner said, it seems like something is getting hot.

 

[MrRedHat]

I pulled all of the cache on the MB and it seems to be running fine now. It’s been several hours that it’s been working ok. I changed the jumpers for 128k of cache instead of 256k. I tried half the cache and it wouldn’t boot MS-DOS. I tried the other half and it wouldn’t boot MS-DOS. With no cache it seems to work decent, but a tad slow.

The motherboard seems to support 1MB of cache, so maybe I’ll try upgrading it to 1MB of cache and see if the system runs stable with it.

 

[lucasdaytona]

I had a motherboard with the same problem, it was cured with a cpu change. I was using a AMD 486 DX4 100, I replaced with a identical CPU, and the problem was solved.

 

[MrRedHat]

I had a motherboard with the same problem, it was cured with a cpu change. I was using a AMD 486 DX4 100, I replaced with a identical CPU, and the problem was solved.

A different CPU was one of the first things I tried. I wish it were as simple as a CPU change. It seems like a sweet MB.

 

[RJBJR]

I pulled all of the cache on the MB and it seems to be running fine now. It’s been several hours that it’s been working ok. I changed the jumpers for 128k of cache instead of 256k. I tried half the cache and it wouldn’t boot MS-DOS. I tried the other half and it wouldn’t boot MS-DOS. With no cache it seems to work decent, but a tad slow.

The motherboard seems to support 1MB of cache, so maybe I’ll try upgrading it to 1MB of cache and see if the system runs stable with it.

One thing all the L2 cache has in common is the tag ram (besides the processor , & chipset, etc. ) . Is the tag ram chip the same chip as the other L2 cache chips? If it is then you can change them around and test, if you havn't already tried that. If the tag ram is a different chip then maybe all you need is the tag ram. The bad thing there is you would probably have to buy one just to try it unless you have a spare, and that would be just to test with no guarantee it will work. Going up to the 1MB limit of the L2 cache will accomplish the same thing as you will have to replace the tag chip for that.

It could also be a CPU problem like Lucasdaytona suggested, but you mentioned that a different CPU has been tried.

 

[orion24]

I've also had cache related problems with a 386 board ( 4386-VC-HD ) . It had 128K, worked fine. I tried to upgrade to 256K initially using a 16Kx8 TAG (that was what the board I got the cache from had, and it worked for it). It didn't work (it was posting but was stalling right before boot started). I checked the online manual and it said it wanted a 32Kx8 for TAG, if 256K was to be used. I tried a 32Kx8 and still had no luck.

 

[MrRedHat]

I think there are several bad chips, there are a couple chips that, when put in the right configuration, the motherboard won’t POST, or it’ll report keyboard errors.

I’m wondering if the sram chips here on eBay will work. The cost per chip seems pretty pricey. I hate eBay because half the time the crap never works.

 

[RJBJR]

I’m wondering if the sram chips here on eBay will work. The cost per chip seems pretty pricey. I hate eBay because half the time the crap never works.

That says they are SOJ Package

I believe you may want a DIP Package. If the socket has 32 pins then you would use the DIP-32. Be careful, the DIP-32 comes in a skinny version (DIP Package) and a wide version (SDIP Package). You would want the skinny version.
Sometimes SDIP is described as a DIP. Best to see a picture of the chip you are getting if buying from ebay.

Anyone with a good understanding of this stuff please chime in.

 

[MrRedHat]

That says they are SOJ Package

I believe you may want a DIP Package. If the socket has 32 pins then you would use the DIP-32. Be careful, the DIP-32 comes in a skinny version (DIP Package) and a wide version (SDIP Package). You would want the skinny version.
Sometimes SDIP is described as a DIP. Best to see a picture of the chip you are getting if buying from ebay.

Anyone with a good understanding of this stuff please chime in.

I bet I need some of these then. The costs for those are insane though. Especially when some of them probably won’t work. It seems as if I'll have to shelve the motherboard and hope that I run across some sram in the future. I paid $10 for the motherboard and it came with a 486DX2/66 CPU with a gold plate on the bottom. Those are getting harder and and harder to find.

 

[RJBJR]

After looking at the board specs, it says for the 128k cache setting there should be one 8kX8 tag ram chip and 4 32kX8 cache chips, maybe that's why the 128k setting isn't working. I don't know if a 32k X 8 chip can be substituted for the 8x8 tag ram.

Maybe only one of the 32kX8 sram chips is bad, it might be worth the effort to locate one 32kX8 to try 256k cache, and one 8kX8 to try 128k cache.

I agree, the sram is expensive. That's why PCChips was making 486 motherboards with the fake cache chips, it kept costs lower than the competition.

 

[Agent Orange]

After looking at the board specs, it says for the 128k cache setting there should be one 8kX8 tag ram chip and 4 32kX8 cache chips, maybe that's why the 128k setting isn't working. I don't know if a 32k X 8 chip can be substituted for the 8x8 tag ram.

Maybe only one of the 32kX8 sram chips is bad, it might be worth the effort to locate one 32kX8 to try 256k cache, and one 8kX8 to try 128k cache.

I agree, the sram is expensive. That's why PCChips was making 486 motherboards with the fake cache chips, it kept costs lower than the competition.

This won't help much but here a little info on TAG RAM . . .

The area in an L2 cache that identifies which data from main memory is currently stored in each cache line. The actual data is stored in a different part of the cache, called the data store. The values stored in the tag RAM determine whether a cache lookup results in a hit or a miss.
The size of the data store determines how much data the cache can hold at any one time. The size of the tag RAM determines what range of main memory can be cached. Many modern PCs, for example, are configured with a 256K L2 cache and tag RAM that is 8 bits wide. This is sufficient for caching up to 64 MB of main memory. If you add additional main memory, however, it won't be cached unless you also expand tag RAM. Some motherboards allow you to add additional tag RAM chips for this purpose but many do not.
For Pentium Pro and Pentium II microprocessors, the tag RAM is integrated in the chipset. Pentium Pros have an integrated L2 cache capable of caching up to 4 GB of main memory. Pentium IIs use a SEC daughtercard for L2 caches and can cache up to 512 MB.