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Trouble with 486 build

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First post, by Brutus814

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Hello all! I have been reading quite a bit on these forums recently as I am building my first retro gaming PC, but this is my first post. I have built a few modern PC's, but haven't build a 486 since the 1990's. I am getting parts/pieces from eBay and local sources. I have run into a problem and I am hoping to pick the bright minds here on VOGONS and see if I can get some help. My system consists of the following parts:

a Chicony CH-471a Rev 3.0 VLB motherboard
Intel 486 DX2-66 (SX955) processor
Diamond Speedstar Pro VLB graphics card
Sound Blaster Pro 2.0 sound card
2x36 (8MB) FPM Parity 70NS 72-pin SIMM x2 memory modules
ISSI IS61C1024-15N 128k x 8 High Speed CMOS Static RAM x4 for 512 KB of L2 cache
ISSI IS61C256AH-15N 32k x 8 Static RAM x1 for TAG SRAM for L2 cache
Imation 3.5" internal floppy drive
Chinon 5.25" internal floppy drive
Western Digital Caviar 420 MB 3.5" IDE hard drive
HP Panasonic CR-583-B 8x IDE CD-ROM drive
Tyan S1345 VL400GW-VI VLB IDE/Multi-IO controller card
UMC UM9008F NE2000 compatible 10Mpbs 16-bit ISA LAN network card
Bestec BPS-2994-4U AT 350W power supply
Microsoft serial PS/2 compatible mouse
IBM Model M keyboard

The problem that I am having is that approximately 98% of the time it will freeze on boot-up. When I turn the computer on, the initial screen will appear and it will display the processor type and then go through the memory test. It will flip through all of the memory then the "press DEL for setup" and "press ESC to skip memory test" messages will disappear. It will then freeze at this time, requiring a reset or turning off/on. In troubleshooting the problem, I have removed all of the cards except the graphics card and I/O card. I have also changed and replaced the memory and cache multiple times. I have gone through the BIOS and changed almost all of the settings in there to get it working. Since completing the build (about a week) it has booted all the way through about 5 times. The next screen (after the memory testing) is the screen that shows the processor type, speed, memory, cache and ports installed. After that, it will try to load a disk/hard drive. During one of the 5 times I have gotten it to go this far, I was able to install MS-DOS 6.22 to the hard drive. During one of the other times I was able to boot to DOS, I was able to install a game (King's Quest IV). The game loaded and I played it for about 5 minutes before it froze and required a restart. I have gone through the motherboard manual and made sure all of the jumpers are correct. I even realized that the CPU is one of the later Intel CPU's that has write-back cache instead of write-through cache. My motherboard has special jumper settings for this processor (P24D). Changing to these jumper settings didn't make a difference either.

One interesting thing is that when I disable the CPU cache in the bios, it will get past the usual spot it freezes at (after the memory test) and will get to the next screen. It will then freeze after it lists all of the ports and requires a restart. When I turn the CPU cache back on, it will again freeze after the memory testing. Again, I have tried dozens of different bios settings over the past week without any consistent success. One other interesting this is that when I do get it go boot all the way to DOS, when I press the reset button, it will continue to boot to DOS, however, when I turn the power off and turn it back on, it will again freeze at the usual spot.

My thoughts are: I am stupid for trying to use 2 VLB boards at the same time. I didn't realize this when I was building the system, but after doing some further research, it looks like getting 2 VLB cards to work at the same time is very difficult. I have ordered an ISA I/O controller and will try this as soon as it gets here. This would be an easy problem to fix. In the meantime, I did take the VLB I/O controller card out and tried to boot but it froze at the same spot, with the same change when disabling the CPU cache, so I'm not sure if replacing the I/O controller will do the trick, but I am hopeful.

I have also ordered a new CPU, thinking it may be a CPU problem, especially given the change when disabling the CPU cache.

I currently don't have a CPU heatsink/cooler installed, but the problem happens during the first start-up after sitting all night, so I don't think heat would be an issue. I did buy a heatsink/fan to install and see if it makes a difference.

Is it a graphics card issue? I have another VLB card that I have tried and it has the same problem. Would it help to get an ISA graphics card and try it?

Is it a motherboard issue? Would it be worthwhile to buy a new motherboard and try it?

The motherboard did not have a battery when it was listed on eBay, so the guy I bought it from soldered a CR2032 connector to the battery connections. I have installed a fresh CR2032 battery. Could this be an issue?

Anyways, I know this is a very lengthy post and many people won't make it this far, I'm sorry. I just wanted to give as much information as possible. I am frustrated and eager to get playing some vintage computer games. I have a Roland MT-32 and SC-55 waiting to get some use! 😀

Thank you all in advance for any advice you can provide!

Reply 1 of 6, by Anonymous Coward

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Do you know for certain if your cache chips are good? Try disabling the L2 cache and see if the problem persists.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 2 of 6, by Horun

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Brutus814 wrote:

My system consists of the following parts...

Did you bench test the motheboard before assembling the computer ? Seriously the first mistake most make (even on Asus and Asrock forums with new hardware) is to assemble everything and then try to troubleshoot it. Being old hardware it is even more critical you bench test motherboard with known good working parts and then swap your recent purchased parts in one by one, testing each before added another. After you are sure it works with Video and HD controller then put in the case and redo testing before adding sound and NIC>

Brutus814 wrote:

My thoughts are: I am stupid for trying to use 2 VLB boards at the same time.

No. VLB boards are designed to run with say two, like IDE controller and Video.
I suggest you yank the board out and start simple with a known good ISA video card and just a floppy hooked up to the controller and try to boot DOS from a floppy, and do it multi times.

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 3 of 6, by Anonymous Coward

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You're using ISSI 128kbit cache modules. Chances are you bought them on eBay. I think it's been established that these are mostly fakes. I own some. In my experience they work, but are prone to failure. They're only viable if you have a memory tester.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 4 of 6, by assasincz

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I too suspect a L2 chache issue, as I also had bad luck with ISSI sram chips off Ebay. Are you sure your cache jumpers are set correctly? Coincidentally, did you try different HDD?

Reply 5 of 6, by Brutus814

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Thank you for all the great suggestions. I have tried disabling the L2 cache and still have the problem. If the cache is bad will it still cause a problem if it is still installed but disabled in the BIOS? I thought maybe there was a problem with the type of cache chips and the TAG chip. I wasn't sure if they need to be the same type or speed or something? I have been out of town for the past couple days and will get back home in 2 days. Hopefully some new parts will be there to try also.

Reply 6 of 6, by Brutus814

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While is was gone over the weekend, I ordered a few parts to try when I got home. Last night, I replaced the CPU and it booted right up without problem. I enabled the CPU cache and it also loaded without problem. I then enabled the L2 cache and it started to load MS-DOS, but then it stopped and gave me an "internal stack overflow" error and "system halted." The motherboard states that it supports 1024K of L2 cache, so that is what I had installed. I did some searching on the internet and people suggested to add/increase a STACKS=n,s line to the config.sys. My config.sys did not have a STACKS line, so I added it. This did not make any difference. The system would still boot when I disabled the L2 cache. I removed half of the cache so it was 512K and made the appropriate jumper changes and I would still get the internal stack overflow error. I tried messing with the size and number of STACKS in the config.sys which didn't make a difference. The motherboard came with 128K of L2 cache and the seller stated that it was working with this configuration, so I went back to these cache chips and the system started with the L2 cache enabled without problem. So, I'm not sure if I just have bad ISSI cache modules as stated by someone above or if there is something that needs to be changed in the config.sys and STACKS to support more cache?