What happened to my 486?! \ VOGONS

What happened to my 486?!

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First post, by dacow

Posted on 2012-12-05, 12:23

dacow Offline

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For those of you who like a bit of a challenge, something seems to have happened to my 486 this evening and I'm not exactly sure whats gone wrong. Any help would be good 😀

Motherboard = Freetech 486F38 (massive 0kb cache!! 😮)
CPU = 486SX33
Video= Genoa 8500 VL (Cirrus 5428) 1MB
HDD= CF 4GB..
Sound: Mediavision Jazz 16
OS: DOS 6.22

I pulled the CF card out to put 3dBench on it so I could update the 3DBench CPU Benchmark spreadsheet. Put it all back in, fired her up and scored 25 on the Bench.

I thought I'd go into the BIOS to see if she would go any faster. Started tweaking, went to pull the CF card out to copy some more stuff over, put the CF card back in and bam, started getting corruption errors on the CF card.

At first I thought it was just the CF->IDE adapter was doing funky things, but long story short I hadn't plugged the IDE adapter back in tight and corrupted the CF (bloody Layer 1 issues!). Quick reinstall of DOS 6.22, copied my things back over and we were off and running.

Except, my PC was now a lot slower. I could instantly tell when I ran 3Dbench and the animation was going so much slower. New result was 7.1?!?!

Bios & Sysinfo showed that I was still running a 486 @ 33Mhz (Sysinfo mistakenly reports it as a DX but whatever), but the CPU bench shows 14.0 (386DX33 = 35.9). I thought maybe the Turbo button was stuck and I pressed that and it just slowed it down even more! SpeedSys shows a 486SX34Mhz with a huge score 5.12!

I went back to basics, cleared the CMOS jumpers, booted into DOS without loading config/autoexec and still no go.

Is it just my PC is failing? I noticed after a few soft reboots (ctrl+alt+del), even navigating through the BIOS is slow. You can actually see the screen draw when you switch between options!

Any thoughts? 😀

Edit: OC'd to 40Mhz and CPU bench shows 22.0 now... 3DBench has gone up to 10.1.

The computer stopped posting after a while so I ripped the whole thing apart just to find out that one the VLB slots looks like it might be going. It controlled the I/O card, as soon as I moved the I/O card to a different VLB slot the whole thing started posting again but still no cigar.

I've got a UMC 486 SX33 in a dead mobo at work, I might bring that home if I remember to test it *grin* RedHill doesn't think much of them 😀

Reply 1 of 9, by MaxWar

Posted on 2012-12-05, 17:14

MaxWar Offline

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Did you get HDD controller failure error at some point? I have been experiencing this one quite often on my old machines.

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Reply 2 of 9, by dacow

Posted on 2012-12-05, 21:37

dacow Offline

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MaxWar wrote:
Did you get HDD controller failure error at some point? I have been experiencing this one quite often on my old machines.

Nope, I got system instability from the CF card not plugged in correctly (system hanging, reporting sectors missing). But once I figured out the problem she's been fine since, albeit a tad slower than before 😀

Reply 3 of 9, by dacow

Posted on 2012-12-06, 11:39

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Right this is just weird. So I put the UMC486SX33 in @ 40mhz and I now have a 13.1 3dBench. I then plugged in the 128KB cache and nothing happened except a nice burning smell. I touched the cache chips and they were burning.

I pulled all the cache chips out and the tag chip. Plugged it all back in and now I'm receiving weird results. BIOS states that I'm running a U5-S CPU type @ 40Mhz CPU clock.

Sysinfo shows I'm running a 486 68Mhz, benching @ 111.8 mhz.
Speedsys shows the processor as a UMC UMC UMC 233Mhz with a result of 21.91
3dBench returns 41.6..

Is it just me or is this motherboard about to blow up on me?

Reply 4 of 9, by nforce4max

Posted on 2012-12-06, 13:50

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That board could be sol 🤣, that I why I don't tinker with 386/486 much due to rarity and the likely hood of blue smoke if I screw up. Did you pug the cache chips correctly?

On a far away planet reading your posts in the year 10,191.

Reply 5 of 9, by MaxWar

Posted on 2012-12-06, 14:59

MaxWar Offline

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I think i know what is happening to this board, remember Johnny 5?

Ok joking aside, that is definitely weird but non the less interesting!
Is there a chance you connected the cache backward or something?

I have a 486 dx33 that is very slow like that, however cpu seems to be running properly, instead memory bandwidth is utterly crappy for some mysterious reason.

FM sound card comparison on a Grand Scale!!
The Grand OPL3 Comparison Run.

Reply 6 of 9, by dacow

Posted on 2012-12-07, 00:54

dacow Offline

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I may have inadvertently plugged the cache chips the wrong way around 😀 I'll give it another go this evening.

Incidently, how do you guys get the cache chips out? I have a bank of chips which are right next to each other. So you can get the chip puller hooked in on one side, but the inner side there's a cache chip right next to it so you can't get the hook down? If that makes sense?

Reply 7 of 9, by dacow

Posted on 2013-01-06, 10:11

dacow Offline

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I managed to purchase some new cache chips 8 x 64k and a new TAG chip 32k. I've put them, set the cache jumpers to 512kb cache.

:edit: the system now seems to work successfully at 512kb cache. I need to tweak some of the BIOS settings because the system hung after booting DOS when I turned it on the first time. Just need to figure out which BIOS setting I changed to make it now work! 😁

:edit2: figured out, setting "VIDEO SHADOWING" to "Cacheable" seems to cause the system to hang. Not 100% sure what this does but setting "SYSTEM" to "Cacheable" works, but VIDEO SHADOWING needs to be "Non-Cacheable"

Reply 8 of 9, by idspispopd

Posted on 2013-01-06, 21:28

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The two "cacheable" settings should refer to using shadow RAM to cache the video BIOS or main (system) BIOS.

I don't think this would give a big performance boost, especially not for video BIOS.

Reply 9 of 9, by dacow

Posted on 2013-01-07, 09:35

dacow Offline

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idspispopd wrote:
The two "cacheable" settings should refer to using shadow RAM to cache the video BIOS or main (system) BIOS.

There is the Video BIOS Shadow settings under the second BIOS option named "BIOS FEATURES SETUP"

Then under the "CHIPSET FEATURES SETUP", there is the "System Shadow" and "Video Shadow" options.

The Video BIOS Shadow settings are enabled, but it's the Video Shadow option that fails.

I'm not sure if this is because I am using a VLB Video card?

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