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486 Overdrive no boot

DonutKing

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Mar 24, 2011
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Hi guys, really scratching my head on this one.
I have an IH4077C motherboard. I think its made either by Mitac or Chaintech.

Note that there is an IH4077D on TH99/stason but its very different to this board. For starters, my board doesn't have onboard IDE/floppy/serial, and only supports 5V CPUs.

This board has 2 VLB slots and I am using an ET4000 VLB video card and a VLB IDE/IO card. I've also got a Gravis Ultrasound and an SB16 CT2800 in there.
It has 8x 30 pin SIMM slots, currently using 4x 4MB SIMMs. Chipset is a UMC82C491F. 256kb of 20ns cache.

I am trying to run a 486DX4/100 Overdrive in this system. I've tried 2 different DX4 overdrive processors, and they both do the same thing- as does a Pentium Overdrive 83MHz.

The machine will POST and I can get into the BIOS setup, change settings and save, but it won't go any further than that. After the memory test, instead of beeping and going onto the screen displaying the system configuration and continuing to boot the OS, it just hangs there with a blinking cursor. The 'Energy star' logo fades away and the CPU info is still on screen but thats it. The CPU is correctly identified as a DX-4 or a P24T at the right clockspeed.


If I use a DX2/66 it works perfectly.


Things I have tried:

-Went into BIOS, tried auto configuration for chipset features. Also tried slowest options/ max wait states for all options.
-both settings of the '>33MHz'/'<=33MHz' jumper
-both settings of the 'VLB 1 WS/0 WS' jumper
-For CPU selection I have tried both 486DX or P23N/T (only other option is 486SX)
-Tried changing bus speed from 33MHz to 25MHz
-There is an undocumented jumper, JP1 near the keyboard connector. Tried both settings, no difference.


Is there anything else I can try? or is this board simply incompatible with the 5V overdrives?

I could try pulling cards etc but its kind of not very useful to me if I can't use the parts I want in it.... its the only woring VLB board I have at the moment. When I get home I might try an ISA multi-IO card instead of the VLB one and see if that makes a difference.

If anyone has a manual or jumper settings for this board please let me know :)
 

luckybob

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my 386 was doing EXACTLY this yesterday. I fixed it by using my port 80 diagnostic card. I found that it was hanging during the cache detection part of booting. Re-seating my cache fixed this problem for me. Do you have a diagnostic card? they are worth their weight in gold. even the cheap $5 ones from china.
 

DonutKing

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Gold Coast, Australia
I used to have one of those cheap chinese diagnostic cards but it went BANG. It didn't fit very well in the ISA slot, there was a lot of freeplay so I think it might have been able to wiggle enough to make contact with the wrong pins.

Maybe I should buy a more expensive one....

someone else suggested disabling cache and trying again. I might try that and reseating and see how it goes.
 

Agent Orange

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DonutKing:

I'm looking at three 486 chips and a Pentium Overdrive in front of me.
1) AM486DX-4, rated at 3 volts and requires a heat sink and fan.
2) Intel DX4, also rated at 3 volts.
3) AM486DX2-66 (no voltage marking but is know to require 5 volts).
4) POD5V86 (P24T)

If your mobo does not have voltage setup jumpers, then you will almost certainly need a cpu voltage adapter module for you particular chip if it's rated other than 5 volts. The POD will sense a 3.3 volt setup and adjust to it.
How about a little more info on your CPU and RAM? The fact that it will POST is a good sign. Also, what OS do you have installed?
 

DonutKing

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Both DX4's I've tried are the Overdrive variety with an integrated heatsink and voltage regulator on the surface of the processor. Like this: http://www.cpu-world.com/CPUs/80486u/Intel-DX4ODP100.html
These CPU's are designed to run from 5V.

I have a couple of 3.3V DX4's which lack the heatsink/VRM and actualy have '3 VOLT' written on top, and I haven't tried using those since the board appears to only support 5V CPUs. They look like this: http://www.cpu-world.com/sspec/SX/SX900.html

As for RAM, I will have to confirm but I believe they are 60ns FPM. I don't think its a RAM issue seeing as the bus speed is staying the same, and setting the loosest memory timings possible makes no difference.
 

DonutKing

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Hmmm. I have managed to get the Pentium Overdrive and the DX4 Overdrive to work, by changing the jumpers on the board to 128kb.

I have swapped the 20ns cache chips with 15ns chips off a dead board but this doesn't seem to help... if the jumpers are set to 256kb and a DX4/POD is installed, it will hang at the end of the first POST screen.

Even with 128kb, and the new cache chips, the system is unstable at the fastest wait states/burst settings. However, a DX2-66 works perfectly at these settings.

I've been fiddling for a while but haven't quite found a stable combination.
I wonder if there is some limitation of this board or chipset, that if an overdrive is installed you are limited to 128kb or certain minimum RAM/cache wait states.

EDIT: after a couple of hours of fiddling and being unable to find any stable settings (system would hang when trying to boot DOS, or initialise the sound card, or give EMM386 errors when running programs) I've put the DX2-66 back in, set everything up for max performance, and the full 256kb cache, and its working fine without issue.
I might fiddle around tomorrow but it seems that the overdrives are off limits :(
 
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Agent Orange

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Hmmm. I have managed to get the Pentium Overdrive and the DX4 Overdrive to work, by changing the jumpers on the board to 128kb.

I have swapped the 20ns cache chips with 15ns chips off a dead board but this doesn't seem to help... if the jumpers are set to 256kb and a DX4/POD is installed, it will hang at the end of the first POST screen.

Even with 128kb, and the new cache chips, the system is unstable at the fastest wait states/burst settings. However, a DX2-66 works perfectly at these settings.

I've been fiddling for a while but haven't quite found a stable combination.
I wonder if there is some limitation of this board or chipset, that if an overdrive is installed you are limited to 128kb or certain minimum RAM/cache wait states.

EDIT: after a couple of hours of fiddling and being unable to find any stable settings (system would hang when trying to boot DOS, or initialise the sound card, or give EMM386 errors when running programs) I've put the DX2-66 back in, set everything up for max performance, and the full 256kb cache, and its working fine without issue.
I might fiddle around tomorrow but it seems that the overdrives are off limits :(

What I know for sure is the the POD is fickle beast. I have two 486 mobo's that are capable of running just about any Intel/AMD 486 combination, but will not tolerate a POD. The POD compatiblity issues are fairly well known and go to the heart of your system. It requires that you expertly tweak your BIOS with respect to caches, etc. I will not attempt another POD install until I am 100% certain that the mobo will support it. I know that this is not helping your present situation, but I would like to pass on my not so successful experiences with the POD. The POD will, in fact, post on two of my 486 mobo's , but is unstable and the data is often corrupt. On the other hand, this forum is loaded with folks that swear by the POD. You may want to look for a mobo with better documentation and a little more in the main stream.
 

DonutKing

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unfortunately 486 motherboards are pretty scarce over here, and they fetch outrageous prices on ebay...

Here is something interesting:

I took the plunge and put in an AMD DX4-100, which clearly had 3 VOLT written on the surface.
Stuck a heatsink/fan on it, didn't change any jumpers from the 486DX2 setting, and fired it up.

It booted first go, at maximum performance settings. Didn't need to change a thing and it worked fine.

Intrigued, I pulled out the AMD DX4 and put in an Intel DX4- a standard 3 volt one, not an Overdrive.
The same problems I had with the overdrives occurred.

Interestingly, the AMD chip was picked up by the BIOS as an 80486DX2 while the Intel chip was detected as a DX4-S. Both were picked up at 100MHz. I confirmed this with cachechk and sysinfo.

The AMD DX4 only has 8KB L1 cache while the Intel DX4 has 16KB. I presume this is part of the issue- perhaps my board has trouble with CPU's with 16kb of L1 cache?
It's very odd.

I'm not sure how long the AMD DX4 will last running at 5V but I'll see how it goes... with the heatsink/fan on there it doesn't get very hot at all (certainly much colder than a DX2 with no fan). I have a few spares anyway, and if the chip smokes I'll just put the DX2 back in. I left it running PCPBENCH for about half an hour yesterday and it was very stable, and the heatsink barely got warm.

Although the CPU socket is clearly labeled "Socket 3" as far as I can tell it only supports 5V CPUs. Wikipedia seems to think that Socket 3 always supports 3.3V/5V but this board has no jumpers to switch between voltages, and there is definitely no voltage regulator on the board that I can see.

Interestingly, I found this page: http://www.pcguide.com/ref/cpu/fam/g4I486DX4-c.html
Which suggests that the 8KB AMD DX4's can handle taking 5V.... whether its true or not, I guess I'll find out soon enough :p
 

Agent Orange

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Looks like you're on the right track. I have my favorite 486 mobo (486-PVT-IO) running an AM586x133 oc'd to 150 Mhz w/ 128 mb total RAM. Check this link: http://computers.shop.ebay.com/?_from=R40&_trksid=p5197.m570.l1313&_nkw=486-PVT-IO&_sacat=58058

I bought this mobo from this very vendor back last fall. It was like opening a time capsule - everything was there, cables, manual, the whole 9 yards. The price is rediculously low (I thought) for NIB classic 486. The kicker is look what that other yo-yo underneath is trying to sell for 6 time as much and its only a refurb! The shipping may be worth it to you in the long run. Heck, get a few of them at the current going price and you could be the big wheeler-dealer down there in Australia. Keep us infrormed and best of luck.
 

DonutKing

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Unfortunately that seller won't ship outside the US, otherwise I'd snap that up in a heartbeat. :(

The other guy ships worldwide but I don't particularly feel like paying triple the price :/

Anyway, I tried overclocking the AMD DX4 to 120MHz with some interesting results.

It was not stable at 40MHz bus speed without introducing some wait states. Even thoguh I set the bus speed to 40MHz the BIOS detected the processor as 133MHz. There are no options for multiplier on the motherboard, just bus speed. Sysinfo even agreed that the processor is running at 133MHz. Not sure whats going on there, I'm assuming the BIOS doesn't have an entry in its CPU table for 120MHz. CACHECHK reports 120MHz.

going from 100MHz to 120MHz increased my 3dbench score from 66.6 to 71.4 However, DOOM timedemo 3 went from 41 to 38 - The additional wait states seem to be more of a hindrance than the benefit gained by the extra bus and CPU speed. Likewise, PCPBench mode 101 (640x480) also went from 6.8 at 100MHz to 6.5 at 120MHz. This is with 15ns L2 cache and 70 nanosecond fast-page memory.

At the moment I think I'm better off just running at 100MHz, not much sense in accelerating this Am486DX4's already shortened lifespan for little practical benefit :p
 
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Agent Orange

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Unfortunately that seller won't ship outside the US, otherwise I'd snap that up in a heartbeat. :(

The other guy ships worldwide but I don't particularly feel like paying triple the price :/

Anyway, I tried overclocking the AMD DX4 to 120MHz with some interesting results.

It was not stable at 40MHz bus speed without introducing some wait states. Even thoguh I set the bus speed to 40MHz the BIOS detected the processor as 133MHz. There are no options for multiplier on the motherboard, just bus speed. Sysinfo even agreed that the processor is running at 133MHz. Not sure whats going on there, I'm assuming the BIOS doesn't have an entry in its CPU table for 120MHz. CACHECHK reports 120MHz.

going from 100MHz to 120MHz increased my 3dbench score from 66.6 to 71.4 However, DOOM timedemo 3 went from 41 to 38 - The additional wait states seem to be more of a hindrance than the benefit gained by the extra bus and CPU speed. Likewise, PCPBench mode 101 (640x480) also went from 6.8 at 100MHz to 6.5 at 120MHz. This is with 15ns L2 cache and 70 nanosecond fast-page memory.

At the moment I think I'm better off just running at 100MHz, not much sense in accelerating this Am486DX4's already shortened lifespan for little practical benefit :p

Late edit: Find someone to throw in with yourself and make that guy an offer he can't refuse. Tell him you'll take 6 or 8. You can contact him through eBay.
Not bad numbers. What's your video card? When running DOOM how does it look - any jerking or stuttering?
 

DonutKing

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Video card is a VLB ET4000W32/P with 2MB video memory- brand is 'Hercules Dynamite'.

The rest of the system specs:
CT2800 Vibra 16, with XR385 DB
Gravis Ultrasound Classic 3.4 with 1MB memory
4x 4MB 70ns FPM 30-pin SIMMs
Winbond VLB I/O controller card
Quantum 1280AT HDD, with Ontrack DDO


Doom runs perfectly fine even with sound enabled (using the GUS). I'm running timedemo with no sound and one slot less than max screen size (so the status bar is visible). Hexen can get a little choppy particularly when smashing glass windows but apart from that its very playable.
 

Agent Orange

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Looks like decent system. I like your video card choice. The biggest problem I have with the 486's is that I expect too much. After a hour or so playing HAWX on the 'big machine' you naturally expect the poor 'ol 486 to do back flips. Let us know if make any progress with the POD.
 

DonutKing

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Thanks for the offer, I appreciate it. I'm basically after a board with 2x VLB slots. I have some spare 15ns cache chips so it doesn't matter if it has empty cache sockets. Support for 3.3V CPU's would be nice but not a necessity since I have 2 5V DX4 Overdrives.

I have a spare socket 3 board but its a PC-Chips M912 with fake cache chips soldered to the board, and it seems a bit unstable once it warms up. Good for testing but thats about it.
 

DonutKing

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Messages
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Either 30 pin or 72 pin memory slots is fine. I have plenty of spare SIMMs, both parity or non-parity.
Not worried about 20MHz bus, doubt I'd ever use it.
Cheers
 

Neon_WA

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Jan 15, 2010
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I will just keep editing this post as I go thru and find ones in my boxes of boards

first one probably wont suit u
Aopen VI15G
http://www.stason.org/TULARC/pc/motherboards/A/ACER-INC-486-VI15G.html
http://motherboards.mbarron.net/models/486vlb3/vi15g.html

2nd is probably a lost cause to find info on
IPEX VL486 Rev 2.0 IPX-UM-486IV6201
4 banks (8 slots) of 30-pin
4 x 32 ISA
2 x VESA
UMC 82481 / 482 chipset
20 - 50 FSB
no jumpers for CPU type
similar layout to this (minus one ISA slot) http://stason.org/TULARC/pc/motherboards/B/BCM-ADVANCED-RESEARCH-INC-486-LX400A-P-VLB.html

3rd one is probably a good one for you
ASUS VL/I-486SVGO Rev 1.2
almost identical this board in layout & specs, but has 2 x 72-pin & 2 banks (4 slots) of 30-pin
http://stason.org/TULARC/pc/motherboards/A/ASUS-COMPUTER-INTERNATIONAL-486-VL-I-486SV2G-VL-I.html
 
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Neon_WA

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