486 build - trouble at birth

Discussion about old PC hardware.

486 build - trouble at birth

Postby assasincz » 2019-6-18 @ 11:05

Hi all,

I am currently refurbishing my best friend's old 486 setup for him, taking this on as a presonal challenge, basically rebuilding it from scratch.
As I am working on the case (retrobrighting, new stickers, overall cleaning), I have the functional HW in sort-of open-bench setup, trying to make it work, I am mostly at the beginning, but already the setup has proven to be quite tricky for me to make it work.

I would therefore like to establish this thread in order to consult with you guys any issue that I stumble across, specific for this setup.
I will skip over the details on the cosmetics (like new CPU fan, new CMOS battery mod).

Currently, the intended list of HW in the setup as follows (CPU and MB are fixed, other components could change):
CPU AMD A80486DX4-120SV8B
MB VEXTREC GMB-486SPS
RAM 4x8MB 72pin SIMM (I have several additional modules of various timings and capacities on hand)
HDD SD-to-IDE adaptor off Ebay with Transcend SDHC 8GB UHS-I 400x Premium (replacing very old and very noisy HDD, plugged on its own to primary on-board IDE channel, and is properly detected)
Video card PCI - undetermined (I have three different S3 PCI VGA cards to chose from)
Sound card ISA - undetermined (I have a SB16, and some ESS ISA cards to chose from)
2x CD-ROM IDE drive (4x speed, 52x speed) plugged to secondary on-board IDE channel
1x FDD 3.5''
PSU Fortron HEXA 400W ATX with ATX-to-AT converter off Ebay

For OS, I would like to eventually have MS DOS 6.22 combined with Windows 95, and option to select the OS to boot on startup (I am not even there, yet)

First thing I did for the actual HW configuration was that I upgraded on-board L2 cache from 256kb to full 1024kB with brand-new chips off Ebay:
8x 128Kx8 DIP32 chips
1x 64K x 8 DIP32 chip (for tag ram)
I have set the jumpers in accordance with the manual, and on-startup full 1024kB L2 cache is correctly detected.

Issue #1 I want to solve is booting; The setup hangs on booting - either from floppy, or HDD of any sort - unless I disable internal cache in BIOS.
This solves the issue and boot-up works fine, but this probably is not the correct way, needing to disable internal cache in BIOS.
Do any of you have any advice what settings (on-board or in-BIOS) I can check and/or change to be able to boot with both internal and external cache enabled?

Issue #2 that leaves me scratching my head - I am trying to make the SD-to-IDE drive work properly. I have partitioned drive using fdisk on my WIN95 start-up diskette, enabled large drive support and the primary partition is set at full 8GB (FAT32, actual capacity is a little less, of course). The drive is accessible but the PC freezes on C:\>dir command, freezes during WIN95 installation scandisk, and C:\>format c: does nothing. What are your suggestions?

Issue #3 what steps do you recommend taking when I want to have a option to select OS on startup - MS DOS 6.22, Windows 95?
assasincz
Newbie
 
Posts: 52
Joined: 2019-1-30 @ 15:05

Re: 486 build - trouble at birth

Postby Aragorn » 2019-6-18 @ 11:45

perhaps your internal cache is set to the wrong mode?

does the machine work with the original hard drive installed?
Aragorn
Newbie
 
Posts: 90
Joined: 2018-11-05 @ 21:05

Re: 486 build - trouble at birth

Postby Tiido » 2019-6-18 @ 11:58

Do the cache chips get hot when the machine runs ?

What happens when you change the FSB to 33MHz rather than 40MHz ?
User avatar
Tiido
Oldbie
 
Posts: 862
Joined: 2018-1-14 @ 04:40
Location: Estonia

Re: 486 build - trouble at birth

Postby appiah4 » 2019-6-18 @ 13:22

Dualbooting DOS 6.22 and Windows 95 is absolutely useless.

For Issue 1; you probably have L1 cache set to Write Back on a board that does not support it..
A500:+512K|ACA500+|C1084S
i386:Am386SX-25|4M|TVGA9000B|Gold-16
i486:U5SX-33|8M|GD5428|CT2290/S2
i586:P133|32M|S3T64+/MX2|V1|CT3980/32M
i686:K6-2/400|64M|V2/SLI|CT4500/32M
S370:P3-1200|384M|GF4Ti4200|MX300
S754:A3700+|2G|X1950PRO|SB0350
User avatar
appiah4
l33t
 
Posts: 3587
Joined: 2017-2-19 @ 07:36

Re: 486 build - trouble at birth

Postby BinaryDemon » 2019-6-18 @ 13:30

Looking at your manual, It looks like the JP5 Jumper controls if the L1 cache is WriteThru (2-3) , WriteBack(1-2), and possibly disabled if OPEN? I would try some alternate settings with that.

Is your Win95 version OSR2? The original Win95 does not support fat32 or partitions larger than 2gb. I would forget about fat32 and just do 4ea 2gb fat16 partitions to ensure that MSDOS 6.22 can access all the filespace.

Personally I would just stick with Win95/Dos7.x.
Check out DOSBox Distro:

https://sites.google.com/site/dosboxdistro/ [*]

a lightweight Linux distro (tinycore) which boots off a usb flash drive and goes straight to DOSBox.

Make your dos retrogaming experience portable!
BinaryDemon
Member
 
Posts: 316
Joined: 2018-1-17 @ 00:35

Re: 486 build - trouble at birth

Postby assasincz » 2019-6-18 @ 20:54

I have spent a few minutes with the setup now and here is what I can find

Aragorn
perhaps your internal cache is set to the wrong mode? 
The BIOS shows no option to set mode for internal cache.

does the machine work with the original hard drive installed?
The hhd works, but it comes with Win95 which freezes at loading no matter the settings

Tiido
Do the cache chips get hot when the machine runs ?
Yes, apart from the transistor next to the CPU, they are the warmest components on the board after a few minutes

What happens when you change the FSB to 33MHz rather than 40MHz?
Not tried this yet

appiah4
For Issue 1; you probably have L1 cache set to Write Back on a board that does not support it..
BinaryDemon
Looking at your manual, It looks like the JP5 Jumper controls if the L1 cache is WriteThru (2-3) , WriteBack(1-2), and possibly disabled if OPEN? I would try some alternate settings with that.
No way to set L1 cache mode in BIOS, also changing setting of the JP5 yeilded no change of behavior.

Any other ideas, guys and gals?
assasincz
Newbie
 
Posts: 52
Joined: 2019-1-30 @ 15:05

Re: 486 build - trouble at birth

Postby Aragorn » 2019-6-18 @ 21:05

OK so crashing on both your new CF card and the original drive suggests the problem isnt the drive. Perhaps bad RAM? Or the CPU itself is unstable for some reason?

Also, stick the original cache chips back in and see if that changes the behaviour.
Aragorn
Newbie
 
Posts: 90
Joined: 2018-11-05 @ 21:05

Re: 486 build - trouble at birth

Postby Tiido » 2019-6-18 @ 21:56

assasincz wrote:Yes, apart from the transistor next to the CPU, they are the warmest components on the board after a few minutes

This means you have fake cache chips, remarked 3.3V parts that will die eventually and possibly take the motherboard with it. Normal cache chips should only get slightly warm.
User avatar
Tiido
Oldbie
 
Posts: 862
Joined: 2018-1-14 @ 04:40
Location: Estonia

Re: 486 build - trouble at birth

Postby BinaryDemon » 2019-6-19 @ 01:07

Have you done any extensive testing with dos games or benchmarks that might stress the system? If it's only Win95 having issues, I might suspect you have a bad SIMM.
Check out DOSBox Distro:

https://sites.google.com/site/dosboxdistro/ [*]

a lightweight Linux distro (tinycore) which boots off a usb flash drive and goes straight to DOSBox.

Make your dos retrogaming experience portable!
BinaryDemon
Member
 
Posts: 316
Joined: 2018-1-17 @ 00:35

Re: 486 build - trouble at birth

Postby assasincz » 2019-6-23 @ 11:56

Update:

L2 cache problem:
So I was trying various configurations of L2 cache, swapped to DX20DPR66 Overdrive processor for a while, tried changing FSB, and also swapped SIMMs around, but the erratic behavior of the L2 cache still remained.
Regarding temperatures, I did some measurement (outside of PC case):
1 - At 1024K configuration, the possibly-fake 128K ISSI chips and 64K ISSI tag chip off Ebay settle to around 41-43°C, I do not think that's too bad...
2 - Changing the configuration to the original 128K config (vintage Winbond branded SRAM, 4pcs 32K W24M257AK-15 chips and 16K W24129AK-15 chip for tag), I measure after a while basically the same temperatures as with the iffy chips: 41-43°C
3 - the transistor next to the CPU socket I referred to previously got to around 62°C - just for reference

Nevertheless, I still could not make any configuration with the iffy 128K ISSI chips to work (neither 1024K, nor 512K configs) unless I disabled internal CPU L1 cache in BIOS. Luckily I had other SRAM chips around - specifically new 32K ISSI chips (again, off Ebay), and some vintage Alliance-branded 128K and 32K chips from my own 486 build, so I tried swapping this around.
Eventually, I settled on working 256K L2 config (8pcs new 32K ISSI chips, and one original 32K Winbond chip for tag RAM. I checked the temps with these as well, again the same. Weird thing was that when I put the 32K ISSI chip into tag RAM slot, it freezed on boot. Maybe a bad piece. Well, that is why the tag RAM chip is different to others.

So in conclusion, either are the ISSI chips off Ebay (128K and 64K) iffy in some way (even if not by operating temp), or I am missing something. I also eliminated SIMM modules as well as CPU itself being the culprits (now back at 120Mhz DX4 and 32MB of RAM (8+4+4+16MB modules).

Weird thing is with the JP5 on-board. The A80486DX4-120SV8 processor should support L1 in W-B mode, but when I switch the JP5 to 1-2 (WB), the computer hangs on boot. It works on 2-3 (WT) or OPEN. I leave it to OPEN for now, but...hm....

SD-to-IDE drive
The problem was easily solved, as outlined - making just 2GB partition using Win95 diskette instead of 8GB using Win98 diskette as before → works no problem. The Win95 installation was a breeze afterwards.

I now need to settle on VGA and sound cards of choice, and proceed with all kinds of driver installations. After that, I will move all the HW from open test bench to its original AT case.
assasincz
Newbie
 
Posts: 52
Joined: 2019-1-30 @ 15:05

Re: 486 build - trouble at birth

Postby chinny22 » 2019-6-23 @ 18:20

My recommendations

The SB16 is probably the safer bet.
Video, S3 is probably fine, depending on what they are will decide what's best for a DX4 120 (nice choice of CPU btw, something different)
HDD, If it was me I'd keep the original drive for the OS, and put the SD card as slave, or Primary on the other IDE channel, that way you don't loose the authentic HDD spin up sound at boot.
The 4x CD-Rom may have trouble reading CD-R's otherwise its the better option as a 486 cant keep up with a 52x drive so the stupid thing will keep spinning up and down which delays everything by 2-3 seconds unless you run a slowdown utility on it.
User avatar
chinny22
l33t
 
Posts: 2299
Joined: 2011-8-26 @ 12:02
Location: Australian but living in the UK for now

Re: 486 build - trouble at birth

Postby assasincz » 2019-6-26 @ 19:48

Hi guys

So I decided to not pursuit the dual booting and stuck with default Win95 boot. I went with S3 Vision864 PCI VGA card (4MB) for video and SB16 CT2980 for audio. Only trouble after that was figuring out the sound card's IRQ/DMA to set for each game and I am done!

Today I finished putting everyrhing to the original case. The case itself underwent some refurbishing - faceplate retrobrighting, new stickers (reverse-designed), a mount for SD-IDE adapter in place of original HDD and as a finishing touch, new thumbscrews for the cover. So satisfying....

20190626_213634.jpg


20190626_213714.jpg
assasincz
Newbie
 
Posts: 52
Joined: 2019-1-30 @ 15:05

Re: 486 build - trouble at birth

Postby Srandista » 2019-6-26 @ 19:56

Lol, those stickers, they're perfect :lol:
My overkill "retro" PC - ASRock 4CoreDual-VSTA, Pentium E6500K, 512MB/4GB RAM, Radeon 9500@9700 (Softmod), ESS Solo-1 + Dreamblaster X2, 80GB IDE HDD, Win 98/XP
User avatar
Srandista
Member
 
Posts: 318
Joined: 2017-4-07 @ 17:14
Location: Czech Republic

Re: 486 build - trouble at birth

Postby Deksor » 2019-6-27 @ 06:42

This cache don't look fake to me. However are you sure your chips are inserted properly ?
Deksor
Oldbie
 
Posts: 1664
Joined: 2016-6-07 @ 14:37

Re: 486 build - trouble at birth

Postby assasincz » 2019-6-27 @ 07:29

Deksor wrote:This cache don't look fake to me. However are you sure your chips are inserted properly ?

What "cache" are you reffering to exactly?
assasincz
Newbie
 
Posts: 52
Joined: 2019-1-30 @ 15:05

Re: 486 build - trouble at birth

Postby assasincz » 2019-6-27 @ 14:21

Made one final mod before handing it over...
The inherent lack of Turbo switch of the case was bugging me more than it should
20190627_161925.jpg
assasincz
Newbie
 
Posts: 52
Joined: 2019-1-30 @ 15:05

Re: 486 build - trouble at birth

Postby appiah4 » 2019-6-27 @ 14:42

assasincz wrote:Made one final mod before handing it over...
The inherent lack of Turbo switch of the case was bugging me more than it should
20190627_161925.jpg


Nice. I am also working on one myself!
A500:+512K|ACA500+|C1084S
i386:Am386SX-25|4M|TVGA9000B|Gold-16
i486:U5SX-33|8M|GD5428|CT2290/S2
i586:P133|32M|S3T64+/MX2|V1|CT3980/32M
i686:K6-2/400|64M|V2/SLI|CT4500/32M
S370:P3-1200|384M|GF4Ti4200|MX300
S754:A3700+|2G|X1950PRO|SB0350
User avatar
appiah4
l33t
 
Posts: 3587
Joined: 2017-2-19 @ 07:36

Re: 486 build - trouble at birth

Postby Katmai500 » 2019-6-27 @ 21:21

Such clean quality work. I love the discrete turbo switch. Very nice build.
User avatar
Katmai500
Member
 
Posts: 162
Joined: 2017-10-31 @ 14:08
Location: USA

Re: 486 build - trouble at birth

Postby Deksor » 2019-6-28 @ 00:35

The L2 cache. Is it working now ?
Deksor
Oldbie
 
Posts: 1664
Joined: 2016-6-07 @ 14:37

Re: 486 build - trouble at birth

Postby assasincz » 2019-6-28 @ 04:59

Deksor wrote:The L2 cache. Is it working now ?


It is now, however only in 256kB configuration, see my update from 2019-6-23 @ 11:56, above I just could not make it work with 128kB SRAM chips
assasincz
Newbie
 
Posts: 52
Joined: 2019-1-30 @ 15:05

Next

Return to General Old Hardware

Who is online

Users browsing this forum: Artex, mothergoose729, mrgreen, SirNickity, watson and 16 guests