Congrats! So it's indeed a PC Chips board like Deksor said. Yeah sounds like PSU has developed bad caps already. You could open it up and take a look. I would also run cachechk or speedsys to check out the cache, as PC Chips is infamous for making boards with fake cache 😃

Theodinator wrote on 2020-08-18, 21:33:

Today the video card came in and I got the computer to POST!
IMG_20200818_232821.jpg

The computer doesn't seem quite stable however. If I plug in the power cord and flip the switch, it posts. But if I power it off, wait 10 seconds and flip the switch again it doesn't post anymore. After leaving the power cord out for about a minute and trying again it posts again. Bad PSU maybe?

Possibly the power-on reset circuit failed. The job of the reset circuit is to apply a reset signal until power is stable. If the reset circuit misses that you turned off the supply and does not provide a reset signal, the processor does some strange stuff after power-cycling, but does not do anything useful. The easiest way to test this theory: Push the reset button if it doesn't post. If it posts immediately after you pushed the reset button, it's most likely the power-on reset circuit. This circuit is near to the CMOS battery on a couple of mainboards, so if there are signs of corrosion near the battery, that might be a reason for a failed reset circuit. Other boards rely on the POWER GOOD signal from the power supply to generate the reset pulse, so a bad contact on POWER GOOD or a supply that does not properly generate POWER GOOD might also cause reset failures.

mkarcher wrote on 2020-08-19, 08:07:

Possibly the power-on reset circuit failed. The job of the reset circuit is to apply a reset signal until power is stable. If the reset circuit misses that you turned off the supply and does not provide a reset signal, the processor does some strange stuff after power-cycling, but does not do anything useful. The easiest way to test this theory: Push the reset button if it doesn't post. If it posts immediately after you pushed the reset button, it's most likely the power-on reset circuit. This circuit is near to the CMOS battery on a couple of mainboards, so if there are signs of corrosion near the battery, that might be a reason for a failed reset circuit. Other boards rely on the POWER GOOD signal from the power supply to generate the reset pulse, so a bad contact on POWER GOOD or a supply that does not properly generate POWER GOOD might also cause reset failures.

I don't think that's it because pressing the reset button doesn't resolve it. Once it doesn't POST the only thing that helps is unplugging the cord and waiting a few seconds before plugging it in again. I'll test with another AT PSU tomorrow to see if that makes a difference.

I ran cachechk and speedsys:

The cache is real! From what I've read online, the fake cache chips didn't appear until '94/'95, this board is from '92/'93. The benchmark results are about right for what you can expect from this system I guess. The HDD seems awful slow to me or are those rates normal for this generation of hardware? A CF-to-IDE adapter is on the way so I can stop using the old hard drive.

Great! I guess the HDD performance is about there, here is a benchmark result of the Quantum Maverick 540 from another forumer for reference, which look almost identical to yours.

What are memory & cache wait state, etc. settings in BIOS? Shouldn't those be faster for 50MHz?

jakethompson1 wrote on 2020-08-20, 01:36:

What are memory & cache wait state, etc. settings in BIOS? Shouldn't those be faster for 50MHz?

Can't find settings related to wait state in BIOS..

I've fixed up a battery solution:

Attached with some double sided tape to the case:

I didn't want to use a 3xAA or 3xAAA battery holder because those batteries can leak as well. Although 3V is a bit low compared to the original 3.6V battery, it works fine so far. I found this article: https://vswitchzero.com/2018/02/20/the-486-re … oration-part-2/ before and that guy also had success with this solution.

Still waiting on the CF-to-IDE adapter before I can create a new DOS installation. Also I've bought a sound card (Sound Blaster Vibra 16 CT2890) to make the system more suitable for some games 😀

A little update:
The CF to IDE adapter works fine, I've used a 4GB CompactFlash card and installed DOS 6.22 😀

Overall the computer works okay but there's an issue with reading from floppies. Whenever the system reads from a floppy, the screen gets mangled/corrupted. For example, when I boot from the first DOS 6.22 disk, some random characters appear during 'Starting MS-DOS'. Then the setup screen appears and all is well again (screen refreshed). But as soon as the setup program starts reading from floppy again the random characters and colors appear until nothing is readable anymore. The setup completes just fine however. Could this be a resource conflict between the video card and floppy drive controller? I'm not sure how to tackle this, any help would be appreciated!

Also I've received the SB VIBRA 16 CT2890. This card is not without issues in this computer. I've installed the drivers and in the diagnose utility the 8-bit sound crackles, 16-bit sound and MIDI both work fine. Most games sound okay but others like Wolfenstein 3D have problems. The sounds of gunshots and doors opening seem way too loud and distorted. Besides that I find the card quite noisy..
I've tried the card in my other old system (Pentium 133, Windows 95) and Wolfenstein 3D sounds fine on that machine when I run it from Windows 95. I've read that these types of compatibility issues are common with SB16's? I've also bought an ESS AudioDrive 1668F as that card should have better DOS compatibility and is non-PnP.

Theodinator wrote on 2020-08-27, 07:52:

A little update: The CF to IDE adapter works fine, I've used a 4GB CompactFlash card and installed DOS 6.22 :) […]
Show full quote

A little update:
The CF to IDE adapter works fine, I've used a 4GB CompactFlash card and installed DOS 6.22 😀

Overall the computer works okay but there's an issue with reading from floppies. Whenever the system reads from a floppy, the screen gets mangled/corrupted. For example, when I boot from the first DOS 6.22 disk, some random characters appear during 'Starting MS-DOS'. Then the setup screen appears and all is well again (screen refreshed). But as soon as the setup program starts reading from floppy again the random characters and colors appear until nothing is readable anymore. The setup completes just fine however. Could this be a resource conflict between the video card and floppy drive controller? I'm not sure how to tackle this, any help would be appreciated!

Also I've received the SB VIBRA 16 CT2890. This card is not without issues in this computer. I've installed the drivers and in the diagnose utility the 8-bit sound crackles, 16-bit sound and MIDI both work fine. Most games sound okay but others like Wolfenstein 3D have problems. The sounds of gunshots and doors opening seem way too loud and distorted. Besides that I find the card quite noisy..
I've tried the card in my other old system (Pentium 133, Windows 95) and Wolfenstein 3D sounds fine on that machine when I run it from Windows 95. I've read that these types of compatibility issues are common with SB16's? I've also bought an ESS AudioDrive 1668F as that card should have better DOS compatibility and is non-PnP.

On the screen corruption, this is a shot in the dark but if you have not already, try cleaning the ISA edge contacts of both the video card and i/o card with a pencil eraser. My only suspicion about this is that floppy controllers use i/o ports 3f5, 3f4, and 3f2, while VGA cards use (among others) i/o ports 3d4 and 3d5 which are only one bit different.

With the SB I would only say to double check settings - the "usual" configuration was i/o port 22o, irq 5, and dma channel 1. I'll note that Sound Blasters and floppy controllers are likely the only things using ISA DMA in your system, so perhaps there is a connection between the screen corruption and sound card issues. ESS made good cards and that one is worth trying. If it doesn't have jumpers, there is an ESSCFG.EXE program you run to load settings into the card.

Also, you might try AMISETUP. It will show BIOS settings that are hidden in the usual setup, and may let you speed up cache and RAM timings. If you set them too aggressive you'll have to reset your cmos though through bios setup and try again.

jakethompson1 wrote on 2020-08-27, 15:51:

On the screen corruption, this is a shot in the dark but if you have not already, try cleaning the ISA edge contacts of both the video card and i/o card with a pencil eraser. My only suspicion about this is that floppy controllers use i/o ports 3f5, 3f4, and 3f2, while VGA cards use (among others) i/o ports 3d4 and 3d5 which are only one bit different.

With the SB I would only say to double check settings - the "usual" configuration was i/o port 22o, irq 5, and dma channel 1. I'll note that Sound Blasters and floppy controllers are likely the only things using ISA DMA in your system, so perhaps there is a connection between the screen corruption and sound card issues. ESS made good cards and that one is worth trying. If it doesn't have jumpers, there is an ESSCFG.EXE program you run to load settings into the card.

Also, you might try AMISETUP. It will show BIOS settings that are hidden in the usual setup, and may let you speed up cache and RAM timings. If you set them too aggressive you'll have to reset your cmos though through bios setup and try again.

Thanks for the tips!
I already cleaned the ISA edge contacts, doesn't seem to make a difference. It doesn't really bother me that much because I'm not using a floppy that often.

With AMISETUP there were indeed some settings related to wait states, I've finetuned it and that makes quite a difference:

Settings are now:
TURBO Cache Function - Enabled
Cache Read Hit Burst - 3-2-2-2 (Anything lower gives problems)
Cache Write Hit Wait State - 0WS
DRAM Read WS Options - 1WS
DRAM Write WS Options - iv (I think this is a bug, the setting has four options just as DRAM Read WS Options. They are labeled i,ii,iii,iv so I guess that for 3WS, 2WS, 1WS and 0WS.)

Thanks for your help!

Where did you found "Also, you might try AMISETUP." utility?
And if somebody looking for external battary polarity: https://media.digikey.com/pdf/Catalog%20Drawi … Bottom_View.jpg

Can you please dump the BIOS ? 😀
You can use this little DOS program to copy the BIOS http://cd.textfiles.com/microhaus/mhblackbox3 … MORY/GETROM.ZIP

Deksor wrote on 2021-03-23, 19:10:

Can you please dump the BIOS ? 😀
You can use this little DOS program to copy the BIOS http://cd.textfiles.com/microhaus/mhblackbox3 … MORY/GETROM.ZIP

Sure! I've attached a zip for you. I've backed it up using AMISETUP and the GETROM utility you mentioned. The AMISETUP bacup is larger, 128k instead of 64k but the first half of the file seems to be empty.

made a page in UH19
http://www.win3x.org/uh19/motherboard/show/8433

Maybe at some point we'll find a model number.

In the mean time, can you please tell what is printed next to the ISA slot near the edge (that ends in 024A)? Maybe we can keep that as a placeholder identifier until an actual M4xx or M6xx model number crops up.

evasive wrote on 2021-05-25, 13:17:

In the mean time, can you please tell what is printed next to the ISA slot near the edge (that ends in 024A)? Maybe we can keep that as a placeholder identifier until an actual M4xx or M6xx model number crops up.

Here's a better picture of that text:

I'm still trying to figure out what causes the screen corruption during reading from a floppy drive. To me it seems as if the IO controller is writing to the video RAM (if that's even possible..)
Here's an example copying all files from a floppy to the CF drive:

This only occurs while reading data from a floppy. After a 'cls' or other screen refresh everything is fine again. It also doesn't seem to impact the system stability. It happens with bootable disks as well so I don't think it's a DOS EMM/XMM related setting. If I remember correctly, changing the cache wait state also didn't change anything.

To confirm the culprit can you try, a) a different IO controller, b) try a different video card. If with either of these the problem is solved you found the culprit, i.e. either the IO controller, video card or motherboard. As an extra you might also try a different floppy drive.

Sounds more like the capacitors near the floppy controller or the VGA memory are shot.

Theodinator wrote on 2021-05-25, 16:55:

I'm still trying to figure out what causes the screen corruption during reading from a floppy drive. To me it seems as if the IO controller is writing to the video RAM (if that's even possible..)

Data from the floppy is transferred to main memory using DMA. The mainboard (the DMA controller) asks the floppy controller to put a byte onto the bus by asserting DACK2 on the ISA bus, and puts the address where the data from the floppy drive should go to to the bus at the same time, and it asserts the MEMW# line to tell any ISA card that might contain the destination memory to pick up the byte from the floppy controller and write it to its own memory. If you read a floppy disk normally, the address on the ISA bus during floppy reads should not be the address of the video RAM, but it seems your VGA card still responds to that cycle.

This might be an incompatibility between the mainboard and the VGA card regarding ISA bus timing. You might want to check your BIOS setup, whether you have some "fast DMA" settings like "ISA Type-F DMA" enabled, or you use DMACLK=ISACLK instead of DMACLK=ISACLK/2, i.e. you run the DMA controller at 8MHz instead of 4MHz (which is the usual frequency it runs at, for compatibilty).