Re: Dead Forex 386 motherboard :-(. Any solution?

Posted on 2019-03-31, 13:46

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Deunan, the BIOS replace bin didn't help again :-(. Here are the results of the test: It wasn't supposed to help as in boot the system. Just to let me figure out things. The results are a bit unconclusive though. What I gave you is a "BIOS" filled with HLT instruction so it should just stop the CPU …

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Re: My new 486-386 junk boards [IT gore]

Posted on 2019-03-31, 12:34

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

What regulator/transistor do you have installed there now? And are you sure you're measuring the CPU voltage in the correct spot - which socket pin did you use? Rather than measuring voltage you should check the resistance from CPU socket VCC pins to that jumper(s). It should be well below 1 ohm.

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Re: Suntac 80286 Mainboards

Posted on 2019-03-31, 10:43

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

What also might be inteersting: The status of the LEDs on the Post-card: All lights on, except the IRDY, which is blinking during POST sequence and turns off at the end. Therefore the Reset-LED is "on" all the time. Think this should not be correct. Even more strange that the board powers up in …

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Re: Dead Forex 386 motherboard :-(. Any solution?

Posted on 2019-03-31, 00:50

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

It didn't work? That complicates things. Okay, another approach. Burn this file as BIOS, replace, boot. Ignore the test card, probe the BIOS chip pins again and write down the LED behaviour.

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Re: Suntac 80286 Mainboards

Posted on 2019-03-31, 00:43

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

But there is no conection of all adress lines to the ST62BC004. Oops, sorry about that. I looked at the wrong bus and gave you data lines to check. So, actually it's like this: Addresses A1-A12 go to 003 chip, and A13-A19 to 002. I haven't yet found which chip decodes A0. For now though check the …

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Re: My new 486-386 junk boards [IT gore]

Posted on 2019-03-30, 18:18

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Also : ATC1415 has a new VRM ! I took the same that was soldered there before ... Except it doesn't seem to really work ... I can either have 5v or 1.x/2.x volts, I assumed the one that was there before was the original one, but now I'm doubting ... Also, the CH471A finally has a new socket ! ... …

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Re: My new 486-386 junk boards [IT gore]

Posted on 2019-03-30, 18:13

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Reason I do that is that you cannot see if a chip is 256 or 512 from the outside if there is a label on it. Therefore I use 512 as standard not to miss anything... That's a problem, yes. You could always check the resulting file and if the lower and upper halves look identical, discard the lower …

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Re: My new 486-386 junk boards [IT gore]

Posted on 2019-03-30, 13:20

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Do you intend to program these images into '512 parts as well? That would actually work as-is because the socket on the mobo will have a 5V power on Vpp pin so only the upper part of the chip will be addressed, ever - the A15 line will be always kept high. So even if the lower 32k is somehow bad, …

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Re: My new 486-386 junk boards [IT gore]

Posted on 2019-03-30, 12:50

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The ROMs are already 64kb. I read them in my TL866 as 27E512, therefore each image should contain 2 identical 32kb parts. You can flash them to your 27C512 without modification. Did you try to exchange the H and L? I am also not 100% sure if the image is OK as the board was not working. But most …

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Re: Dead Forex 386 motherboard :-(. Any solution?

Posted on 2019-03-30, 11:33

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Great, program the binary file I've attached to the chip and put it in place of the BIOS. Remove all cards except the test card and boot the system. Do you get a code displayed now?

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Re: Dead Forex 386 motherboard :-(. Any solution?

Posted on 2019-03-29, 11:32

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

On pins 11-13, the RED LEDS light up, although very faintest. The good news is you get a lot of activity on pins 20 and 22 so the chip is being addressed - most likely CPU clock is running and it's fetching code from BIOS. But since it doesn't work the reads return wrong values and either the CPU …

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Re: need info: detailed comparision of ways accessing above 1mb ram in dos

Posted on 2019-03-29, 09:29

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I guess we'll have to agree to disagree then. DOS is single-threaded only in theory. I used DOS for many years, I remember what "TSR hell" is and how users would run various programs like accented letters input, screen grabbers / print spoolers, handy calculators, clipboard managers, various …

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Re: need info: detailed comparision of ways accessing above 1mb ram in dos

Posted on 2019-03-28, 22:45

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Unreal mode is *VERY* practical and easy to implement as a small ASM stub that can be linked with 16-bit C real-mode code for the simplicity of real-mode without using DOS extender libraries. (...) Unreal mode does work with the presence of XMS from any version of HIMEM.SYS. HIMEM.SYS does not put …

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Re: Suntac 80286 Mainboards

Posted on 2019-03-28, 21:51

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

This indicates an error accessing/adressing the Video memory? Tried several VGAs, same result. To my surprise, the board is up after finishing the POST. I can switch the keyboard LEDs and a reboot with Ctrl-Alt-Del works. My guess would be a problem with one of the address lines on the ISA bus. The …

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Re: Dead Forex 386 motherboard :-(. Any solution?

Posted on 2019-03-28, 11:10

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hi again!. Just to be sure that I am doing it correctly and before continuing with the tests, would this circuit be correct? the leds are of different color: green +5 and red GND. These days I will put the results! :-) It's OK, though as I've mentioned with just 1 LED per color you will get them to …

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Re: need info: detailed comparision of ways accessing above 1mb ram in dos

Posted on 2019-03-28, 10:25

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I'm too lazy to make a table and going into details would take pages of text on each and every of those points - so you get this: What OS? Because there is DOS and "DOS" aka Windows 95+ command line. You might be able to get away with some tricks on 95/98 but not on NT kernels. In general, the well- …

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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Posted on 2019-03-27, 14:58

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hi, just got the new '245! Already installed it and the pc is now running, even the keyboard error got fixed. Excellent! Hopefully it works now, you've already fixed everything else that was damaged by the spill. Would be happy to read a summary what parts had to be fixed at the end...? Well, the …

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Re: OAK OTI-037c - 800x600 mode ?

Posted on 2019-03-27, 14:09

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by Deunan

in Marvin \ Video

in Marvin \ Video

Edit: How about Realtek cards ? Just seen a few online, approx. from the same time period. Stay well away from any Realtek VGAs. If you think the OAK you have is crappy, you'll find yourself at a loss for words when you test a Realtek. Both performance and video quality are terrible. I found …

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Re: Dead Forex 386 motherboard :-(. Any solution?

Posted on 2019-03-27, 08:42

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hm, no effect huh. Since you're able to replace the clock gen now I assume it's socketed? Is it inserted in correct orientation (don't just try to rotate it, might get damaged by reversed voltage!) - double check the PCB markings to be sure. I can't see that detail on YT video. This mobo seeems to …

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Re: Dead Forex 386 motherboard :-(. Any solution?

Posted on 2019-03-27, 00:10

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

RDY led is not lit, which is strange. Remove VGA card (Is that a Trident TVGA8900C? Decent VGA for a 386 system.) and try again. Remove RAM and try again. Put a jumper on JP2 middle pins (2-3) and try again. I wonder why it has 40MHz CPU if the clock generator is only 66MHz. Also, someone replaced a …

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