Re: 286 board post fail

Posted on 2019-04-09, 16:31

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I have a 386SX mobo (or two) that lacks HDD auto-detection as well - if you don't have another PC with this option then try booting from a floppy with HDD/CF card connected but not set in BIOS, and run NSSI. I think it detected the parameters by probing the IDE ports directly.

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Re: Help: Funky BIOS behaviour

Posted on 2019-04-09, 13:49

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Let me start from the end. £100 for an old BIOS chip that you can't even be sure is OK or that it will work correctly in your mobo is a big NO-NO in my book, but perhaps you're rich and don't care about silly little details like that. But I'm assuming that's not the case. AT27C010-70PU is OTP EPROM, …

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Re: Making a removable heatsink for PGA-132 TI 486SXL2-66

Posted on 2019-04-09, 11:31

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

In general if the chip has a plastic package it's not supposed to heat up a lot. Obviously though the manufacturer might have just went the cheap route and you do need both heatsink and a fan - my point here is, the package will limit you way more than proper thermal adhesive tape. So there's little …

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Re: mainboard clock flies too fast

Posted on 2019-04-09, 10:04

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

It's the part marked Y1, a small metal cylinder next to the keyboard controller with AMIKEY logo. EDIT: That's the crystal resonator you should replace (or test if you have a scope). It'll be connected to that 4069 below it, and that in turn will feed a MC68HC68-like chip, that'll be the RTC itself …

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Re: Making a removable heatsink for PGA-132 TI 486SXL2-66

Posted on 2019-04-09, 09:59

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I have an IBM SLC mobo that someone tried to identify by removing the heatsink from CPU with such a method. The result is missing CPU and 2 of its solder pads gone - because it was only 100 pin package and the bond with the heatsink was greater than force needed to shear the solder joints. So this …

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Re: XT clone motherboard repair advice/help needed (KT 10 M/B)

Posted on 2019-04-08, 23:00

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Just FYI the AT28C256 is pretty cheap 5V EEPROM from Atmel, comes in DIP28 package with 150ns latency. Should be enough even for 486 systems (since there's usually plenty of wait states during BIOS ROM reads). Supported by TL886. Though if there is a problem with ROM signals then swapping the chip …

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Re: XT clone motherboard repair advice/help needed (KT 10 M/B)

Posted on 2019-04-08, 20:47

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I still think it's not reading the BIOS ROM correctly. Since you own EPROM programmer, do you have any electrically erasable 5V parts (FLASH or EEPROM) in 64-512 size? I can prepare some test images for you but I expect at least a few attempts will be needed to figure things out. Having to erase a …

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Re: Suntac 80286 Mainboards

Posted on 2019-04-08, 20:11

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Well it's much easier if you have schematics. Plus we got lucky and all the "big" chips are still functioning properly. Starting your electronics repair adventure with PC boards is probably not the best idea, but then again if you're willing to learn - why not. These 286 and even early 386 mobos and …

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Re: XT clone motherboard repair advice/help needed (KT 10 M/B)

Posted on 2019-04-08, 11:04

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Just had a quick look at that BIOS, it does indeed seem OK. The checksum is zero, as it should be in this case. But then I noticed the card used is a CGA? Well then, the dip switches are set to monochrome so that's wrong. Try SW1/6 to ON (or 1/5 to ON).

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Re: XT clone motherboard repair advice/help needed (KT 10 M/B)

Posted on 2019-04-08, 10:07

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I'd say the mobo is running but executing random data rather than BIOS image. This is mostly TTL logic there, it's stable without input signals (basically all inputs are pulled-up). So it should not "go crazy" - though it just might if the CPU is CMOS and clock line is cut. I can't tell from the …

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Re: Requesting help diagnosing potential CRT geometry issue

Posted on 2019-04-07, 20:20

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

You know, if this problem only affects 2 modes, and other work just fine (especially the higher frequency ones) it might not be an electrical problem at all. Modern CRT monitors and TVs are fully digital, all the parameters for different modes are stored on EEPROM memory and the chips insde use that …

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Re: Suntac 80286 Mainboards

Posted on 2019-04-07, 17:44

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Everything is OK then except this: No continuity between 001 pin 17 and ISA slot pin B2. Well that'a your problem right there. This might be interpreted by the video card as reset being asserted all the time so it's just not working. This is sort of a global reset signal, generated by the 001 chip, …

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Re: Can you save made in U.S.A. 486 ?

Posted on 2019-04-07, 10:44

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Keyboard LEDs will blink once on their own as long as power is applied - there is another MCU in there that does that as a part of it's own init sequence. So that's is no indication of any motherboard activity. In fact, unless you have some serious ISA slot issues, the test card not showing any …

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Re: Suntac 80286 Mainboards

Posted on 2019-04-07, 10:29

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Somehow I missed your first reply. Anyway, the values look good so I wonder what is up with the LED. Just to make sure I did not misunderstand, the test card RESET LED is on at all times and even when the reset switch is connected and used it doesn't change the LED state? Next round of tests then: - …

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Re: Evergreen revto486.sys parameters and manual

Posted on 2019-04-06, 15:35

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

7-zip is free, WinRAR is not - that's my main argument. Also LZMA2 on ultra is maybe slower but offers better compression so a one-time CPU cost is perfectly acceptable I think. Lastly, LZMA2 can be multi-threaded pretty well, RAR on the other hand not so much and the program itself is very Intel- …

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

Posted on 2019-04-06, 12:34

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Ah, so it is burned out after all. I did notice the darker area but I thought it was also flux residue you mentioned. These mobos start with no cache and no RAM, just CPU fetching code from BIOS ROM. So just the CPU, BIOS and test card should give you codes, first for the missing RAM and then maybe …

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Re: Requesting help diagnosing potential CRT geometry issue

Posted on 2019-04-06, 12:18

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Significant (as in, noticable) loss of detail in dark areas of the picture is also a sign of wear. Internal circuitry monitors both the cathode current and HV value, and will raise HV to compensate for current loss (due to lowered emission). This will usually let you keep the brightness but at the …

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Re: Where do I find SMC for repair?

Posted on 2019-04-06, 10:51

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

It's hard to tell with SMD components. C* is always a capacitor but the value can be anything form pF to uF range. These are power filters so the smaller ones are probably 100nF and the bigger ones can be 1 or 10uF I guess. Look like 0603 and 0805 size, but possibly the zoom is tricking my eyes and …

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

Posted on 2019-04-06, 10:38

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Huh. Okay, then test a few VCC pins in the socket against each other, do you get close to zero resistance? Chances are someone put in a bad CPU (or not correctly) and the copper trace that supplies VCC to socket, and which probably goes through the middle PCB layers, is toast. You simply have to …

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Re: Evergreen revto486.sys parameters and manual

Posted on 2019-04-06, 09:54

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

feipoa wrote: ychh0, I am unable to open your rar archives. I tried, both, 7-zip 9.20 and WinRAR 3.0. Are you able to archive them in an older RAR format or ZIP? 7-zip 9.20 is ancient. It works for me, I'm using 7-zip 18.04 x64 version. Note you need both RAR files in the same folder to decompress …

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