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Re: SUCCESSFUL K6-2+ to K6-3+ Full Cache Enable Mod

Posted on 2022-04-05, 03:13

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Finally got around to doing my first one the other night. Found moving the resistor much easier than anticipated, just my fat fingers made lining it up afterwards a bit difficult! Tested my Gigabyte GA 5AA (With dead on motherboard cache) and its stable at 130Mhz, but not at 135. This particular CPU …

Re: IBM AT RAM expansion

Posted on 2022-04-05, 02:42

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Thanks all, some thoughts for consideration there. I'll admit my wording in the initial post was a little poor, I really meant am I actually likely to run software on an 8MHz 286 that will benefit from lots of memory. I think the answer is probably not. I'd really like to upgrade it to 640K, but …

IBM AT RAM expansion

Posted on 2022-03-31, 17:46

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hi all Picked up an IBM AT the other week in good condition, but its currently only fitted with 512k of RAM on the motherboard. As far as I'm aware, this has to be upgraded in two parts. An official IBM 128k upgrade card to take it to 640k, then another card to add anything over and above that. From …

Re: 286 motherboard repairs

Posted on 2022-03-08, 06:56

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I had some issues with FDC not working properly with certain CF cards. This was mostly (only?) on UMC based Super I/O, even though it has 2 chips, none is a dedicated FDC or HDC, both seem to have some ISA logic and other stuff in them. I prefer Prime 2C cards, way less issues with those and …

Re: 286 motherboard repairs

Posted on 2022-03-04, 04:44

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Another update. All the bigger (0.6") DIP sockets and 4x of the smaller ones replaced with round pin sockets tonight. Still not working right, but less flakey now. It always fails in the same way. But now that I'm pulling the sockets off, I'm realising just how bad they are. From the top they look …

Re: 286 motherboard repairs

Posted on 2022-03-02, 07:42

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

One failed 74LS07 not supplying a clock signal to pin 3 on the KBC later and we have major progress! Still very flakey, but I'm pretty certain thats just down to these awful single wipe DIP sockets. Andrew

Re: 286 motherboard repairs

Posted on 2022-03-01, 07:01

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Apologies, I've been flat out all weekend. So, I've been looking at the pwr good signal. It goes from the in on the AT power connector, straight to pin 80 on the 82C201, marked Reset 1. This stays low for a second, then goes high. It also goes to pin 1 on U115, an HCF4069UBE. The corresponding …

Re: 286 motherboard repairs

Posted on 2022-02-24, 14:24

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I think we can conclude the issue is most likelty with missing mobo signals, for whatever reason, and not one of the removed chips breaking the bus. So at this point it's probably best to re-populate the mobo, including some RAM (it takes 18 chips to have one full bank, 16 data bits + 2 for parity, …

Re: 286 motherboard repairs

Posted on 2022-02-24, 07:39

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Ok, so I'm probably getting ahead of myself here... But I found a pair of good PLCC sockets. So I socketed 204 and 203. Just for laughs I decided to try the original BIOS. I now get 0A,09 on the POST card, but more excitingly, beeps! Its well past my bed time, so I'll do some proper investigation …

Re: 286 motherboard repairs

Posted on 2022-02-24, 07:04

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

That looks promising so it's worth further investigation. So it would appear we do have a stuck bit on XADDR bus, XA4 is always zero. I think ISA slots are on SADDR bus so we can't use that as reference, and XADDR bus is kinda complicated in how it works because the chipset does at least some …

Re: 286 motherboard repairs

Posted on 2022-02-23, 21:37

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Here it is https://youtu.be/vONWmfSc0CU Andrew

Re: 286 motherboard repairs

Posted on 2022-02-23, 20:54

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Deunan wrote on 2022-02-23, 19:57: OK, try this version then, see if there are any differences. Exactly the same! Andrew

Re: 286 motherboard repairs

Posted on 2022-02-23, 19:55

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Post 7 has been run. I get 81,01 82,02 83,03 84,04 85,05 86,06 87,07 88,08 89,09 8A,0A 8B,0B 8C,0C 8D,0D 8E,0E 8F,0F Then it loops. Andrew

Re: 286 motherboard repairs

Posted on 2022-02-23, 18:44

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Right, I've tried POST 6. I don't get a code and its binary opposite on the card at the same time, but it does seem to be a regular, repeatable pattern now. The code on the 2nd pair is always the code that was on the 1st pair the previous time, I.E. AA,00 - FF,AA - 55,FF etc So, now the codes in …

Re: 286 motherboard repairs

Posted on 2022-02-23, 07:09

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

This is the latest version of POST 4 https://youtu.be/5PRavSbwt9w And the latest version of POST 5 https://youtu.be/L-G-y5c7Cz4 I had a quick play with a 1k resistor and the unidentified pin headers. No joy so far, but I'll have a better look some time. I should also have said in response to your …

Re: 286 motherboard repairs

Posted on 2022-02-22, 17:28

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Nope, that actually failed the sanity check. The first code should be C003, not C0--, which mean the first write failed to register on the POST card. That really should not happen, I've been using similar code on 386 and 486 mobos without such issues. But I do know the POST cards can be slow to …

Re: 286 motherboard repairs

Posted on 2022-02-22, 06:46

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Next update! Even with pin 10 pulled to ground on the two sockets that the 8237's go in, nothing. - Gently pry other 82C20x chips out of their sockets and re-insert them. We need them all, but perhaps a bad contact is preventing correct operation? Unless you already did that. They have all been …

Re: 286 motherboard repairs

Posted on 2022-02-21, 21:25

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Videoing works fine for me, makes it nice and easy to share too. The two other big DIP IC's are; Directly under the two 8237A's, its a SN74LS612N and next to the 8259 its a P8254 "interval timer" I have now removed everything in a big DIP package except the P82C202 and both 8237's, as once they are …

Re: 286 motherboard repairs

Posted on 2022-02-21, 05:44

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I've run the latest one you posted up Deunan, rather than typing out what I get, I've taken a video of it. https://youtu.be/kC70e06ZmBU The 0.25 playback speed makes it so much easier to keep track of whats going on!!! Andrew

Re: 286 motherboard repairs

Posted on 2022-02-19, 17:16

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

So, POST 4 , I get; 01,-- 02,01 04,02 08,bb (66?) 10,08 20,10 40,20 80,40 01,80 02,b9 (69?) 04,02 08,04 10,08 20,10 40,66 80,40 01,80 02,01 04,02 08,bb (66?) So, that doesn't tie up at all with what you said I should see. My understanding though is that the first 2 characters on the post card are …

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