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Trying to repair an IBM 5160 System board, could do with some input

One longshot thought. You say you are bread-boarding this w/o a chassis? What about proper grounding? Ground the metal chassis of the floppy, metal cage of the power supply to the metal ground of the motherboard like the keyboard jack area. I forget if the XT has any motherboard ground screws or just the nylon pins. Your display is not near the floppy ribbon is it?
 
gave it a go, no luck unfortunately same issue, and the floppy cable isn't anywhere near the display no, but surely if that was the only issue the other board wouldn't work either? I guess things could be on the edge. the only possible thing I can think right now is something to do with U10, its on the floppys DMA line and its right next to the other chip that was dead and has the same dark tarnishing to its pins, though Im not even sure what its doing apart from that it must have something to do with dma, maybe I should try and boot to something else other than a floppy? something that uses a different DMA line? I do have an XTIDE card but I need to bootstrap it with a floppy first to install the firmware, which I cant do on either board, I will try to set it up in the 5170 I also got with the 5160 that has at least got a working mainboard and see If I can get it to boot (I got it broken for 99p on ebay, so even with the new flash chip it still may not work)
 
What about the four ground wires on P8 and P9? Don't they count for anything?


for grounding the power yes, but I get where he was coming from, a good ground plane across all devices really helps remove noise from any electronic system.
 
Humor me one more time. You say it was the last gate where the drop in CLK amplitude was? What is the Vcc on pin 14? That's U74? It should be >4.5 and hopefully 5V. You could scope the signal lines on U10 for good 5V signals. Hmmm, U10 is fed by U74 ...
 
Sorry if this is a stupid question - but have the floppy drive and cable in question been tested in another system? Or another type of drive attempted? (even a 3.5" 1.44 drive would do for this test - and you can boot these). I'm just not sure I noticed this being covered off earlier in the thread.
 
Sorry if this is a stupid question - but have the floppy drive and cable in question been tested in another system? Or another type of drive attempted? (even a 3.5" 1.44 drive would do for this test - and you can boot these). I'm just not sure I noticed this being covered off earlier in the thread.

Yes, I tried the drive and controller on another 5160 board (keyboard doesn't work on it but it still reads the FDD) and it works fine on that board I can even fully boot and use DOS from that drive and controller on a 486 board I have(when I disable the onboard controller on it of course) , I have also tried a different controller card with the same result.

Humor me one more time. You say it was the last gate where the drop in CLK amplitude was? What is the Vcc on pin 14? That's U74? It should be >4.5 and hopefully 5V. You could scope the signal lines on U10 for good 5V signals. Hmmm, U10 is fed by U74 ...


5.4V on VCC and I have looked at the signals on U10 but the majority of the pins are on the address and data bus so there is a lot of activity anyway but no real way to see from where, there is a v4.48V signal on the pin from U74 though
 
Nothing real definitive. Could replace U10 and/or U74 but ??? However, I've learned from my real job in IT hardware support that passing diagnostics is not a sure thing.
The proximity of a known bad chip is a good possibility.

Larry G
 
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I think I'm gonna try U10, will have to order one though so will take a bit of time. the xtide was a bust, it will boot with it, it comes up with the xtide BIOS, booting to the floppy from that produces the same result of the system hanging on read, and booting from the xtide... well, I tried 15 different IDE HDDs ranging from 40MB to 160GB and it didn't recognise even ONE of them! the ONLY IDE device I could get it to recognise was a 128MB DOM (which happened to have XP embedded on it so it wasn't going to boot as is) only problem is, I can't format it, while it was the ONLY IDE device recognised by the xtide, the xtide was the only thing to recognise the disk! all other IDE interfaces on any machine ranging from a 486 to a core 2 duo just see nothing when its connected! I can see the device on my 5170 in the xtide and fdisk sees one dos partition of 3MB and one non-dos partition of 120MB but since fdisk can't remove a non-dos partition I can't do anything with it. if I DO try booting from it on the 5160 I get the message "missing operating system" which is obviously true but I'm not sure if this says anything, as its either from the xtide BIOS, the 5160 BIOS or the boot sector of the disk, if the message IS from the boot sector, maybe that says something about what's working? if it can at least read a boot sector from a fixed disk?
 
....it comes up with the xtide BIOS, booting to the floppy from that produces the same result of the system hanging on read, and booting from the xtide... well, I tried 15 different IDE HDDs ranging from 40MB to 160GB and it didn't recognise even ONE of them! the ONLY IDE device I could get it to recognise was a 128MB DOM.....

Just curious What "XTIDE" card do you have ?, If it's the Lo-Tech ISA CF Card it'll work with CF / Microdrive or DOM and probably ATA-2 compliant hard drives.
 
it is one of those yes, its just I'd assumed out of my random pile of IDE disks at least ONE would have supported ATA-2 is all. and I believe I have worked out now why the DOM only works on the XTIDE, it takes power from 5V on the IDE key pin, which no normal IDE controller provides, guessing from what I have found online here but seems likely, when I get home ill try providing that and formatting/installing dos on another machine and see if I can get the 5160 to boot from it.
 
Ok, getting somewhere, I finally managed to install an OS on the XTIDE (will install but can't be booted from with the original PC DOS 3.00 I have, had to mess around a lot to get a 5 1/4 " 360K msdos 6.22 boot disk to do it) and when I put this into the XT I can boot into DOS! and can even run programs without a problem from the fixed disk, now when I try to switch to the FDD (i.e. typing "A:") I get the same issue, the machine just locks up, except for the very first time when I tried this when I just got "divide overflow" so the machine works and can run programs from the fixed disk but just can't read the floppy even though the controller and drive are definitely working, this has to mean something? I have already ordered a replacement for U10 and as I said I already happened to have replacements for the DMA controller on hand but I really feel like i'm stabbing in the dark here, the issue may not have anything to do with DMA, does any of this give someone here any idea? is there something I can do from within a working dos install to try and shed some more light on this?
 
Ok, one more thing, I decided to try some other cards in the machine and set up a sound blaster 2.0 on the AT and got that working on the xtide, when I put it in the XT and try to run a program that uses it I get exactly the same issue as I get with the floppy controller, the machine just locks up as soon as it is accessed, so the issue is something used both by a standard IBM floppy controller and a sound blaster 2.0 (specificly I used the midi player PLAY.EXE that comes with the card), so it definitely sounds like its DMA? but that's used by the DRAM refresh too... could it still be an issue? could it be the interrupt controller?
 
ok right, definitely DMA there is a diagnose.exe for the soundblaster that tests all the parts in turn, address 220 , successfully found, irq 7 successfully found, dma channel 1, error dma channel not found, so IRQs are working (and the address but we already knew that for the other cards to work) the issue must be DMA related yes?
 
Wow that's some progress !! I was thinking the hard drive would also use dma but from what I read it depends on the controller. Does XTIDE manual indicate dma is used? I assume not.
Odd that your diagnostic rom indicated dma ok, but dma has several modes so maybe rom can't test all modes. Can you get diagnostic software on your hard disk via putting in the other pc?
Maybe others could suggest the best diagnostic to use for dma testing from DOS. Maybe hammering dma with diagnostics while scoping the pins will reveal a problem.

PS - actually I could compare waveforms on my 5150 which also uses the 8237. I have more fun doing this to a pc than actually using it !!!

Larry G
 
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XT-IDE does NOT use DMA due to how the 16-to-8 bit bus conversion is done. It's solely based on IO polling, and the port you poll alternates between two ports for every byte read. This way you can read both the hi and low byte of 16 bits over the 8 bit bus.
 
Wow that's some progress !! I was thinking the hard drive would also use dma but from what I read it depends on the controller. Does XTIDE manual indicate dma is used? I assume not.
Odd that your diagnostic rom indicated dma ok, but dma has several modes so maybe rom can't test all modes. Can you get diagnostic software on your hard disk via putting in the other pc?
Maybe others could suggest the best diagnostic to use for dma testing from DOS. Maybe hammering dma with diagnostics while scoping the pins will reveal a problem.

PS - actually I could compare waveforms on my 5150 which also uses the 8237. I have more fun doing this to a pc than actually using it !!!

Larry G

yes, I can transfer files to it, by copying files to a flash drive, putting that in my XP core 2 duo machine with a 5.25" FDD in it, copying the files to a 360K disk (both that drive and the AT's drive are 1.2MB but I only have 360K disks), putting that disk in the AT, booting the XTIDE in my AT, copying the files over to the XTIDE, then disconnecting everything from the AT, connecting it all back to the XT and booting the XT, so easy! but yeah I can copy stuff over with no issues if someone can point me to some diag software. and as for that last part, I understand! when I actually get it working I probably wont spend nearly as much time on it! (I will spend some of course!)

on another note I got the other XT motherboard I got on ebay working now! I was right about it, it just had U27 dead (interestingly BIOS version 1 still give a RAM error code, but runs anyway, V2 gives a floppy error code, but boots from it anyway but V3 works fine so I'm using that on it) I connected that up to the XTIDE and the floppy works on that board I ran the soundblaster diagnostic.exe and on that machine it reports the DMA as found successfully! so it really IS DMA on the other board that's wrong as this is an identical board (almost, this one has a chip in the "spare" slot and the other doesn't) interestingly enough though, it still doesn't actually work in that machine, the same thing as happens on the other board happens on this one if I try to play anything with the card, it just hangs, is the SB 2.0 just not compatible with the 5160? it works in a 5170? could it just be that it needs more RAM? I only have 256KB in the XT
 
Well, huge success! I have finally got the mainboard working! the final issue was U11, though I only found it after having replaced U10 and U28, luckily I had managed to remove U28 without damaging it (lots of solder wick applied to the pins of the IC on top rather than the board) so I just put the original back in the socket I added to the board.



That means the final damage on that board was:-

-U20 (parity calculator in RAM circuit) failed so board always gave parity error even with known good memory.
-U11 (octal latch in DMA circuit) failed so board passed DMA controller test but hung on any (non-RAM refresh) use of the DMA, for example reading from a FDD.
-(multiple) 6 4164 DRAM ICs failed and gave memory errors.

for anyone's reference the board was a 64-256KB SYSTEM BOARD and came with the V1 BIOS installed.



well, I must thank everyone here who gave me a hand on this, I probably wouldn't have got this far without you! and while I haven't finished restoring this machine by a long shot, the mainboard is fixed and the other problems are for another thread!

oh, and the SB 2.0 still doesn't work in this board either, even though it finds its DMA now, can't work that one out...
 
Awesome work, I love threads like these.

RE: SB2.0 - make sure it's set to IRQ 7 (not IRQ 5), and make sure to set your blaster variable (SET BLASTER=A220 I7 D1 etc).
 
Great !! Quite a compound set of failures. It would be interesting if your 6 DRAM chips were actually good since there were other failures involving shared address and data lines but those chips are cheap so best to leave well enough alone.

Larry G
 
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