Yeah, MC1489P and MC1488P are definitely busted.
Fortunately, I have replacements amongst my spare parts.
If I have the time, i'll swap them out this weekend, otherwise it will happen next year.
Update: I actually managed to swap the chips today.
And let me tell you, it's extremely difficult to desolder thru-hole components on this board.
Normally, I have no problems soldering on multlayer boards, but I had a lot of trouble with this one.
However, in the end, things turned out better, than I expected, but I still did a terrible solder job.
Sadly I managed to rip off a smd capacitor during the process.
It's C46. Can someone, who also has this board, please meassure it's capacity for me?
I'm starting to notice a pattern here. First I blew up that poor chip, then the cabel got destroyed and now this.
I'm a bloody idiot. No matter what I touch, it always breaks. How can a person be this clumsy?
Today, I overestimated myself way too much. Silly me.
On the bright side, I now have a reason to practise how to solder, before working on boards like this again.
Wilius wrote on 2020-12-27, 00:36:Update: I actually managed to swap the chips today.
And let me tell you, it's extremely difficult to desolder thru-hole components on this board.
That's a common problem. The biggest issue are the supply and ground pins, because they are directly connected to big power planes in the inner layers. I like the joke question: "How do you call a heatsink for soldering joints?" - "Groundplane". As the groundplane pulls away the heat from the groundplane quite quickly, your only chance is to apply heat even faster than the groundplane is able to pull the heat away, which essentially means: Don't be afraid of too much power! If you use too low power, you are just heating the whole thing up, without getting the sondering joint hot enough to clean it up. If you use a classic soldering station, you need to be aware that the temperature sensor measures the temperature at the heating element, and controls the temperature there. The temperature at the tip will be lower. If you are soldering a supply connection on a through-hole chip on a PC mainboard, the temperature at the tip will be considerably lower. Use the biggest tip you have (in case you have multiple tips), because heat resistance in the tip is an acutal issue. Don't be afraid to turn up the temperature to 400°C if desoldering is difficult at lower temperatures. Adding fresh solder with flux helps a lot sometimes. But if you turned up the temperature to 400°C, and you first wet the tip with fresh solder, the flux is burnt before it helps you desoldering, so the better way is to put the soldering iron from one side to the pin you want to desolder, and put the fresh solder from the other side agains the pin. If the solder doesn't melt, the soldering joint is not hot enough yet. Either you need to wait some seconds until the ground plane is heated up a bit more, or you just need more heat. In case you use an unregulated iron (which I wouldn't recommend for delicate electronics soldering), don't even start below 30 Watts! Also make sure your soldering tip is clean. You need solder as "heat conductor" between the tip and the soldering joint. Just touching the PCB without any liquid solder between the tip and the PCB will not work. For the heat conducting to be effective, the solder needs to stick well both to the PCB and the tip. It won't do so if the tip is not in good shape. For the PCB, it might mean adding fresh solder, so it mixes with old corroded solder, suck it away, and repeat the process. The dull layer on top of old solder is a good heat insulator.
If components are known to be blown, a common way of removing a chip is cutting all the pins with a small side-cutter, removing the chip, and finally desolder the pins one-by-one. This does away with the problem that you need to either completely drain all the connections, so the pins are free to be removed, or you need to heat all the connections at once.
Wilius wrote on 2020-12-27, 00:36:However, in the end, things turned out better, than I expected, but I still did a terrible solder job.
Sadly I managed to rip off a smd capacitor during the process.
Shit happens. And if all damage you created is ripping off a capacitor, it's a very easy fix. Even if you damaged a trace going to the capacitor, fixing that trace with a bodge wire is not a problem at all.
Wilius wrote on 2020-12-27, 00:36:It's C46. Can someone, who also has this board, please meassure it's capacity for me?
That's a good approach. You also could try to reverse engineer the circuit around the capacitor and have a good guess what value that capacitor might have had. For example, if it is directly connected to +5V and GND, it's a so-called "bypass capacitor" to stabilize the power supply for the ICs. It was common those days to have bypass capacitors distributed over the whole board to make sure the power is stable everywhere. If C46 is a bypass capacitor, it most likely a 100nF multilayer ceramic capacitor. Those are extremely common and dirt cheap. Your computer will most likely work (quite) stable even with some bypass caps missing.
Wilius wrote on 2020-12-27, 00:36:I'm starting to notice a pattern here. First I blew up that poor chip, then the cabel got destroyed and now this.
I'm a bloody idiot. No matter what I touch, it always breaks. How can a person be this clumsy?
Today, I overestimated myself way too much. Silly me.
Please don't be too hard on yourself. I also see a pattern, but it paints your work in a better way. First you blew a rare component due to carelessness. This is idiotic, but you can't change it. Then, while trying to fix it, things don't go along smoothly, but in fact it gets better every time. You managed to obtain a replacement for the BIGJIM, and you managed to swap that chip and some other burnt components. That's great! Then you had your puppy destroy a cable, and as there was no damage directly at the connector, so you don't necessarily need to source spare parts. That's a much less severe problem. You also solved this problem. Finally, the only problem thats remaining is a single missing SMD capacitor. That's a component you can pull off any broken electronics board your might have at home, and one can solder such a capacitor within minutes. So every new problem you have is a smaller problem than you had before; while you don't reach the goal as fast as you intended to, you are still making progress.
Don't worry about the board looking ugly after the repair attempts. If the case of the computer is closed, no one is going to see the board at all. I hope all works out well in the end and you can enjoy a board you fixed yourself and learned a lot about it in the process.
Wilius wrote on 2020-12-27, 00:36:On the bright side, I now have a reason to practise how to solder, before working on boards like this again.
If it makes you feel better, I recently got issues with desoldering on a computer board, too. A friend had a 386SX mainboard with broken SIMM sockets (those bloody plastic clips...), whereas I had a 386DX board that was already declared a donor board, which had nice SIMM sockets with metal clips. So I took out my cheap heat gun from a home-improvement store (I don't have a hot air rework station) to desolder the SIMM sockets from the donor board, and it worked out quite well. As soon as the board got hot enough, the SIMM sockets just fell out, with minimal damage to the board and no damage to the sockets. Then I tried the same thing on the target board. The first mistake I made was trying to protect other parts of the board using aluminum foil. It was not mounted firmly enough (maybe I should have glued it to the PCB using sticky kapton tape - if I had some), and the hot air (those simple hot-air guns always put out a lot of air) got under the foil that was wrapped around the edges of the board, and heated some components on the component side even more than they would have been heated without that foil. Luckily, it was only DIP sockets for DIP RAM, we were not going to use them anyway, so these sockets got removed in the end. Furthermore, the SIMM sockets just didn't fall out, even with more heat than I used on the donor board. Instead, the layers of the board started delaminating. It turned out that SIMM sockets have 30 soldered pins and 2 plastic pins for stabilization and orientation. The target board hat tighter holes for the plastic pins, so even with the solder melted, the sockets stayed in the board because the plastic pins were clamped inside their holes. In the end, I got the whole stuff working, but I accidentally removed around 5 resistors and 10 capacitors that needed to be reinstalled as well as all the bypass caps for the DIP memory sockets. Removing the DIP sockets turned out to be as difficult as removing the SIMM slots. This time, because DIP sockets are not heavy enough to readily fall out of the board if the soldering joints melt. The board doesn't look pretty, no replacement sockets were soldered into that board (and the split 14/16 pin sockets used for the parity chips are not easily obtainable), but the board works fine with 8 new SIMM sockets that properly clamp the memory modules, so mission accomplished.
I am confident that even if it looks like you made a big mess now, you will also be able to fix your board in the end.
Emu10k1 wrote on 2020-08-10, 00:53:Mine its an AT40...
Excuse me, could you dump BIOS of your system for me? I see in your photos that this is v2.03. I have v2.01a but it stuk with XUB@NIC when system cofigured for 12.5 MHz. A newer version may solve the problem.
Lyawon wrote on 2021-03-29, 17:22:Emu10k1 wrote on 2020-08-10, 00:53:Mine its an AT40...
Excuse me, could you dump BIOS of your system for me? I see in your photos that this is v2.03. I have v2.01a but it stuk with XUB@NIC when system cofigured for 12.5 MHz. A newer version may solve the problem.
Someone in the MAME project contacted me about this too sometime ago, it seems that its the only version of the bios thats still not dumped. I should have done it right away when I measured the PSU for that user that asked for it... but life has its own ways to ensure that there is no free time left for the hobby.
Please, ask me again in two weeks or so, i cant really get to the machine right now. I planned to do it with an eeprom reader, but someone told me to use the debug command on DoS to dump it. While you wait, you could try to dump yours and tell me what values to use. That way i wont have to guess it out when i get to it.
Emu10k1 wrote on 2021-03-30, 11:36:... but someone told me to use the debug command on DoS to dump it. While you wait, you could try to dump yours and tell me what values to use. That way i wont have to guess it out when i get to it.
Here is DOS debug method:
Downloaded from this forum.
I'll check it in few days but dr.zeissler succesfully uploaded several dumps of the BIOSes from Schneider Tower systems so it should be correct.
Lyawon wrote on 2021-03-30, 21:49:Here is DOS debug method: GETBIOS.ZIP Downloaded from this forum. I'll check it in few days but dr.zeissler succesfully uploaded […]
Emu10k1 wrote on 2021-03-30, 11:36:... but someone told me to use the debug command on DoS to dump it. While you wait, you could try to dump yours and tell me what values to use. That way i wont have to guess it out when i get to it.
Here is DOS debug method:
GETBIOS.ZIP
Downloaded from this forum.
I'll check it in few days but dr.zeissler succesfully uploaded several dumps of the BIOSes from Schneider Tower systems so it should be correct.
Just have checked DOS debug method on my Schneider. I've dumped BIOS by debug command and then compared the dump with EPROM ICs content using universal programmer. They were identical.
Lyawon wrote on 2021-04-02, 21:50:Lyawon wrote on 2021-03-30, 21:49:Here is DOS debug method: GETBIOS.ZIP Downloaded from this forum. I'll check it in few days but dr.zeissler succesfully uploaded […]
Emu10k1 wrote on 2021-03-30, 11:36:... but someone told me to use the debug command on DoS to dump it. While you wait, you could try to dump yours and tell me what values to use. That way i wont have to guess it out when i get to it.
Here is DOS debug method:
GETBIOS.ZIP
Downloaded from this forum.
I'll check it in few days but dr.zeissler succesfully uploaded several dumps of the BIOSes from Schneider Tower systems so it should be correct.Just have checked DOS debug method on my Schneider. I've dumped BIOS by debug command and then compared the dump with EPROM ICs content using universal programmer. They were identical.
Could i ask you what values did you pass to it? I dont want to end up with only half a bios dumped just because I passed the incorrect address to it.
Next weekend (10/4-11/4) i´ll have access to that computer. ill post it in this thread for archive purposes : 80286 BIOS image collection.
Emu10k1 wrote on 2021-04-03, 12:15:Lyawon wrote on 2021-04-02, 21:50:Lyawon wrote on 2021-03-30, 21:49:Here is DOS debug method: GETBIOS.ZIP Downloaded from this forum. I'll check it in few days but dr.zeissler succesfully uploaded […]
Here is DOS debug method:
GETBIOS.ZIP
Downloaded from this forum.
I'll check it in few days but dr.zeissler succesfully uploaded several dumps of the BIOSes from Schneider Tower systems so it should be correct.Just have checked DOS debug method on my Schneider. I've dumped BIOS by debug command and then compared the dump with EPROM ICs content using universal programmer. They were identical.
Could i ask you what values did you pass to it? I dont want to end up with only half a bios dumped just because I passed the incorrect address to it.
Next weekend (10/4-11/4) i´ll have access to that computer. ill post it in this thread for archive purposes : 80286 BIOS image collection.
Emu10k1, all you need is in the archive attached by me previously. You have to run getbios.bat (the commands for debug located in getbios.txt). As a result you will get three files: two halves (F000.BIN and F800.BIN but they aren't EVEN and ODD, just first and second part) and BIOS.BIN - the full dump (64 kB).
I looking forward to the BIOS v2.03 dump from you.
The BIOS v2.03 have user type for HDD but v2.01a - is not.
Hello and Excuse me.
I know I havn't posted for a while, but this has a reason.
I'm surprised, that there's still activity on my thread.
Anyway, I digress. I just wanted to say, that I gave up my project completely.
The reason is quite stupid. Earlier this year, my window just decided to shatter in pieces and snow got inside.
The fact, that I wasn't at home and nobody noticed, when this happened is beyond me.
My entire room was covered in water, after the snow melted.
Luckily, things are looking good for me. While the water caused some damage, we managed to remove everything from my room and dried it out before mold could form. A lot of furniture got soaked in moist pretty badly. Fortunatelly, we managed to rescue most of my furnitur, except for one drawer. And here's the thing. Of all things that could have been destroyed, it was the drawer, where I stored some of my miscellaneous PC parts. Because, I was too busy clearing/drying out my room, I didn't pay attention to the stuff, which was stored in the drawer. Therefore a lot of PC parts, including the Schneider PC, started to rust. Some of the parts were destroyed beyond repair.
The damage on the Schneider PC is only minor, but it is enough for me to give up hope.
Not paying attention to my drawer was the most stupid thing i've ever done. I pretty much regret this. But there's no going back. It sucks, but I can live with it.
I gave the ruined parts to a friend, who hopefully can use them as spare parts.
Feel free to continue this thread, but I hope you don't mind, that I abandoned this project. On the bright side, I have now time to focus on other projects.
Still, I feel very sorry for wasting everyone's time. This is just embarrasing. Nothing of this was planned.
Lyawon wrote on 2021-04-03, 18:53:Emu10k1, all you need is in the archive attached by me previously. You have to run getbios.bat (the commands for debug located i […]
Emu10k1 wrote on 2021-04-03, 12:15:Lyawon wrote on 2021-04-02, 21:50:Just have checked DOS debug method on my Schneider. I've dumped BIOS by debug command and then compared the dump with EPROM ICs content using universal programmer. They were identical.
Could i ask you what values did you pass to it? I dont want to end up with only half a bios dumped just because I passed the incorrect address to it.
Next weekend (10/4-11/4) i´ll have access to that computer. ill post it in this thread for archive purposes : 80286 BIOS image collection.
Emu10k1, all you need is in the archive attached by me previously. You have to run getbios.bat (the commands for debug located in getbios.txt). As a result you will get three files: two halves (F000.BIN and F800.BIN but they aren't EVEN and ODD, just first and second part) and BIOS.BIN - the full dump (64 kB).
I looking forward to the BIOS v2.03 dump from you.
The BIOS v2.03 have user type for HDD but v2.01a - is not.
Got to it a week faster than expected.
Re: 80286 BIOS image collection
Hope its useful. Enjoy!.
Oh wow, I totally missed this thread. Glad you got the PSU working, but sorry that the PC ended up damaged due to all the other issues.
I think I eventually managed to figure out what the “unknown” pins were in my original PSU connector schematic but never got around to updating it. I’ll try to do that since it seems to be more useful to other people than I expected.
Emu10k1 wrote on 2021-04-04, 18:41:Got to it a week faster than expected.
Re: 80286 BIOS image collection
Hope its useful. Enjoy!.
Thank you so much!
I've burnt onto EPROMs and have tested my VGA Tower System 40 tonight. It works=)
Unfortunately it doesn't solve my XUB@NIC problem. Anyway v2.03 gave me the ability to use "user type" for HDD.
