Trying to revive a dead Amiga 2000

hi everyone welcome back to adrian's digital basement on today's video i'm going to be working on an amiga 2000. this machine was donated to me from a viewer named andy and he told me that the machine had suffered battery leakage which is really common for these machines and it was no longer working he had taken the machine apart and decided after looking at it that it was beyond his ability to fix so he donated the machine to me now i started working on the machine and i didn't think i was going to make a video because there's already a ton of really good videos out there on fixing amiga 2000s that i've had battery leakage but as i started working on this machine i found that there was maybe some stuff that would make an interesting video because i was trying some new techniques on the corrosion and then i had to do a bunch of troubleshooting and fixing to get the computer working so where this video begins i'm already part way through the cleaning process when i realized i probably should make a video on repairing this computer so anyways let's get right to it [Music] so on the amiga 2000 motherboard the battery which is right here very commonly leaks if it's old and discharged for a long time it's a nickel cadmium and of course it leaks its gunk all over the motherboard in this area here's the cpu socket this is the rom and keyboard port here along with the mouse port and then this slot here which you see this purple stuff on it this is the accelerator slot for the cpu upgrade a telltale sign of leakage is that you see this green crustiness all over the socket now you're not seeing it on this one because i've actually already dealt with the problem i soaked this area of the motherboard in vinegar and what i do is because i don't want to soak the entire motherboard in vinegar as i lay paper towel strips over the parts that have been exposed to the electrolyte like on the rom socket here and of course the cpu socket and i pour vinegar on it and i let it sit there for quite a few hours and it has the effect of getting rid of a lot of the corrosion now when you take a close look at the cpu socket though you'll notice that there's some permanent damage on this socket and there's no way this computer is going to work anymore without at the minimum replacing this socket notice that the dual wipe contacts on the cpu socket a bunch of them are broken now so if i stuck a cpu into there even a good cpu it just wouldn't make good contact you're probably asking what is this purple liquid that i have poured over the cpu expansion slot now just like the cpu socket and the rom socket and some other stuff around here there was a lot of this green blue corrosion on the gold fingers that make contact with the card that you plug into this slot and even though i put vinegar with paper towels over this for just as long as this cpu socket and the rom socket it didn't seem to really get rid of any of that blue-green corrosion at all and i really wanted to clean that up before i try to get this computer working and plug an accelerator card into this slot now what i've gone ahead and done and this might be the wrong thing or the right thing i don't know is i've poured this navel jelly which i normally use to dissolve rust on iron and steel parts onto this connector and what's nice about this stuff is it's a really thick viscous pink color gel so when you pour this onto areas you it sticks to it and it doesn't just immediately pour off and kind of run off the edges of the board this is what happens with vinegar which is why i take pieces of paper towel and the paper towels kind of keep it in the appropriate areas a couple hours ago i poured this onto the entire slot so now i want to wash this off and see if this had the effect of getting rid of the blue-green corrosion incidentally on this motherboard there was a lot of the blue-green corrosion on the keyboard connector and on this mouse port but wrapping the paper towel around this with the vinegar seemed to have cleaned off the corrosion off of both of these the board is still wet because i just washed it off in the sink but there is no blue-green corrosion left on this connector i don't see anything at all now i'm assuming where the corrosion was now that it's gone because of the navel jelly it's probably bare copper because the plating usually gets eaten away and that's what the corrosion comes from so i'll probably have to make sure that i keep deoxide on this because it creates a sort of a film a little bit of a barrier to prevent corrosion now this were a normal trace that was exposed copper i would just paint over that with a lacquer of some kind or a pcb paint but you obviously can't do that on these fingers because they need to maintain their connectivity and their contact with the cards you plug in there so i think the best thing will be for this is once it dries deox it of course it goes without saying the cpu socket will need to be changed as well the rom socket on the other hand seems like it's going to be fine i am noticing in the back of the mouse port there's still some corrosion there so i think i'm going to turn the board up on its end like this and put some navel jelly right into the port there hopefully knock that out as well so first i want to do the smoke test the power supply is connected of course there's no cpu or accelerator so the computer will not work it is plugged into the video output let's just see what happens if i turn this on now i assume you get some kind of a video signal yeah it looks like it's synced up because you know i have the entire chipset installed just no cpu so okay no smoke is coming out of anything here is a commodore 2630 this accelerator card was actually installed in this machine so unfortunately it suffered the corrosion issue as well all that green corrosion that was on the accelerator socket i already cleaned this up by soaking this part of the board in vinegar and then i sort of scraped away any of the corroded solder mask and then put lacquer over it a couple fingers had bad plating so i've actually re-tinned those and on the back there's a similar story although it's a little bit worse because there was actually a bad trace from this finger to its nearby via so i added a barge wire and then i tin these and looks one of the fingers is partially broken off there but it doesn't cause a problem i've already tested this in another computer and this this board works perfectly so let's put this accelerator in there it is let's just bend the wire so it's not getting pushed on by the power supply and now place your bets for what's going to happen there's no cpu installed on the motherboard but the accelerator card which works is in the socket there might be bad traces it might not work because the cpu there could be a lot of things but let's just turn it on see what happens here we go i'd say we have a computer that is not booting properly i've hooked up an led which i'm holding right here over the accelerator car to the motherboard so let's see what happens we'll be able to see if this changes brightness which may indicate the computer is trying to boot here we go there would be no change to the led which would indicate that this computer is not executing any code right now incidentally on this computer i haven't tested any of the other chips on here any of the custom ics for the amiga chipset so any of those could be faulty actually as well but because i really need to be switching this socket out anyways because i know it's bad i might as well do that first before i do any of the other testing because switching this out and putting the original cpu or a 68 000 back in maybe we'll make this computer work and i won't need to test these other chips so for efficiency standpoint i just should do the things i already need to do which is change out this socket check out that really nice socket that i've installed there here's what's left of the old crusty socket i kind of cut it up i find it easier to get it out sockets are not as easy to take out as ics at least to me because i can't use my hot air trick to pull the chip out cleanly without you know possibly lifting a trace so i cut it up into pieces and then i work on the little pieces individually even though i had cleaned up the socket with vinegar there was still some of the green corrosion on the underside which may mean that the rom socket also has corrosion underneath it but hey if we have a problem with this then i can always change it later i knew that the cpu socket definitely needed to be changed one thing to make sure when you have the socket off is double check that all of the traces underneath the socket have good continuity between them and the things that they go to because if a trace is bad underneath the socket it's far easier to figure that out and then fix it while the socket is off then after the fact this is the original cpu that was in this thing now it had a lot of green corrosion on it as well now i did sand down the legs with sandpaper both sides this side is just the raw sanding after i did it but this side here i actually tried to apply some solder onto each of the legs wasn't really pleased with how it turned out i mean i guess it's working you don't really see the copper color while you see copper on this side but i'm just going to call this good enough for now at least for testing let's pop this cpu in the notch is down here while i was working on the board i also pulled out the old residual bits of the battery that were in there it was just cut off so the little legs were still in there so i did that and then i added two pins as well and then i applied clear locker to anything that was exposed copper in this area i know lots of people have suggested that i use pcb paint that's green color well i've ordered some from china and you know due to what's going on in the world right now it still hasn't arrived it's been forever so i will continue to use my clear locker which yes is nail polish but it's basically good enough i've never had a problem with it you might notice i have the oscilloscope out on the bench and that's because i anticipate that this is not gonna work and we're gonna have to do some troubleshooting so here's the amiga 2000 power supply let's plug this into the power connector here make sure i don't misalign it there we go this cable goes to my 1084 monitor which is just over here to the left and this is the original rom that was in this machine along with all the other custom ics i put everything back in that was original this is a 2.04 rom it looked a little corroded but i cleaned up the legs on this one a bit too and stuck it back in and that is the original socket and here's the green led i just stuck it right there so we can take a look at that when i power this on all right and we are ready here we go where's the power switch here it is just like before dead just in case anyone's wondering if there's this is on the right input or whatever it is because right now i see a faint line at the top of the screen that's because i've shrunk the picture down and i'm seeing what's normally off the top and this monitor always shows that at the top of an ntsc picture kind of like a little rgb line there i don't know what it is maybe it's these 1084 monitors always do that but it's actually a good tip because now when i turn this off that line goes away so i know this was generating a video signal to this thing but of course we were getting nothing power led also was just solid on so we're having exactly the same problem as before when i had the co-processor card in there without the original cpu so now for testing i am armed with the 68 000 pin out and i'm going to check the basics we need to check the reset signal and the clock here's the clock signal that looks good it's a little over seven megahertz that's great and here's the reset signal which should stay low and then go high once the system is running there it is it was low to high perfect next let's check one of the address lines just to see if there is activity okay so oh no there was a split second and right now that indicates that the address bus is high impedance so basically it's in a tri-state configuration right now where the processor is not trying to drive the address bus i'm going to pick a different random address bus same thing it kind of went high for a split second and then went back to high z so i just checked all the data bus lines and all 60 of them are high but on this particular motherboard this is a version 4.4 they're all pulled high so even if the cpu is not trying to drive them they will be high but the address bus in their hand is not pulled high so the fact that we're just seeing floating lines here indicates that nothing is driving the address bus right now now the next pin to look at is the halt pin let's take a look at this this is active low so when it's held low the cpu was halted up it went high for a second and then instantly went low now on the 68000 the halt pin can either be an input or an output if the processor detects a problem like say bus contention it will halt itself to protect the chips on the board from shorting against each other or also one of the chips on the board can actually instruct the processor to halt as well which basically just stops it from executing after it finishes what it's doing so it's not unusual for the hull signal to go into the processor but the fact that it's just solid low indicates that the processor is definitely not executing any code right now and that explains why the address bus is floating and the data bus is just high with no activity because when the processor is halted whether it halts itself or something else holds it it disconnects itself from the bus entirely address and data bus it's it's the almost the equivalent of the processor chip just being removed from the socket entirely now i need to figure out if the processor is halting itself or something on the board is telling it to halt so i'm thinking that a good way to do that is actually to just take it out of the socket and i'm going to bend out the halt pin out of the socket so it's floating outside and then i can actually just measure that pin versus what i see on the socket and then that will tell me if the processor is halted itself the pin will be low but the input on the socket will should be high i'm definitely wary about bending pins on this cpu because the the legs are so corroded already i'm a little afraid that if i do it carelessly and enough times i might just break the entire leg right off i have a replacement cpu but i'd rather just keep this original one if it's working all right the leg is bent out let's power this back on it's not going to run i'm sure it might if actually if something's halting the processor no we're still getting a black screen so first of all let's check the output of the processor on the hull pin so it's low and actually if i turn this off and turn it back on let's see what happens so it just stays low entirely now i can stick the probe past the pin into the socket and look at that it's high let's turn the power off and on so it's load right now and then it goes high as the computer comes out of reset and yet the processor itself is low right now which means it has halted itself it is not being instructed to halt when you look at the data sheet for the processor it halts itself when you have bus errors you have contention errors i'm just going to bend this tip pin back carefully good it didn't break off so right now what i need to do is go look at the schematics for the amiga 2000 or the b2000 which is what this motherboard is and look to see how the address and the data bus is configured on this thing there are lots of things on the address and data bus but i have a feeling on this motherboard it's probably pretty buffered meaning there are 74 ls 245 transceivers between the processor and these various chips so that means if there's something wrong with the address bus like on one of these cia chips it's not going to affect the processor directly because it's on the other side of the transceiver the same goes for the data bus the processor is probably on its own or has a few things on its own local data bus and then the rest of the stuff is off on the other side of transceivers all right sure enough there are six ls245s right here that handle buffering of address and data buses there's also ls244s over here by the ram there's also two more ls245s over here that are doing data bus buffering as well so yes things are quite buffered on this machine what i found is that these buster chip which is this i see up here it's the 5721 this handles all the bus arbitration between the zorro slots and the code processor card and the processor now all of these things can be bus masters meaning that one of the cards in here can take full control of the address and data bus in this computer to do like dma memory access and stuff like that and this chip is what arbitrates all of that and allows that to happen what that means though is that if this chip is having a problem it could be instructing the buffers to do things while the processor is trying to use the bus which would cause bus contention errors and would cause the processor to halt itself so i think a good test is i'm just going to pull the buster chip out of this motherboard looking at the schematics this chip is what makes the zorro two slots work as well as a coprocessor slot but since i'm not using either right now for testing let's see what happens when this is out of the computer if it boots up or if we at least see activity on the bus or or what all right let's see what happens oh hey look at that we got some activity we're getting the green death uh you know i don't know whatever let's see let's turn this off and on that's like what uh it's kickstart 2.0 so that indicates what like a ram error potentially but hey you know what it's actually executing code and the led is flashing so that means code is actually executing on this machine right now excellent now what i happen to have right here is the amiga diagram this is a diagnostic kickstart rom for the amiga it replaces the regular kickstart and offers some nice diagnostics so let's pop this in instead of the regular kickstart here make sure i have it the right way around i don't know what happens if you plug these eproms in wrong way but it might kill them who knows okay pop that in let's power this up now hey that's a good sign that's what this rom does when you first plug it in diagram nice okay i just had to change my frame rate because this is running in pal right now but there we go 68 000 1024k of ram no fast ram of course there's not and this thing worked i'm going to plug a keyboard into the front here and let's see if i can control it yep there we go system info oh this keyboard doesn't work very well the enter key there we go is not good all right yeah i don't know sis info i don't know that's not particularly useful i'm going to run a memory check though let's do two and we're going to do extended shipment tests and we'll let this run through now i do know for a fact that this chip mem test will test from zero to two megabytes and this computer only has one meg of chip ram so once it passes the one meg barrier if we don't see any errors what will happen is we're going to get an address error because the processor is going to try to address memory that doesn't exist so it will crash basically or you know will give us a big full screen address error that happens on all amiga 2000s and 500s that i've ever seen with this picker rom i guess it's just the way it's written i wish i could tell it to only check up to 512k or 2 megabytes sprinting what kind of machine i'm using so anyways let's see what happens we're just about to one megabyte here and it's probably going to crash but so far no ram errors which is a great sign 991k here we go it's about to hit one meg there it is and then it crashed okay so no ram errors though excellent so there's no problem with the memory on this machine so it's definitely weird that we're getting that green screen with that other rom chip now this is the eeprom i burned right and it's working so the socket is fine now it's quite possible this chip which is all corroded on the legs it's just flaky it could be like trying to address like a higher part of memory or something and then it fails i'm going to put it back in i'm going to give it a good push see what happens oh just the back to the green screen again [Music] okay well i have another kickstart rom here this is a 1.3 rom sitting here so let's put this in see if this works any better oh hey oh yeah this is looking good this is this is normal you get the white screen while i was trying to look for a disc i don't have a drive plugged in oh yes look at that it's working all right so i have a floppy drive here and here's amiga test kit boot disc let's pop that in i'll just stick this over here all right here we go will it work it's booting it is booting oh look at that test kit oh it worked sweet and keep in mind this is all with the buster chip removed from the motherboard so that just shows if you have a bad buster chip your computer will work you just won't be able to use your xero 2 or the coprocessor slot so if you have a stock 2000 with nothing in it you don't actually need the buster chip well i'm not sure if anything else is broken but obviously booting software and the diagnostics are running properly with this chip removed so just something to think about the fact that the 2.0 rom does the green screen i'm just wondering if it's the chip that's bad maybe 2.0 is smarter and can actually detect that i don't have the buster chip in there i mean that's possible i suppose i don't know okay so the next logical thing is that this buster chip is bad so i'm gonna go find another buster chip in another machine and try it in this motherboard see if that fixes this problem and no it didn't fix it i tried two other buster chips and the machine behaved in exactly the same way the cpu halted itself due to a bus conflict interesting all right well i guess i need to study the techno manual some more just to look at how this buster chip works or what it's actually doing to try to see what it's controlling exactly and where the issue may be okay so i've made some progress you can see here that kickstart 2.0 rom is working fine now that's the original one the one that i thought was maybe bad causing the green screen no it's actually working now what did i do here exactly well you may notice that buster is installed in the computer right now but i also have this clip lead that goes from here which is actually just picking up five volts and it's going over here to a pin on this ls245 now you might be saying aha bad trace right because that's typical with battery damage not necessarily i can't actually figure out what's wrong when it comes to traces but what was i able to do buster is inserted in the socket but one of its pins is lifted and is not in the socket right now here's a little snippet from the service manual and you'll notice there are two ls245s u604 and 603 and they are buffering or they are transceivers used on the data bus from the cpu to the zorro slots the bd 0 to 15 goes to the slots and there are two signals that come from buster active low dboe and active low d2p d2p is the direction control that controls which way these chips are sending the signal you know from the slots to the cpu or vice versa and then the other signal is the enable signal for these ls245s what i did is i lifted dboe so buster is no longer able to control these chips anymore and then i just hot wired them using this clip lead here directly to five volts which keeps these two chips permanently disabled it's these two right here in the schematics you'll see that the enable pin is tied together so i have it clipped onto one of them but that's actually disabling both chips and when i do that not only does the computer work but with this hot wire in place kickstart 2.0 also works if i remove the hot wire then it will go do the green screen now here's something interesting let's look at that pin that i lifted on the oscilloscope hopefully i'm not blocking the camera the computer is currently running there it is and if i turn this down there's full on activity so buster is commanding those chips to turn off and on all the time which is weird in a way because i don't have any cards installed in these slots but maybe this is normal behavior i'm assuming this is normal behavior because i tried different buster chips and they all do exactly the same thing and then also let's take a look at the direction pin which is the other output that goes to these from buster and it's just solid high five volts it's pulled up to five volts but buster is connected to that pin there's continuity and it's not doing anything so for sure what's happening is buster is turning on these two transceivers and they are trying to drive the bus at the same time the cpu is doing that which immediately creates a bus conflict and then the cpu just goes into halt mode and disconnects itself from the bus to protect the whole computer so it doesn't keep running and damaging itself so i have to ask myself two questions is it normal that buster is trying to instruct these transceivers to drive the bus like that if it is normal then maybe there's something wrong with these two transceivers where when they transition between on and off they caused a bus conflict a very quick and momentary one these were both bathed in a lot of battery leakage so they could possibly be bad sometimes that corrosion can make its way inside of chips and cause issues they don't have any of that blue gunk on them i don't think they ever did but you know i just i don't i don't know what's wrong here just for fun i inserted one of my other buster chips and i lifted the same pin let's take a look at it and yeah we're seeing the same activity on the oscilloscope and the computer is working with that chip pin lifted with it in there definitely same black screen same halted performance so it really feels like the fault has got to be either with what's telling buster to activate those or it's with these transceivers themselves maybe one of these transceivers is bad i forgot to show you something earlier while i was troubleshooting so i'm going to probe the direction pin that's the one that i bent out it's currently back in the socket so everything is operating you know as it should and i'm going to turn this on and i'm going to quickly hit single shot here watch this okay what this captured is buster instructing those to turn on and then i guess around here the cpu has enough and it halts execution entirely which stops buster from trying to turn on those transceivers anymore and we just get these pulses here and every time it goes low it turns on the transceivers and then it stops so that kind of clued me in that that was driving these buffer chips to turn on and that was causing the bus to go into conflict so i'm really suspecting that one of these two 74 ls 245s is bad so what i'm going to do is i'm going to use my cutters here and i'm going to snip the leg and if i snip one of them i'm going to cut half the bus off from causing bus conflicts so if this is the one that's causing issues and i cut the enable pin and i just hold that high using my little clip lead here then potentially the system will run without a bus conflict but if that makes no change i'll put a little blob of solder to reconnect that one and then i'll snip the other one and then if that makes no difference then i think i'm kind of back to thinking that something is wrong with buster or not buster because i know that chip is good i've tried different ones but whatever signals are going into buster that caused this selection to happen is the issue anyways let me cut one of these all right so i've cut the left pin and i'm going to hold this clip on it which is going to hold it high so that chip will stay disabled but the other one will work and let's turn on the computer and nothing same thing we're still getting a bus conflict even though only half of the bus is going into conflict so cutting the lake on the right chip was unsuccessful i just don't have enough clearance there so it's a little mangled but it's still connected so what i've done is i've lifted the leg on buster i've connected my little clip lead to it and i'm going to manually collect connect it to the left chip because that's still cut so that will leave the right chip with no signal at all it's just going to float and let's see what happens okay so that's some progress buster is connected to the left chip and it is driving it is instructing it to turn off and on and the computer while we're getting that flashing green screen it is booting it's because i have the 2.0 ram in there the other chip is not being enabled so i'm going to remove this right chip entirely put a socket in there and a new ls245 i'll just fix the pin i cut on this one i'll resolder that back together and let's see if that fixes this computer all right sockets installed i put a new old stock from 1991 gold star ls245 in here this is the old one i just took out the buster is back in the socket all pins nothing is bent out so let's see what happens oh look it's fixed i can't believe it let's boot the uh to test kit here i'll plug in the keyboard okay so it looks good now i want to test out the zorro slots because with no transceivers with a buster out or these transceivers not working you're not going to get working 002 slots i'm going to stick a memory card into here and see if the new memory shows up in the test kit here here is a commodore 2 megabytes zorro 2 ram card hopefully i can get this in yes i can with the power cable like that there we go turn this on and what will we get working two extra megabytes of memory in addition to the one meg of chip f1 for memory and would you look at that one mig chip two makes fast it's working all right next test let's take the amiga 2630 i tried earlier and let's plug this in oh it's not going to work with a power cord like this though will it okay well let's reposition things a little bit i'll pop that out all right power supplies over on that side let's plug this in i'll plug it into a different zorro two slot just to make sure it's working and then the accelerator card 68030 go into the coprocessor slot let's power this on here we go it's all precarious oh yes it's working it's booting this is awesome f1 for memory and there we go seven makes of total memory fastest four megabytes because the accelerator has four megs on board plus i have the two meg zoro two in there and we have one meg of chip let's run through the memory test here and i'll allow it to just just make sure everything is stable on here so i went through all the tests in the amiga test kit everything is working great including the mouse which i haven't showed working but i did test it and it works and ram tests are good and everything is great this thing is now fully operational well this amiga 2000 is definitely working and everything i've thrown at it seems to work perfectly i'll reassemble it into a case later put a hard drive stuff like that in there but for now i've booted various things on here and everything seems to work great so the last thing to do is to take this ls245 and test it in the old mini pro here and see if it detects it as bad i'm always curious to see if it does or not okay we'll just pop that in there and we'll hit test look at that test error failed total fail so there is the bad chip did it fail because it got battery corrosion all over it or did it fail just because it failed incidentally my cutting attempt did end up weakening the leg and it broke off so i soldered on a new one just for testing purposes but i think everyone knows what time it is it's time for the old dead part spin which is looking pretty full and this chip goes right in well that's going to be it for this video there is one repaired amiga 2000 motherboard i've actually never worked on an amiga 2000 before so this was kind of fun to try to figure out how this all worked i had no idea what the buster chip did for instance now i'm going to say one thing people are going to point out in the comments that there's probably some corrosion underneath the solder mask and to really fix the sport i have to desolder these components in the affected area sand the board down reapply new paint et cetera et cetera i'm not going to go through all that for this board and i think this board is going to work fine for a long time to come but on the other hand it might be an experiment to see if this board does degrade and fail over time and in that case this may become a donor board for its part to go on that replica pcb amiga 2000 i got that'd be kind of interesting wouldn't it anyway a huge thank you to andy for donating this machine to the channel and that's going to be it if you like this video i'd appreciate a thumbs up if you didn't you know what to do thumbs down subscribe for more videos hit that bell icon if you want to be notified and put your comments and your suggestions in the comment section below thanks very much stay healthy stay safe and i'll see you next time goodbye [Music]

Channel: Adrian's Digital Basement

Views: 101,417

Keywords: commodore, Amiga, Amiga 2000, Motorola 68000, battery damage, retro computer

Id: SjZ9MJ64CaE

Length: 33min 45sec (2025 seconds)

Published: Sat Aug 29 2020

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Amiga Schematics

Amiga Hardware Database: Amiga 2000

https://en.wikipedia.org/wiki/Amiga_custom_chips

The Motherboard he's working on is a Rev. 4.5 (High Resolution version).

Spoiler: an 74LS45 Octal Bus Transceiver chip was the villain.

DiagROM

Amiga Test Kit