Fixing a Commodore 1541 Disk Drive

well hello there and welcome back to Adrienne's digital basement for today's video we have a 1541 disk drive repair video it's the first I've ever done and we'll be working on the 1541 that I got from desi in Lincoln City Oregon let's get right to it [Music] right here is obviously 1541 a very dirty 1541 it's like someone has done some modest little square hole there and on the side of the drive is also a rectangular hole very nicely cut but this thing is very very dirty let's take a look at this disk drive I just wanna see if it powers on tell a lot about 1541 by how it powers up let's just see what happens yeah so this this indicates some type of a fault the red LED is on and this thing is just spinning and it hasn't stopped it should just come on spin for a second then stop let's just open up this 1541 disc drive and take a look see what's inside of this thing see why it might be busted I was trying to undo screws but there are no screws in this thing it already had the screws removed well it's a 1541 short board and considering there's all these holes for various mods this board is looking pretty bog-standard I even seen absolutely nothing different and custom on here now it is not working so I'm wondering if someone sort of swapped this board with a different one or I don't know what's going on but other than just being dirty it all looks pretty much bone stock I don't see any kind of wires modded onto the drive select spots here so yeah that's interesting the 65 22 chip here is from 1989 so this has been replaced this here is from 84 the 6502 is from 82 this seems to be a little bit of a hodgepodge of things that are sort of switched all over this I see is 84 84 84 but obviously someone's been in here working at some point switching some of these chips out so I took the entire chassis out of the case and I've also dismounted the motherboard so something happened before I was filming while it was still mounted in the case I had the power connector that was turned on and strange is when the drive powered up the red LED came on but it wasn't spinning which was different than it was doing earlier when we were testing drive was still totally together while was sitting there on the bench and after a little bit of time some smoke started coming out of it uh and while it was smoking I just took a look in the part that was smoking was right here it's marked C 21 the board and it's a tantalum capacitor and if you've seen my previous videos or you just know of what tantalum is do they have a tendency to short out let's take a look at the schematics for this particular disk drive so this board uses 251 seven forty eight as a schematics because it's actually two fifty four four six the PCB number is written right here as 254 for two and it says right here that this schematic is good for 254 for two looking around on the board there is C 21 which is the one that blew up and as you can see it goes between 12 volts and ground typically that is what a tantalum does and that obviously shorted out internally and it overheated and blew up smoked so the very first thing I need to do before we do any more troubleshooting it is I'm gonna need unplug this and we're going to have to cut that out and install a new tantalum capacitor back to the service manual we need to look up what C 21 is C 21 tantalum 4.7 micro farad 25 volts so I need to replace it with something similar or higher voltage than that here I have a box full of tantalum so I've labeled what they are just for my ease of use this row here I put little arrows to say that these are the ones that represent these and 4.7 micro farad is right up here I don't feel like getting the desoldering iron out so I'm just gonna use some solder braid here to get this out of here there we go it's gonna hold it with my thumb and the pins on the bottom side so it doesn't fall out and we'll just zap this baby in and what's left is to crop off the legs which one of them just went flying before we test this out I was just taking a look at the bottom of the board generally looks okay there's a little bit of rework that's been done this I see right here has been swapped out and it's looking rather ugly what's happening down here a lot of flux that's kind of dried and gotten crusty it's this part right here so it's in a socket which obviously was installed after the fact and it's some type of chip it says SK / 4 LS 123 so right off the bat that's suspect to me that that might have failed causing the problems of this drive is having I'm just gonna spray a little IP down here clean it up so I can kind of see what's going on really crusty with flux Ain to blow away the soot that's on here okay let's see what happens we turn this on alright the drive is spinning so that's a good sign so we're getting 12 volts or at least we're getting some kind of voltage I wanted to check that the regulators were working correctly so that this tantalum here are seeing the correct 12 volts eleven point seven five eight volts so Smoltz is looking okay and we'll check a logic chip make sure that it's getting a nice solid 5 volts 5.0 4 so that looks absolutely fine but the red light is on drive is spinning it's not stopping so there's something faulty here going on which is kind of an obvious thing I think the first thing I'm gonna do is pull out all the socket of chips and I will put them back in just sort of the ox if this drive is dirty you know me with my deoxys I love it ah okay actually hold on a second so I was checking the schematics and see here I says neutronics short j6 Alps j6 is open well j6 on this board is a jumper link hopefully it's not out of focus but j6 is there and it's currently enabled well neutronics it should be shorted Alps it should be open I'm quite positive that this here is an Alps mechanism this is the type that you pops down like this which is sort of the more common at least what I've found of the drive mechanisms this is an Alps mechanism it doesn't have a brand name anywhere on here but I actually have another drive here which has the other type of mechanism to flip up one and look says neutronics right there and definitely j6 should be open for Alps drives and not closed so I'm just gonna cut it just like this lift it out of its way I'm not sure on these drives if you have it set wrong what the what the symptom is but okay so I've cut j6 and I moved the wire out of the way so it's not gonna short and let's turn this on and see if that makes any difference little lights on but it's not spinning wait a second before I cut that jump right pulled this one I see out of this socket right here so let's deoxys this socket and reinstall this I see all right drive is spinning again so definitely that that IC is necessary for that but it's still just the light is solid it's not stopping you kind of hear that the noise it's making there so alright that was an unrelated issue this jumper and I don't know that I mean how how important is it to have that jumper cut when you're using the Alps mechanism versus of the neutronics I actually didn't even know that that was a thing I thought these were inner all interchangeable but apparently with this type of board you do need to set the jumper appropriately well at least according to the schematics ok I've removed all of the socket at ICS and you know what it is if you're doing this drinking game it's time to take another drink it's time for detox it and just for good measure I'm going to use this toothbrush to really rub it into the pins of the sockets all right I've broken out the oscilloscope and I have this Maddox over here on the iPad and the board is here I have ground hooked up to the 6502 and it's time to start checking some of these signals first thing we have to think about is that this is an actual computer the disk drive it has RAM and ROM and 265 2200 chips and the CPU so if anything's not happening correctly on the CPU like the reset line is not being brought high it's gonna keep this thing from operating at all and I've been chatting with the repair expert I said eight DWF from Italy he is so good at fixing all these old Commodore machines including disk drives so he's given me some really good tips on where to start to diagnose this drive he has a great channel where he repairs all sorts of Commodore stuff including his recent excellent repair on a Commodore 1540 long board disc drive so I'll put a link in description definitely check out his channel okay I'm gonna power on the drive and it's doing that spinning thing now he told me that the default state of a 1541 is the drive to spin and a disk drive led to be on that is how it's going to be until the CPU initializes the i/o chips which stops the drive from spinning and turns off the light so if you're in this state it could be pretty much anything on the board that has to do with the execution of code for the CPU so the roms the Rams it could be the i/o chips could be the data bus could be the CPU itself it just could be all sorts of different things so the first thing we need to do is start by checking the signals to the 6502 CPU so first off I'm gonna check the clock signal okay I broke out the oscilloscope and I have the drive here and I have this iPad with the schematics and I was gonna start showing you how to troubleshoot the drive and I was just having all sorts of problems on my oscilloscope measuring the signal and it turns out that the little ground probe which connects up to my oscilloscope probe just like this that this this part went bad and that's there's a break-in here I thought maybe it was inside this clip right here but it's not I test the continuity from this little metal clamp to the wire right there and nothing so there seems to be a break somewhere inside of this thing like in here or I don't know and this was causing crazy measurement issues with my oscilloscope I was getting really unusual things that just didn't make sense so that's a first for me this is the actual Reigle probe part that came with my oscilloscope probe - and it's bad now lucky for me I have a little parts kit that came with the oscilloscope and in here I have the other ground probes but I didn't end up using oh wait this is actually for a different probe set ah here we go here's another bag of parts these have the extra Brown straps in here so here's another one okay so I have the multimeter on resistance so when I put the probes together yeah we're getting point Oh something tumor there ohms I'll clamp this one on that side and I'll hold this on and there we go Oh point Oh looking good and we'll take this one which I think is bad we'll clamp that on there hold that on there and look nothing nothing at all this this dies Wow so I'm curious making my viewers have had this issue where these things die like that in a non obvious way where none of the wire is frayed or cut or anything wire all looks absolutely perfect so that that's really annoying I spend quite a bit of time trying to figure out what the heck was going on and it turned out that it's just bad all right here we go power on the disc drive so it's spinning and let's check pin three for the clock very nice we got a perfect 1 megahertz clock signal there it looks totally sharpened nice there is an output of the clock signal or a second phase here on pain 37 and that also looks good we're looking at 1 megahertz which is perfect so we know the clocks are good reset signal this is reset pin 40 so when I turn the drive off we'll go to low and when I turn it back on it should stay low for a second and then go high there we go it went low high if it was staying low it would keep the CPU permanently reset and it would never execute any code also on the CPU are the interrupts and the non-maskable interrupt lines so that's pin 4 which is high and pin 6 which is also high if either these were held low continually that could mean that the CPU also is not running depending on what code is executed how those are set up so those look absolutely good so we're on pin 34 which is read/write pin if I turn this on it just goes high and it's not pulsing this is as the CPU reads and writes from the RAM this will be pulsing up and down and it's just sitting there doing nothing okay the probe is on 6502 pin 25 which is address line 15 when you first initialize a 6502 it has the reset vector which just goes to memory location ffff which is in ROM and it starts executing the code and if I turn this on so we're just getting a high which means the CPU is trying to read in the F location now if I go down these pins and I look at the other address lines I actually see no activity every single one I touch is just high so I'm kind of going through um high high high so that's not normal on a 6502 what happens is when it first initializes it goes to ffff tries to read out of the ROM and it starts to execute usually jumps to a different location and you'll see activity on the address lines as it's reading the ROM and moving through the different parts of memory nothing is happening whatsoever it's just sitting here all doing nothing and then if I look at the data bit lines like there's 0 & 1 they're also just sitting there at high oh that one's low but that would be explained if the CPU is pointing to the ROM chip and trying to read out the ROM chip so the fact that the data lines have no activity they're just sort of frozen in time either high or low really implies that the CPU is not executing anything so looking at the schematics on the iPad there are two ROM chips on this which are these two chips here and their chip select lines are driven off of these simple decoding logic right here with these logic chips let me just quickly check to see that the correct ROM is being selected as you start to go to that initial ffff location in memory the correct ROM needs to be selected so that it will read out its contents to give back to the CPU okay and then with the two ROM chips its pin 20 as the chip select line and at any given time only one chip should ever be selected at give in time if the decoding logic the decodes which rom or which Ram it should be selected to screwed up somehow then we might have multiple chip selected right now this rom chip has a high input signal on the chips like line which means it's not selected to what's discounted from the bus and then this ROM chip right here is currently low which means it is being selected and when lookup what this ROM chip is 901 to - 905 this is the upper ROM chip the one that contains the code at ffff that executes when you first power on the drive so it's being selected but because no address line activities happening is just frozen in time this thing is just outputting one solid set of data bits which I see on the bus cuz some are high and some are low and that's all that's happening nothing is moving so with that said I think my hunch is that the CPU is probably bad with the clock signal being good and the reset line being good going into it it should be executing code it should be we should be seeing strobing on those address lines as it runs through the memory and we're not seeing that the ROM seems to be being selected correctly but the CPU just doesn't seem to be doing anything but the thing is because I went through and checked all the address bus lines and all the data bus lines none of them look screwed up if some of them were like in the middle like they weren't zero or they weren't five volts so they were like at two volts or three volts that would imply there might be a some kind of a conflict or when these other chips might be bad but all the address and data bus lines look good so that's always a good thing to check when you're diagnosing something like this okay so I think it's time to swap out this CPU and let's see what happens now I'm gonna say that 6502 cpus are pretty reliable even the Commodore mas ones like this 6502 be from the 46th week of 1982 the chip is physically in decent shape made in Hong Kong but let's put this aside and I went into my parts bin and I dug out this 6502 it's from 1985 so it's a little bit newer but it's a moss original part so new CPU is in here's the old one right here let's power this up and see what happens oh look at that the drive stops spinning the light is off as well all right the ground was hooked back up the CPU is in there let's go check the address bus lines and see their activity and the driver I think should be working now we'll have to plug it into a computer to check let's just double-check what the activity looks like on the bus so that's address line zero and as you see on the scope that is normal activity on on the address lines it's going through and it's doing stuff and I'll just quickly check some of the other ones yep it all seems like it's executing code right now it's it's running okay and now we're on the data bus and also activity looks completely normal on the data bus lines this is how it should be and if I turn it off and I turn it back on you'll see it should be idle for a second as it's in reset and then it will start executing yep there we go totally normal activity now so there we go at least so far the CPU was a bad part and this appears to be executed so I think before we test this on a computer I'm gonna power it off and I'm gonna lift the board off the machine and I'm going to spend a little bit of time cleaning the inside of the disk drive here because this is looking a little crusty in here in it really could use a good cleaning alright first up I have a little IPA on this cotton swab here so I'm just gonna lift the heads and clean the head although actually I gotta say heads look really really clean sorry I'm not getting a good view of this for you but it's nice and clean commodore disk drives are single sided so this top part it's just a little pressure pad it doesn't actually do anything when it comes to reading the discs just don't lift this little lever up too high when you're using the cotton swabs clean the heads next up we have the movements of the head and actually it seems to be moving quite freely but I'm going to take some silicon here and I'm gonna put that on a cotton swab dab this on and then I'm going to rub that on these little sliders that are in the drive here I'm going to move the heads back and forth and actually get on here there's when you move the heads it sort of exposes a little bit a little bit more of the Ray so just try to get as much of this on there kind of give it a little lubrication and then move the heads back and forth manually like this just make sure it's nice and smooth operation which it is a little bit more of the silicone here I'm gonna put some up here on this little metal part here this is what the head slides on when the drive is not in the down position see how it works okay I have a random floppy disk here let's uh let's insert this in there it is in and pops out good so this appears at least mechanically it's working okay now right under here is where it clamps the disk so this top part clamps the disk onto this lower area I actually like to use a little cleaner and just give this a bit of clean it's this needs to be not greasy or slippery or the disk is gonna slip inside the drive so it's pretty clean right now to be honest I just sort of use a cotton swab with some cleaner on it and you don't wanna use any oil or anything on this this this needs to be able to grip the disk firmly otherwise it will slip in there and you'll have trouble reading discs and what's happening is the actual disc is not spinning inside the sleeve because there's a quite a bit of resistance you know to spin it so this has to be able to clamp it with enough force so just sometimes if you're having trouble you might have dripped a little bit of lubricant onto that area and then that will cause that issue so I noticed one thing is this is pretty noisy when I turn on the drive listen kind of makes some crusty noise and that's that's this whole assembly right here on the top that's spinning so I'm gonna take some silicon grease specifically I'm just gonna dab a tiny bit right on here and this little spinny part on the top basically you don't want to use something that's too liquidy like this stuff cuz it might drip down onto the drive when the disk below and that's that gets that whole thing slippery let me turn this off see if it makes it see if it's quieter no that's not really quieter I'm gonna put a tiny drop of the silicone right there to try to get that to work in a little bit and I'm just gonna give this a little clean on the front panel cuz the whole thing is pretty filthy oh yeah that's that's a dusty drive now that looks good now this looks pretty clean probably could use a little 303 to restore the luster of the plastic but this mechanism goes in and out much nicer than it was plus it's nice and clean okay time for testing I have the computer hooked up to the PBM over here might as if machine let's power this thing on okay looks good like turned off turn the computer on alright let's go into jiffy das first off I'm gonna hit the @ symbol which will tell us the error channel and I am seeing Commodore DOS version 2.6 1541 so this drive is talking at least over the IEC 264 without issue so I have a floppy disk we have Ultima 6 stick this in we're just gonna go right for broke load on my 8 it says ready hit run Oh actually I think this one has to be load star comma a comma 1 for it to work properly lights blinking but that's what the fast loader does on Ultima so this is still a little bit noisy here a little look clunky sounding but whatever it's it's seemingly reading the disk fine let's hook up the audio oh listen haha Lord British presents so I'll turn the volume down so that's amazing this Drive seems to be working now a full test would involve formatting and reading and writing a disk so let me quickly do that before I declare this good but for sure I can say that this CPU is faulty 6502 bad Wow I don't think I've ever had to see stuff I want to go bad but hey that's pretty nice that this was the only fault but remember I pointed out that this had already had a 65 22 replaced that's this chip right here and also this chip here had been replaced which is the LS 1 2 3 now this chip wouldn't prevent the drive from booting up you know where I could communicate with the computer but I think it would interfere with the reading of the disk if this chip are bad so that chip does seem to be working ok at the moment now on the easy flash I actually have some 1541 Diagnostics on here it's a diagnostic cartridge and I loaded that on to here it has alignment check and show BAM and some other things let's see if we do show BAM that's sort of like the allocation table on the drive yet it's reading that without an issue I'm gonna stick this blank disk into the drive that way we can see if it's formatting and reading and writing properly there's a s for speed check option here speed check press return it's telling me that it should be 300 rpm but it's 297 or 298 so it's a little bit under but you know I think that's close enough for it to work properly hello this is so noisy this clamp thing on the top here I think I might try to take this apart because this this is annoying this is annoying to use this because it sounds so crappy alright I'm not too familiar with this I took the screw out here on this and I took this little circlip off so you I usually take a little piece of tape and I cover this up and then I use the these like pick tools to get it off and the tape just helps it not go flying off into the distance of the room to never be found again I can lift this off I guess I didn't need to take that screw off I there's some glue there I'm just gonna leave that in place ok look and when I lift this up we're gonna need to take the faceplate of the drive off and that will allow this this part to come up so I can lift that up more to get that mechanism underneath there out there's like a spring and the clamp and all that stuff so now this faceplate should come out and the LED is still connected there now I can lift this up a little bit more and this whole clamp mechanism is just sitting down in here and there it is yeah this looks really crusty like whatever lubricant was on here at one point kind of rusted and got got gross that's probably why this is so noisy I'm gonna clean this up a little alcohol get this kind of crusty grease off here and that'll try to re lubricate it you all right it's back together I actually put that clip on first without putting this little top cover back on but the question is is when I turn this on will it be quiet now I clean all the little parts and I use this silicon grease on them when they reassembled it and let's turn it on nice much quieter it's still not probably as quiet as I'd like it but there's a little bit of corrosion inside there I can't get rid of but it's a lot better than it was that's for sure in fact let's put a floppy disk in turn on the computer and I'm gonna do performance test which is gonna put this thing through its paces see if it's working yeah and this just this sounds a whole lot better this there's a little bit of noise here and there little tick sound but it's not doing horribleness alright so it passed his performance test without issue this formats the disk reads and writes a bunch of files onto it does a bunch of tests everything passed without issue so thumbs up this drive is fully functional [Music] well that's gonna be it for this video you may have noticed I actually put the mechanism into a white 1541 c-drive case and that's because of an upcoming project I'm working on where this better suits the color of the machine I'm going to be using this with so it was a bad 6502 processor and a bad tantalum capacitor that brought this drive down but it's back and working better than ever I've actually left the drive turned on for the past several hours and it's still working perfectly I just loaded up Odell Lake on this Commodore 64 so couldn't be happier with this disc drive now if you like this video I appreciate if you can give me a thumbs up on this video if you didn't though you know what to do you can hit that thumbs down button definitely you can subscribe more videos there'll be lots more in the future especially troubleshooting videos which lots of people seem to like and I'd love it if you put your comments and your suggestions down in the comment section below I read all those comments and thank you very much for watching I will see you next time goodbye

Channel: Adrian's Digital Basement

Views: 83,634

Rating: 4.965035 out of 5

Keywords: Commodore, Commodore 1541, alps drive, Alps mechanism, 6502, retro computer, retro computers, vintage computers, repair video

Id: Gl_WRg6jDR8

Length: 30min 23sec (1823 seconds)

Published: Sat Feb 08 2020