How Piggybacking RAM Works: Fix Computers With Just Your Fingers | see pinned comment


Hello and welcome to Restro Retipes.. Restro Reti… Hello Well, on the menu today on Retro Recipes We’re g… I said it! We’re gonna be exploring our fingers Yeah, no, no not those.. fingers Although, fish and chips.. hmm Well, actually today, funnily enough, we’re gonna be fixing chips See I think it’s fair to say that on the Commodore 64 There can be many different faults You’ll notice if you saw my hammer repair video Or the three-hour live collaborative repair attempt video But I think it’s also fair to say that more often than not Problem comes down to one thing Actually, eight things Yeah, the ham.. the RAM Not ham.. hm Now I do understand, and I see in the comments of my videos That a lot of people who haven’t tried soldering before are understandably wary of doing that So today we’re going to be showing you a way that you can both diagnose and fix Perhaps the most common Commodore 64 fault Using just.. your fingers Welcome to Retro Recipes So, here’s the machine in question T his was given to us by David Philippe Gil and you can see here the problem Similar story with Jupiter Lander, which is a handy car crush to use because it doesn’t require the kernel and some other chips. We can help narrow things down If we consult the pictorial C64 fault guide You can see the section with, by far, the most faults is the RAM section And this looks pretty similar So, let’s verify this using the (American accent) Commodore Diagnostics and Utilities Cartridge.. .. Thing Now this is interesting It’s giving one flash and then waiting and repeating that one flash So let’s check the (American accent) Diagnostics Manual It says here if a RAM error id Detected the screen will begin flashing It seems like what’s happening One flash means Chip U12 So, so far we haven’t used any tools Now if you’ll excuse the use of a screwdriver here I do want to show you that how you can diagnose and fix this using just your fingers So here is U12. Oh, sorry! That’s the LEGO version Here, is U12 But while I remember, please if you haven’t voted for Lego to mass produce this BrixtyFour, please do So in the intro, I mentioned that we’re going to be exploring just our fingers Or of course we could use the Paws So what I’m gonna do is feel each chip And.. ow.. That one is noticeably hotter than the others And that is U12 Now I’ll just prove the point here using the (American accent) Thermo Meter It’s just a thermometer You can see there, that Chip U12 is indeed at least 5 degrees hotter than all the others So we’re gonna need some new RAM chips Excuse me. Hi, sorry. Do you sell RAM Chips? Um.. there we go. Sorry, what’s that? Is a Ham Chip. (laughs) Not ham chips, RAM chips. Do you sell RAM Chips? Oh Oh, sorry, they’re out of stock Oh, you’re out of stock of RAM? Okay. Thanks anyway Yeah, where’s Ashley when you need it, Well not to worry cuz I found these at ASDA So what I’m gonna do is piggyback this new chip on top of the faulty one And piggybacking just means push it down using the spring tension of the new pins So that it makes contact with all the pins Right down to the PCB And the same on the other side all making good contact there Now if we turn it on Yes! The blue screen of .. life And out there test works As does the SID Chip We can leave this running for a number of counts Now it’s important to note that this piggybacking technique Is generally only possible with RAM Chips But why is that and why does it work? Well, you see, RAM chips are what’s known as tri-state logic This just means that the chip is capable of three states It can either be pulling current from the bus Creating a zero Supplying current to the bus Creating a one Or in a high impedance state High impedance, also known as High-Z, basically means the chip is electrically.. Sort of invisible to the rest of the circuit The use of this is really essential in shared electronic buses Just like the one the 8 Commodore 64 RAM chips share I can demonstrate this pretty simply with a multimeter And set it to continuity mode The meter will beep whenever it detects a connected circuit or trace And so you can see here how the aged RAM chips are indeed all sitting in seats on the same bus That’s terrifying And with RAM, if the chip is faulty, usually signified by it overheating like that It falls into that third high impedance state Effectively just becoming invisible to the rest of the circuit On screen, this causes that garbled data that we saw A simplified explanation of why it feels hot to the touch Is that the voltage sort of accumulates in the chip rather than passing through to the rest of the circuit When you piggyback a working chip on top of that invisible faulty chip You’re really just connecting a chip to a motherboard that thought that there was no chip in there at all So that’s how you diagnose and fix the most common Commodore 64 fault using just your fingers And a screwdriver Now if you wanted and you weren’t gonna be carting this Commodore 64 to your mates house everyday You could leave this as is maybe secure it down there with some thermal tape But because we have got the tools here We’re gonna do it properly and desolder socket and reinstall this new chip in its place And while we’re doing that I think we’ll just beautify this board a little bit and recap it just for good measure But first.. Well, we didn’t have any luck with our HAM Chips of RAM chips, but I did find this Now this reminds me, I want to give him very special thanks and shouts out to all of my Patrons Especially Jonathan Howard who didn’t join the Silver Patron level But even higher he joined the Rhodium level Which includes a special on-camera greeting and a thank you So at some point I’ll have to film that But thanks seriously to all my Patrons You really helped support this small retro channel And I couldn’t do it without you Or that Maybe next time So we can definitely give this board a bit of a cleanup Ew. Yeah, this RF shield is effectively useless Put that on eBay (crashing noise) Let me get out our anti-static brush And then to remove the bottom RS shield We’ll use the fence (desoldering tool noise) We’ll use the Fanta we’ll use this We’ll.. uh.. we’ll use this.. Let me just leaver off of these tabs after sucking them dry Eh.. removing the solder (crashing noise) Calm down From time to time we do need to empty the chamber Which is easily done (desoldering noise) Then we’ll just clean up nicely where those tabs were And then we can actually desolder that faulty chip Firstly we’ll add some new solder to get all the flux flowing We’ll drop in our socket I’m just gonna hold it down here with some thermal tape And then what I like to do is solder both opposing corners first And that way it holds it in tightly while you solder all the other pins And here’s our new chip from ASDA I found it in the freezer section And let’s test our work Yay! (higher pitched) Yay! So we’re gonna recap the board now, but first we need to move the dog out of the way And this recap kit is again from the excellent Retroleum By the way, if you can’t even get to this stage in your Commodore 64 PCB is just beyond repair You could always design your own completely new one Like this one by the fantastically named RJAM Verse Loot I’ll put a link in the description And they could send the designs off to PCBWay Because as we all know PCB stands for Piggybacked Clone Board (desoldering tool noise) Oh, pardon me Now just to recap, we were just about to recap Make sure we put on new ones in the correct way around Polarity does matter Looking good so far! That’s weird.. So the solder actually went through that hole and came out the other end like a metal worm To save myself turning around the board constantly, I’m gonna desolder all of the same type of capacitor now in one go There’s the old ones There’s the new ones Ladies and gentlemen, the world’s first Commodore 64 Guitar Now removing this VIC shield to get to lead capacitor under there is always tricky But I’m gonna try this soft plastic Lego brick removal tool Hey that worked really well! I’ve got some thermal paste on my thumb there Um.. Yeah, we’ll just clean off this old one (struggling) It glued itself shit Just a little dab Not that kind of DAB kids There you go, there’s the heat chip for the Vic sink.. or something And then we’ll just spray our alcohol And clean up all the flux from those new capacitors Looking really nice Hey, that’s me! We’ll do one final test although I’m pretty sure I got them all in the right way round And yes time for a nice game of Jupiter Lander I will do one final test That is, have the keyboard in place So it just remains for me and the Commodore 64 To say I hope you found this video about how piggybacking works illuminating. Thanks for watching. Please like and subscriiiibe Comment below and Cheerio! Is a ham chip

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