Main channel: Let's give the Mac Classic 4 megs of RAM (without using the RAM expansion card) (Patreon)

Published:

2024-03-02 19:00:31

Imported:

2024-05

Content

Hello my patrons! Next up on the main channel I wanted to try some hardware hacking on a spare Mac Classic motherboard. On the recent Mini Mac Repair-a-thon I stole a 74LS174 chip off my spare motherboard to fix the machine stuck at 512k. Once the repair was done, it goe me thinking that perhaps I could have just worked around that repair entirely by eliminating the need for the LS174 by upgrading the Mac Classic motherboard to 4mb, all without needing the external RAM expansion card!

So in this video, I give my hypothesis a test and see if I can get this machine running with a full 4mb right on the motherboard.

Thanks for all your support!

Direct link: https://youtu.be/_iE-CKcyR2E

Files

Hardware hacking: Let's give the Mac Classic 4 megs of RAM (without using the RAM expansion card)

After the recent Mac repair-a-thon, I had a Mac Classic motherboard with a missing 74LS174. I thought about just replacing that IC but realized I could actually do a simple mod to the motherboard to give it 4mb of onboard RAM instead of just 1! (And I wouldn't need to replace the 74LS174, so it would actually save me money. -- Info How to modify the Mac Classic for 4mb onboard as seen on Adrian's Digital Basement ** Remove two chips: Remove UL1 CAS PAL (no longer needed!) Remove UH6 74LS174 (no longer needed!) ** Modify system to think it has 4MB on the motherboard: Pin 13 of UI4 BBU: Remove R42 470ohm (under motherboard - this pulls pin to ground) Pull up PIN 13 via 10K to 5V (I did this by running a jumper between the left side of R42 and R41) Pin 17 of UI4 BBU: Should be pulled up to 5v already (verify but mine was already at 5v) ** Remove old 44256 RAM chips (8 of them, UK1-UK8) ** Install 4400 RAM chips (4x1mbit - I took these off a 4mb 72pin SIMM) ** Make connections to connect CAS lines from UI4 BBE to RAM: Connect UL1 PIN 7 CAS0H to UL1 PIN 24 (CAS0H to UK1/3 DB8-14) Connect UL1 PIN 6 CAS0L to UL1 PIN 25 (CAS0L to UK5/7 DB0-7) Connect UI4 PIN 16 CAS1L to UL1 PIN 27 via 22ohm (CAS1L to UK6/7 DB0-7) Connect UI4 PIN 19 CAS1H to UL1 PIN 26 via 22ohm (CAS1H to UK2/4 DB8-14) (22ohm is just to make sure shorted DRAM doesn't kill the UI4 BBU) Remove (optionally) and jumper over R43 and R56 (22ohm resistors) as these are in series with R3 and R19. This gives the CAS lines just 22 ohms (versus 44 ohms) This replicates the Mac SE design exactly, in fact the Mac Classic is really a Mac SE... The UI4 BBU chip is the same one on the Mac SE, even though the part# is different, it seems to work in an identical way. -- Links Mini Mac Repair-a-thon: Part 1: https://youtu.be/lHvGc4LWR0g Part 2: https://youtu.be/nSoSX6XV7t4 Part 3: https://youtu.be/xx08YXkUOnQ Recapping the Mac Classic II Motherboard https://youtu.be/rpVAg6hG__Y Previous Mac Repair-a-thon from 2020: Part 1: https://youtu.be/lKD65I86XGQ Part 2: https://youtu.be/kNhVQWH318M Part 3: https://youtu.be/uatqcZRzmt0 Part 4: https://youtu.be/zC0qi5dQsWs Part 4.5: https://youtu.be/YikOY8WTnLU Part 5: https://youtu.be/PHTnauC020o Part 6: https://youtu.be/mqWCPkfcr1A Adrian's Digital Basement Merch store: https://my-store-c82bd2-2.creator-spring.com/ Adrian's Digital Basement ][ (Second Channel) https://www.youtube.com/channel/UCbtwi4wK1YXd9AyV_4UcE6g Support the channel on Patreon: https://www.patreon.com/adriansdigitalbasement -- Tools Deoxit D5: https://amzn.to/2VvOKy1 http://store.caig.com/s.nl/it.A/id.1602/.f O-Ring Pick Set: (I use these to lift chips off boards) https://amzn.to/3a9x54J Elenco Electronics LP-560 Logic Probe: https://amzn.to/2VrT5lW Hakko FR301 Desoldering Iron: https://amzn.to/2ye6xC0 Rigol DS1054Z Four Channel Oscilloscope: https://www.rigolna.com/products/digital-oscilloscopes/1000z/ Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier: https://amzn.to/3adRbuy TL866II Plus Chip Tester and EPROM programmer: (The MiniPro) https://amzn.to/2wG4tlP https://www.aliexpress.com/item/33000308958.html TS100 Soldering Iron: https://amzn.to/2K36dJ5 https://www.ebay.com/itm/TS100-65W-MINI-Digital-OLED-Programmable-Soldering-Iron-Anti-static-Structure/113382669853 EEVBlog 121GW Multimeter: https://www.eevblog.com/product/121gw/ DSLogic Basic Logic Analyzer: https://amzn.to/2RDSDQw https://www.ebay.com/itm/USB-Logic-DSLogic-Basic-Analyzer-16Ch-100MHz-4Ch-400MHz-Xilinx-Spartan-6-FPGA/202543965672 Magnetic Screw Holder: https://amzn.to/3b8LOhG https://www.harborfreight.com/4-inch-magnetic-parts-tray-90566.html Universal ZIP sockets: (clones, used on my ZIF-64 test machine) https://www.ebay.com/itm/14-16-18-20-24-28-32-40-pin-IC-Test-Universal-ZIF-Socket-Fs/303206721971 RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI) http://www.retrotink.com/ Plato (Clone) Side Cutters: (order five) https://www.ebay.com/itm/1-2-5-10PCS-Micro-Scissor-125mm-PLATO-170-Electronics-Cutter-Side-Cutting-Pliers/163458746184 Heat Sinks: https://www.aliexpress.com/item/32537183709.html Little squeezy bottles: (available elsewhere too) https://amzn.to/3b8LOOI --- Links My GitHub repository: https://github.com/misterblack1?tab=repositories Commodore Computer Club / Vancouver, WA – Portland, OR – PDX Commodore Users Group https://www.commodorecomputerclub.com/ --- Instructional videos My video on damage-free chip removal: https://www.youtube.com/watch?v=XQVjwPsVFd8 --- Music Intro music and other tracks by: Nathan Divino @itsnathandivino