We are back with the broken Plexus P/20. In this video I talk about some amazing discoveries we've made on this machine which gives me the right information and the tools I need to attempt to repair it.
Part 1: https://youtu.be/iltZYXg5hZw
Part 2: https://youtu.be/lCPZAYvk940
Part 3: https://youtu.be/_IrxvDE6Fyo
Part 4: This part
00:00 - Plexus Recap
01:23 - Intro
01:40 - Fixing the Reset Fault
10:22 - WTF is Error 4F02?
16:42 - Enter Usagi Electric's Community
18:55 - A Literal Pot of Gold
25:44 - Back to the Community
27:04 - Error 4F02 - No Ram Detected
28:02 - 68000 Memory Management
32:58 - Looking for a Mapper Signal
36:01 - A Huge Smoking Gun
38:36 - Troubleshooting Memory Again
45:06 - Replacing the Flip-Flop (Chip U4F)
50:45 - This is Freakin' Good
53:05 - Trying to Boot Into UNIX
55:17 - What's Next
-- Links
Plexus P/20 Discord channel at Usagi Electric:
https://discord.gg/rYX6es6cbA (Plexus channel)
General Adrian's Digital Basement channel:
https://discord.gg/Nhe8VHqZny
My Github Repo (with ROM dumps and images)
https://github.com/misterblack1/plexus-p20
Plexus P/20 Brochure:
http://www.bitsavers.org/pdf/plexus/brochures/Plexus_P15_P20_Brochure_1985.pdf
Plexus Unix:
http://www.bitsavers.org/pdf/plexus/brochures/Plexus_SYS_5.2_Brochure_1985.pdf
MFM emulator:
https://www.pdp8online.com/mfm/mfm_old.shtml
Fujitsu Hard Drive Brochure:
https://archive.org/details/bitsavers_fujitsubro1984_2565589
Omti 5200 Manual:
https://oldcomputers.dyndns.org/public/pub/roms/omti-5400/omti_5000_series_reference_aug85.pdf
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
My GitHub repository:
https://github.com/misterblack1?tab=repositories
-- 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
--- 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