Retrobrighting worked well ... until it didn't (Atari ST 520)

It's time to finally get this almost-trashed Atari ST booting off the external floppy drive. Also, it's time to try to improve the cosmetic look of this very yellowed machine. Will this result in a disaster?

Part 1:    • This Atari was nearly trashed! Can I ...  
Part 2:    • I figured out what is wrong with the ...  
Part 3: This part!
Part 4:    • Finally, a reliable inexpensive RAM u...  

--- Video Links

Display Turntable I use for retrobrighting:
https://amzn.to/3zXIIZw

Indoor retrobrite process using blue light:
   • A new way to fix yellowed plastics in...  
   • Indoor Retrobrite Followup: Scaling u...  

Using a heat gun to fix sun damaged plastic:
   • Using a Heat Gun  to get your bumpers...  

Adrian's Digital Basement ][ (Second Channel)
   / @adriansdigitalbasement2  

Support the channel on Patreon:
  / adriansdigitalbasement  

-- Tools

Deoxit D5:
https://amzn.to/2VvOKy1
http://store.caig.com/s.nl/it.A/id.16...

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/digi...

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/33000...

TS100 Soldering Iron:
https://amzn.to/2K36dJ5
https://www.ebay.com/itm/TS100-65W-MI...

EEVBlog 121GW Multimeter:
https://www.eevblog.com/product/121gw/

DSLogic Basic Logic Analyzer:
https://amzn.to/2RDSDQw
https://www.ebay.com/itm/USB-Logic-DS...

Magnetic Screw Holder:
https://amzn.to/3b8LOhG
https://www.harborfreight.com/4-inch-...

Universal ZIP sockets: (clones, used on my ZIF-64 test machine)
https://www.ebay.com/itm/14-16-18-20-...

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-...

Heat Sinks:
https://www.aliexpress.com/item/32537...

Little squeezy bottles: (available elsewhere too)
https://amzn.to/3b8LOOI

--- Links

My GitHub repository:
https://github.com/misterblack1?tab=r...

Commodore Computer Club / Vancouver, WA – Portland, OR – PDX Commodore Users Group
https://www.commodorecomputerclub.com/

--- Instructional videos

My video on damage-free chip removal:
   • How to remove chips without damaging ...  

--- Music

Intro music and other tracks by:
Nathan Divino
@itsnathandivino