I figured out what is wrong with the Atari 520 ST!

Time to continue working on the almost-trashed Atari ST. In part 1, I found that the machine was dead. In this video, I un-mod the modified system and do some fault finding to figure out what's wrong with this machine.

Part 1:    • This Atari was nearly trashed! Can I save it?  
Part 2: This part!
Part 3:    • Retrobrighting worked well ... until it di...  
Part 4:    • Finally, a reliable inexpensive RAM upgrad...  

--- Video Links

Ian's channel: (Tales of Weird Stuff)
   / @talesofweirdstuff  

Atari 520 ST schematics:
https://www.gossuin.be/images/schemas...

Marpet MP210A Xtra-RAM:
https://www.atari-forum.com/viewtopic...

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 the c...  

--- Music

Intro music and other tracks by:
Nathan Divino
@itsnathandivino