{"id":1293,"date":"2024-07-25T22:27:25","date_gmt":"2024-07-26T02:27:25","guid":{"rendered":"https:\/\/claymccauley.info\/?p=1293"},"modified":"2024-08-01T20:24:18","modified_gmt":"2024-08-02T00:24:18","slug":"homebrew-floppy-controller-repair-part-2","status":"publish","type":"post","link":"https:\/\/claymccauley.info\/index.php\/2024\/07\/25\/homebrew-floppy-controller-repair-part-2\/","title":{"rendered":"Homebrew floppy controller repair – part 2"},"content":{"rendered":"\n

After my previous efforts to clean up the board were successful and the floppy controller started working again, I thought I’d solved the problem. What a simple fix I thought. (it wasn’t a simple fix) A week later, I sat down to test out my new gen 2 GoTek floppy emulator and was having all sorts of trouble in the form of hangs and parity errors. I hadn’t seen this before, so at first I assumed I had a broken or misconfigured GoTek. I did some detailed troubleshooting and couldn’t find anything that helped, so I took out the GoTek and put a real 1.44M drive in its place. To my surprise, I was getting the same behavior. Great, the controller went bad again.<\/p>\n\n\n\n

I re-checked everything on the controller, from the individual traces, to inspecting each chip and socket and making sure everything was making good contact. Stumped, I started looking around for anything that didn’t seem quite right and noticed the Ti logo on the 2 74LS138 encoder\/decoder ICs didn’t look quite right. It was also super obvious because there was a legit Ti chip right next to them with a logo that wasn’t warped. Great, these must be counterfeit chips I thought. Off to ebay I went and ordered some vintage Motorola chips for a few bucks. What I really should have done was just test the chips.<\/p>\n\n\n\n

Long story short, the replacement 74LS138 chips didn’t solve the issue either. Strange I thought, what else connects to the ISA bus that could be causing this?<\/p>\n\n\n\n

\n
\n

Then it finally hit me… This controller also has a serial UART with an external connection. It also has a multiple driver\/receiver IC that sits inline. I don’t really use the serial port right now, so I just pulled those 2 chips and amazingly everything worked perfectly.<\/p>\n<\/div>\n\n\n\n

\n
\"\"
SK Floppy\/Serial board running without the UART<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n
\n
\n
\"\"
Original Exar ST16c550<\/figcaption><\/figure>\n<\/div>\n\n\n\n
\n

I’m guessing that the UART went bad, or there’s an internal fault in the driver IC. (which my tester doesn’t support of course) I’m just glad that it works, because now I can get back to playing with the XT clone board I’ve been restoring! (**update: it was the 16550 UART that was to blame. Ordered a replacement chip from TI that will hopefully be more reliable.)<\/p>\n<\/div>\n<\/div>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

After my previous efforts to clean up the board were successful and the floppy controller started working again, I thought I’d solved the problem. What a simple fix I thought. (it wasn’t a simple fix) A week later, I sat … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[212,2],"tags":[],"class_list":["post-1293","post","type-post","status-publish","format-standard","hentry","category-retro-computing","category-tech"],"_links":{"self":[{"href":"https:\/\/claymccauley.info\/index.php\/wp-json\/wp\/v2\/posts\/1293","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/claymccauley.info\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/claymccauley.info\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/claymccauley.info\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/claymccauley.info\/index.php\/wp-json\/wp\/v2\/comments?post=1293"}],"version-history":[{"count":4,"href":"https:\/\/claymccauley.info\/index.php\/wp-json\/wp\/v2\/posts\/1293\/revisions"}],"predecessor-version":[{"id":1300,"href":"https:\/\/claymccauley.info\/index.php\/wp-json\/wp\/v2\/posts\/1293\/revisions\/1300"}],"wp:attachment":[{"href":"https:\/\/claymccauley.info\/index.php\/wp-json\/wp\/v2\/media?parent=1293"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/claymccauley.info\/index.php\/wp-json\/wp\/v2\/categories?post=1293"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/claymccauley.info\/index.php\/wp-json\/wp\/v2\/tags?post=1293"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}