{"id":4759,"date":"2018-07-17T13:40:46","date_gmt":"2018-07-17T13:40:46","guid":{"rendered":"http:\/\/41j.com\/blog\/?p=4759"},"modified":"2018-07-17T13:42:06","modified_gmt":"2018-07-17T13:42:06","slug":"corning-pc-420d-hotplate-stirrer-repair","status":"publish","type":"post","link":"https:\/\/41j.com\/blog\/2018\/07\/corning-pc-420d-hotplate-stirrer-repair\/","title":{"rendered":"Corning PC-420D Hotplate\/Stirrer repair"},"content":{"rendered":"<p><a href=\"http:\/\/41j.com\/blog\/2018\/07\/corning-pc-420d-hotplate-stirrer-repair\/corning420d\/\" rel=\"attachment wp-att-4765\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-4765\" src=\"http:\/\/41j.com\/blog\/wp-content\/uploads\/2018\/07\/corning420d.png\" alt=\"\" width=\"447\" height=\"636\" \/><\/a><\/p>\n<p>I picked up a Corning 420D on eBay, the device was listed as not powering up and was relatively cheap so I figured worth a risk. It turned out to be a very simple repair, but I figured I&#8217;d write it up anyway&#8230; perhaps the reference images will be of use to someone.<\/p>\n<p>The device indeed showed no power LEDs, but the hotplate was heating up&#8230; Taking a look inside you can see that the design is pretty simple. All through-hole, there&#8217;s what looks like an 8bit MCU of some description. The stirrer has a optical interrupter sensor on it, which is attached directly to the PCB.<\/p>\n<p><a href=\"http:\/\/41j.com\/blog\/2018\/07\/corning-pc-420d-hotplate-stirrer-repair\/img_7889\/\" rel=\"attachment wp-att-4764\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-4764\" src=\"http:\/\/41j.com\/blog\/wp-content\/uploads\/2018\/07\/IMG_7889.jpg\" alt=\"\" width=\"619\" height=\"464\" \/><\/a><\/p>\n<p>There were no obvious issues on the top side of the PCBs so I removed the main PCB and discovered the ugly mess below&#8230; I guess there had been some lab spills&#8230;<\/p>\n<p><a href=\"http:\/\/41j.com\/blog\/2018\/07\/corning-pc-420d-hotplate-stirrer-repair\/img_7890\/\" rel=\"attachment wp-att-4763\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-4763\" src=\"http:\/\/41j.com\/blog\/wp-content\/uploads\/2018\/07\/IMG_7890.jpg\" alt=\"\" width=\"605\" height=\"454\" \/><\/a>Cleaned things up with some IPA and touched up some of the joints, but the device still didn&#8217;t work (unsurprising). So I started probing around. There&#8217;s a 74HCT7541 on the front which was a convenient location to measure digital supply voltage levels&#8230; VCC was less than 2V and fluctuating&#8230;<\/p>\n<p>I probed the transformer this was putting out ~10v AC and was being rectified&#8230; But there was nothing coming out of the regulator (probably a 7805 but I didn&#8217;t even get round to checking). Turns out the trace was broken just before the regulator, when I bridged this everything started working&#8230; Sorry not a very exciting repair!<\/p>\n<p>You can see the bodge in the picture below (I used a small piece of wirewrap wire). I could do with cleaning the PCB up a bit more, but I&#8217;ll leave things as they are for the moment.<\/p>\n<p><a href=\"http:\/\/41j.com\/blog\/2018\/07\/corning-pc-420d-hotplate-stirrer-repair\/img_7892-2\/\" rel=\"attachment wp-att-4766\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-4766\" src=\"http:\/\/41j.com\/blog\/wp-content\/uploads\/2018\/07\/IMG_7892-1.jpg\" alt=\"\" width=\"538\" height=\"403\" \/><\/a><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I picked up a Corning 420D on eBay, the device was listed as not powering up and was relatively cheap so I figured worth a risk. It turned out to be a very simple repair, but I figured I&#8217;d write it up anyway&#8230; perhaps the reference images will be of use to someone. The device [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1],"tags":[],"class_list":["post-4759","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p1RRoU-1eL","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/4759","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/comments?post=4759"}],"version-history":[{"count":3,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/4759\/revisions"}],"predecessor-version":[{"id":4769,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/4759\/revisions\/4769"}],"wp:attachment":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/media?parent=4759"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/categories?post=4759"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/tags?post=4759"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}