Draft of next reverse engieneering blog post

content/posts/2018-06-20-Reverse-Engineer-a-Saike-858D.md

@@ -30,7 +30,7 @@ room for improvement. That is what I am trying to do here.
 This first post will not cover everything so here is a Table of Contents where I can link the next posts:
 
 * Mission Statement and Teardown (This)
-* Reverse Engineering (WIP)
+* [Reverse Engineering]({{<relref "2018-06-21-Saike-858D-Original-Schematic.md">}})
 * ...
 
 ## Problems

content/posts/2018-06-21-Saike-858D-Original-Schematic.md

@@ -0,0 +1,59 @@
+---
+title: "Saike 858D Rework Station - Original Schematic"
+date: 2018-06-22T14:50:00+02:00
+author: eNBeWe
+type: post
+categories:
+  - Allgemein
+  - Bastelkram
+tags:
+  - 858D
+  - DIY
+  - Arduino
+---
+Recently, [I posted the teardown]({{<relref "2018-06-20-Reverse-Engineer-a-Saike-858D.md">}}) of my Saike 858D SMD rework station.
+Now it is time to really reverse engineer the main PCB.
+Some of the parts are similar to other "flavors" of the 858D, but some seem to be different.
+<!--more-->
+
+## Approach
+
+My process of reverse engineering can be seen in the following picture (click for large version).
+
+[![Saike 858D Reverse Engineered](/posts/images/858D/Reverse-Engineering.jpg)](/posts/images/858D/Reverse-Engineering-big.jpg)
+
+I started with a picture of the copper side of the PCB which I flipped horizontally,
+so this view is kind of an "X-Ray" view through the front side of the PCB.
+
+Then I started with marking most of the copper traces in different colors.
+Most of the colors are just randomly chosen, but the yellow area is the +5V VCC line and the 0V areas are marked blue.
+
+Afterwards I added all the components on a second layer. Due to the mirrored back side graphics,
+I can match the position to the image of the front side of the PCB and still read parts numbers.
+
+Lastly, I added all part references and as much part information as possible, i.e. part names, pin names, etc.
+I took the values from resistors from their marking visible on the images. However I am not entirely sure
+that all values are correct, because at some places I have the nagging feeling that the values are not matching my expectations.
+
+## Schematics
+
+I rebuilt the schematics of the PCB in KiCad. Here is the complete schematic in all it's glory.
+
+[![Saike 858D Schematic](/posts/images/858D/858D_Schematic.png)](/posts/images/858D/858D_Schematic-big.png)
+
+Let's go through the parts one by one.
+
+### Mains connection and Heater driver
+
+[![Saike 858D Mains Heater](/posts/images/858D/858D_Schematic_Mains_Heater.png)](/posts/images/858D/858D_Schematic_Mains_Heater-big.png)
+
+The left part of the schematic is about as simple as possible. 
+The mains power is bridged over to the connector for the transformer.
+The only notable part is a big suppression capacitor (0.1uF 275V) by Tenta.
+
+The right part of the schematic is the heater control circuit.
+The microcontroller can control the NPN-transistor Q1 through the limiting resistor R4.
+This pulls down the cathode potential and activates the optocoupler U2 which is a MOC3041.
+The MOC3041 is a triac driver and that it does. It contains a zero-crossing detection 
+circuit and controls the triac U1, which in my device is a BTA16.
+