Draft of next reverse engieneering blog post

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Nis Wechselberg 2018-06-21 17:18:00 +02:00
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@ -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: 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) * Mission Statement and Teardown (This)
* Reverse Engineering (WIP) * [Reverse Engineering]({{<relref "2018-06-21-Saike-858D-Original-Schematic.md">}})
* ... * ...
## Problems ## Problems

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---
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.

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