Philips 170S Repair

A couple of months ago a friend brought me this monitor. Each time it was switched on, the image appeared for about one second and then the screen turned black but the power LED was still on.

After browsing the web searching for a solution I found out that most of the failures were related to the backlight circuit and could be repaired by replacing the power supply capacitors. So I picked my multimeter and started testing the capacitors and the oscillation on the supply voltage. Everything looked fine.

The capacitors didn't seemed to be causing the failure. I could not find the schematic for this monitor so I started to search for causes of the failure on the circuit board.
I identified the backlight inverter controller (BIT3193G) and after reading the datasheet I found out that this IC has a protection feature that, in case of failure, can disable the PWM output after a certain period of time defined by the capacitor present on the TIMER pin.

One of the pins related with failure detection is the ISEN (pin 15), this pin senses the load current and can detect a load malfunction. If the voltage on this pin is less than 1.3V, then there is a load failure and the controller shuts down the PWM. Because this was an old monitor, the only this that I needed was to make it work, I wasn't interested in buying new lamps to test if that worked and I didn't care much with failure detection so my goal was to make the controller think that everything was alright.

It was really simple, I just connected a 220K ohm resistor to the ISEN pin and the IC supply and that did the trick. The monitor is now working and I'm testing it for the weekend.

Rigol DS1052D Oscilloscope

This is my story about my Rigol DS1052D Mixed Signal Oscilloscope (MSO).
Until a few months back I was using a Fluke 123 Scopemeter to debug my digital circuits, but as the circuits got more and more complex and specially the serial communication needed more and more bytes to be sent, then the 512 bytes memory length of the Fluke 123 become too short for such amount of information.

So it was time to take the Fluke 123 of the bench to give room for a new instrument. After a couple of months analyzing the characteristics of the low cost oscilloscopes available on eBay, I decided that Rigol DS1052D (photo above) was the best for my needs.
A 1MB memory depth for a single channel or 512KB for dual channel along with their 16 channel logic analyzer makes this scope one of the best low priced scopes for most digital circuit debugging.

Until a couple of weeks ago, everything was perfect, but then, while exploring the menus, accidentally I selected a 'Special Mode' menu (if you have one of these oscilloscopes, do not press this button unless you are really bored and want to try 4096 code combinations to have your oscilloscope back). That's right, after pressing the 'Special Mode' menu button I got myself a MSO with a locked keyboard that could only be controlled through the PC via a USB cable.

Well, next step, e-mail Rigol, then wait. And while I'm waiting why not to try some codes? I've tried about 500 codes, including the more obvious, ie, 111111, 222222, etc, with no succeess. A few days later, while still waiting for reply, and with my fingers starting to hurt, I come to an idea. "If I can control the oscilloscope with the PC I must be able to send the key combinations as well.". That was my next goal, while still waiting for a reply from Rigol.

After trying (with no success) to communicate with the oscilloscope via the RS232 port, I searched the net to find something about the USB communication. So a little search and I found all the information I needed at http://www.circuitsonline.net/. So was time to code. I wrote a small program that sent sequential codes for the oscilloscope and instead of taking about 15 seconds for each code I was now trying a code every second, after a couple of hours I had my DS1052D unlocked, while still waiting for a reply from Rigol.

Any way, it is a excellent oscilloscope with a professional look and feel. By the way, the code was 424132 just in case you need it, I don't know if all the oscilloscopes have the same code but if so I hope this is useful for someone because I could not find anywhere on the net information about this. Please comment and if you try this code let me know if it works.

Welcome

In this Blog I intend to discuss some subjects about electronics with the main finality to exchange ideas, problems and solutions.

A little introduction about myself:
County: Portugal
Formation: Computer Engineering; Audio, Video and TV Electronics
Areas of interest: Digital Electronics, Home Automation, Display Systems, Microcontroller Programming

My main language is Portuguese so sorry for my English, please let me know if I write something stupid.
I hope you enjoy and collaborate with your comments.