Service Forum

[Maeglamor]

Thanks to Victor's efforts I managed to successfully repair my T20 thinkpad very quickly, he kindly sent me a eeprom image to fix CRC-0175. I know a thing or two about electronics so I thought I'd show anyone who wishes to build the driven circuit a couple of additions that I had added to ensure everything was working correctly. I used 0.1uF electrolytics, I had part of the circuit built from the last time I had used it as a phone unlocker so I knew it worked. The circuit isn't too fussy.

The first addition was a 5V regulator with a power indicator, quick way to verify that you have power connected and the circuit is recieving the 5V DC it requires. It works off a single 9V PP3 battery which was handy for me as I had the parts (78L05's are cheap if you're thinking of picking a few up).
The second is a LED indicator that you can connect to the SDA in or out (CTS, DTR) lines (or both) as a verifier that the data is flowing to or from the serial port on the computer.


Victor's circuit works fine without these additions (as you may have guessed given the number of success stories posted on the forum) so think of the LED's as a visual indicator that the circuit is working as it should.

[victor]

Hi,

Thanks for the feedback.
I only can say that the LMpart needs an elco 100uF right after the the LM regulator. Also the part with the LED on pin 2 would rise the overall output voltage with at least the LED Vak open voltage which is 0.7-1.2V, the pin2 is working as the reference. So has no sense to be put there. On the LM output, maybe....

But all this power is not recommended. Even if is strange to say so. Usually the eeprom and other logical circuits works at 3.3V. They are compatible with 5V TTL level (not all) but if the current is a bit to high the response drops drastically. That's why is recommended that the level to be lower than 5V.

The best circuit there would be based on MAX3232 (which works at 3.3V) and supplied with 3.3V through a LM circuit. But I made this on classic MAX232 which is more easy to find.

Sorry, I didn't mean to sound critical, he.

Thanks again for the input!
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Victor Voinea
ALLservice HQ, Romania.

[Maeglamor]

Thanks Victor, I appreciate the feeedback. I have to admit that I wasn't paying too much attention to the voltage on the I/O lines to the serial port, I saw another design that used something similar and copied it. Had it not worked I'd have simply taken the components out of the circuit instead of trying to troubleshoot it.

I think I get what you're saying re: the LED on pin 2 of the voltage regulator, I've effectively changed the reference to ground so the regulator would be providing over 5V to the circuit due to the LED and resistor I added.

[victor]

Thanks Maeglamor!

Yes, that is what I wanted to say..
_________________
Victor Voinea
ALLservice HQ, Romania.