Service Forum

[noyp]

hello everyone,

im just started collecting parts for my driven serial programmer although i dont know how to read a circuit, now my question is i bought a 1uf (micro farad) capacitor with 50 volts printed on its side is this ok for my interface as my chip is labeled MAX232N and one more thing is there a sample driven serial programmer pictures where i can just copy from start to finish, im using breadboard for my interface.

[rkawakami]

Check the following topic for a discussion of how people have sucessfully built interface circuits and unlocked systems:

http://www.allservice.ro/forum/viewtopic.php?t=123

I have created a web page with a description of how I built my driven interface circuit and read the password from a locked IBM 600X. You can find it at:

http://www.rkawakami.net/ibm_600x/bios_pass

The 1uf, 50V capacitor is okay for the MAX232N (you need five of them). Actually, anything over 15V should work fine for this circuit. You can substitue 1N914 diodes if you can't find the 1N4148. The photos of my breadboard show how I laid out the components. The only things to watch out for is that since the board I am using has two power strips on both sides of the board, I tied them together on the left side using a series of wires (see the first photo in the section titled "Starting the proces to read the EEPROM". I also have a couple of "extra" capacitors plugged into the board only because I wanted something that I could attach the small clips to.

Good luck!

Ray

[noyp]

hi ray,

thank you for the reply, as you know i tried for the first time my driven programmer this morning and thought that it was working already as i got the message "eeprom not available error" which is obvious since i did not connect it to the eeprom yet, but when i tried it again this time connecting it to the eeprom i got the same message which is strange. i just copied wolfman's layout from top to bottom checked and verify that all connectors are ok. i suspect the problem lies on the capacitor since im using the electrolyte type not the ceramic one, and i never see any electrolyte type capacitors that works.

ill try looking for a ceramic type capacitor, let you know on the result.

BTW, is there any picture layout of the simple circuit as im going to try this one also.

[rkawakami]

The 1uF (MAX232) or .1uF (MAX232A) capacitors work best with the ceramic type as opposed to the electrolytics, simply because you don't have to worry about the polarity. If you do want to continue using the electrolytics then I can refer you to the following datasheet:

http://www.ortodoxism.ro/datasheets/texasinstruments/max232.pdf

Check page 7 to see the proper polarity of each of the capacitors. All of them, except the one connected to pin 6 of the MAX232, are connected logically. That is, the + side of the cap is connected to the appropriate + pin on the MAX232. The cap on pin 6 must have the + lead connected to GROUND since that pin actually goes negative with respect to ground. The caps, if they are of the electrolytic type, should have a lead marked as the positive one. Sometimes it's an actual + sign, other times it's simply a line or stripe next to the pin.

Also double-check that the SDA, SCL and GND pins are being connected correctly. I had a problem with one of my attempts when I had the GND and SCL wires swapped. I kept getting the "EEPROM not available" message as well.

I have not seen any layout of the simple interface circuit (the one using the zener diodes). I have read that it does work but from my point of view, the driven circuit using the MAX232 should work better since it more closely matches the actual signal formats.

edit: I just noticied you said you copied "wolfman's" layout. There is an error in the way his diodes are connected in the picture of his breadboard. Compare his breadboard picture with mine and you should be able to see the difference. His diodes are vertically in the same column of holes in the breadboard. Since each column of holes above and below the centerline of the breadboard are connected together, his diodes are being shorted out and therefore are not working properly.

Ray

[victor]

Max232N which is made by TI uses 1uF. It does work with 0.1uF but the internal charge pump is a bit weaker.

To see if the IC does well, check the voltage on pins 2 and 6:
2= ~+8V;
6=~-8V;

In rest, there are connection issues.

Wolfman circuit worked (erraticaly) due to the pull-up internal resistors (old good MAXIM ICs, he he), but you must do it right with the diodes, as Ray stated here.

Good luck!

[rkawakami]

In response to a couple of questions posed by "noyp", I have put up another web site describing in detail how I laid out my driven interface breadboard. Hopefully it contains enough information on the "whys" and "hows" that one would encounter when trying to duplicate what I did.

http://www.rkawakami.net/ibm_600x/max232_if/

Ray