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Old 04-01-2009, 06:50 PM   #1
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Default Can anyone shed any light on this problem?

Megasquirt Diy Problem Page - MX5Nutz

Already been stuck with this for a week :( Getting me down now. Anyone got any fresh ideas?

Thanks
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Old 04-01-2009, 07:06 PM   #2
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**** usb-->serial adapters
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Old 04-01-2009, 10:45 PM   #3
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If your loopback at the cable works but your loopback on the TTL side of the MAX232 doesn't, then the problem is between the DB9 and the chip socket. It's not the USB adapter or the PC. You mentioned you had the MAX232 in backwards. That most likely killed the first one, did you replace it with a brand new one? If so then you have another problem in addition to the orientation problem. To make a MAX232 work you need 4 capacitors, 5 volts, and ground. Check the caps, check for voltage on the power pins of the MAX232. If the voltage checks out replace the caps.
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Old 04-02-2009, 03:17 AM   #4
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Thankyou ^^^

Yes I did replace the MAX232 with a brand new item as I have a 2nd kit sat here. Ill check those voltages tonight then thankyou
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Old 04-02-2009, 05:59 PM   #5
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Lol its so bloody annoying because I have no idea if its my board, my pc or my DB9/usb adapter, my stim etc etc etc.

I replaced the MAX232 with a new one yes but now just trying to see what I get from my chip.

Heres the voltages I got. Note some read negative values, this correct??? The ones without a voltage were 0v. This was all taken with the heatsink as ground and not plugged into the computer, just a battery.




The image on the right is a drawing of a capacitor like c16/17. Have I missed something, or is the right hand leg on that ^ image the positive leg and therefore goes nearest to the posi logo printed ont he board?

Thanks
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Old 04-02-2009, 06:49 PM   #6
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Look at figure 5 on page 17 of the MAX232 datasheet. I've usually seen non-polarized caps used for the charge pumps (though I don't remember the details from my MS 3.0 build), but if yours are polarized and were in backwards that would cause problems. But your voltages look reasonable from a quick look. If you short pins 11 and 12 on the max232, does the loopback to the pc work?
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