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io board voltages all inverted
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io board voltages all inverted

by jcoplin on Thu Jun 02, 2005 11:36 pm

In trying to figure out my envelope woes and looking into someone elses LED problem, I noticed that one of the latch readings I took was negative instead of positive. I started checking other values and it looks like everything is negative voltage! I checked my multimeter against a battery and it is reading polarity correctly.

I went back through the calibration / testing procedures starting with the IO board and I'm seeing some values that look completely whack! The IO board is disconnected from the main board except for J3. Some readings I took on the board show that:

IC20, 2: -5.33v

J4, 1: 0v
J4, 2: -5.33v
J4, 3: 6.49v

J5, 1: -5.33v
J5, 2: -5.33v
J5, 3: .6v

J3, 1: -.42v
J3, 2: -.25v
J3, 3: 0
J3, 4: -.29v
J3, 5: 0v
J3, 6: -.27v
J3, 7: -5.33v
J3, 8: -5.33v
J3, 9: floats between -2.72 and -2.83 is a regular cycle
J3, 10: -5.33v
J3, 11: -5.33v
J3, 12: -5.33v

Everything was correct polarity when I built the power supply, now it seems to be off after doing the IO section. Is something seriously screwed here or is this correct? I've reflowed all the connections, I've checked all the components a dozen times, everything looks to be in the correct orientation. I'm really about ready to throw the whole project in the dust bin. HELP!!!!:cry:

James
******************
If anyone asks of my whereabouts
simply tell them I've gone out the window
for a spot of tea and am not
expected back anytime soon.
******************
jcoplin
 
Posts: 18
Joined: Sat May 28, 2005 11:18 pm
Location: Minneapolis

Re: io board voltages all inverted

by adafruit on Fri Jun 03, 2005 12:19 am

jcoplin wrote:J4, 1: 0v
J4, 2: -5.33v
J4, 3: 6.49v


without going further, it may be insightful to look at the schematic... pin 2 of J4 is "ground", not pin 1. Remember that "ground" is really a reference (voltages are measure from ground), so if you change your reference (from pin 1 being ground to pin 2) then you get
J4.1 = 5.33V
J4.2 = 0V
J4.3 = 6.49+5.33 = 11.82 (12V)

which is correct ;)

adafruit
 
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by jcoplin on Fri Jun 03, 2005 10:32 am

I was using R179 on the IO board for ground per the fab manual. If I use pin 2 J4 as ground the numbers work out but R179 leads to all the inverted and shifted values. Is this correct or am I seeing a ground problem here. If all the voltages are relative to pin 2 J4 and not R179 (at least after all the circuits are built) maybe a change in the fab manual?

Also, is the beta schematic also the final schematic or at least the current schematic?

James
******************
If anyone asks of my whereabouts
simply tell them I've gone out the window
for a spot of tea and am not
expected back anytime soon.
******************
jcoplin
 
Posts: 18
Joined: Sat May 28, 2005 11:18 pm
Location: Minneapolis

Please be positive and constructive with your questions and comments.