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getting ~4.39 instead of 5.333... help!
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getting ~4.39 instead of 5.333... help!

by tospasto on Sun Aug 05, 2007 5:54 pm

okay, the first problem I had was that the voltage across the power jack terminals is around 9.7 V (instead of 12V), although the wiki says it can vary between 10 and 14 so I didn't worry too much about it at first. I am using the US wallwart bought with the x0xb0x but with a transformer to use with the UK mains, might have anything to do with it?

Now I have finished the power supply and the voltage at pin 3 of J4 is also around 9.7V. The voltage at pin 2 is about one volt too low at 4.4ish instead of 5.333. I wonder if the low voltage I am getting at the jack terminals has anything to do with this?

I've searched and found two people who had similar problems getting 5.333V, although neither mentioned low V at the jack terminals.
http://www.ladyada.net/forums/viewtopic.php?t=608
http://www.ladyada.net/forums/viewtopic.php?t=529
I have checked everything that was suggested in these topics, namely the voltage drops across the diodes in D44-D47 (seems to be roughly 0.6V), re-checked that I used the correct resistors in R3, R4 and R5, and checked that I had used the 202 potentiometer.

Any advice is very welcome, I'm not experienced with this kind of thing at all. The only thing i can think of is that the initially low V is causing this problem, and maybe getting a proper UK wallwart will help.

Thanks!

tospasto
 
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by guest on Mon Aug 06, 2007 11:02 am

what are the voltages
on all of the pins of ic23
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by tospasto on Mon Aug 06, 2007 2:17 pm

i measured V from one corner across each pin, thought this drawing might be the easy way to show you what I got:

Image

tospasto
 
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by guest on Mon Aug 06, 2007 4:53 pm

the opamp seems to be doing the right thing
check r2 r3 r4 and r5 to make sure they are correct

what is the votlage at
r2 and r1 juncture
r2 and r3 juncture
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by tospasto on Tue Aug 07, 2007 8:58 am

r1, r4 and r5 are fine. r2 is giving me about 0.8K instead of 1. On r3 i am only getting about 4.5K instead of 6.8, but it rises very slowly when i have the multimeter contacts on it, I don't know what is going on there.

cant seem to get a voltage reading between r2 and r1 or r2 and r3, maybe im being stupid...

thanks for your help

tospasto
 
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by guest on Tue Aug 07, 2007 1:45 pm

does turning tm6 change the voltage any
is ic22 the lm336z-5.0
and is it in the correct orientation
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by tospasto on Tue Aug 07, 2007 2:06 pm

turning the tm6 does change the voltage, between 4.38 and 4.41. it is definitely the right part (202) and in correct orientation (indented semicircle matches the circuit board)

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by guest on Tue Aug 07, 2007 4:29 pm

connect the ground probe of your meter to ground
and then touch the positive probe to the following points
and see what the voltages are

d44 d45 juncture
d45 r5 juncture
r5 tm6 juncture
tm6 r4 juncture
r4 d46 juncture
d46 d47 juncture
d47 r3 juncture
r3 r2 juncture
r2 r1 juncture
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by tospasto on Wed Aug 08, 2007 9:32 am

okay i think im doing this right...

d44 d45 juncture = 6.61
d45 r5 juncture = 9.67
r5 tm6 juncture = 9.65
tm6 r4 juncture = 9.60
r4 d46 juncture = 9.55
d46 d47 juncture = 8.94
d47 r3 juncture = 8.31
r3 r2 juncture = -10.34
r2 r1 juncture = -13.11


does any of that mean anything to you?

tospasto
 
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by guest on Wed Aug 08, 2007 12:58 pm

did you leave the negative probe of your multimeter
on the same point for all of those readings

are you sure those last two readings are negative

none of the voltages make any sense

check your multimeter on a 9v battery
to make sure it reads approximately 9v
your meter may be having troubles
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by guest on Wed Aug 08, 2007 1:04 pm

can you double check that r4 is 5.6k
and that r5 is 2.4k
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by guest on Wed Aug 08, 2007 1:06 pm

also make sure that tm6 is 2k and not 5k
this is more likely the problem than r4 and r5 being swapped
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by tospasto on Thu Aug 09, 2007 6:17 am

sorry, i think i was doing something very stupid, these should make more sense hopefully

d44 d45 juncture = 3.07
d45 r5 juncture = 3.30
r5 tm6 juncture = 3.30
tm6 r4 juncture = 3.30
r4 d46 juncture = 3.45
d46 d47 juncture = 3.89
d47 r3 juncture = 4.32
r3 r2 juncture = 23.4
r2 r1 juncture = 26.2

doublechecked r4 = 5.6K, r5 = 2.4K, tm6 = 2K

tospasto
 
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by guest on Thu Aug 09, 2007 2:05 pm

d44 is busted
try replacing it with one of the other diodes in the kit
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by tospasto on Thu Aug 09, 2007 6:55 pm

ah youre amazing, that fixed it! thanks again!

tospasto
 
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