Not quite the right output voltage range on ic23 pin 5

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tlann
 
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Not quite the right output voltage range on ic23 pin 5

Post by tlann »

I've built my Willzyx kit up to the point of the trimpot. Everything has been in an acceptable range until this point.
When I turn the trimpot, the voltage goes from 4.93V to 5.32V on pin5 of ic23.

Things I've tried,
Verifying the resistor values are correct. Verified the Diodes are placed correct.
I also reheated the solder to make sure it has a good connection.
The trimpot also has 202 on it. The trimpot is 1.946k Ohms from the two furthest pins.
Diodes D44 thru D46 all measure voltage drops of about 0.533V.
Measuring from ground the voltages are
D44 0.533V, 0V
d45 1.065V, 0.533V
d47 5.32V, 4.79V
D46 4.79V, 4.26V

The voltage range bothers me. Although, I can almost meet the criteria of 5.33V. I'm out of ideas on what to try.

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mmm
 
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Re: Not quite the right output voltage range on ic23 pin 5

Post by mmm »

tlann wrote:I've built the kit up to the point of the trimpot. Everything has been in an acceptable range until this point.
When I turn the trimpot, the voltage goes from 4.93V to 5.32V on pin5 of ic23.
The voltage on pin5 is un-trustworthy; please check on pin7 instead. I usually get different voltages for pin5 and pin7. AFAIK this has something to do with the internal impedance of the multimeter.
If that voltage is also too low we'll check further.

tlann
 
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Joined: Wed Dec 09, 2009 12:55 am

Re: Not quite the right output voltage range on ic23 pin 5

Post by tlann »

MMM wrote: The voltage on pin5 is un-trustworthy; please check on pin7 instead. I usually get different voltages for pin5 and pin7. AFAIK this has something to do with the internal impedance of the multimeter.
If that voltage is also too low we'll check further.
Thanks for replying so quick.

Pin 7 is 0 Volts.

My electronics chops aren't that good. I haven't got to the step where I put in IC23. I'm right before that one. And looking at the schematics, it looks like pin7 would supply the 5.33 volts and if it isn't in I wouldn't see anything there. I don't remember my circuits, but is first op-amp some sort of negative feedback?

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mmm
 
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Re: Not quite the right output voltage range on ic23 pin 5

Post by mmm »

Yes, you need to put IC23 into the socket before you can measure anything meaningful at pin7.

The first op amp circuit is a buffer which means that theoretically you should see the same voltage on both pin5 and pin7. However in reality this seems to depend on the impedance of the multimeter.

tlann
 
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Joined: Wed Dec 09, 2009 12:55 am

Re: Not quite the right output voltage range on ic23 pin 5

Post by tlann »

MMM wrote:Yes, you need to put IC23 into the socket before you can measure anything meaningful at pin7.

The first op amp circuit is a buffer which means that theoretically you should see the same voltage on both pin5 and pin7. However in reality this seems to depend on the impedance of the multimeter.
So I soldered it and the caps in last night and the voltage is the same as pin 5.

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mmm
 
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Re: Not quite the right output voltage range on ic23 pin 5

Post by mmm »

Could be that IC22 is faulty. This has happened before, too.

tlann
 
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Re: Not quite the right output voltage range on ic23 pin 5

Post by tlann »

MMM wrote:Could be that IC22 is faulty. This has happened before, too.
What should the voltage be at the pins of ic22? I realize this varies depending on the trimpot. I would like to figure out some way to test ic22.

tlann
 
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Joined: Wed Dec 09, 2009 12:55 am

Re: Not quite the right output voltage range on ic23 pin 5

Post by tlann »

MMM wrote:Yes, you need to put IC23 into the socket before you can measure anything meaningful at pin7.

The first op amp circuit is a buffer which means that theoretically you should see the same voltage on both pin5 and pin7. However in reality this seems to depend on the impedance of the multimeter.
I just got a Rigol DS1052. I haven't measured the voltage yet but I'm thinking if it still incorrect then it is definitely not the impedance of my multimeter.

A funny aside, I took a circuits class once and the teacher pronounced impedance as impotence.

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