69599Re: [softrock40] Bad chip?
- Oct 30, 2012
----- Original Message -----
Subject: [softrock40] Bad chip?
> I'm running the tests for the tx opamp stage of a tx/rx ensemble build, per the instructions at
> Everything checks out fine except for 2 voltages. Pin 1 of U6 is reading 5 volts instead of 2.5, and pin 7 of that same chip is
> reading near 0, instead of 2.5. This is unbridged, with or without the USB connected, with power.
> It has passed all prior tests, including receiving a signal in CW over the air. I have continuity-tested every pin of both chips
> U6 and U7 to make sure each pin connects to each solder joint, and I have checked that no pin shorts to any other pin, except pin
> 3 to pin 5 on both chips, as they should. Pin 1 to Pin 6 shows 10k resistance, as it should, on both chips. I have double-checked
> the value of every resistor in the TX circuit. I even pulled R21 to do a direct measure because it was reading about half its
> actual value plugged in. Pulled it read 2.21k as expected. Pin 1 and 7 of U7 both read correct values of 2.5 volts. So my question
> is, do I have a bad chip? Something else I can check?
> The voltage to R23 hairpin is 2.5, as is R15 and R16, R24, R22, R21, R20, R19 and R18. Only R17 reads 5 volts. I can't see how it
> is coming anywhere but from the chip.
> R25 is -1.2, R26 is 2.5, R27 is 2.5, and R28 is 1.6. The weirdest one there is R25, so I checked the other side of it and it
> reads -.9. The last chip is uninstalled at this point, but I'm not sure where the negative voltage is coming from.
Where have you got the meter negative clip?
73 Alan G4ZFQ
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