XScope shows 20V on empty channels

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7 years 4 months ago #1311 by skostrub
My beautifull Xprotolab is broken.
Both channels shows 13V voltage (in meter or scope mode) and do not react on input signals.
Can someone ?kindly point me how this can be fixed?
I tried to replace the nagative voltage genarator (according to the troubleshooting guide) with no luck - now it shows 20V...

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7 years 4 months ago #1312 by ganzziani
Do you have all the correct voltages? (-5V, 3.3V, 2.048V)

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7 years 4 months ago - 7 years 4 months ago #1313 by skostrub
U4 OUT shows 0.54V (input is 5.1V and all capacitors are OK)
U1 pin 40 shows 0.27V (instead od 2.048V) pin 39 shows 3.3
U2 out shows 3.28V
?
tl064cdr pin voltages:
1?? 4.39V???? 8?? 1.95V
2?? 0.98V???? 9?? 1.95V
3?? 0.15V?? 10?? 2.03V
4?? 5.11V?? 11?? 0.54V
5?? 0.14V?? 12?? 0.64V
6?? 3.94V?? 13?? 1.05V
7?? 4.39V?? 14?? 1.25V
Last edit: 7 years 4 months ago by skostrub.

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7 years 4 months ago #1315 by ganzziani
Those voltages do not look good. I don't see the negative 5v nor the 2.048V. The negative voltage generator is bad and probably the 2.048V reference.

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7 years 4 months ago - 7 years 4 months ago #1316 by skostrub
I've already replaced negative voltage generator (TPS60403DBV according to BOM), but the new one also does not show -5V.
So I thinks it can be burned after powering on. If so? what component can damage it?
?
I have one more TPS60403DBV. Is there a risk to burn it after replacement again?
Input is 5V - OK.
?
D1 LM4040D20IDBZ pin 1 shows 2.048V






Last edit: 7 years 4 months ago by skostrub.

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7 years 3 months ago #1318 by agmihos
I suggest you the following:/\r\n/First, while power is off, measure the following:/\r\n/1) Resistance on charge pump output (pins 1,4) . If resistance is less than 10? then probably you have shortcircuit at the output (accententaly soldered together pins), or damaged charge pump. Less like to have damaged capacitors C26, C27. If you have accintentaly place voltage to AWG, may the problem caused by a damaged TL064 (U3)/\r\n/2) Resistance on charge capacitor (pins 3,5) . If resistance is less than 10? between or by any other pin of charge pump, then you have damaged charge pump. Less like to have damaged to capacitor C25./\r\n/If no problem found, power up circuit./\r\n/1) Measure the input voltage of charge pump (pins 2,4). Should be 5V. If not, problem is before charge pump. Check for a broken PCB line. If voltage is over 5.5V then the problem is power supply./\r\n/2) Measure directly output voltage of charge pump (pins 1,4). If you found -5V then check for a broken line after charge pump. If no volt, then, while circuit is powered place an external power supply on -5V. Be careful to place correct voltage and polarity. Also, after test completed remember to cut first external -5V, and THEN xprotolab power supply. If current is high, then a cheap infrared thermometer can help you to find the damaged part./\r\n/

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