dfarrington
Member
Q13 is -40v
I am going to pull R259 and R260 and check them. I may have blown them while working to fix Q22 and Q24. Will check tomorrow night.
Q13 is -40v
I am going to pull R259 and R260 and check them. I may have blown them while working to fix Q22 and Q24. Will check tomorrow night.
I believe so, and it also looks like the Protection circuit is working correctly with the current inputs. We are seeing major (different) DC offset from both channels. Still have 1KΩ in place of STKs.late to the party again . just checking if power supply voltages are all good right now ?
pins 1 and 3; 0 and 8 on both STK'smight be worth checking if the 1k resistors are in the correct places . something to rule out .
I will do this tomorrow night. just desoldered .22 ohm and soldering in another set. Measures are .3 to .4 ohms on each resistor. I will solder back in tomorrow and then check if I can adjust to 17.1vdc. Yes all the same as you state for Q5. I had just remeasured Q5 before pulling the .22 ohm resistors. it wont be until tomorrow night.dfarrington, do you still have 0vdc on the base of Q5, +39.9vdc on the collector and -0.619vdc on the emitter? If so is the junction of R237 and VR5 about -17.1vdc? Does it change when VR5 is adjusted? If so set for -17.1vdc.
I will do this tomorrow night. just desoldered .22 ohm and soldering in another set. Measures are .3 to .4 ohms on each resistor. I will solder back in tomorrow and then check if I can adjust to 17.1vdc. Yes all the same as you state for Q5. I had just remeasured Q5 before pulling the .22 ohm resistors. it wont be until tomorrow night.
OK. Note that when measuring very low resistances the leads contribute to the reading you get. You can compensate by touching the probes together and noting that reading, then measure the resistor, subtract the lead resistance you noted before, then the result gives you a closer, more accurate measurement of the very small resistor.
I can only get it to -.6v. I can adjust to -17v but not positive 17v
OK, that is good, and it adjusts up and down. The schematic I have shows an arrow to that point labeled "-17.1V". Is the common emitter on Q7 +0.6vdc as marked on schematic? Or are the voltages still as you previously reported:I set it at -17.1v
OK, that is good, and it adjusts up and down. The schematic I have shows an arrow to that point labeled "-17.1V". Is the common emitter on Q7 +0.6vdc as marked on schematic? Or are the voltages still as you previously reported:
Q7
B = -1.7v right side on schematic?
C = -38.5v
E = -1.1v <<==
C = -39.2v
B = 0v left side on schematic?
Should be +0.6vdc, let's eliminate the feedback path. Remove Q11 and lift one end of R255. Then power up again and recheck the voltages on Q7 and Q9. Without the feedback they should balance out. This will verify the transistors and other components in the differential amp (Q7) and the current mirror (Q9).
No problem, I was feeling the same way , you're welcome and goodnightOkay, I am sorry and would love to do more tonight, but I have to get some sleep. I will start again tomorrow night and should be able to stay up later. Will do then and as always, thanks for the help.
OK, that is good, and it adjusts up and down. The schematic I have shows an arrow to that point labeled "-17.1V". Is the common emitter on Q7 +0.6vdc as marked on schematic? Or are the voltages still as you previously reported:
Q7
B = -1.7v right side on schematic?
C = -38.5v
E = -1.1v <<==
C = -39.2v
B = 0v left side on schematic?
st
still the same at -1.1v
We eliminated the STK by removing it and putting in the 1kΩ resistors. Lifting the feedback will verify that the diff amp and current mirror are not the problem, unless they are not in balance without the feedback, which will then verify that the problem is in the diff amp and current mirror.3
You're going to drive yourself crazy at this arm. The -1.7 and -1.1 is because of the negative voltage on the output. Lifting the feedback will only make measurements more impossible.