[volt-nuts] DAS-46 CSA repair - fixed

[Jerry Hancock]

Hello, again all:

Interesting thing happened today as the MFE3002 FETs showed up.   You might remember I was using the NTE/ECG 220 knock offs.   I plugged them into the board tightly and I wasn’t able to zero it.  I then put the ECG knockoffs back in and they zeroed.  I thought, what the heck, I paid for them, so I put the MFE3002 back in this time reversing them as the board uses two.  The risk in touching these is they are very, very static sensitive.   It then zeroed with the devices reversed.  The circuit must be sensitive to the gate or base voltage somehow.  I don’t know, but it zeroed so I soldered them in and the board is working fine now.  It zeros and the +/- (normal/reverse) voltages are balanced.  

I can now say I am the expert on the DAS-46, DAS-47 and 57 CSA assembly!

Again, if anyone wants to play with the chopper model in LTSpice, please drop me a note.  I am adding part numbers where available, etc.  This will make it easy for those knuckleheads that follow me.  Now I know why they wanted $400 plus 10 weeks for another one!

Jerry