what am i doing wrong?

[m3vuv]

Hi all im building this octopuss as in the pdf attached,i ham having issues trying to set the voltages on r3+ r4,both sit at about 2.3v and only change about 100milli volt each way i turn the pots,the circuit is built exactly as per the schematic,exept my trans former is a center tapped 20v unit,im just using one leg,do i need different value components,the ac output of the transfo is 14.4v unloaded acording to my fluke 83 and avometer mk 8,any ideas whats going on here?

[m3vuv]

well  ive noticed something wierd,on the part where you have to set the voltage on the probes using the pots on channel a,the black probe goes to ground,ground of what exactly?,i had the grounds on the schematic going to mains ground and the body of the transfo,like that i couldnt alter the voltages with the pots more than a couple of hundred millivolts,if i measure between the red probe and the side of the transfo output,oposit the junction with c1,it adjusts fine,any ideas,is it some sort of wierd ground loop?

[m3vuv]

well using the lower leg of the transfo all the voltages setup bang on,could it be a mistake in the schematic?,i dont fancy connecting this to my dso and using that as the ground reference as i can see if i do i will be back with the original issue and all the voltage settings will be off againe,am i loosing the plot??

[m3vuv]

found the issue,it was a leak on the transfo primary,nearly drove me mad,fitted a new 12volt 1.5va transfo and works fine.

[Terry Bites]

 Are you talking to yourself again? - its ok.

[m3vuv]

is it a sign of madness?,i do it all the time,its this darned schematic driving me nuts!

[m3vuv]

Quote the pdf,on how to set output test probe voltages.
output voltages following these steps.
(1) – Check to make sure that you have 12 V ac at the Octopus input. If so, solder a temporary jumper between CH1A and R3.
(2) – Set the variable resistor R3 for 1 V ac between the red and black lead outputs on the PC board. Then disconnect the temporary jumper from R3.
(3) – Connect the jumper from CH1A to R4. Set R4 for 5 V ac. Then disconnect the temporary jumper from R4.
(4) – Connect the jumper from CH1A to R5. Set R5 for 10 V ac. Then disconnect the jumper from R5 and keep it to CH1A.,how can this work?, as the black wire has no connection to ground without 1b connected!should 1b not be connected in order to set 1 a?