trouble adjusting J99's

[dandeurloo]

Does anyone know what the Voltage should be set at for the AD797's that ship with the new kits. Mine are reading around 14.6v. I know the 990's can go to 24.v but not sure what to set these to.

Also, not sure what to do with the info in the J99 sticky as far as adjusting R45 and R50 with SW2. Does that info apply to these op amps? If so not clear on what it is suppose to do. I tested them and they read 0 or real close to it?

[tpryan]

Does anyone know what the Voltage should be set at for the AD797's that ship with the new kits.

+/18v

Also, not sure what to do with the info in the J99 sticky as far as adjusting R45 and R50 with SW2. Does that info apply to these op amps?

Yes.

If so not clear on what it is suppose to do. I tested them and they read 0 or real close to it?

R45, R50 and the associated resistors form a source for bias current that is separate from the current paths through the input and feedback resistances. Adjusting R45 and R50 for minimum offset makes the servos' job easier.

[dandeurloo]

ok, i as I was adjusting U1 and U2 up to 18v I only had to adjust R28. By adjusting R28 it rasied the value at U2 to match the 18v setting. No adjustment made to R32 at all. That seem odd? Is something not functioning properly or does this make sense.

It does this on both of my J99 pres?

[dandeurloo]

Basically, R32 doesn't do anything when I adjust it anyway? This is the case once again for both pres.

[tpryan]

As you can see from the schematic, U1, pin 3 and U2, pin 3 are both connected to +B, which is adjusted by R28. R32 adjusts -B, which you will measure at U1, pin 5 and U2, pin 5.

[dandeurloo]

Also, when I measure v on the op amps the negitive and positve sides don't match any more. The positive side is up around 18 and the negitive is still around 14.6?

[dandeurloo]

Well now it makes sense! thanks.

[dandeurloo]

Tim, now when Biasing these babies my meter jumps all over the place and steadily drops with time. SHould I use the intial reading of each direction of the switch or wait until it settles down at a number? it drops a lot.

[dandeurloo]

How many volts or milvolts should these numbers be apart. After tweaking for about 40 mins. I can't get them very close.?

u1: -6.3 to -2.0
u2: .98 to .03

second kit

u1:-7.0 to 39.0
u2: -.05 to 1.98

[tpryan]

It sounds like you are trying to make adjustments with the servos connected. You need to move J6 and J8 to the "adj" positions while adjusting R45 and R50. Get the voltages as close as you can at either extreme of SW2, then move the jumpers to their usual positions.

[dandeurloo]

I had them with the jumpers away from the switches on both j6 and j8? is that correct. I figured the pins went from front to back? What is the correct config for testing? I can't tell from the schematic. I noticed on the bards the ADJ position is marked on the outside of each.

Also, does it matter that the op amps are installed?

[tpryan]

I had them with the jumpers away from the switches on both j6 and j8? is that correct.

Nope.

I noticed on the bards the ADJ position is marked on the outside of each.

That's correct. For normal operation, jumper the "inner" pins.

Also, does it matter that the op amps are installed?

The op-amps must be installed to make these adjustments.

[dandeurloo]

ok, I have them jumpered correctly now. I got U1 to be around -2.2 to -3.6 with my DMM set to 200m DCV. U2 still is a problem it measures at -.6 to .05 with my DMM set to 20 DCV.

Does this seem correct?

[tpryan]

That's good for U1, you should be able to do better at U2.

[dandeurloo]

U2 on both of my kits is really jumpy? Is that the nature of it or am I possible doing something wrong?