Hi,
I'm working on an HP 3325a function generator that I've neglected. Power is fine. I found one problem in that the sine works (up to a point, see later) but the square, tri, ramps, don't at all. I get an "A Cal Fail" error. This looks like a U32 issue as U31 pins 6 and 8 (outputs of an inverter into U32) are low all the time. This is a posted problem in the manual (repair group J). I ordered a replacement sn74ls290, about the only 74LS IC I don't have.
Later:
Setting aside the problem with U32, sine wave frequencies under 5Mhz look ok. Above that they start distorting until at 20Mhz, the lower half of the sine wave is pretty much gone. But, if I set the DC offset to anything above zero, no matter the P2P voltage value, it clears up. Setting it to 1/2 the amplitude in P2P is the cleanest. Having typed that, I'm going to dig around in the offset area but was wondering if anyone had bumped into this? I found this after ordering the 74ls290 at a ridiculous price from Jameco. I ordered the 74ls290 as well as the other ICs after U32 just to make up part of the minimum. So it looks like I am going to have another minimum order to make up.
earlier:
I found a burned IC in the output attenuator. Complete toast. It is the size of a 1/4w resistor and looked like one. It is just to take the spikes off the relay coils. This could be another minimum order once I have the other two issues fixed.
I studied the offset and everything up to the output amp, checked voltages, etc, they look OK but something is clearly wrong as it should be floating the output unless a DC offset is applied. I know I'm not giving much input here, but if you've worked on a 3325, then some of this might sound familiar, I hope.
Thanks,
Jerry