Wavetek 288 unknown calibration error

[Ground_Loop]

My Wavetek 288 has developed the sniffles and gives an error TORFR7 upon auto calibration which is not listed in the service manual apart from a troubleshooting procedure to isolate the offending card.  Do any of you happen to know what that fault is.  It still performs as it should as far as I can tell, but will not complete the auto calibration routine without that error.  I followed the troubleshooting procedure and ended up swapping a card, but no joy.  It's not imperative that this be resolved because as I said it still appears to be working ok.

[wn1fju]

My unit has always exhibited mysterious behaviors as have a few other people's units who have had similar problems.

If I had to take a wild guess, perhaps the TORFR7 has something to do with the frequency range switching.  One of the block diagrams shows some FR5, FR6, FR7, etc control lines in that area.  Does the unit operate at all frequency ranges?   Again, just a wild guess.

My 1288 threw an auto-cal error when I first got it.  Then, after I ran through the manual calibration, it threw a different auto-cal error.  Then I ran the auto-cal a few more times and it finally passed.  Many months later, I turned it on and threw yet a different auto-cal error.

So, all I've been able to do is remove the battery, wait until the RAM contents evaporate, go through the manual calibration, and then run auto-cal (several times).  Doesn't make any sense, but like your 1288, I never noticed anything wrong with the unit and it seemed to pass the specs.

Post an answer if you ever get to the bottom of this!

[Ground_Loop]

I went through the calibration routine several times in order to get the 'calibration required' message to go away. It's really annoying they don't describe the fault messages.  I saw the FR5, FR6, FR7 lines in the block diagram, but without a description and schematic I'm stuck.

[Ground_Loop]

It turns out there was a problem after all.  In the 20KHz - 200KHz range, the SIN wave output was badly distorted on the positive half.  The triangle wave that feeds the SIN converter had positive amplitude problems but frequency was correct.  I traced the problem to the High Frequency Compensation (HFC) circuit.  HFC voltages are set by a DAC which has reference voltage inputs from a previous stage.  The reference voltages were correct for each frequency range, so I began to suspect that there might be a DAC problem.  However, all other frequency ranges operated correctly, so my attention turned to a problem with stored data from the uC driving the DAC.

So, not suspecting any failed parts at this point I shut down and pulled the keeper battery.  Upon restart, the uC pulled in baseline data and produced perfect sinewaves. After performing a calibration and executing a self calibration, my sig gen is completely happy.

I'm not sure what happened to corrupt the stored data, but for sure an odd problem.