While sitting at home today sick (Bad head and chest cold) I decided to try my luck at repairing a function generator I recently picked up for 5 bucks. I quickly knew the fault was a shorted component and decided to use a 1.5 volt battery as a load to trace down the faulty component. I was able to repair the unit and now need to do an alignment on it and give it a good cleaning.
And no I am no ways a master video blogger, just an old country boy trying to learn more things.
I hope some enjoy it.
Hey Radio Tech,
I am aware this is an old thread, but I know you are still active on Youtube, so I'm hoping you are also still checking this forum. I was wondering if after the repair you managed to properly calibrate your IG-1271 as described in the manual, mostly in terms of the output frequency dial linearity properly aligning at the 0.1, 1.0 and 10 dial marks.
Got actually an SG-1271 off ebay, so this was factory wired, not a kit. No problems with this unit, so just wanted to do the cal procedure to make sure everything is on spec. First one is instructed to do the lo/hi dial calibration, which is basically to adjust both the Low Freq Dial adjust and Symmetry adjustment trimmers to get an even 100Hz triangle wave output at 0.1 dial position, CHECK. Then rotate dial to 10 position and calibrate High Freq Dial adjust trimmer for a 10KHz output, CHECK. And finally set dial back to 1.0 position (where before any further adjustment I'm now reading 833Hz output at this point) and readjust Low Freq Dial adjust trimmer for 1KHz, CHECK. Everything dandy so far, but now when I go to check the frequency output at the 0.1 dial position I do get 225Hz, instead of the expected 100Hz. At this point I am still getting 1KHz at the 1.0 position, and 10K at the 10 position, but apparently there is no way to get 100Hz at the 0.1 dial position without disturbing the calibration of the 1.0 position. I've done the calibration steps several times over as indicated in the manual, but always arrive at the same result: 225Hz at the 0.1 dial position, while 1.0 and 10 are still correct. And if I set the 0.1 dial position to be back to 100Hz, the 1.0 position will read 833Hz instead of 1KHz. The 10 position on the dial will still be accurate at 10KHz output.
So given that Heathkit has not always exactly been known for accuracy, I wonder if this error on the 0.1 dial position was considered a "normal", or if there might be an actual still undiscovered problem in this unit, or maybe an error in the calibration procedure? I've also checked voltages around the main variable oscillator circuit and everything agrees to what is shown in the diagram. Even checked resistance and tracking of the R103 dial pot which is 1K LIN, and it seems ok as well. Function-wise everything else seems to be working fine in the generator, besides the 0.1 dial position error.
So what gives? Before I start what might turn out to be a wild goose chase, anyone have any ideas or suggestions, or maybe ran into the same calibration problem? Anyone out there with an IG-1271, could you please check your output frequency at the 0.1, 1.0 and 10 dial positions (use the 1K range) and report back findings?
UPDATE: replaced all 10uF 35V Tantalum caps (seven in total) because I saw some switching noise on both +15 and -15 buss supplies. I did not help much. Switching spikes exactly correspond to highest and lowest part of sine and triangle waveforms, and rising and falling on square wave. So I guess that noise is part of the design as well.