Here is a more recent "how to use an oscilloscope" video, that is geared towards looking at signals inside a working AM radio. Please pardon the music/radio in the background.
Very good explanation Janoc. Thank you.
I have tried other old scopes in there, but result is more or less the same. As you said, maybe it is because I have been using the AC settings.
I will try again with DC settings, and see how it will show.
I tried with the DC before, but many times, the signals in the display of the scope kept disappearing, and I had to pull it down or up using vertical control.
And on some freq. settings, nothing was showing in the display, so I switched it back to AC. In AC settings, at least signals are present most of the time.
I will also watch the Youtube video, and try to learn more about the scopes. Thanks.
Here is a more recent "how to use an oscilloscope" video, that is geared towards looking at signals inside a working AM radio. Please pardon the music/radio in the background.
Thank you. It seems a great video for Scope Fundamentals.
I tried with the DC before, but many times, the signals in the display of the scope kept disappearing, and I had to pull it down or up using vertical control.
And on some freq. settings, nothing was showing in the display, so I switched it back to AC. In AC settings, at least signals are present most of the time.
That is actually completely normal - if the signal has a DC voltage superimposed on it (= DC offset), the trace will move up and down to match if you are in DC mode (same thing as when you have tested the scope with your power supply). Make sure the DC offset knob on your FG is set to zero if you don't want to have it there.
In AC mode the DC offset is blocked - at the expense of some potential distortion/attenuation and you not being aware that the signal actually has a DC offset. Which could be in many cases important - e.g. 50V DC superimposed on your signal due to some fault could blow out an input of the following amplifier. Also DC offset on the amplifier output is really bad news for loudspeakers because the speaker coils will burn out. So it is typically something you want to know about.
Here is a more recent "how to use an oscilloscope" video, that is geared towards looking at signals inside a working AM radio. Please pardon the music/radio in the background.
Ah, mention the devil ...
I liked the older video better, because there has been an explanation of some things I didn't know neither when I have got my scope - like the probe compensation or how to use XY mode to measure phase. But both are good material, your channel is a real treasure trove, Alan.
I also have the Thandar TG2001 function generator and although waveforms start to get somewhat distorted particularly above 10MHz, it should be producing very clean triangle and reasonably nice square waves on the 200KHz setting. You were getting something resembling a square wave on the triangle setting and the waveform produced on the square wave setting was unrecognizable. I have attached some photos to illustrate what the output should look like on the scope for comparison. These were taken with the function generator set to 200KHz and the scope input at 1v/div and timebase at 5uS/div. The waveform display you would get on the 2KHz setting with the timebase set to 0.5ms/div should be identical. I had the amplitude set to 4.06v which is quite close to your 4.37v. Although I was using a 50ohm RG58 co-ax cable rather than a 75ohm satellite co-ax cable to directly connect the two instruments as per your video, I don't think this kind of difference can be accounted for simply by impedance mis-match or abscence of terminators. The wave forms (other than sine) shown in the video were simply not correct and would unfortunately seem to indicate that your function generator is not only malfunctioning when trying to display wave forms at 2KHz and below, but is also not displaying square and triangle wave forms correctly. Sorry to be the bearer of bad news, but it looks it will definitely require repair.
PS, while what has been said about DC offset is essentially correct, if you have not depressed the Offset button and set an offset using the DC offset control, then the DC offset should be zero. The trace should not move from the center position on the oscilloscope screen regardless of whether DC or AC coupling is being used. If it does, then this means that there is a DC element present on the output when there is not supposed to be which might also suggest a problem with the generator. The DC offset can be displayed on the LCD by switching the display mode switch to the Offset position and depressing the offset button. It should change as you rotate the DC offset control. On the oscilloscope, the trace will move up or and down vertically as the DC offset adjusted. As soon as you turn off the Offset button, the DC Offset should change back to zero and the trace should return to the center position.
Thank you WaveyDipole for your detailed explanations and also the photos of the devices. It is very comprehensive, and clear proof that my FG2001 is faulty needing repair. It seems OK up to about 200Khz down to 150Khz, but below that the signals just diminish into thin lines. It is happening with when connected to other scopes too.
My IWATSU SS-5702 is also faulty on Channel 2, not reading any DC Voltages at all, and responding erratically which made the whole thing very complicated for me to figure out.
But with all the advice and info on this forum, I am able to know now these device I have needs repair before put to use.
Thanks again & kind regards.
With regards to CH2 on your oscilloscope, having read the thread, I'm not sure whether you are not getting a reading on DC only, or whether its dead on both AC and DC signals? Your video makes clear that you are not getting a DC reading, but your comment that CH2 is "responding erratically" suggests that you are getting a response to a signal sometimes?
If you are getting a response for AC signals but not for DC signals, this may be down to the channel switch. Looking at the circuit diagram, the AC signal passes through a single set of contacts, but a DC signal must pass through two sets of contacts in the switch before it reaches the input attenuator and amp. If it is behaving erratically in the sense that sometimes it picks something up and other times it doesn't then this also might suggest switch contacts. A squirt of Servisol (don't be tempted to use WD40 - it is NOT a switch cleaning lubricant nor the right stuff for the job) or similar switch cleaning lubricant into the switch contacts and then working it a few times might help.
Of course if you are consistently not getting any input on any volts/div setting on AC or DC, then the problem probably lies elsewhere in the CH2 input amp, perhaps a blown input FET or something. The good news is that it should be a relatively minor repair since the scope is otherwise working.
Although it seems that there is more going on with the FG, I did wonder whether dirty switches might be at least partially responsible for the problems you are getting with that device as well. It does appear to work for some frequencies - at least with sine waves. It might be worth trying a squirt of switch cleaning lubricant into one of the switches for a frequency range that does not work properly and working it a few times to see what happens. From the circuit diagram it looks like the 20M switch (SW9-A) in particular looks like it might cause just about every frequency range to fail if it were not making contact properly, except for perhaps the 200KHz range... The type of switches used in this instrument allow their operation to be easily checked using a multimeter via the pins protruding from the top.
Great points WD.
The Ch2 of the Scope is not reading DC at all, but it displays sine waves from the FG when set to AC but only above 100 Khz.
As you say, I am not sure if it is dirty contact on the Voltage selection switch, or if it is more serious such as blown FET, diodes or Transistors, or even burnt out resistors or dried out Capacitors.
I would think it would be straight forward process of checking every suspect components one by one on CH2 PCB, and compare them with the ones on the CH1 PCB, and if there are noticeable differences in values, or bad components, then I would know what to replace. But it would be much time and effort consuming process I would reckon.
Another point is, although the scope seems operating OK on AC, I am not sure if it is working 100% accurately either. I could compare it with other scopes on this issue, but they are all very old vintage scopes which dont give much trust. For that, I would need a FG and scope which work perfect, and then compare properly all the aspects of the operation of the devices?
Yes, I will open up the FG2001 and try to apply the Maplin switch cleaner in the pots of the freq. selection buttons first, and see if it will improve things.
Well, we know that your FG is malfunctioning and only produces signals on the 200KHz range only, a behavior which you have duplicated on another scope. However, if you are getting a sine wave on CH2 when switched to AC mode then it would seem that the input amp is actually working, in which case this does likely point to a dirty or possibly worn switch as the source of the problem. The switch that I am talking about is not the volts/div switch, but the AC/GND/DC switch. It should be straightforward enough to squirt a bit of switch cleaning lubricant into where the contacts are and flick it up and down a few times so see if that helps. The decoupling capacitor is switched in for AC mode and would therefore seem to be OK.
Does the sine wave match what you are getting on CH1 with the same volts/div and time/div settings?
I would not worry too much about calibration or 100% accuracy just yet - that can come later. You are correct not to expect vintage scopes that may have been in storage or of unknown provenance to be accurate and a comparison with another scope that is in calibration and showing the same signals will give you an idea of how accurate it is. Quite often they are adequate enough and even if not working perfectly, will still be a useful tool that will help you visualize what is going on in a circuit even if you can't measure it accurately. Your basic DC test seemed to be quite accurate though. I have a vintage Hameg and Tektronix scope. neither is 100% accurate, but both are fairly close to the mark and more than adequate for what I require.
With the FG, start with the 20M switch. That may be the source of the problem with the other frequency ranges. Please don't be tempted to twiddle with any of the presets! If you would like the circuit diagram for the FG then please PM me your e-mail address.
I had to do some other jobs around the house, so left tinkering with electronics gear for a while. I will get around, and trying to fix the devices when time is available soon. But yes, your instructions sounds practical and very clear.
If I need the service document and circuit diagrams for the FG, then I will be in touch. Thank you very much indeed.