You are right. The Iwatsu Oscilloscope has fault in the 2nd channel. The 1st channel seems ok, but the 2nd channel does not read DC Voltage from a battery. Nothing happens on display. I have been using the faulty 2nd channel all the time.
It also seems have problems with trigger and time base too. The display of the signals are not consistent on both channels.
Are you sure you don't have the channel set to AC coupling? There is a switch on your scope for that - a three position vertical switch for each channel, labeled DC-GND-AC. Make sure the lever is in the DC position (down). Also make sure the V-Mode switch is in the CH2 or DUAL position if you want to see the channel 2. Setting it to CH1 will turn the channel 2 off and you will see at best some cross-talk noise, while CH1 seems to work fine.
However, even on AC coupling the scope should be able to display a signal of few kHz unless it is defective.
Thank you for your info and advice. I have never imagined or doubted the Iwatsu 5702 scope would be faulty.
But it is clearly showing the fault. Maybe these old electronic gears are not reliable anymore without proper servicing and repairing them time to time, or even all the time.
That scope is 30 years old at least. If nobody has ever cleaned it, there could be poor contact in the switches and pots from the accumulated grime and dust. The capacitors could be dead, connectors could be broken, etc. That's par for the course for such old gear. It needs maintenance as anything else.
Time to go and get the new DSOs like RIGOL, Agilent, OWON or even Teks?
If you have the money, sure. Teks are expensive junk today, they don't have a competitive model for some years now. Agilent is expensive ($1000-$2000 at least for an entry level scope but good), Rigol is the king of the low end, entry level stuff today, with the $400-$500 getting you a great four channel 100MHz scope. Owon is cheap and buggy junk, not really worth the money, IMO. If you want to buy a scope, there are other threads on the forum about the pros and cons of the individual models.
However, I think your problem is more that you are missing some theoretical and practical basics about how to troubleshoot things - buying a new scope will not help you there, really.
For audio gear your old Iwatsu is plenty enough. In fact, the simplicity of the instrument is an advantage for you while you are learning, because it doesn't hide anything from you, unlike some modern digital instruments - e.g. no chance for a signal to alias or averaging "cleaning up" a noisy signal, making you think everything is fine. The modern digital scopes are insanely powerful tools, but the learning curve is quite a bit higher than with an old style "button & knobs" analog scope.
I am pretty sure the bad channel on your Iwatsu can be easily fixed. Most of the scope is working since you have a one good channel - so the screen, power supply, time base, triggering are all in working order. The problem is most likely in the input for the channel 2 - which you could actually troubleshoot using the working channel of the scope! Just be careful if you decide to poke around it - as with any CRT equipment, there are high voltages inside. My tip is that simply some switches for the channel 2 are stuck/not making contact, not letting the signal through correctly.
BTW, since your other scope doesn't display the low frequency signal from the FG neither, I think that the generator has a problem as well. It is fairly unlikely that two scopes would be having the same sort of fault. But make sure you can get your scope show a flat trace matching a battery voltage first, as suggested by AG6QR above, before attempting to troubleshoot the FG. If you need a test signal, your Iwatsu has the probe calibration output. That should display a square wave signal of 0.3V at about 1kHz. It is labeled Cal Out and is next to the external trigger connector on the right side.
Don't worry about the lack of proper probes - at audio frequencies or DC it really does not matter.