Nida Trainer Model 207 Oscilloscope - Not Working

[mrnateytatey]

Excuse me but I am 14 and don't know very much about oscilloscopes.  Ive have this oscilloscope ( Its a NIDA Trainer Model 207) in my possession and got it for about 20 US$ a few months ago just about half of that time it started showing A single dot in the middle bouncing around.  It does nothing even after putting a known working source into it it does nothing. Please Help!

I don't know what happend

[rbrown044]

Greetings mrnateytatey,
     I don't suppose you want to sell that trainer for $20?  O0
     I am a student at a technical college and we use the Nida Trainer Model 207 that you have. We're issued a Trainer Manual, as well as a Trainer Workbook with experiments. Basically the device you have (and the printed material I have) was designed to be used to better understand HOW oscilloscopes operate    First in understanding the basic theories, controls, components, features, signal path(s) and how they all coexist    Essentially the end result is being able to take measurements from different points within the machine and identify where the trouble is originating from 
     I would suggest trying to get your hands on the Training Manual and/or the workbook. The workbook we use is rife with errors, but perhaps Nida has some updated materials you can get your hands on 
Sincerely,
     rbrown

[PA0PBZ]

just about half of that time it started showing A single dot in the middle bouncing around.

Welcome to the forum! How is the dot bouncing, horizontal, vertical?
Can you make a better picture of the front panel so we can see the settings?

[onlooker]

The NIDA Trainer Model 207 I have had the same problem from time to time. The cause was that all the transistors were socketed and it can form bad contacts, especially, after it set in the shelf for some time.

I used to wiggle the transistors in the oscillation circuitry (and other parts). When I got tired of opening the case (easy to open, heavy to flip), I started to just knock the case a few times and/or wait it to warm-up.

If you try to open the case, just be very careful about the high voltage circuity in there.

It was my first scope and I bought it 2nd hand a long time ago (for $100?). I have not touched it for a long time too. I think the BW is about 5MHz or less.