The light meter is not working, in AV mode the shutter speed constantly remain at 30 seconds.

If your Canon AV-1 is only shooting in Bulb (B) mode, it could be due to a malfunctioning shutter or aperture control. However, since the light meter is working correctly, it is possible that the issue is with the camera's shutter speed dial. The shutter speed dial is located on the top of the camera and should be set to a specific speed when shooting in aperture-priority mode. If the dial is stuck in the Bulb (B) position, then the camera will only shoot in bulb mode.

I would recommend taking your camera to a professional camera repair shop to have it inspected and repaired if necessary.

Okay lets put some "joy" back into your photo's The reason you aren't getting anything is because your shutter speed is to fast. Your setting I think you are trying to say are F5.6 100 ISO and 1/100 shutter speed "M" manual setting. Actually if you looked closely on your "nothing there" there would be something. Anyway, Moon shots as simple as they look are anything but simple. The earth is moving and you are trying to take a still shot. I don't know where you are on this earth and every star system is different. Starting with a good solid tripod, next the lens needs to have a great enough focal length so the moon covers 2/3rds of the view (first shot) ISO 100 is good. In manual mode look at your light meter try to have your F-stop at F8 or F11 and adjust the shutter speed for proper exposure, you may need to adjust your aperture up or down once you have a "normal" exposure either increase your shutter speed or preferably stop down the lens two stops.
Your camera will meter down to 30 seconds if it goes below this then this is where you take your start (first shot) meter reading and count how many stops of light you require beyond 30 seconds.
For practice though attempt to stay within the 30 seconds by increasing the aperture but not wide open say F8 is as low as you go, need some speed adjust the ISO up to ISO 200 then ISO 400 don't go beyond this because other factors come into play at this point. the thing is you need to establish a metering point then stop down two stops and see what you have as far as exposure.

I know this may all sound really complicated but it's not the most important thing is to have a good tripod use F8 as your widest aperture don't increase beyond ISO 400 and keep your shutter speed at 30 second or above. Another problem that will occur is focus actually the lack of, your camera requires contrast to focus one you have established this shift the lens into manual and recompose your scene. What we aren't done yet don't touch the camera when your release the shutter. Use the 2 second time delay to give the camera time to stop vibrating after the shutter has bee depressed remove your hand DON'T touch it until the picture is finished. If it were me I'd be looking at doing a few landscapes at night to get use to all this stuff then tackle the moon so to speak. In the mean time here is a picture of The Fork Of the Thames in London Ontario Canada.
Picture here

You need to understand the relationship and teractivity of aperture, shutter speed and iso. In Av mod, you choose the aperture and the camera makes thw shutter speed agjustment, In Tv mode, you set the shutter speed and the camera makes the aperture adjustment, In manual, you have to set both shutter speed and aperture manually. If the ISO mode is set to AUTO, the camera chooses the sensors sensitivity to light automatically. Change to specific ISO
(200-400 for daylight and 799-1600 for night). Take a picture in AV mode and note what shutter speed the camera chose. Then switch to TC mode choose the same shutter speed and see if camera chose the same aperture(f-stop) you chose in first shot. Change to Manual and choose same f-stop and shutter speed the camera chose for you in the other modes. Compare all three photos. They should be almost if not exactly the same exposure wise.
In Tv mode choose a dlowers shutter speed, In Manual choose a combo of slower shuuter and wider f-stop(smaller number). Read your manual.

Basically putting the camera in modes other than Manual, TV or AV means that's you've given up a lot of control, so the camera is left to its own devices to solve the scene. When shooting landscapes you need a large depth of field, which means the camera chooses a higher F-number for your photo. Higher F-numbers mean less light gets into the camera, since the shutter speed has to stay high enough for you to shoot handheld. So now you've got two things t work which reduce the amount of light hitting the sensor: small aperture (high F-number) and fast shutter speed. Since the camera meters the scene and has only one remaining factor to get "correct" exposure, all it can do is set the ISO according to the two other mandatory settings of F-number and shutter speed. If there's enough light (bright, sunny day) then it can remain at ISO 100, which is usually the best quality image. If there's insufficient light though, then it may go as high as ISO 800 or even ISO 1600 to allow the small aperture and fast shutter speed. This will make your photos look grainy.

Instead, I recommend that you set the camera to AV Mode, put your F-number to F8.0, set your ISO manually to ISO 100, and use a tripod. Additionally you can use the custom functions menu to lock up the mirror (prevents "slap" which shakes the camera and makes the image less sharp) and also use 2-sec timer (select it using the button to the left of "set" on the back of the camera).

Following those steps you should get the sharpest photos your lens and camera body will allow. Be sure to use autofocus by defeault and switch to manual if you want to fine-tune (or if AF is "hunting" and not locking on a target) and also turn Image Stabilization OFF if using a tripod. Good luck!

needs repairing at a qualified shop
when was it last cleaned or serviced ?
if you think the camera is worthy, since its old how much is it worth to you vs a new one

OM-20 was basically a upgraded OM-10 with the manual adapter built in and a number of other refinements.

The viewfinder has LED's to show the shutter speed recommended by the camera's lightmeter for the ISO and aperture selected. It also has an exposure compensation indicator (the +/- symbol) and an indicator for flash ready which doubles up as a post-exposure flash confirmation. There is also the indicator lamp to show manual mode has been selected. OM-10 lacks the manual mode lamp and the +/- indicator.

Like the OM-10, the OM-20 is primarily an aperture priority automatic camera. In this mode you set the ISO film speed, choose which aperture you wish to use (with the ability to use the lens depth of field preview button) and then the camera selects the correct shutter speed. The +/- exposure compensation control allows the user to tell the camera to modify the recommended shutter speed by up to two stops either way.

In manual mode, there is no manual metering. The light meter behaves exactly as it does in aperture priority mode and the viewfinder shows the recommended shutter speed and not the manually selected one. Correct metering is therefore a case of adjusting the aperture first, and then choosing the correct shutter speed indicated in the viewfinder. If the user then decides to select a different shutter speed, then the aperture ring must be adjusted to maintain the correct exposure. For example the aperture is set to f8 and the camera recommends 1/60th of a second. The user decides that a faster shutter speed is required and chooses 1/250th, but the viewfinder remains showing 1/60th. In order to keep the same exposure value the user must open the aperture by two full stops to f4. The camera's light meter will detect the new aperture setting and providing the light on the object is unchanged the viewfinder shutter speed display should now show 1/250th as well to confirm the correct adjustment. Alternatively, the user can choose the shutter speed first by looking at what has been set on the control ring (or by turning the ring to the end of its travel and then counting the clicks from there as all experienced OM users do) and then turning the aperture ring until the shutter speed shown in the viewfinder matches what's been manually set.

It all sounds clumsy and complex but is done far more quickly than I've taken to type this and becomes second nature.

Aperture priority metering is selected on the camera by choosing AUTO on the mode selecter. In this mode the shutter speed ring has no effect and the viewfinder always displays the automatically selected shutter speed.

When you set the camera to "Full Manual" mode, you should be able to dial in your shutter speeds, for most film cameras, including the N55 30 Seconds is the slowest shutter speed. If your camera features a "Bulb" mode, then the shutter stays open as long as you are holding down the shutter release button.

You will need to read the manual. I f you have a basic understanding of how ISO, shutterspeed & Aperture width combine to determine the 'right exposure.

Try this:
Set the camera to Av (aperture priority mode). Half press the shutter button and see the light meter indicator to see how well exposed your shot will be. For most cases you would be aiming for a value of 0 (properly exposed). The metering mode determines what part of the frame is used to compute the correct amount of light. For starters begin with pattern metering. Try and aim for a shutter speed of 1/125 or more if you are using the 17-55 mm EF-S f3/5-f5.6. Try and shoot at 40 mm F/5.6 (in Av mode this can be set by rotating the dial near the shutter button.
All the best

There is nothing wrong here - the camera computes the exposure as the flash is not firing. The flash will fire and it will adapt the power to the received light. You must go into M ot AV, fix your parameters and shoot. The flash will adapt to your whishes - only take care to not choose a shooting time to small (1/200 or 1/60 - you have settings for it).

This is not a bug, but a feature.

First select AV (Aperture Mode) to select the required aperture then switch to M (Manual Mode) and spin the wheel until you get the right speed.

Spurs34