That's pretty easy. There's pics on the web. It is a DT-9205A
Brilliant. I have exactly the same meter.
And the noise? It is continuous. We left the thing on all night by accident and the next morning it suddenly burst into life with this loud continuous noise. And then it would do it again whenever I switched it on, with only a few seconds before it began during which I found I could press a key and get a note just as though it was okay.
That piece of information is important and will help us understand what is going on later.
Mine doesn't have the 'auto power-off', unfortunately. And that push button on/off means tossed in jumbled work bench drawer it can all too easily get switched and drain the battery away..... I found out.... the hard way....
Alright. Let's get your meter to work.
First off, for your safety, please, turn off the organ, if it is not already, and
disconnect the power plug from the wall socket. There are hazardous voltages around that area of the circuit, even with the organ turned off.
Now turn the range switch of your meter to the 20K position (next to the Ω sign). Connect the black lead to the COM binding post, and the red one to the VΩ binding post. Turn on your meter on and short the probes out to make sure it is indicating zero or close to zero ohms.
If that is ok, disconnect both the "IN PUT" and "OUT PUT" plugs from their sockets on the board. That way we will prepare it for probing.
Now, let's concentrate on the "OUT PUT" socket. What you probably have is an octal socket. Locate a notch in the center and count the number of pins like in the picture below.
Connect the meter probes to the pins and report what you read:
Black probe 4, red probe 3
Black probe 4, red probe 2
Black probe 4, red probe 8
Red probe 4, black probe 3
Red probe 4, black probe 2
Red probe 4, black probe 8
We say pin, but of course the socket has holes. If you find it difficult to insert the probes due to the small diameter of the holes, and/or the constraints of space, we will have no choice but to pull out the chassis.
In that case it will be better to probe the socket from the underside, in which case the numbering of the pins will follow what you have in the schematics (just flip the picture above and count 1, 2, etc. clockwise from the notch).
If you do that you have to take care not to bend any components or change the trimpots (those with a red blob of paint).
We're probing for short-circuits. So good electric contact may be established between the probes and the pins.