Audio Out for Eumig 824 Sonomatic

[Ethan Knightchilde]

So what's the verdict here! Does the Eumig 824 only line output a single audio channel ( left stripe 0R right stripe) at a time ?

No idea at this end. I’m hoping it at least does a mix down!

[Ethan Knightchilde]

OK, the thing to do when you get down into the low readings on a scale is shift gears: try that same measurement in the 200 Ohm range. With this you'll see that same measurement, but with more digits of accuracy.

I'm guessing your "1 ." means your measurement has exceeded 200kOhms (as if at the time the probes were just out in the breeze.). Now, if you were actually measuring a 1 Megohm resistor you could shift up to 2,000 kOhms and see that measurement. When you are up in that maximum range and you see "1 ." you can start to call that an open circuit, especially if you are expecting something much, much lower like 50,000 Ohms.

(In the real world there are no true open circuits or short circuits: just "close enough".)

It settles around 9.1 or so at the 200 ohm setting.

[Paul Adsett]

So what's the verdict here! Does the Eumig 824 only line output a single audio channel ( left stripe 0R right stripe) at a time ?

[Steve Klare]

OK, the thing to do when you get down into the low readings on a scale is shift gears: try that same measurement in the 200 Ohm range. With this you'll see that same measurement, but with more digits of accuracy.

I'm guessing your "1 ." means your measurement has exceeded 200kOhms (as if at the time the probes were just out in the breeze.). Now, if you were actually measuring a 1 Megohm resistor you could shift up to 2,000 kOhms and see that measurement. When you are up in that maximum range and you see "1 ." you can start to call that an open circuit, especially if you are expecting something much, much lower like 50,000 Ohms.

(In the real world there are no true open circuits or short circuits: just "close enough".)

[Ethan Knightchilde]

I’ve attached photos of the readout for the “standby/no reading” display (“1 . “) and the zero display it settles to when touching the two probes together (“00.0”). With that in mind, touching the chassis with the black probe and terminal 2 with the red yields 1.0 ohms at the 200kOhm dial setting.

[Steve Klare]

If that's really 1.0 Ohms, it's not unexpected.

What does it say if you just touch the two probe tips together?

[Ethan Knightchilde]

Ok, let's bring this on home:

"6 O'clock"=Pin 2
"9 O'clock"=Pin 3
"3 O'clock'"=Pin 1

Since your connector is installed upside-down compared to the drawing. (Please check my math here?)

"Starts high but settled to about 51.6 with black at 9 o’clock and red at 6 o’clock"
-so: 51,600 Ohms Pin 3 to Pin 2: that's what I'd expect. This should be a line level output.

"No reading with black at 9 and red at 3 o’clock."
I'm taking this to be an open circuit: if it is, you should see the same indications with the probes just dangling in the air.

The more proper measurement would be 3 O'clock' (Pin 1) to 6 O'clock(Pin 2) but if one is open circuit, they should both be open.

This means that Pin 1 may be installed but not used. Maybe there was some other place they needed pin 1 loaded in the same shell and it was less confusing to have a common part in the big bin with all the pins used loaded.

(It's easier to have all the wiring harnesses at the car factory built with the connector for the convertible top switch than straighten out the fifty convertibles that got just assembled with the sedan harness!)

Here's something else to try (just for fun): measure 6 O'clock(Pin 2) to exposed metal on the chassis and/or the third prong on the plug

Agreed. 1,2,3 clockwise starting at 3 o’clock seems correct to me.

I quickly tried red to pin 2 and black to the exposed metal near the lamp housing. Varied a bit but settled around 1.0. I can take the back off a bit later and do it properly.

[Steve Klare]

Ok, let's bring this on home:

"6 O'clock"=Pin 2
"9 O'clock"=Pin 3
"3 O'clock'"=Pin 1

Since your connector is installed upside-down compared to the drawing. (Please check my math here?)

"Starts high but settled to about 51.6 with black at 9 o’clock and red at 6 o’clock"
-so: 51,600 Ohms Pin 3 to Pin 2: that's what I'd expect. This should be a line level output.

"No reading with black at 9 and red at 3 o’clock."
I'm taking this to be an open circuit: if it is, you should see the same indications with the probes just dangling in the air.

The more proper measurement would be 3 O'clock' (Pin 1) to 6 O'clock(Pin 2) but if one is open circuit, they should both be open.

This means that Pin 1 may be installed but not used. Maybe there was some other place they needed pin 1 loaded in the same shell and it was less confusing to have a common part in the big bin with all the pins used loaded.

(It's easier to have all the wiring harnesses at the car factory built with the connector for the convertible top switch than straighten out the fifty convertibles that got just assembled with the sedan harness!)

Here's something else to try (just for fun): measure 6 O'clock(Pin 2) to exposed metal on the chassis and/or the third prong on the plug

[Ethan Knightchilde]

Paperclips are an electronics essential: Insert the wire into the connector to bring the connections out. You can stick one probe on clean metal on the chassis since all the measurements should be to ground anyway. The third prong on the unplugged(!) power cord is also good for this.

(The majority of the paperclips I use these days AREN'T for documents!)

Also, please switch to the 200kOhm range. Even at 50,000 Ohms you would be out of range on the 20k setting.

Starts high but settled to about 51.6 with black at 9 o’clock and red at 6 o’clock. No reading with black at 9 and red at 3 o’clock. That’s progress tho!

[Steve Klare]

Paperclips are an electronics essential: Insert the wire into the connector to bring the connections out. You can stick one probe on clean metal on the chassis since all the measurements should be to ground anyway. The third prong on the unplugged(!) power cord is also good for this.

(The majority of the paperclips I use these days AREN'T for documents!)

Also, please switch to the 200kOhm range. Even at 50,000 Ohms you would be out of range on the 20k setting.

[Ethan Knightchilde]

At the setting shown in the photo and pressing the black probe into the 9 o’clock position and the red into the 6 as much as I can (their contacts are not very long compared to the pins on a DIN connector), I get a brief reading of about 18.xxx. Couldn’t get anything from the 3 o’clock position. Those three terminals all definitely have metal contacts inside.

Maybe part of the problem in getting a reading is that the probes for the multimeter are not long or thick enough to make a good contact?

[Steve Klare]

It's possible: let's see how they ohm-out to ground at your end.

The pin in the diagram at the 9' O'clock position is chassis ground. Since the signal is measured referenced to chassis, there should be only one signal.

For some reason the one at the 6 O'clock position has no connections and they show it (JUST it) anyway. I'd rather it showed something more like "1,4,5 N/U". -but, Hey! I was about 12 when this was drawn, so I wasn't at work that day!

EDIT: An analog meter has a battery for the Ohmmeter part: If you aren't getting a reading you need to replace the battery. A digital meter has a battery for ALL the readings, so if you are even getting a display, your battery is at least trying!

The test for any Ohmmeter is short he probes together, and the display (digital or analog) should swing to very, very close to zero. Separate the probes and then the display should swing up to infinity. Very commonly on a digital meter you will see something like "OL".

[Ethan Knightchilde]

Well, I found a multimeter I kept with my 16mm rig to check my batteries on the road. However, I’m probably doing it incorrectly because I can’t get a reading.

I think you’re right about the “whatever” approach someone took with that wiring diagram.

On a closer inspection of the DIN plug, it seems that there are 3 terminals that have connections. It’s a little difficult for I see. I’m assuming that they are numbers 1, 2, and 3 based on the diagram used for the recording side. 4 and 5 appear empty in the photo by comparison.

Might that be indicative of 2 channel output?

[Steve Klare]

Thanks for the scan Ethan!,

Let's zoom in to where I think the business end of this line level stuff is happening: (Schematics are actually interpreted, not read.)
.

That Eastward pointing triangle up in the NorthWest is an operational amplifier. I believe this to be the pre-amp that boosts the signal from the heads and feeds it to the main power-amplifier. If this was a true twin-track machine I would expect there to be two of these for two independent signals, yet there is only one. The circle down in the SouthEast I believe to be the 5 pin DIN. It has only two connections, one of which is chassis, and the other to be signal (which ultimately connects to that same pre-amp in the big picture). I would expect this to have two signal connections: one for each track.

I can't read the pin numbering: please check? Pin 3 should be at 12 O'Clock and pin 2 at 9 O'Clock.

I'm not so sure this should be interpreted as the end-all of this. It's even possible whoever composed the 824 manual used a single track schematic because they didn't know the difference and after they printed and shipped a couple of thousand copies, even if someone noticed, they just shrugged and said "Whatever!".

(I do a lot of technical document work: what can go wrong, WILL!)

The ultimate test would be to stick an ohmmeter in pin 5 and measure something between 50,000 and 100,000 Ohms to chassis. If it's open circuit then no balance stripe signal will be available at that pin.

[Ethan Knightchilde]

I don't have a microscope, but I do have an electrical engineering degree! (Taxidermy school was all filled up!😉)

I'd love to see a scan!

Here it is! I suspect that this will be the same situation as Rob’s Beaulieu with a single mono output.