Seeburg SCH1-4 APU Missing

[spetersen]

The easiest way is to series 4 100 ohm resistors to ground, and measure across the first one to get your voltage drop, and ground the resistors at each joint through a button.

[ScotK]

Each button is already grounded through resistors except for the high button. The high button doesn't seem to do anything, it's the same with no buttons pressed as if the high button is pressed.

The way the schematic reads I think I should get a different value when no buttons are pressed because there is still a resistor inline. With low and medium pressed it grounds through a resistor to lower the voltage. With high pressed it's a direct connection to the speaker and results in full voltage. When no buttons are pressed I should get something lower than full voltage due to the inline resistor. In real life I get full voltage with high pressed or nothing pressed.

I'm trying to do it without modifying the wiring in any way. Otherwise I would probably have removed the pulse train motor entirely, read the individual buttons as inputs, and converted the entire thing to 5vDC and LEDs. Frankly I'm thinking that would have been easier, but my desire was to preserve it as much as possible.  If that means the buttons stay working the way they are now then I can live with that.

[sooner]

Dec 1, 2019 14:53:27 GMT ScotK said:

The way the schematic reads I think I should get a different value when no buttons are pressed because there is still a resistor inline. With low and medium pressed it grounds through a resistor to lower the voltage. With high pressed it's a direct connection to the speaker and results in full voltage. When no buttons are pressed I should get something lower than full voltage due to the inline resistor. In real life I get full voltage with high pressed or nothing pressed.

That's how the SC boxes work. I think it's a 220 ohm resistor used when no buttons are pressed. Are you looking at an SC or SCH schematic? I remember Ron Rich mentioned somewhere that the volume button circuit was one of the differences between the two models. 

[scudie]

Hi Folks
As far as I am aware the SCH does not have the audio relay mounted behind the volume resistor unit, but the volume control buttons and there resistor unit works In the
same way as a SC.
However the audio does go through the credit unit originally, this is why the SCH has 15 rather than 12 connections, When looking at the socket from the front if we call top left #1 top middle #2 & top right #3 then bottom left is #13 Grey speaker common #14 Left Speaker & # 15 Right Speaker, I didn't have a schemetric for the SCH & on the diagram that I drew myself I have written that # 14 & 15 are speaker negatives. I think that the credit unit switches off the speaker unless there are any credits established on it.
Cheers Scudie

[Ron Rich]

Hi Scudie,
No sir--that why you NEED to purchase, a schematic- The "credit unit, switches" (APU-11) do NOT "cut off the audio unless there are credits established" ! Ron Rich

[ScotK]

I'm using an SCH1-4 schematic. I was thinking about it... I'm not an electronics guy but I think I understand why. There's no voltage drop across the inline resistor because there is no connection to ground without the medium or low button pushed in. There's nowhere for the voltage to go, so the voltage doesn't drop. It's like opening a valve on a garden hose that's closed at the far end. Opening the valve even a small amount will eventually build up the same pressure in the hose as before the partially opened valve. I think if I wanted the high button to work I'd have to put a resistor at the end of the speaker wire and put that to ground.

[ScotK]

I think I'm just going to leave the volume buttons as-is. Right now I get 5v with no or high, 3v with medium, 1v with low. That's a really good range, easy to detect and act upon. I just won't have the mute function, which doesn't really bother me. It was just a nice-to-have.

[spetersen]

Do you have a resistor between the speaker positive lead and the chassis?

[ScotK]

Dec 1, 2019 19:57:12 GMT spetersen said:

Do you have a resistor between the speaker positive lead and the chassis?

No.  There's no load where the speaker was.  

[scudie]

Hi Ron
I stand corrected about the credit unit, just curious do you know why does the audio go to the credit unit?

Cheers Scudie

[Ron Rich]

Scudie,
I don't have access to the schematic here--If I recall correctly, "audio" does NOT go to the credit unit ! "Audio control" does---
Ron Rich

[spetersen]

If you have any resistors, you could put one between the speaker leads, and see if you get a difference between mute and high

[ScotK]

Waiting for parts again. I ordered the 5vDC power supply from Digi-Key, it should be here in another 1-2 days. I can mount that and start working on the power/grounding issues when it comes. And I messed up the optoisolator board and burned my finger in the process. I used too thin of single strand wire on it and it broke, then apparently I overheated the board trying to resolder thicker wires because it doesn't work now and I know it did before because I tested it. So I just ordered another a few minutes ago. That likely won't be here until next week. I'll have to see if I can get some 20 gauge stranded wire for that. The solid core wires I've been using make it hard to work with, but they were easy to come by so that's what I'm using.

[spetersen]

I installed pin headers and used premade jumpers between boards to facilitate easy replacement. Are you using the optoisolator you linked previously?

[ScotK]

Yep, it is.