Determining where to hardwire a DC power supply to a drum machine originally built into an organ

Thread Starter

liamc2019

Joined Jul 30, 2019
10
Hi there, I have a rhythm board and its button assembly that was taken from an old Lowrey L50 organ. I can't find a schematic online but there is the service manual to another model in it's range, the L60, and from that I've determined that the board needs 15v. Is there any way to figure out where on the board I can hardwire a 15vDC power supply to it? My idea was to take the drum machine section of the organ and make it a standalone unit. I'm also quite confused by the fact that some of the wires have two wires inside, one bare standed wire and one regular insulated wire, and that some of these wires connect to two nodes but others only one. Here are some photos of the board https://imgur.com/gallery/C4P4Dps. Many of the wires that are cut were originally connected to other modules in the organ, but the button assembly and volume control are still connected- I'm assuming like a guitar I can wire the volume control to a 1/4inch output jack. I have basic electronic experience and tools (multimeter, soldering iron) and I think I may have jumped into this project without understanding what exactly I was getting into. I'd appreciate any guidance on this matter, thanks!
 

Wolframore

Joined Jan 21, 2019
1,538
haha - i answered you in reddit... buy the $7 service manual that has the schematics... all I found was the L60 online which has 15V going to it.

If you want a guess, I would guess that the power goes to the red and black (thickest) wires.

Those old boards are kind of cool... the pcb traces look like worms :)
 

Thread Starter

liamc2019

Joined Jul 30, 2019
10
haha - i answered you in reddit... buy the $7 service manual that has the schematics... all I found was the L60 online which has 15V going to it.

If you want a guess, I would guess that the power goes to the red and black (thickest) wires.

Those old boards are kind of cool... the pcb traces look like worms :)
Haha, unfortunately I'm in Australia so the service manual would cost me an extra $23 in shipping. I don't think it's the red wire, that connects to a different module, not the DC power supply board. However the black and brown wires both connect to the DC power, I think the black wire might connect to the output jack as well.
 

Dodgydave

Joined Jun 22, 2012
8,688
Can't find a Free copy of the service manual, but the other models use a +/- 30V psu using a Centre Tap transformer, and various +/- regulators to +/- 15V.

You're going to have to use two 15V regulators or one with a +/- output.

Can you take pictures of the Psu section?



Screenshot_20190731-071642.png
 

Thread Starter

liamc2019

Joined Jul 30, 2019
10
Can't find a Free copy of the service manual, but the other models use a +/- 30V psu using a Centre Tap transformer, and various +/- regulators to +/- 15V.

You're going to have to use two 15V regulators or one with a +/- output.

Can you take pictures of the Psu section?



View attachment 182897
Okay, I've attached some photos of the DC power section. Let me know if you'd like different angles etc.
 

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Wolframore

Joined Jan 21, 2019
1,538
Actually 12-15V makes sense for CMOS circuitry for the rhythm section. Can you search for a power rail that is common for all the chips? One would be the ground the other power. You may have some luck by looking at the datasheets for the chips as well. I can’t read any names off the chips in your pictures.
 

Thread Starter

liamc2019

Joined Jul 30, 2019
10
Actually 12-15V makes sense for CMOS circuitry for the rhythm section. Can you search for a power rail that is common for all the chips? One would be the ground the other power. You may have some luck by looking at the datasheets for the chips as well. I can’t read any names off the chips in your pictures.
Here's every chip I could take a photo of, so they should share a power rail huh? How do I identify which one they all share? I will also go and take a look at the datasheets for the ICs and try to track down which pin carries the power I guess? Thanks!
 

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Wolframore

Joined Jan 21, 2019
1,538
Last edited:

Thread Starter

liamc2019

Joined Jul 30, 2019
10
It will be immensely easier with a circuit diagram in the service manual.
Before I spend the $35 or so on the manual, imagine you're in one of those 70s air disaster movies where ground control has to tell a clueless and ignorant passenger how to pilot a plane because the pilot had a heart attack. I found a datasheet for one of the chips here: https://www.ti.com/lit/ds/symlink/cd4027b.pdf the cd4027be chip, and it looks like pins 16 and 8 are the ones. So is it possible to trace one of these pins back to where I need to hook up the DC power input wires to? Or is that completely undoable. Haven't had any luck finding a shared power rail thus far
 

Wolframore

Joined Jan 21, 2019
1,538
That’s the concept... check the L60 schematics I sent you the link for. It should have similarities. Look at the power rails and check the wires and connections.

Nah you crash this one no one gets hurt.
 

Thread Starter

liamc2019

Joined Jul 30, 2019
10
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