Looking for help re-creating broken Yamaha piano PCB in Kicad. Got some noob questions.

Thread Starter

ovmus

Joined Jan 5, 2022
4
I recently purchased a 2002 Yamaha P-80 digital piano with a broken PCB for which I cannot find a replacement. I'm looking for help on re-creating the PCB and components list to make a functional replacement. I've recreated to the schematic I believe and had some questions about the board and components design before I get too far into things. I'm not a complete noob to PCB's but I've mostly followed guides to this point and lack my own knowledge, so I need some help. Any help is absolutely appreciated.

The current PCB has several fractures that affect the audio portion so it powers up but no audio is generated. I had the left channel working working for a moment with my hackjob wiring but it went out again when I moved the board and expanded the cracks, oops. I need to try to rewire the NJM2073D chip as that's on dicey connections and very well may be the culprit currently but for the long term fix I want to create a whole new replacement PCB.


The board in question is the Yamaha P-80 M Board. I've linked relevant images below: Service manual schematic, layout and parts list as well as my own Kicad schematic and photos of the board currently.

SM Schematic
SM Layout
SM Parts List
Kicad Schematic
Top side of broken PCB
Underside of broken PCB

Questions/thoughts:

1. Does my schematic seem to be accurate according to the original? It looks good to me but I don't trust myself alone.

2. There's a few visually thicker traces on the original schematic. Pins 2 & 4 from CN1, Pin 5 on CN3, COM on IC2 and the lines with a gap between GNDA and GNDD under IC2. What does this signify?

3. Related to above, there's a connected line between AGND and DGND near IC2, most of it thick with just a little bit thin in the center. On the board itself there is no continuity between the two GND's. What's the deal with that? I feel like there shouldn't be a line between the two at all but it must be there for a reason.

4. The original schematic specifies different capacitor types on the bottom left, including Semiconductive Capactiors. The caps on the board that are labeled semiconductive are ceramic disc caps. Do I need to worry about the Semiconductive label and get a certain type of cap?

5. There's a label of '1mA' near R9 and R19. What does that mean? Is that the load they see?

6. Everything on the original PCB are Through-Hole components. Is there any reason I couldn't go Surface Mount for any components that come in SM format to make the new board a little cleaner? I much prefer SM.


Thank you in advance for any help!
 

panic mode

Joined Oct 10, 2011
2,110
well what is your experience with KiCAD? if it is anything like your soldering and repair skill i would suggest to forget designing new board and simply clone existing one. that has several advantages, you can be sure that everything is exactly the same as original, you don't have to create footprints for several of components, make sure that drill sizes are correct, you don't have to worry about schematics, noise, cutouts and bolt patterns etc. but that is me.

if you are designing new board and want to have it made by some PCB house, you need to make sure that everything is perfect. you can substitute some of components for SMD types. you can add own artwork have the PCB house assemble it partially (all SMD components) but you will probab;y never be sure it is a correct circuit as original.

the other option would be to make a clone PCB yourself. for this take several good photos of the board, with clear view of all components and traces. then remove all components and rework, assemble all board fragments using clear tape. then scan both sides using flatbed scanner. use paint or some other editor to photoshop the scans and remove cracks, then print them on adhesive paper in correct scale. another good idea is to get piece of styro foam and place extracted components in the same order as they are on the original board.

next get blank PCB, clean it and cover the copper with wide tape used to pack boxes. does not need to be clear but need to have thin adhesive layer, do not go for one with "fat" goopy adhesive. if tape is not wide enough, make sure that next strip covers 4-6mm of the previous strip. the tape will be "photoresist" for etching.

if you have a laser engraver, you can use it to carve the tape. if not, place the sticker with traces over the "photoresist" then but the unwanted area between traces with an exacto knife.

etch the board then drill the holes then peel the "photoresist".
flip the board and make sure it is clean then apply adhesive with copy of silkscreen.

now you have exact clone of the original board. just place back all parts in correct order and solder them.

and in your case things are even simpler - you already have the image of traces so it is easy to use. so you may first make new board then transfer one part at a time from original to replacement board.
 
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Thread Starter

ovmus

Joined Jan 5, 2022
4
Haha, fair concern. I've designed and soldered 100% custom computer keyboards that came out very nice. I have a Hakko FX-888D and a hot air rework station which gives me good results when I take my time. I did this current hackjob after not touching an iron for over a year, was in the freezing cold garage and in a rush so it's far from my best work. I have no problem designing something which would be a lot cleaner without using the wrong type of wire.

Noise is my one concern which I know nothing about. Do you have any good resources to read up on the subject without diving into the deep end? I feel like this is a fairly simple board overall.

I have no problem assembling my own boards. It's part of the fun for me. And while that sounds interesting to etch my own boards I can see that going very poorly. I'd prefer getting them manufactured for me.

Thanks for the reply!
 

panic mode

Joined Oct 10, 2011
2,110
etching is fun and easy. i made hundreds and have no problem with it. described process is what i used in several repairs where original board was no longer salvageable. but its been some time since i made one, getting them made by the PCB shop is just too tempting and one gets multiple boards which you will not need.

as for learning about noise.... that is a big topic. just try to keep things in same place like original and pay attention to connections that in schematics go to a single point (star rather than bussed connection).
 
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Sensacell

Joined Jun 19, 2012
2,983
There is a lot going on on that board.
I would encourage you to focus on learning how to do lasting, robust repairs on the existing board, the chances of successful outcome will be 100x greater than trying to re-make the board.
 

Thread Starter

ovmus

Joined Jan 5, 2022
4
There is a lot going on on that board.

I would encourage you to focus on learning how to do lasting, robust repairs on the existing board, the chances of successful outcome will be 100x greater than trying to re-make the board.
Do you have any leads on proper repair of something like this? I couldn't find anything where anyone bothered trying to repair a board with breaks to this extent. If I were to desolder all the components the board itself would fall apart into 5 pieces at the moment. Thanks.
 

Thread Starter

ovmus

Joined Jan 5, 2022
4
@panic mode & @Sensacell, thanks for the replies. I got it working beautifully tonight so I'll be leaving this for now.

A couple days ago I ordered a couple extra NJM2073D chips which I got in the mail today as I suspected that could be the main culprit. Turns out I was right. I went back in, ripped out the hackjob I did, swapped in a new NJM2073D and found some solid copper wire to make the rest of it much cleaner and it worked first time. Success!
 

panic mode

Joined Oct 10, 2011
2,110
there you go. good job

if it was me i would still make a new board. if you are not into using chemicals and etching, you can also cut the slots between traces using cnc or even manually using knife or dremel etc. those old style phenolic boards are very fragile, fiberglass is way more durable.

note the connection at the capacitor. all traces converge at the capacitor terminals, and only join there.
1641672022768.png
 

old_beggar

Joined Jan 29, 2021
39
1. I'm sorry I haven't checked - print both and scrub each as you check each connection. There should be no "unscrubbed" lines on either.
2. Is a way of denoting a significant (carries more current?) connection (usually, as in this case, power).
3. GNDA = analogue ground, GNDD = Digital ground and are indeed joined, but as in panic mode's post above (#8).
4. Ceramic disc caps will be fine.
5. "1mA" is indeed the expected current there (the mutes). No need to do anything special, it's just info.
6. Board layout (if using SM) might not be optimal for lowest noise. Your choice.

IMHO the board doesn't look that bad - I would remove any components near/across cracks, then make some L-shaped reinforcement strips (out of pcb or Ali) and epoxy the board back together, and put some small (M2.5?) set screws/washers/nuts on each broken piece for good measure (subject to space limitations of course - I don't know how much room there is where the pcb goes back in), making sure there is no electrical connection to the reinforcement. Then repair the cracks electrically using small bits of e.g. wire, (taking note of the advice in the above post #8), redrill any holes that are filled with glue, then refit old (or new) components.
There's more Kudos in making your own pcb, though! And, you might be able to sell them (once proven)?
 
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