Best way to repair broken PCB tracks?

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Mooger5
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Best way to repair broken PCB tracks?

Post by Mooger5 » Mon Aug 15, 2016 10:03 am

This is the DM board from my DX7S. It was either caused by the weight of the keyboard frame that bent and cracked the PCB or by overtightning the mounting screws. Anyway, the front panel doesn´t respond and the screen is all black squares now.

I count 25 broken traces. Soldering wire bridges to the vias will probably fix it, but I wonder if there´s a neater way.

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Last edited by Mooger5 on Thu Sep 29, 2016 7:11 am, edited 1 time in total.
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Re: Best way to repair broken PCB tracks?

Post by Rasputin » Mon Aug 15, 2016 1:32 pm

Mooger5 wrote:This is the DM board from my DX7S. It was either caused by the weight of the keyboard frame that bent and cracked the PCB or by overtightning the mounting screws. Anyway, the front panel doesn´t respond and the screen is all black squares now.

I count 25 broken traces. Soldering wire bridges to the vias will probably fix it, but I wonder if there´s a neater way.

Image
CircuitWriter pen would probably work, if you're lazy.

If you want a neater and proper way then I think that pretty much leaves you with scraping back both sides (at each break) of each trace and soldering thin gauge wire across each trace. That's 50 scrapes and 25 tiny pieces of wire though.

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Re: Best way to repair broken PCB tracks?

Post by Mooger5 » Mon Aug 15, 2016 1:46 pm

It´s a work of love. The copper traces are so thin I´m afraid scraping would do more damage. What about solvents?Tried with pure acetone with no luck though.
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Re: Best way to repair broken PCB tracks?

Post by Mooger5 » Mon Aug 15, 2016 2:19 pm

Here´s a closer view. No clock signal from the resonator is therefore arriving at the secondary CPU (IC6). Frozen behaviour and blank LCD screens seem to happen a lot to the DX7S and the mkII, so this is one probable cause. After some research I bought new RAM chips and a 27C256 EPROM to burn before finding the PCB was broken, so if anyone´s got a DM board in reasonable shape I might buy it.
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Re: Best way to repair broken PCB tracks?

Post by Mooger5 » Mon Aug 15, 2016 2:20 pm

Here´s the detailed view.
Image

Edit- looks like I´m unable to post a better picture. Just zoom in on it. Sorry.
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Re: Best way to repair broken PCB tracks?

Post by Rasputin » Mon Aug 15, 2016 5:57 pm

Mooger5 wrote:Here´s a closer view. No clock signal from the resonator is therefore arriving at the secondary CPU (IC6). Frozen behaviour and blank LCD screens seem to happen a lot to the DX7S and the mkII, so this is one probable cause. After some research I bought new RAM chips and a 27C256 EPROM to burn before finding the PCB was broken, so if anyone´s got a DM board in reasonable shape I might buy it.
Awww... you've got to at least try to salvage the board! :)

I say use a fiberglass pen to remove the coating around the trace breaks. Then tape off all the traces but the one you're working on (masking tape or something not mega-adhesive). Use a CirtcuitWriter pen or conductive epoxy to bridge the damaged trace. Let it dry for a good while and then test the conductivity. If it passes, remove the tape and move on to the next.

If you let each trace dry overnight then you can get the board fixed in under a month. :lol:

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Re: Best way to repair broken PCB tracks?

Post by garranimal » Mon Aug 15, 2016 6:25 pm

I've been in this situation before and had a hard time keeping adjacent bridges from soldering to each other. You need very thin bus wire, at least 26 gauge. You might use a surface mount technique where you dab solder paste on the tracks, position all the bridging wires, and heat gun the whole area at once. I've never done it but next time I run into this I will probably go that way. If you do, practice on something first!

Another idea. It may be more reliable to use coated wire, and put a small U shape with each bridge so that it can flex.

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Re: Best way to repair broken PCB tracks?

Post by Mooger5 » Tue Aug 16, 2016 9:26 pm

Thanks very much for your good replies.
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Re: Best way to repair broken PCB tracks?

Post by Tekhed66 » Wed Aug 17, 2016 8:43 am

Hi

I saw a You tube video on this topic a while ago ... there is a special conductive adhesive tape that only conducts in one orientation. For example, if you tear off a strip of tape, it only conducts along the length of the tape but not across the width. This means you don't short out adjacent wires.

All you will need to do is clean the area either side of the break and then sticky tape across the break.

I can't remember the name of the tape but if you google it, you'll hopefully find it. It's the best fix I've seen.

good luck.

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Re: Best way to repair broken PCB tracks?

Post by Mooger5 » Wed Aug 17, 2016 4:30 pm

Thank you.

All good advices.

I just found the component side of the PCB is also cracked :( I´ll have to trash it. With so many broken traces beneath the integrated circuits it´s freakin impossible to work on the thing. It´s a bugger. Never liked the "if it´s broken don´t fix it, buy another" trend, but I´ll have to look for a replacement part.
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Re: Best way to repair broken PCB tracks?

Post by Rasputin » Wed Aug 17, 2016 7:48 pm

I can sympathize with it not being worth your time, but given that those PCBs don't exist anymore then I hope you'll at least consider donating it to somebody up for a crazy challenge instead of tossing it into a landfill.

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Re: Best way to repair broken PCB tracks?

Post by Mooger5 » Wed Aug 17, 2016 9:54 pm

Provided the replacement part is fully functional, yeah I might do that. Cheers.
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Re: Best way to repair broken PCB tracks?

Post by Rasputin » Thu Aug 18, 2016 2:45 am

Tekhed66 wrote: I saw a You tube video on this topic a while ago ... there is a special conductive adhesive tape that only conducts in one orientation. For example, if you tear off a strip of tape, it only conducts along the length of the tape but not across the width. This means you don't short out adjacent wires.
If you mean anisotropic tape then I don't think that will do the job for this repair. That kind of tape is z-axis, so it would only work if the traces were overlapping each other somehow. That kind of tape is more for overlapping ribbon cable ends and the like. That works because the stands in the ribbon are already separated properly by space or insulation, so if you line up the overlap ends correctly then you're golden.

Feel free to correct me if I'm talking about something different or am misunderstanding the application.

Now, if you can find some x-axis anisotropic tape, that would be just the ticket! I don't know why it doesn't exist because you'd think someone could just make metal filament tape (think strapping tape, but wires not string), but I've never seen it. As long as you laid it perfectly parallel to the traces you'd get the proper result.
Last edited by Rasputin on Thu Aug 18, 2016 2:54 am, edited 1 time in total.

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Re: Best way to repair broken PCB tracks?

Post by rhino » Thu Aug 18, 2016 2:51 am

While on occasion I have jumpered the traces at the break, I have had better luck using longer jumpers (insulated) and going from the nearest componet pad to one on the other side.
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Re: Best way to repair broken PCB tracks?

Post by Mooger5 » Thu Aug 18, 2016 10:27 pm

Best thing to do. The traces are really narrow and the space between them is even narrower. Stray solder bridges would be inevitable.

I´d have to check nearly all connections since the components are so dispersed. For instance the ceramic resonator sits at the top right of the board while the secondary CPU sits at the bottom left. Would have to use about 50 jumpers across the board and these things can go wrong.

If anyone has a DX7S mainboard (DM) for sale, I´ll buy it.
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