EB5AGV's Workbench: YAMAHA SY77 repair

Getting a classic synthesizer back to life

I have always liked music. It is something I enjoy quite a lot. I also enjoy challenges, so getting this old synthesizer back to a good working shape has been a very rewarding experience. I hope this page encourages someone else to pursuit a similar endeavour. You will enjoy it!


SY77 as bought

I knew this was not a pristine unit. The pictures I had got before I picked it up showed some blemishes here and there. But when I saw the unit, it was even worse than I thought.

Being a 1989/1990 unit, so close to 30 years in February 2018, probably used for some years on stage and for sure not too carefully, it was dirty, scratched, with some cigarette burns, lots of faded key labels and, as usually happens on these units, most of the function keys didn't work properly or not at all. Luckily, the keybed was in good shape and all keys worked as they should. Kudos to YAMAHA for such a sturdy and durable design!

Yamaha SY77

Yamaha SY77

Yamaha SY77

Yamaha SY77

Yamaha SY77

Yamaha SY77

Besides dirt, there was a broken corner. Fortunately, the most of the broken part was found.

Yamaha SY77

Yamaha SY77

I decided to perform a functional repair, instead of a fully restoration. There are too many things which are damaged so, in order to generate a pristine unit, as I would like to have, I should buy almost a full set of mechanical external parts.

So the idea is to fix the unit electronically and do some minor cosmetic repairs. This way, it will be feasible and also it will keep some life marks on it, which, as skin scars on humans, will be a tribute to its hard working life.


First setup and checks

I installed it on a keyboard support and connected it to a tubed (valved) amplifier, along a couple SONY monitor speakers. The sound which emmanated from the SY77 was really captivating. I was hooked!

Yamaha SY77

But, checking the unit, I fastly found lots of (anticipated) problems:

So I did a list of what I needed and ordered spares to repair the unit. It was for sure worth it!


Repair work - first part

It is not easy to fit a 1+ meter long unit on my electronic workbench!. I have it configured to work on electronic items about half the width of the SY77... Luckily, just removing some items, I was able to make it fit.

Here you have the unit, upside down on the bench. Please, note that the modulation controls should not touch the bench surface. What I did was putting a large towel on the bench and then folding it so the modultaion controls were kept floating

Yamaha SY77

Here you have some detailed pictures of the unit. It is very important to take them, as getting back all the wiring to the same position, once all is disconnected, is not easy. Also, you need to label the connectors. I use a fine tip permanent pen on the connectors, writting the same number shown on the PCB

Yamaha SY77

Yamaha SY77

Yamaha SY77

Yamaha SY77

Yamaha SY77

Yamaha SY77

First step to disassemble the unit is to remove DM1 and DM2 boards

Yamaha SY77

Yamaha SY77

Then, the black cardboard on the left side could be removed to give access to the DATA and WAVEFORM sockets Yamaha SY77

I am glad I removed them as, on this unit, which I think never used those cards, there was plenty of dirt which would be a problem if I ever use these

Yamaha SY77

Yamaha SY77

The plastic support for the sockets, shown on next picture, should be also removed

Yamaha SY77

Then, I took a look at the power supply. As all the unit, it was dirty!

Yamaha SY77

I checked the filter capacitors with the ESR70 meter and they were healthy. This is a good sign of the quality materials YAMAHA used on these units

Yamaha SY77

But there is a hidden problem, which could cause lots of trouble if you don't take care of it. There are lots of cracked solder joints on this board, as the ones pictured

Yamaha SY77

I reworked all the board, as it takes just perhaps 10 minutes and will save the SY77 from future serious problems.

Next step involves removing plenty of screws and taking out the keybed. It is easy to do, as it uses 4 longer black screws, 2 each side and then a lot of gold screws on the middle chassis side. Once you get all of that out, this is what remains of your beloved SY77

Yamaha SY77

Now you can take out the jacks panel. Again, there was some dirt around. I checked for craked soldering and there was none. Note that the (noisy) inverter for the LCD is located on this board. It is the circuit around the small transformer. I will replace this with an electronic version someday, so I can remove the troubling noise it generates. But, by now, I left it as is. One option is to make this circuit switchable, so you can disconnect it while you don't need the backlight

Yamaha SY77

Yamaha SY77

I checked the inverter capacitors which were also fine

Yamaha SY77

Finally, you have access to one of the troubleprone circuits, the left side (bottom view) keypad, which includes the VOLUME sliders. There I found still more crud. This should be a reminder for all of us: cover the SY77 when not in use!. All keys leak dirt to the underside switch, and that does not help to keed them working fine

Yamaha SY77

By now, I left it aside, as my interest was first to fix the LCD backlight and then work backwards. The LCD can be seen once you remove the keypad circuit

Yamaha SY77

An important hint: as you can see in the pictures, the LCD PCB has a couple of small capacitors, which seem very prone to leak. Those should be removed, carefully cleaned with alcohol all the leakage, and then replaced. They were 4.7uF/35V and 10uF/16V units. On that size I had just 10uF/25V units, and I replaced both with them. It is not critical and 25V is enough on those circuits

Yamaha SY77

Yamaha SY77

Yamaha SY77

Once you get the LCD PCB out, you can see the backlight connection

Yamaha SY77

As the instructions of the replacement unit said, sometimes the backlight is glued, as was on my case. So I left the old one and put over the new one, with the pink side up. It is important to isolate the old contacts, so I put some Kapton tape on them

Yamaha SY77

Yamaha SY77

Yamaha SY77

Yamaha SY77

Another thing which I found was a problem, is that dirt deposits on the LCD and, as it is so hard to reach that point to clean it, I decided to improvise a fix. I added some foam strips, all around the LCD, in a way which should make it invisible from the top, but assuring dirt will not get into so easily

Yamaha SY77

Yamaha SY77

As this adds some height to the LCD assembly, I put some Nylon washers, held by an small dab of glue

Yamaha SY77

That way it fitted perfectly, with enough pressure on the foam strips to get a good seal.

I placed the LCD back, hoping the backlight would work. You won't know until all is back again!

Then the keypad restoration began. First, I carefully cleaned all dirt form the PCB. Then the function keys assemble should be removed, at least partially, in order to access to the switches below. Be careful with this, as the plastic keys are delicate and can break. Work slowly, with a fine tip flat blade screwdriver, until you get the assembly dislodged from the glue tape, which can be reused

Yamaha SY77

This is one of the switches... as you ca see, it seems old a tired. Time to retire!

Yamaha SY77

This is what you have once the switches are removed

Yamaha SY77

And these are the new switches. I used good quality OMRON units. I think it is not worth to save on this, buying cheap ones, as the work involved does not justify saving some money and use unbranded units. But this is your take, if you do this

Yamaha SY77

Now it was the turn of the VOLUME sliders. As you probably know, the original manufacturer no longer makes them and only Chinese copies (yes, all of them) can be found now. The manufacturer price for these is less than US$1 each. People selling tham ask US$7-15 each (yes, there is a BIG profit there!). And then, the units they sell are NOT directly suited for this use, as the shaft is lots longer and it is not just a matter of cutting it. You need to also trim laterally them, so the button will slide, fit and keep on place with some pressure. I did the work before soldering them, it is lots easier.

These are the original units, still on place

Yamaha SY77

Side by side comparison between original and replacement units

Yamaha SY77

This is what would happen if you don't trim them!

Yamaha SY77

New sliders, properly trimmed, on the PCB

Yamaha SY77

And then the keypad PCB, with all the switches replaced

Yamaha SY77

Back to its position. I am eager to check the new controls!

Yamaha SY77

Now it was the turn of the right-side (bottom view) keypad assembly

First, you need to carefully remove the shielding over it, noting how it is mounted

Yamaha SY77

This is the keypad PCB, waiting to be unscrewed

Yamaha SY77

For sure, you didn't expect to find a clean PCB, right?

Yamaha SY77

Yamaha SY77

After a careful cleaning and removing all the old switches, it looks pretty well

Yamaha SY77

And, voilą, here you have all the new switches fitted

Yamaha SY77

I know this would be the perfect time to replace the DATA ENTRY slider... Yes, but I didn't have the replacement (it is a long story), so I know I will be back here soon!

Once thing I noticed is that the wobbling of the SELECT knob was not due to a faulty encoder, as I was afraid, but a cracked plastic knob. So I added an small plastic tie wrap and then put some dabs of glue to fix it and glue the cracks. The result is very good, as now the knob does not wobble. Great (and cheap) solution!

Yamaha SY77

Then the keypad was put back on the unit

Yamaha SY77

This is another small hint: as you will notice, there are some metal adhesive strips here. As the glue becomes old, and also due to the disassembly, they won't keep on place. So I added some Kapton tape to keep the electric contact on them

Yamaha SY77

Now it was time to revert the process, assembling the PCBs in reverse order

Yamaha SY77

Yamaha SY77

Here you have another use of Kapton tape, to keep some cabling on its intended place

Yamaha SY77

Putting back the black separator

Yamaha SY77

Another tipycal fault on these units is the backup battery. On my SY77, it had been previously replaced. They just cut the old one and soldered a new unit. As I prefer the socketed CR2032 approach, I removed the old kludge and put a socket on it. There was some adapting work done, but nothing difficult

Yamaha SY77

Yamaha SY77

Yamaha SY77

And then the DF1 and DF2 were put back on the unit. I had some struggle with the wiring positioning, but the initial pictures helped quite a lot

Yamaha SY77

Yamaha SY77

Once all was on its place, I put a new CR2032 battery

Yamaha SY77

And that was all!. The unit was ready to be checked. I was a bit scared of what could happen... This was my first SY77 work and I had been working from 18:00h to 02:00h, with just an small break for dinner... Before putting back the back cover, I flipped it and powered it. It was great to see that the LCD backlight worked, the system booted and all the switches worked nicely!. I did a full reset of the unit and everything seemed to work. Great!. So I put back the back cover and took it to the other room.

This is the final result

Yamaha SY77


Pending work

There are some items which I should still work on my SY77. I need to replace the DATA ENTRY slider and also the FDD belt. I have both ordered but, as they took so much time to arrive, I decided to do the work I already could. I think I did the right thing, as now my SY77 is lots more useable than it was and I have gained the knowledge to work on it. Also, now I can check all the functions and find if I should take care of anything else.

So, keeep tumed!. I will add more information as I work more on the SY77.


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