SY99 Capacitor list/ Cap Map

[Miks]

Within the next few days I'm going to replace ALL electrolytic caps on my DX7IID - the reason is that I've got the notion that several of the sounds are 'not sounding right' if playing the lower notes on the keyboard. In addition there's a kind of modulation which shouldn't be there - and it's not coming from the use of the modulation wheel
While doing that I will write down a list with the capacitors values (i.e. 10µF/25V) and positions (i.e. C4, C66 etc) for every single PCB of the DX - once I'm finished I will post it here on the forum (DX section of course) so people also willing to replace the caps will have a 'shopping list' with all values and quantities.

Maybe I will do the same on my SY99 - one fine day - if I'll find the times

[HeavyNova]

I had to replace some capacitors on my DX7IIFD because I had faint audio coming out of 1 of the 2 channels and perceptibly scratchy audio when playing the keys with a heavier pressure. Sometimes the degradation is gradual and it is possible to become habituated to the change in sound. Failing/failed caps often show up as a lack of 'sonic definition' whether slight or severe (that is of course when it gets so bad that you actually notice that it is there) I wonder if there are comparable, newer capacitors on the market today that are longer-lasting than their original counterparts? The beauty of soild-state technology, silicon, and pcbs is that they may have the potential of working for hundreds of years if maintenance items are addressed and high humidity and power surges are avoided.

Good Luck Miks! Let's hope the oldies are still intact (sealed) and that you don't come across any more damaged traces. Thank you for your decision to document this re-cap for the future benefit of others.

[Miks]

Thank you for your decision to document this re-cap for the future benefit of others

Your're welcome! I will take some pictures that show where each cap is located on the pcb and its values. So they'll be easy to find and one can replace all caps with the same values in one go - which I find to be easier than replacing one by one and always have to make sure it has the correct values...
I'll take caps with a higher voltage than the original - lets say 33µf/10V will be 33µF/16 (or 20) Volts... if you know what I mean...
I will also create a list with the original values and those I chose for replacement - a 'shopping list' for easy ordering the caps

[rtype909]

The service manual for the SY99 does not cover the regular caps only some of the larger ones eg. 220uf. No idea why, given the document is otherwise quite comprehensive.

[rtype909]

Its also worth observing there are a real mix back of caps in the Sy99, in terms of brand and quality. Elna for the big caps, Nichicon's for the mid caps and then some no-name for most of the 10uf caps.

[Miks]

I would strongly suggest to

1. only use caps which are labeled to resist temperatures up to 105° (don't use those labeled 85° !!!)

2. chose a higher voltage than the 'original', i.e 220µF/16V - -> replaced by 220µF/25V - but keep in mind that the physical dimensions of a cap may vary drastically by 'increasing the voltage' they can bear...

By doing so you'll be on 'the safer side' and the caps should last a long long time...

[rtype909]

newer caps are so much smaller you can comfortably increase voltage ratings and it still fit. plus the yamaha has generous lead spacing. Its quite easy to unsolder with a 40w iron

I think the unbranded 10uf around the op amps should be first to go

[Miks]

Newer caps are so much smaller you can comfortably increase voltage ratings and it still fit. plus the yamaha has generous lead spacing.

You're right mate - many of those 'modern' gear didn't offer that much space for doing such a surgery...

I think the unbranded 10uf around the op amps should be first to go

But take care - there may be several caps that aren't polarized (NP = Non Polarized) - my DX7II/D has some of these at the audio section as well as at the D/A converter circuitry. They shouldn't be replaced by using common (polarized) types of electrolytic caps !

[rtype909]

Yes i noticed there lots of bipolar 10uf around the opamps and two big 47uf bipolar near the 4556, which i assume is the headphone op amp. I wonder why this is so.

[jhulk]

the use of bipolar caps is to only let ac through they stop any dc entering the audio

the use of polarized caps is to stop ac entering the dc lines to an amount of allowed ripple the more caps you put in parallel to ground the smoother the ripple this allows the power regulators to regulate the voltage ripple equals noise on dc lines the more ripple the harder the regulators have to work which means more heat to a point that they reach there thermal overload protection circuit where they shut down

erratic behavior

very unusual to need to change bipolar caps as they are used in low voltage circuits and tend not to suffer from heat problems unlike electrolytic s used in the psu

never just swap out caps test them with a scope for ripple or in bipolar dc

polyester film types are also bipolar caps and are used for frequency applications along with ceramic dip types and ceramic disks these are also used as bypass caps which can stop noise

[rtype909]

I've done mine...had some spare OPA275 so they went in as well