Recapping my Prophecy

[jaminem]

Hi, I have just recapped the main board in my Korg Prophecy - it was suffering from a very low output and this has been somewhat rectified by the recapping, although its still not as higher level as I would expect...

I did however not replace 2 of the caps - these where 16v 100microfarad 5 'K'
there were about 20 16v 100microfarad 5 'J' which I did replace but I was wary about replacing the other 2 as they were physically larger than the 'J's even though they were the same value and I wasn't sure what the J/K meant

so thats my question - what does the letter mean and am I ok to replace them with the same value or was I sensible in not replacing?

Mouser didn't give a value for the caps (I used Nichicon audio grade) so I'm assuming it doesn't make a huge difference (does it relate to what they're made of?) but wanted to be sure before I did anything dangerous...

Thanks all.

[James Perrett]

Any chance of posting some pictures of the capacitors in question? I would guess that those suffixes are manufacturer specific as there isn't any standard way of expressing other parameters (although the max working temperature is sometimes included on the label).

[Folderol]

Are they in the power supply section? It's normal for these to be bigger as they need much better ripple current handling.

[jaminem]

Any chance of posting some pictures of the capacitors in question? I would guess that those suffixes are manufacturer specific as there isn't any standard way of expressing other parameters (although the max working temperature is sometimes included on the label).

yes, I can its all buttoned up now and just popping out, but I did take a lot of photos before doing owt, just popping out - for ref, I misremembered - they were 10 microfarad and all the ones I replaced where 5K, the 2 larger are 5J

[James Perrett]

Just going through the service manual...

If these are surface mount electrolytics from the same generation as the Korg piano that I recapped a few months ago you will need to replace all the capacitors in the signal path which are:

C8,10,11,12,13,14,15,16,17,18,19,22 and 23. There may also be other de-coupling capacitors of the same type on the digital side which, while they may not stop the unit from operating, would be best replaced.

There are also a couple of non-polar capacitors, C20 and C21 on the output of the DAC. Are these the ones you are asking about? If you need to replace these then you need to replace them with non polar capacitors or 2 x 22uF electrolytics back to back.

While I don't normally advocate wholesale recapping, Korg used some very poor surface mount capacitors in some of their gear in the 90s and so it is probably justified in this case.

[jaminem]

Just going through the service manual...

If these are surface mount electrolytics from the same generation as the Korg piano that I recapped a few months ago you will need to replace all the capacitors in the signal path which are:

C8,10,11,12,13,14,15,16,17,18,19,22 and 23. There may also be other de-coupling capacitors of the same type on the digital side which, while they may not stop the unit from operating, would be best replaced.

There are also a couple of non-polar capacitors, C20 and C21 on the output of the DAC. Are these the ones you are asking about? If you need to replace these then you need to replace them with non polar capacitors or 2 x 22uF electrolytics back to back.

While I don't normally advocate wholesale recapping, Korg used some very poor surface mount capacitors in some of their gear in the 90s and so it is probably justified in this case.

aha - C20/21 were the ones I didnt do!

[James Perrett]

aha - C20/21 were the ones I didnt do!

Yes, they need a different type of replacement. For example:

https://cpc.farnell.com/unbranded/np16v ... dp/CA05945

although you may want the surface mount equivalent.

[Wonks]

The J and K normally refer to different physical types of capacitor. Type J – Dipped Tantalum Capacitors. Type K – Mica Capacitors.

[James Perrett]

Type K – Mica Capacitors.

Though I don't think you'd find a 10uF mica capacitor at anything like an affordable price - if you could find one at all. 47nF is the largest that Farnell do and that one costs £68.

[Hugh Robjohns]

The J and K normally refer to different physical types of capacitor. Type J – Dipped Tantalum Capacitors. Type K – Mica Capacitors.

Erm.... yes, the letters can be used to indicate different types... but as these are all electrolytic capacitors I suspect the letters actually refer to the nominal value tolerance. Typically, F =1% tolerance, J=5%, and K=10%.

[Wonks]

D’oh!

[jaminem]

aha - C20/21 were the ones I didnt do!

Yes, they need a different type of replacement. For example:

https://cpc.farnell.com/unbranded/np16v ... dp/CA05945

although you may want the surface mount equivalent.

Ah magic, thank you!
If I do decide to change them this will be very helpful.

[Martin Walker]

Type K – Mica Capacitors.

Though I don't think you'd find a 10uF mica capacitor at anything like an affordable price - if you could find one at all. 47nF is the largest that Farnell do and that one costs £68.

..plus you might well need a separate case to house it!

[Tomás Mulcahy]

While I don't normally advocate wholesale recapping, Korg used some very poor surface mount capacitors in some of their gear in the 90s and so it is probably justified in this case.

Why did Korg often do this? The PS and MS series have a similar issue. Prophecy predates both the Capacitor Plague and the Capacitor Cartel.

[jaminem]

While I don't normally advocate wholesale recapping, Korg used some very poor surface mount capacitors in some of their gear in the 90s and so it is probably justified in this case.

Why did Korg often do this? The PS and MS series have a similar issue. Prophecy predates both the Capacitor Plague and the Capacitor Cartel.

No idea, but Prophecy's developing very low output is known thing, and replacing the caps on the mainboard seems to be the cure...
I have limited electronics knowledge so I wouldn't have attempted it normally but there's YouTube vids from people who've had the same issue and as I've built a fair few 500 series kits so I know my capacitors from my resistors I thought I'd give it a go....

A few of them did indeed look like they'd spilled something on the board, but its such a faff to get the thing out I thought i'd do them all with the exception of the 2 described above to save myself some pain...

[James Perrett]

While I don't normally advocate wholesale recapping, Korg used some very poor surface mount capacitors in some of their gear in the 90s and so it is probably justified in this case.

Why did Korg often do this? The PS and MS series have a similar issue. Prophecy predates both the Capacitor Plague and the Capacitor Cartel.

I think that they just used cheap, poor quality components with a limited lifespan. They seem to start failing after 15-20 years. Fostex had similar issues with their early surface mount electrolytics. It is interesting that many other companies used through hole electrolytic capacitors on boards that otherwise used surface mount components - I wonder if they knew something that Korg didn't.

[MarkOne]

To be fair to Korg, I suspect that the design brief didn't include a 15 year MTBF and also SMT was fairly cutting edge back when the prophecy came out, so I wouldn't be surprised if reliability data on those capacitors was pretty thin on the ground.

Oh yeah, and cost...

[sonics]

Indeed. Korg (and others) know that instrument technology moves on and that these would be replaced by new models within, say, ten years. They are not made to last much longer, and I wouldn't expect them too.