Duo-R cap confirmation

[pulstar]

Hi all,

I bought a Duo-R recently from a guy in England, which was supposed to be fully working, which it is except for a temperamental cd laser . Most of the time it works flawlessly, other times it just comes up with the 'Disc not set' error. This is not the reason for this thread though.

I opened the unit to RGB mod it and for some reason the previous owner has decided a full cap kit was in order. Most was done okay-ish, but some, instead of being done correctly, were soldered onto the legs of old caps. Now, the sound works perfect but I don't like having the unit left like that. So really I'm looking for a confirmation on the value of some caps.

C305 - 100uf 50v?
C325 - 10uf 50v?
C102 - 2.2uf 50v?
C117 - 2.2uf 50v?

Any help would be appreciated in trying sort this mess of a cap replacement out.

[Bernie]

Well, that was crappy work.  I guess technically it wont hurt anything, but still...

[pulstar]

Yeah exactly. Functionally, it works but that doesn't really excuse it. It looks ugly as hell and really shoddy, so while I'm doing the RGB mod I'd like to get this sorted as well.

[Valkyrie]

Yea... I would re-do that mess.  By soldering onto the old caps, he wired the new ones in parallel with the old ones.  That doubles the capacitance of the component.  I have no idea if that would affect functionality, but I wouldn't be surprised if it did.
And plus, you've still got old caps leaking chemicals onto your board, potentially damaging vias and traces.

[pulstar]

Yea... I would re-do that mess.  By soldering onto the old caps, he wired the new ones in parallel with the old ones.  That doubles the capacitance of the component.  I have no idea if that would affect functionality, but I wouldn't be surprised if it did.
And plus, you've still got old caps leaking chemicals onto your board, potentially damaging vias and traces.

This is why I'm questioning the original values of the caps. It's a very confusing hack job. The thing is, a Duo-R doesn't historically have major problems with caps like a  Duo does so that makes it even more confusing.

[Fidde_se]

There are many why's why you should question the original value, first most people don't know what a capacitor is and what it does.

First thing is to be like a fast battery, higher value means more energy can be contained.
Second thing which it can be used for is it's side effect, the filtering function, it's related in impedance vs value to which frequency it will filter, in series it is highpass and in parallel it "shortens" the highpass and therefor becomes lowpass.

So the for most applications we will see, the exact value is not of that importance.
secondly there are the voltage issue, when you buy a capacitor with a certain voltage rating you buying the specs for it not the exact value, and factories that make them don't have separate lines and machines for creating 10, 25, 35 volt ones, they have one line and stamp different on them depending on what you pay for them, so they are all the highest they make in that line, not all are like this but the big mass are, just like when you buy the biggest dvd player the cheaper ones has the same pcb just some functions are removed for each and every model you go down in price.

To make that even weirder, when a big company like Sega (or Nintendo or NEC) makes a bunch of consoles they have a department for buying components, and to do that as cheap as possible, instead of buying many different voltage values they buy the highest needed and use that in several models since they make millions in discounts, hence why some consoles that only use 5v internally and doesn't contain any stepup circuits still have a few 35 and 50v capacitors in them, and still people out there are hunting their ass off trying to find exact values of everything, it's as dumb as the question that gets asked here all the time about power adaptors and that it must be original or this and that, voltage here and there and it must meet the exact spec, the as soon as it gets inside the console it goes into the regulator... end of that story.

Most "original" power adaptors is also a last minute afterthought being made by a contractor for the smallest amount... unfortunately those old adaptors are better in quality then modern cheap ones as they cost under a buck to make, and the MD1 is the most versatile adaptor ever made...

[pulstar]

Just as an update to this. I replaced the caps mentioned above with the values that were there and working (C305 - 100uf, 50v; C325 - 10uf, 50v; C102 - 2.2uf, 50v; C117 - 2.2uf, 50v) and as expected it works fine.

The other issue I had with the drive not reading discs all the time has been resolved as well, but not in the way I expected. It was working intermittently, no matter much I tweaked and adjusted the pots (even with a DMM and a 'scope). Then I noticed something while trying to tweak it with the lid off.

While it was trying to access the disc I applied pressure to the pot on the lens unit as a last ditch attempt to try and get it working and the unit sprang into life, sliding down the rails. Removing the screwdriver made the lens stop in its tracks. I reflowed the joints on the pot and now it works rock solidly all the time, even with backups (which the guy originally said would never work for him).

So now all issues are solved and I'm very happy