DC power jack marginal?

[Agent24]

I have recently finished adding A/V out connections to two Sega Master System 2 consoles.

The SMS2 uses the Sony CXA1145P IC which provides a Mono audio output, and Composite, S-Video and RGB video outputs.

The only thing lacking is the wiring and a couple of components, which are easy to add (see: http://knol.google.com/k/konsole-kra...gsu6gmugnec/3#)

My modification is essentially the same, except it looks much better and uses shielded wire for the signal wires.


Now, everything works fine, the magic smoke is still inside, I don't doubt the modification itself as many people have done it.... BUT with some positions of the DC power plug, I get buzzing in the audio.

If I slowly turn the plug around in the jack, at some points, I can make the buzzing go away, in some places, power interruption, and the console resets.


I get the impression that the jack is worn, there is a bad connection, possibly mild arcing causing the buzzing? Maybe they need cleaning?

Is this a known issue with old power jacks (remember these console were made in 1990) or could it be something else?

[PCBONEZ]

Re: DC power jack marginal?

I'm going with bad connection, worn.

[Krankshaft]

Re: DC power jack marginal?

Bad DC barrel connector try hitting it with some contact cleaner and see if it's just oxidation and dirt. If not and it's the spring steel contacts replace the jack.

Hopefully it's a standard connector and not one of those proprietary ones like on the Super NES. I love how the voltage inputs were similar but Nintendo put a proprietary plug on their console.

Both consoles SNES and Sega Genesis had an internal linear voltage regulator for the logic ICs so any adapter 9 to 12 volts would work.

[Agent24]

Re: DC power jack marginal?

Yeah it's a standard connector, the console requirement says 9v DC @ 500mA but with center negative, just to be different to most things.

Don't have any 'proper' contact cleaner that I know of, is there anything else that would work?

The SMS2 has a 5v Regulator, however there's some circuitry before it, didn't pay too much attention but I'd be a bit wary about giving it a higher voltage, at least until I inspected it to see what it is.

[Th3_uN1Qu3]

Re: DC power jack marginal?

I wish my SMS2 still worked. I bought it a few years ago solely for Streets of Rage... i really liked the moves in that game. It mostly sat unused and when i wanted to play it again it just displayed a green screen. Probably the EEPROM got shot.

[Agent24]

Re: DC power jack marginal?

I don't know too much about them to know what sort of faults they get, if the EEPROM you're speaking of is a standard one I could probably read mine and send you a copy if that would help.

[Th3_uN1Qu3]

Re: DC power jack marginal?

Yes the EEPROM is a standard format (i believe it's 32-pin DIP like those old BIOS chips), but i don't have a burner unfortunately, and the SMS2 was one of those things i didn't use too often anyway.

[Scenic]

Re: DC power jack marginal?

if it's a standard eeprom you might be able to flash it in a computer motherboard using uniflash or something..

[Th3_uN1Qu3]

Re: DC power jack marginal?

Good idea. I'll take a look the next few days.

[Agent24]

Re: DC power jack marginal?

I've taken some photos of mine, and it looks like my BIOS chip is a MPR-12808
MPR series according to the Internet means that it's a mask-ROM
(See: http://www.smspower.org/Development/ROMPartNumbers)

On the good side I can't see it would be able to get corrupted or anything, But of course on the bad side, you can't reprogram it to find out either...

BIOSes appear to be available here: http://www.smspower.org/Development/BIOSes

I guess if you can find an EEPROM with suitable pinout you could give those a try or something, but it may not be the BIOS ROM which is causing your problems, might be something like a bad voltage regulator causing the CPU to lockup, who knows...

[Th3_uN1Qu3]

Re: DC power jack marginal?

For all i can remember it just powered up to this green screen when i tried to use it after it's been stored for an year or so. Could even be bad caps...

[Agent24]

Re: DC power jack marginal?

Could be, though considering everything is powered with a single 7805 I don't see much going wrong in the power supply department..maybe if something went totally open or shorted...

All the electrolytic capacitors in mine appear to be Elna RE2 series (General purpose 85 degrees)


On-topic - I took a closer look at my DC jack with a magnifying glass and torch, the spring contact doesn't look too good, I see what could be rust, or carbon deposits.. (quite hard to see well actually)

I think I'll replace the jack tomorrow and see what happens.

[Agent24]

Re: DC power jack marginal?

Well this is interesting, I now have a completely different theory about this problem!

Replacing the jack solved nothing, in fact if anything the problem was made worse ('what!' I hear you say?)

At this point I should probably admit that I am not using the official Sega power adaptor (yeah I know, I probably should have said this in the beginning, and I should know better...)


As it turned out that may be the key to the whole mystery....

The Sega itself has on its label "9v DC @ 500mA" - now my multi-voltage dual-polarity adaptor just happens to be 500mA and has a 9v setting.

HOWEVER - the official Sega power adaptor is actually rated for 850mA, a whole 350mA higher than the current drawn by the Sega (assuming that's what the label means). I was not given the official adaptor at the time as the wire near the plug is broken, but since it's twice the size of mine I have theory number 2:

The official power brick is rated higher than needed, runs only at 58% of capacity and possibly has better filtering, maybe even a regulator on board.... While my own adaptor would have been running at 100%, isn't regulated and probably has a horrible Fuhjyyu or something for a filter capacitor, knowing my luck.

So my theory now is that my adaptor was supplying a high ripple, otherwise noisy power to the device and causing problems. The brand new jack only allowed this noise to come though even better!


So, after picking up the proper adaptor this afternoon I will be getting a new plug for it tomorrow and seeing how that goes....

[Agent24]

Re: DC power jack marginal?

So the conclusion to this dramatic and exciting story... haha


Official power adaptor works great after wiring a new plug on it, notice it's ouputting about 12.8v DC no load so I expect not regulated.

Either way, it works perfectly, no buzzing on the audio, both with the new and the old DC jack.

(I decided to put the old jack back and leave it there, after testing resistance it was flawless, I guess my eyes deceived me, it's not rusty or problematic at all, and I'd rather have a brand new jack for something else)

Sadly I can't really confirm my high ripple current theory as I still don't have an oscilloscope.... but the thing works now so that's what really matters