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Naomi 1 - assistance needed with repair

S

Stupid Dufus

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Hi all,

Got a lead on a Naomi 1 that is described as non-working. A few pics and description list it as having missing caps that "came off". No mention of possible other problems.

I have a working Naomi already, so I could get the cap values from that one.

I'm not too excited about having something else to repair, but thinking maybe if it was an easy fix (so far I'm 50/50 with arcade parts and easy fixes) I could give to a friend who's interested in home arcade use.

Thoughts? For around $20 I figure it might be worth it.
 
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Might be worth to try. At least it's a good practice platform for caps changing. Even if it wont start up after recapping or in worst case (which is unlikely) something burns up, it's not a $500 to work with...
 
For $20 I would grab it to tinker. If it's caps or fan related then it's an easy fix. Even the memory seems to be a fairly cheap repair. However If it's the surface mounted CPU the ONLY person I know who can fix those is Ken at irepairsega.com and I promise you it wont be cheap.
 
Took a gamble on it and picked it up. Missing 11 caps. Otherwise it's remarkably clean and almost dirt/dust free.

I compared to a working Naomi 1 I have, and found the following caps were missing (and looking at the pads, look like they either got corroded and fell off or were ripped off (though no ripped pads/traces that I can see):


Locationfv
C231016
C241016
C119??????
C1071016
C251016
C261016
C1931016
C281016
C12710010
C271016
C1331006.3


Two questions though:
C119 - I wasn't sure how to read the label on the cap.
47
6S
8MD

Anyone know what values though would be when I order the replacement?

Also--and I'm sure this is a simple, silly question--but all the values above, would those be F or uF? i.e., 10F or 10uF? 100F or 100uF?

Lastly, I will be ordering new supercaps, as both had already started to leak.
 
C119 sounds like 0.47uF or 47uF 6V to me, and all other values are uF as well.

This is what a 1F cap looks like...
C5451DD0-100A-4D61-9E04-EEE7DCB0DFD2.jpeg
 
Hahaha, might be a tight fit to get the a 1F in there, let alone 10F! :P

Can anyone confirm whether C119 is 0.47 or 47uF?
 
Thanks!

Seems like 47uF, 6.3v according to that site.

Will order the new caps and hopefully report back in a week or so.
 
Got the caps and installed, but still not getting a picture.

Going to try and swap the filter board tomorrow to see if maybe that's the issue.. but if not, anyone have suggestions on what to try next?
 
Well, the filter board isn't the problem. Something in the mainboard itself.

Thoughts on what to try next?
 
I assume you know that the fans need to rotate and sent some speed pulses to the board, or it won't boot.
 
There is a goldcap that might have start leaking. The spillage is corrosive and can damage pcb traces. You could have a good visual inspection at that.

Another thing you can try is switching the bios proms between the working and non working unit. At least, you will know that is functional.

I can imagine one capacitor falling off, but that many is suspicious. Maybe there is a voltage rail internally missing.

I personally have bad experience with things being sold as defective. It's usually an assembly of all defective parts they could find.

As an example, my chihiro had a bad main board, a bad dimm board and a defective base board. As cherry on the cake, the cable between the main board and base board was broken as well. And obviously, the 2 fan's were stuck as well. How can a system become broken that bad all at once?

If someone sells it and thinks it's somewhat fixable, he will sell it as untested.

I don't want to temper your enthousiasm. Maybe it's not as bad as it looks.
 
obcd said:
There is a goldcap that might have start leaking. The spillage is corrosive and can damage pcb traces. You could have a good visual inspection at that.

Another thing you can try is switching the bios proms between the working and non working unit. At least, you will know that is functional.

I can imagine one capacitor falling off, but that many is suspicious. Maybe there is a voltage rail internally missing.
Click to expand...
Goldcap? Would that be the supercap next to the CR2032 battery and the bios? There was a very slight amount of leakage from the cap, but the traces all looked ok. There was even less leakage than on the still working naomi.

Hadn't thought of swapping the bios. I'll try that in a day or two.

As for the voltage rail, how would I go about checking that?
 
For the voltage rails, there might be test points. Another option is checking some easy accessible chips and checking their data sheets to see what pins are used to power the chip, and what voltage it's expecting. The larger electrolithic capacitors are usually also connected between a voltage rail and GND to stablise the voltage and reduce ripple on it. So, you can measure on those as well. Finally, you can look for voltage regulators on the board, and look up their datasheet. Next, you can measure the voltage at their output or after the coil if they are switching step down regulators.
You need to do it very carefully so that you don't short nearby points if your meter probe slips away. You can use your working system as guidance, but be very carefull as you don't want to end up with 2 broken systems.
Even the bga chips might have some decoupling capacitors nearby that are mounted between it's supply and gnd.
 
Other things you can check is the heatup of some components. If you have 4 identical ramchips, and one is becoming 2 hot to touch, it's likely bad. An infra red thermometer is ideal to view such hot spots, but your finger is an indicator as well. Just don't be mad at me if you have a chip logo burned into it. Again, your working unit can function as a reference for the expected temperature.
 
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