SMS won't power on

[chadtower]

I have an SMS1 here I'm working on. It won't power up at all from what I can tell... nothing on the TV indicates a signal is being sent, weak or not. The light does not come on. I know the power supply works as I've tested it with two other SMS units and both worked well.

Where do I start in diagnosing the problem? I'm trying to build my repair skills and have quite a stack of nonworking hardware here to plough through.

[Raccoon Lad]

I'd start with the power connector, then look for burnt fuses. Wouldn't hurt to check the on switch either.

[chadtower]

Right... the solder under the power socket and switch. The problem with the switch, though, is that it's mostly self contained... you can't disassemble the thing without desoldering it off the board.

I'll take a look at those later on today and get back to you.

[FABombjoy]

You wouldn't want to disassemble it anyway, as metal pieces and springs will go flying everywhere.

Usually you do a resistance check across the switch terminals to see if the NC and NO contacts function correctly.

The next step is to check operation of the +5V regulator(s). Don't remember how many it has.

[chadtower]

You wouldn't want to disassemble it anyway, as metal pieces and springs will go flying everywhere.

Usually you do a resistance check across the switch terminals to see if the NC and NO contacts function correctly.

The next step is to check operation of the +5V regulator(s). Don't remember how many it has.

WOOT. That's beyond my current knowledge... these are the things I need to learn. :)

I'm taking some pics of what I think are relevant things to look at, I don't see anything out of the ordinary here so far other than that it's dirty. I'll have pics here in a bit.

[chadtower]

Okay, it's about as clear as I could manage with my old digital camera. You get the gist of the board, though... the bottom of the board.

The bottom right corner is the underside of the power socket. The solder looks intact on all contacts... BUT something you can't tell from the photo is that the solder on the bottom contact runs into the solder on the rightmost contact. Could that be causing some type of power fault? From my limited understanding it could, but if that is the case then this sucker was faulty right out of the factory, right?

Does someone know of a reference where I could read up on how to do a resistance check and what a +5V regulator is? I know, I'm starting out with a serious lack of knowledge here, but I had to start someplace.

http://www.gis.net/~tower/gamefix/SMS/board_power_issue.jpg

[chadtower]

Okay, my investigation continues. Last night I searched usenet and turned this up:


http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=19990717145317.12878.00001947%40ng-fr1.aol.com&rnum=2&prev=/groups%3Fq%3D%2522sega%2Bmaster%2Bsystem%2522%2Bre pair%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26selm%3D19990717145317.12878.00001947%2540ng-fr1.aol.com%26rnum%3D2



This post is basically stating to replace a 7905 component, but NOT TO
REPLACE IT WITH A 7805, even if a Radio Shack employee tells you it's
the same thing. Well, I'm looking at the board under the heat sink
and there is a component here labeled 7805 and it appears as though it
may have been poorly soldered in after the fact. Note the dirt on the motherboard as pictured above, it's loosely centered around the underside of that 7805 and is the only dirty spot on either side of the board. Could this have been a poor attempt at repairing this thing before it got to me? As I
said, I'm very new to this, but... this looks like it may be the case. Any advice at all would be highly appreciated.

[omnedon]

I usually give up at this point and move on to the next system. I'd use a unit like this one for parts.

I know that's not what you are after, but it is why I don't have anything more specific to offer. :o

[chadtower]

I found a schematic here:

http://www.smspower.org/dev/docs/sms_schematic.gif

This schematic lists the 7805 in that place... not the 7905. So it looks like I'm back to square one. I'm about to pick up the TTL Cookbook and spend some time reading it, then grab a multimeter and learn how to use it.

Note that I'm not doing this for monetary profit, so parting this sucker out wouldn't benefit me in the least. That and I have about 15 more consoles here that probably have similar problems.

[Raccoon Lad]

I'm pretty sure the 7805 is the standard part for a SMS. It basically takes the +9V input and puts out a stable +5v to all chips.

[chadtower]

That's my conclusion, too... basically, I'm going to get the TTL Cookbook and a multimeter and learn to use it... then I can figure this out.

[§ Gideon §]

... basically, I'm going to get the TTL Cookbook and a multimeter and learn to use it...
Please tell me what this magic book is. I must know.

[FABombjoy]

That's a pretty weird schematic you've dug up there. Notice the video modulator is spelled "modulador" (either Spanish or Portuguese). Also, what's a "slotbovias" or "blotbovias" or "5lot50vias" or whatever that word is? It's also set up for a +5 & +12 voltage input. Plus it lists seperate a/v jacks along with the RF jack.

In short: I don't think it's the schematic for the US NTSC SMS v1

[chadtower]

In short: I don't think it's the schematic for the US NTSC SMS v1

That's entirely possible... that's one reason I'm going to learn to use a multimeter and find the problem myself rather than relying on the diagram.

[MrKitt]

dude in 99% cases when your sms doesnt power up its the 7805 thats broken or the dc adaptor, these things can read ok but still be broken so remove it and replace it once youve replaced it try adding something in between 7-35V to pin 1 thats the left one if your reading the text on it and ground in the chunk of metal its connected to.

http://www.elfa.se/images/highres/h6689.jpg