oof - dropped my symetrix

cities · Post by **cities** » Tue Nov 22, 2011 11:44 am

I was cleaning my desk the other day, and clumsily managed to knock my symetrix sx-202 onto the carpeted floor. I figured these things are built like tanks so I didn't think much of it, but of course now it doesn't power up. I opened it up and don't see anything obviously broken, and the fuse seems ok (though I don't exactly know what I'm looking for).

Any suggestions to a total electronics noob about how to troubleshoot this?

Thanks!
Han

Snarl 12/8 · Post by **Snarl 12/8** » Tue Nov 22, 2011 11:50 am

What kindof tools do you have at your disposal? If you don't know what to look for in a fuse, it's kinda hard to tell if it's good. Most of them are little glass tubes with a filament running down the middle. Make sure the filament isn't broken. Even if it looks OK, I'd run out and get a different one of the same value and swap it out. I've a had a couple that I ruled out based on visuals, but were really bad. I actually had one that tested OK for continuity, but wasn't strong enough somehow for actual voltage. That thing is glass and a teeny, tiny filament, sounds like the weakest link to me. Unless you've got some other type of fuse. Like the kind they have in cars or something.

cities · Post by **cities** » Tue Nov 22, 2011 12:20 pm

Re: tools -- not much -- I do have a multi-meter, if that helps in any way.

Re: fuse -- yeah, I popped it out of its bracket and I could see that the very very fine, wavy filament still intact, so I assumed it was ok, but if visual inspection isn't a reliable way of determining if it's dead or not, then I should probably track down a replacement and see what happens.

The fuse says BUSS AGC 3/4 250V

Snarl 12/8 · Post by **Snarl 12/8** » Tue Nov 22, 2011 12:57 pm

I might be the only person that that looked ok but wasn't thing ever happened to.

Test the fuse for continuity next with the MM.

Basically, I think (I'm a noob, even though I've been hacking electronics forever) the troubleshooting process involves plugging it in, turning it on and then (CAREFULLY! WITH ONE HAND AND INSULATED TOOLS!) follow the flow of electricity and/or signal until it stops. Then whatever thing it was between where you had electricity or signal and where you don't is the problem. You could have knocked loose a solder joint that's not visible, but not good anymore either. You can push on components with a chopstick to see if that makes anything work too.

If you're lucky, Mr. Scum will chime in with exactly what your problem probably is.

cities · Post by **cities** » Tue Nov 22, 2011 1:31 pm

Heh - fair enough.

Fuse continuity checks out ok....

cities · Post by **cities** » Tue Nov 22, 2011 9:42 pm

I opened it up, took out the board, dusted it off with some compressed air, put it back together, and suddenly it works again! I have no idea what I did (or even if I did), but thanks so much for your help Snarl!

The Scum · Post by **The Scum** » Tue Nov 22, 2011 10:10 pm

Any chance that the power supply jack on the back got clobbered in the fall, and power isn't making it onto the board? Those barrel connectors break off PCBs pretty often - common point of failure for a lot of gear.

Are there any markings for checking power supply voltages inside?

Schematics here:
http://www.symetrixaudio.com/kb/SX202_sch.pdf

Check that the 7815 and 7915 are regulating +/-15 VDC.

Snarl 12/8 · Post by **Snarl 12/8** » Tue Nov 22, 2011 11:24 pm

I'd at least take a look at the parts Mr. Scum is mentioning, he seriously knows his shit.

cities · Post by **cities** » Wed Nov 23, 2011 5:52 pm

Hi -- thanks for the reply.

I opened it up again, and took another look. The power supply jack seems ok. I don't see any markings for power supply voltages -- I added a link to a photo of the insides -- and it took me a lot of googling to figure it out but I finally found 78M15 and 79M15

. as far as I can tell, they're regulating properly.

It does seem to be working fine since yesterday, so at least that's promising.

The Scum wrote:Any chance that the power supply jack on the back got clobbered in the fall, and power isn't making it onto the board? Those barrel connectors break off PCBs pretty often - common point of failure for a lot of gear.

Are there any markings for checking power supply voltages inside?

Schematics here:
http://www.symetrixaudio.com/kb/SX202_sch.pdf

Check that the 7815 and 7915 are regulating +/-15 VDC.

Snarl 12/8 · Post by **Snarl 12/8** » Wed Nov 23, 2011 6:18 pm

Man, that is a sweet photo. I can almost verify the fuse is good from here. Are some of those caps bulging a little bit on the tops, or is it just the lighting on those particular caps?

vvv · Post by **vvv** » Thu Nov 24, 2011 8:37 am

You know what? I'm not the electronics geek like Snarle mebbe is, but that is a sweet photo!

cities · Post by **cities** » Thu Nov 24, 2011 11:53 am

Ha, thanks! That photo (and the ones below) were all taken with my trusty Canon S95, which is just an amazing little camera.

Re: (not) being an electronics geek -- I had to do a search to confirm that what i thought was a cap was in fact a cap.

Here are some more pics -- I'm not sure if the caps are bulging or not -- if they were, would it be dramatic? To my eye, some of them look perfectly flat, and some of them have just a little bit of roundness to the top....

And the fuse, just for snarl's benefit:

Snarl 12/8 · Post by **Snarl 12/8** » Thu Nov 24, 2011 1:04 pm

Bulging caps are indeed bad. Do you see those score marks on the tops of the caps? Those will allow it to bust open there (like a pressure relief valve (that will never close again)) instead of exploding like a pipe bomb if they really need to expand.

Those all look fine to me, but again, I'm not a super expert. The way I judge best is by feel. I put my finger on the tops and they should feel indented a bit, not at all convex. I hope someone will correct me if worrying about bulging caps is bullshit. Again, yours look fine from these new angles.

Also, bulging isn't the only thing that caps can do that is bad. Sometimes they just leak out the bottom. Or invisibly dry out. Or just stay perfectly fine for a really long time.

RickvH · Post by **RickvH** » Thu Nov 24, 2011 10:57 pm

After a fall, I would be inclined to push down a bit on the two socketed chips, just to make sure they are firmly seated in their sockets.

To my eyes, the caps look okay.

Andy Peters · Post by **Andy Peters** » Sun Nov 27, 2011 6:36 pm

Ooooh, sockets.

Sockets suck. Especially when gear gets jostled.

Sockets have no business being in production gear.

Thanks for asking.

-a

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oof - dropped my symetrix

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