using a multimeter

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brianb
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using a multimeter

Post by brianb » Fri Sep 03, 2004 6:24 pm

So I got a symetrix 202 with the intention of modding it and managed to short the thing out by haveing it powered up and sitting in the enclosure but not screwed in while checking to see if one of the channels worked. Well it DID work before I blew the fuse now it doesn't. I just got a solder station from CSI and enough other stuff to get a multimeter. I was wondering if anyone had any advice on how to use it to see what I might have fried. I googled "how to use a multimeter" but didn't really find anything useful. Any help greaty appreciated. Thanks.

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Re: using a multimeter

Post by Milkmansound » Fri Sep 03, 2004 6:29 pm

sci.electronics.repair - google it -there is an FAQ file that should help you out
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Re: using a multimeter

Post by brianb » Fri Sep 03, 2004 7:40 pm

Thanks. From what I read it seems like doing a "continuity test" is probably the best place to start. Is there any basic method that people use when doing something like this. I guess I'm just going to try totrace the circuit and keep moving the probe until I don't get "continuity" does this seem right? Anybody know of an intrductory book that might be helpful?

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Re: using a multimeter

Post by I'm Painting Again » Fri Sep 03, 2004 11:20 pm

try replacing the fuse first and see if that works first if you have not done that already..

i dabble in tech stuff a little and from what it sound like your trying to do(trace bad components down) i think you will need two different kinds of multimeters, an oscilloscope, and an indepth knowledge of electrical engineering..on a board there are all kinds of sneak paths that will give regular multimeters readings that wont make any sense in a continuity test..

i could be wrong though..im no expert on this stuff..

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Re: using a multimeter

Post by brianb » Sat Sep 04, 2004 1:15 am

Thanks. Replaced the fuse. One channel seems to work fine. The other channel won't pass any signal but the clipping light is on. The output on that channel is a weird oscillating hum. Any ideas?

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Re: using a multimeter

Post by I'm Painting Again » Sat Sep 04, 2004 11:40 am

the 202 seems to be 16volt..that makes me think its an opamp based circut?

i know bad opamps can cause oscillating/humming..

but really i wouldnt know but thats my best guess here..

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Re: using a multimeter

Post by brianb » Sat Sep 04, 2004 3:59 pm

Yeah its got opamps on the input and output stages. The mod is based on replacing the out put opamps and the caps around it so I suppose I might as well just do the mod and see what happens. I was looking at the pot on the channel and the solder looks kind of funky. Wondering if a bad pot can cause oscillating hum.

On the upside I'm figuring out how to use my multimeter. I checked the voltage on every single battery inthe house. Checked the ones on the remote to my DVD and found out that they both had 1.6 volts instead of the 1.5 marked. Looks like I'm"sticking it to the man" to the tune of .2 volts. Think I'll cash 'em in and head to Reno for the weeknd.

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Re: using a multimeter

Post by puffpastry » Sat Sep 04, 2004 10:00 pm

Man, I love those CSI solder stations...I just got a couple at the shop. A very nice deal for the money.

Don't do the mod yet--check your voltage rails first. Hum can be caused by many things, and if you blew a fuse, you might have a missing or sagging voltage rail on one channel (especially if your meters are maxed!). Check the filter capacitors in the power supply--often you can spot a bad filter cap because it will swell up and the top will dome.


I wrote an article about using a multimeter--you can check it out here. It covers measuring resistance, current, voltage, forward bias, etc. I also wrote one about troubleshooting audio equipment here

Keep us posted on your progress, and please feel free to ask more questions. It's always a good thing when you have an opportunity to learn a little something about your equipment.

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Re: using a multimeter

Post by brianb » Sun Sep 05, 2004 12:57 pm

Wow. Thanks for the links. I'm printing the articles out for future reference. Inspected the caps and a few of them look a little buldged. Didn't have time to trace the circuit to see if they were connected to what I think are the power rails. Thanks for the encouragement too. Even if I end up wrecking this thing I"ve already learned a lot.

On a related topic I opened up my Art tube pac last night to see if I could use your mod for the tube mp to mod this. I've been waiting to hear how the mod for the levelar is going because this thing is supposed to be a combination of the mp and the levelar. After looking at the guts of the thing I'm not optomistic about applying the mods. The board is packed and the tubes are mounted to another board that is mounted perpendicular to the first. Two of the op amps are stuck under a bank of resisrors that are attached to the tube pcb. It'll be a real challange to get them out. I don't know how anyone could possibly trace the circuit either. Still I'm not giving up. Hopefully I'll be able to use at least some of the modifications you come up with.

Anyway thanks again. I never ceased to be a amazed with the generosity of people like you on these boards. Hopefully one day I'll know enough to put alittle back.

Brian

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Re: using a multimeter

Post by brianb » Thu Sep 16, 2004 2:04 pm

So I deceided to replace all the ceramic caps on this thing and was wondering about a couple of them. One says 103z on it and I'm wondering how to tell if it's 100v or 50v the other says 102k and I can't find out anything about it.
also -matt in the thread on the bellari mod you said that rreplacing pots with 100k ones helped the sound I need to replace the pots anyway (they broke off-don't ask) and wad wondering how to check the value of the pot and if replacing the pots on the 202 would be worthwhile. Thanks.

Brian

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Re: using a multimeter

Post by puffpastry » Thu Sep 16, 2004 8:08 pm

I don't really know much about the 202, so I can't tell you whether different values of pots would help. The best way to tell the value of the pot is to measure it--turn the pot all the way in one direction and measure the resistance between the wiper (middle terminal) and the input or output terminals. Resistance readings should be 0 ohms between two of the terminals and the value of the pot between the other two.

I have a chart that tells how to read ceramic caps--unfortunately it's at the shop, and I never seem to remember what values the numbers refer to off the top of my head (yes, I always consult the chart at work--shame on me!) Unless someone else can fill in the info, you'll just have to wait till tomorrow.

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Re: using a multimeter

Post by Milkmansound » Thu Sep 16, 2004 9:46 pm

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Re: using a multimeter

Post by aurelialuz » Thu Sep 16, 2004 11:16 pm

Milkmansound wrote:How about here?
nice.
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Re: using a multimeter

Post by brianb » Fri Sep 17, 2004 10:36 am

Thanks for that link looks like I'm all set for the caps.

I'm also doing the additional mods you recommend for the 105. I was wondering how much differnce there is between the Clarostat pot and a Vishay. I don't mind spencing the extra couple bucks if it means better sound. Also do you need to replace both pots or just the one on the input. I was also wondering where besides digikey you can get the Clarostat pots. Digikey has them backordered and mouser doen't carry them.

Thanks.
Brian

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Re: using a multimeter

Post by puffpastry » Fri Sep 17, 2004 11:09 am

That's the capacitor info I was going to post, thanks for finding it--I was feeling too lazy to google the info.

You can use either Vishay or Clarostat--I usually use Clarostat, but the Vishays are very good too. Also, I've experimented with dropping the values of R4/R5 (I think those are the ref #'s) from 5k to 1k.

edit: correction, the ref#'s are R5/R6, not R4/R5. I should mention that you can't just drop the values of these two resistors without making a lot of other changes to the input circuit, so don't do it unless you know what you're doing.

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