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SX-580 120hz hum

The reason for the 3 readings is that the meter blinked between them consistently in that order. while holding the lead into that location, it cycled through those numbers on the meter.
 
So, I'm in the process of attempting this measurement but here is a photo of that resistor. Obviously I'm not a regular electronics person but this doesn't look what I would describe as "good". That is r410 that the poorly drawn arrow is pointing to. At R410 I measured 166Ω on the last one but I took a lot of measurements and that was by far the highest. I could only get a measurement once at each polarity (example red on one side would only measure once, then switch red and black and measure again). I'm guessing that's normal? Electrons shifting from one side to the other?? idk, anyway, another note is that I've enclosed a photo of the -side of c413 solder. The reason I've added it is only because it is different than the others in that it doesn't connect with the nearby solder point like the others do. May not matter but thought it was worth mentioning. As a layman it just looks different but it may have value for you.
 

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R345 99.6Ω
R346 98.3Ω

One question, if I'm replacing this 100ohm resistor, what's the Watt rating for it? I looked at the parts list but can't find a spec sheet for that resistor part number.
 
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one or both output power packs might be bad ..do they unplug or are they soldered in ?
also best check the transistors on the amp board ..something caused that resistor to burn
 
Are the power packs the STK part numbers?

Nevermind, they literally say Power pack on them. They look like the just clip in, no solder.
 
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maybe best remove them for now . you will need to add some resistors for testing purposes whilst the packs are removed .
 
The Power Pack STK is a current amplifier power output stage in one package, They are virtually impossible to test manually. Sometimes, if they are bad they can be tested with the meter to see if they are shorted internally. Since you had sound from both channels (albeit with hum) they are probably OK for now. Lets not get off track from the power supply problem.
R410 measurement look like your meter is autoranging because it cannot figure out what it should be measuring. There are multiple possibilities for a resistor reading low while in circuit, but nothing (unpowered) that can make it read high.
R410 should have a color code striping of brown black brown gold for a 100Ω 5% resistor. Unsolder and remove it. The resistor your arrow points at looks like brown black green, which would be 1MΩ.
Was this unit working and then died, or did it have the hum when you got it?
 
i was thinking if the packs are out of circuit then they cant get damaged . then test the rest of the circuit and see if its safe to put the packs back in .
 
It made that noise the first time ever turned it on (week or so ago after I got it). I'm getting setup for the first soldering experience currently so bear with me. Would rather get a comfort level after some videos before starting.
 
Ok, got it off the board. I believe there's some brown black and gold but it's pretty cruddy in general so tough to tell.

Cleaned it up and added a pic. In addition, I put the meter on it but it didn't register anything (no sound to indicate that it even connected)
 

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Meter doesn't acknowledge that it connects.

Is it ok to measure this on paper or wood? Or should be in the air? Any tips on that?
 
Paper or wood are good surfaces for resistance measurements, below a few megohms. If the meter does not measure any resistance it is open (not conducting). Note the triangle with ! in it next to it on the schematic? That means it is a safety rated component, usually fusible and flameproof.
It did its job by going open instead of catching fire. Pull C415, it is probably bad and may be what took out the resistor. In any case, it was reverse biased by the positive voltage that was on it, which probably damaged it. replace R420 R410 and C415.
Pete's suggestion to remove the STKs to protect them is a good idea. You can add a couple of resistors to the board to bypass them for troubleshooting purposes, as he suggested, also.
 
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J A said:
STK's removed. R410 & c415 removed. Was r420 a typo? or is that in addition to?
Click to expand...
Yup, typo :oops:. My electronics is good, my typing skills suck. I have to reread every post three times to catch typos, and even then they still slop in.

I downloaded your meter's Manual and read it. The continuity sounds only if the resistance is below about 50Ω. Continuity is good for tracing wires, but is meaningless for resistance. The meter defaults to continuity mode, you have to turn it off to avoid the beep.
 
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