Buzzing power supply....

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cjacek

cjacek

Analogue Enthusiast
Hey guys,

This is just a general question, having nothing to do with my gear. I just want to be educated a bit.

In a nutshell, is it reasonable to assume, when dealing with an old piece of electronics gear, that if the power supply is buzzing (not humming), just with the unit on and not plugged into anything, that it (the PS) is on its last legs? Would you toss that aside as a possibility or not?

Thanks! :)
 
Hard to say if it's really on its "last legs"?

I've a couple of pieces of gear over the years that had buzzing power supplies and it never stopped them from working normally otherwise...maybe I was just lucky?

Cheers! :)
 
Thanks Jeff! OK, lets add this to the equation: The piece of gear (any vintage kind), after many years of non-use, is mistakenly left powered ON for the entire night. The person then realizes, after a long night's rest and turns it OFF (but only after spending another few hours using it - works fine) and then turns it back ON again. It doesn't power on anymore and the voltage (from the PS is all over the place (using a multimeter). It was fine the day before. Ideas?
 
Regulator is shot would be my first assumption.

What kind of supply would this hypothetically be?

Multi-rail DC?

What piece of gear would this hypothetically be in?
 
Cory,

It's an old synth that a friend has. I'm asking on his behalf. Don't know the specifics, just want to get a general feel for things and this is helping so thanks! At least we'll know "ballpark". Not sure what type of supply but it does switch from 120 to 240. Here's a photo of it. You mention "regulator" and that's interesting 'cause the batteries are right next to it, which are leaking. But why was it working before and then after a long night being ON, not working anymore? PS overloaded perhaps? How would a voltage regulator go bad after what had transpired with the unit? Then you add the buzzing and all the others...? What's your hypothesis?
 

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That's just the main transformer there Daniel...how many batteries go into it and how old is it?

See where the wires go down to a PCB? That's where the regulator would be. It converts or rectifies the stepped-down AC voltage to DC...probably 9V.

It could have just died...it happens. There could also bad caps on it.
 
OK, I see.. :o

It's about 30 years old. There's in fact a small PCB with 3 AA type batts but nicads I think and 1 or 2 what appears voltage regulators (chips). So you think they got overloaded?

OK, so now we know what to look at. Thanks Cory!:)
 
Why would a regulator fail? Does that mean it was on its last legs? Would that "all night on" scenario be the straw that broke the camel's back? How does the buzzing come into play?
 
If the unit is 30+ years old, I can pretty much guarantee that all the electrolytic capacitors in the power supply will be shot. Replace these before replacing regulators. The old capacitors no longer filter properly, the DC going into the regulators isn't nice and smooth anymore, and the regulator can't regulate.

I can imagine a situation where the capacitors are on their last legs, they work, just. Because they are leaky, they get warm, and this kills them. You then power off, the caps cool down, now when you power on it don't go anymore.

I have an old Ensoniq ESQ1. There is an article on the web somewhere, can't find it right now, that recommends recapping the power supply if it starts doing all manner of strange things.
 
cjacek said:
Why would a regulator fail? Does that mean it was on its last legs? Would that "all night on" scenario be the straw that broke the camel's back? How does the buzzing come into play?
Click to expand...

A regulator which might be a couple of transistors, might have lost their thermal coupling to their heat sink or been subjected to a voltage or current spike beyond what their tolerances might be. As Corry stated, the filter caps might have been dried up and become unstable, overloading the regulator. Things like this are more common on gear that sits for too many years without use. A physical buzzing might be caused by a loose part, such as a transistor that's longer firmly seated to its heat sink and the thermal cycling of turning it off and then back on again could have been the spike that killed them.

Bottom line in all this is that if the unit is worth repairing, then it makes sense to get an estimate from a local repair shop. Odds are its a few bucks in parts and an hour of bench time to have it done professionally. Otherwise, source out the parts, change them and cross your fingers!

Cheers! :)
 
cjacek said:
... is it reasonable to assume, when dealing with an old piece of electronics gear, that if the power supply is buzzing (not humming), just with the unit on and not plugged into anything, that it (the PS) is on its last legs?...
Click to expand...

It's like a 50 old guy with a heart murmur, he might die in 5 minutes or live another 50 years.

This last year I "reboxed" a few amps. Two were Behringers with transformers that were humming pretty loud, so I mounted them on some pretty thick cushioning, being careful to not make them get hotter because of the mounting stuff. For one I used that thick flotation foam they sell at Kmart for kids in pools.

The cushioning made a huge difference to the quietness of the amps. Since that, every time I hear a noisy amp (especially tube amps) I can't help but think that probably 70% of the noise of the amp could be eliminated by mounting the transformer differently.

I don't know why the manufacturers haven't addressed this, it seems so basic. But then there's lots of stuff that's accepted as normal that is pretty stupid when it comes to gear.
 
You said 30 years old?

I'd suspect cracked solder joints on a voltage regulator.

Lots of stuff built arund that time skinped on heat sinks in the power supplies. Leaving it on for a long time could have let enough heat to build up to damage the solder joints.

Question. Did you move the unit right after finally shutting it off?
 
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