[C38368]

First off, hello again Head-Fi; it's been ages!
 
 
Background:
 
I recent pulled my Mapletree Audio (Ear+ Purist HD150, if it matters) out of a box, and thought it would be a fun idea to set up a listening station in my office. Also brought out of storage was one of two Squeezebox 3s in my possession, this one fully modified by Vinnie, back when RWA was still a thing, and still did work on the Squeezebox.
 
But the thing is, some years ago, the SB's battery enclosure got really hot for about two weeks, and then quit working. Because the battery exploded. Which is, apparently, not good for the battery. Anyway, it remained dormant for about a year, when I got the wild idea (for me) to open the enclosure and, lo and behold, you can buy those SLAs on Amazon for like, $30 each. So I bought one, and tried to install it.
 
Emphasis: tried. The battery went in, but in doing so, I managed to break one of the power jacks. I want to say that it was the center jack (battery charger). Ultimately, I attempted to solder everything back into place, because hey, I know nothing about this kind of electronics work, and would have no idea where to go for an intact replacement part (or rather, what to buy).
 
I think I messed up the soldering, and again but the RWA SB back into storage. On a whim last week, I took it out and plugged it in and... holy crap! It started up! But only properly on battery. If I use the wall wart, it powers on, but the VFD output is incomplete, inconsistent, and flickers. So yeah, that's a problem, too.
 
But here's what I'm trying to diagnose:
 
When I plug my amp into the SB and turn it on, I get a very noticeable, heartbeat-like throb or "thrum." The frequency is always constant (peaking every second or so), and there is an obvious, constant, hum in the background, as well. This happens, both, with the Mapletree, and with an RSA XP-7 running on fresh batteries. It happens even if I plug the Mapletree into another outlet. It does not happen if I plug either amp into another radio that's laying around the office, so I'm now 99.999999% certain that it's the Squeezebox, and thereafter about 87.3% certain that it's the battery pack, specifically.
 
So, might anyone have any ideas as to what's going on? Things to look at? Things to test?  The extent of my diagnostic equipment is an old digital multimeter of questionable functionality now, a fork, and my tongue. Well, I suppose eyes, ears, and extremities, as well, but, yeah...
 
Side question:
 
Can anyone confirm that the RWA-modified SB3 runs off 12V power? If so, I can I grab another wall wart of the appropriate polarity and output and have it re-terminated in one of those three-prong jobs that's on the SB's power umbilical?
 
Second side question:
 
Does anyone even remember the Squeezebox, or RWA, at this point?
 
Thank you all for reading. And for humoring me!

 

[NA Blur]

Check the battery lead terminals and make sure they are soldered / connected properly.
 
What if anything do you actually have plugged in when you hear the hum?
 
To check the voltage you need just measure the battery and then you can use that voltage for your DC power supply.
 
Sounds like you have a grounding problem. You can try running a wire from the various grounding pins / terminals to something metal that is properly grounded. If the hum goes away you have your problem isolated and just need to ground that pin / terminal.
 
It might be as simple as grounding the case of one of the components like the Squeezebox or amp and see if that does the trick.

 

[C38368]

Thanks for the input. I have my doubts about the overall wiring of the battery at this point, but the terminals themselves appear to be solidly attached to the leads. I took the case apart yesterday after posting this, and confirmed that it was the charger's input jack that I tried to solder back together, and possible jacked up. The direct-from-wall input was undamaged. The original ground wires are solid, at least where they attach to the ground. Can't promise that one of the other ends isn't messed up, and I also don't know why I have two red and two green wires going to ground? Presumably, there's one pair per power input, but I always thought that you only grounded, you know, the ground?
 
As far as everything in the power strip, there's a desk lamp, laptop charger, desktop monitor, and a pair of iPhone sugar cubes without cords, plus the amp and both wall warts for the SB3, all plugged into a surge protector-style power strip. This is similar to how it used to be set up (one lamp, one sugar cube, both wall warts, a desktop PC and monitor, sometimes a laptop, and two amps). This wasn't a problem back then.
 
I'd like to think that this is a ground problem, and that's how I was leaning initially, but I've never seen anything about that constant, rhythmic, throbbing hum with grounding issues before. Could it be an artifact of the charger module? (The wall wart for the battery's power input is actually a trickle charger, specifically represented as a "battery charger and maintainer.)
 
On the direct-to-head power, the battery pack's output jack is a three-prong job. Testing one pair of pins shows just over, either, +12VDC, or -12VDC. I assume that the negative output is the result of reversing polarity with the multimeter. The other If I test the ground and third pin, I get a reading of about ±4.8VDC, while the hot and third pin read about ±7.8VDC. Any idea that the point of that third pin is?
 
The numbers in the last paragraph are off the direct-from-wall setting. If I switch to the battery, the hot and ground result drops to about 8.8VDC, which tells me that the battery isn't charging, which leads right back to a problem with the charger's input jack. Cool. But then that doesn't explain why the VFD flickers when running directly from the wall.
 
Crap.

 

[NA Blur]

It may be a bad transormer because those cause hum.