Here's another power supply electrolytics story. I watched in horror this morning as my Squeezebox Controller gave a light show of button backlight, showing the logo briefly on the LCD, then rebooting.
At first I thought that the Controller is on its way out for no good reason, or its battery. Checked a lot of things inside and out but nothing really helped. Trying a different battery didn't really help but that was probably because the second battery was also discharged.
Then I had the idea that the power supply for the Controller's charging cradle is similar to the SB3 classic one that fails ever so often and makes it appear like the SB3 itself is at fault while it's just the PSU.
If the cradle PSU fails, it is no longer capable of powering the Controller, and the Controller won't get to charge the battery long enough for anything to finish correctly.
So I hacked the PSU case open with a hammer and spudger because it is ultrasonically sealed like all of them and can't be opened without a lot of violence. This is what I found inside:
For perspective, this is what you see when the mains adaptor was removed. The high voltage side where the adaptor connects is facing down in this photo.
The two capacitors indicated are heavily bulged and the one on the left had also started leaking. Luckily, only at the top that was designed to let pressure escape, not at the bottom, so the PCB was unharmed. Replaced these two capacitors (680µF / 10V) by new ones and the power supply was completely dead. Oh my...
So I checked around and did a close visual inspection. Turns out my opening procedure had me whack a choke and severed two or three of the tiny wires from the legs of the component. This is the one I mean:
Let's remember for next time that we should be *very* careful around this corner. It was very fiddly to repair the choke after I damaged it, I needed to desolder it entirely, resolder the microscropic wires (with no room or length to spare) to the legs which had partly separated, and put the fixed component back in. All in close proximity to the capacitors holding a high voltage charge. But eventually that brought it back to life. The Controller charges again and starts up normally.
The cradle PSU is a 5V / 2A one, probably identical to the SB3 stock power supply. So that one might be repairable just the same way.
Eventually the plastic case needs to be closed again to ensure that none of the components can be touched accidentally. I put the two halves back together and used Kapton tape to go two times around the "waist" of the PSU.
Some advice for you in case you want to DIY:
At first I thought that the Controller is on its way out for no good reason, or its battery. Checked a lot of things inside and out but nothing really helped. Trying a different battery didn't really help but that was probably because the second battery was also discharged.
Then I had the idea that the power supply for the Controller's charging cradle is similar to the SB3 classic one that fails ever so often and makes it appear like the SB3 itself is at fault while it's just the PSU.
If the cradle PSU fails, it is no longer capable of powering the Controller, and the Controller won't get to charge the battery long enough for anything to finish correctly.
So I hacked the PSU case open with a hammer and spudger because it is ultrasonically sealed like all of them and can't be opened without a lot of violence. This is what I found inside:
For perspective, this is what you see when the mains adaptor was removed. The high voltage side where the adaptor connects is facing down in this photo.
The two capacitors indicated are heavily bulged and the one on the left had also started leaking. Luckily, only at the top that was designed to let pressure escape, not at the bottom, so the PCB was unharmed. Replaced these two capacitors (680µF / 10V) by new ones and the power supply was completely dead. Oh my...
So I checked around and did a close visual inspection. Turns out my opening procedure had me whack a choke and severed two or three of the tiny wires from the legs of the component. This is the one I mean:
Let's remember for next time that we should be *very* careful around this corner. It was very fiddly to repair the choke after I damaged it, I needed to desolder it entirely, resolder the microscropic wires (with no room or length to spare) to the legs which had partly separated, and put the fixed component back in. All in close proximity to the capacitors holding a high voltage charge. But eventually that brought it back to life. The Controller charges again and starts up normally.
The cradle PSU is a 5V / 2A one, probably identical to the SB3 stock power supply. So that one might be repairable just the same way.
Eventually the plastic case needs to be closed again to ensure that none of the components can be touched accidentally. I put the two halves back together and used Kapton tape to go two times around the "waist" of the PSU.
Some advice for you in case you want to DIY:
- Dremel might at first look like a good idea to open the case, but be aware that components are very tightly packed inside the PSU, and are also close to the outer shell, so you may accidentally grind into one of them. Also, using anything that grinds away the seal will cause material to be missing once the time comes to reassemble
- again, be especially careful in the corner indicated above, but also be aware that there are components almost all around that could be nicked or heavily damaged if you go too far with whatever you drive into the seal to crack it open
- the two larger capacitors on the primary side (flip-side to where the AC connection sits) are charged with up to 400 Volts, and as far as I could see, there is no discharge resistor so they will hold this voltage for a long time. Stay away from these as far as possible, or safely discharge them before handling the board. I would assume that they will self-discharge in about 12 hours after unplugging, but don't take my word for it. If a multimeter is in your collection, use it to measure the voltages in these caps
- discharging is best done with specific equipment (best choice), or a high-value resistor (something like 1M Ohms, second-best choice) or an oldschool mains-voltage light bulb with a Tungsten filament (third-best choice) connected across the capacitor's pins. It is generally not recommended to just short out the capacitor legs because it may create a heavy arc and may also damage the capacitor or components around it in case anything else gets connected in the same instant
- after discharging, ensure with a multimeter that the charge is actually gone and won't return
- the two secondary capacitors were the only ones bad in my power supply. It may look differently in yours. Bulged or leaky capacitors should be replaced for good at all times. Replace them all if you want to be completely safe against future defects. The electrolytics are polarized, so you need to ensure to put the replacement caps in the same polarity as the originals were. A stripe along one side indicates the NEGATIVE terminal (usually the same color as the rating print). The silk screen print beneath the caps on the PCB indicates this negative terminal with some highlighting, and also shows a "+" symbol where the POSITIVE side needs to go
- both secondary capacitors are in parallel (+ and - of both are joined) for double capacity
- be sure to measure the PSU output before you put the Controller into its cradle. If anything looks off, voltage appears reversed, too high, or too low, DO NOT connect the Controller and fix the issue first
- in case you plan to replace the PSU entirely, you will need to connect another one to the wire that goes to the cradle. The white wire is +5VDC and the black one is GND. Inside the cradle, the left spring is GND and the right one needs to be +5VDC.
. Use a quality USB cable, ideally a thicker charging cable, as it'll be easier and better done that way. Do not use the thinnest old spare you find in the junk draw! Shrink-wrap electrical tubing is easy to use (hair dryer, even candle, cigarette lighter or match at a push). Use a 2 amp or more USB PSU and, if in doubt about your quality of work, only initially charge it when you are there, and check the wiring for any heating up.
Dump the other USB wires.
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