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synth
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RB2011UIAS-2HND-IN completely dead

Fri Aug 23, 2019 8:53 pm

Hi,
I hope I've chosen the right category for my case, but "Hardware" seems fitting.

I own a RB2011UIAS-2HND-IN since 2014 and it's the center-point of my home-network. Sadly, it died over night, and now shows no lights or functionality at all when connected to its powersupply. I already tested the powersupply with a multimeter and it delivers fine 24V DC. (The Router/Switch was installed at a wall, with its official bracket and was never moved since 2014. There where no Thunderstorms over the last days, and to my knowledge no power-malfunction in my house.)

After opening the case, I wasn't able to find much out of the ordinary via visual inspection. No ruptured or charred parts, Caps look ok. Only a little bit of white residue on the backside of the board, but no obvious corrosion on parts or the board, even in the area with the residue. I guess its either left over flux or condensation.
Image

I tried to follow the conducting path and was able to get 24V for a short segment, but the traces soon became so confusing, without the schematics I can't test any further. (I repair 70s Hifi-equipment as a Hobby, SMD is a horror to me, but I'm willing to get over that.)

Are there known cases where this total malfunction happened and why it did? Maybe someone has an idea what I could try.
Or, maybe, I have to get a new Router/Switch? :(
 
mkx
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Re: RB2011UIAS-2HND-IN completely dead

Fri Aug 23, 2019 10:41 pm

I'd try with another power supply anyway.

The modern switching type of power supplies tend to fail in the way that they provide correct voltage when not under load. When loaded, they drop the voltage and as the time goes by, voltage drop increases to the point when powered device no longer works (correctly). So when checking power supply, you should do it when it's loaded.
BR,
Metod
 
synth
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Re: RB2011UIAS-2HND-IN completely dead

Fri Aug 23, 2019 11:31 pm

Thank you for your quick reply. :)

I tested the unit with two other Power supplies, but no luck. Also, the 24V from the original supply are measurable an the board of the rb2011, if it would drop with load attached and that would be the problem, I would measure lower Voltage in circuit. I poked around a bit further, but without the schematics and most smd parts not labled its not very insightful. :/
 
r00t
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Re: RB2011UIAS-2HND-IN completely dead

Sat Aug 24, 2019 4:28 pm

Measure voltages on big capacitors, you should see 3.3V, 2.5V,1.8V etc.
If these are not present, it's probably PSU/voltage regulators that failed. This can possibly be fixed by replacing mosfets and their controller chips...
If all caps have good voltages and you still don't get any output on rs232 console, CPU/memory is probably dead and board is not worth fixing...
 
guipoletto
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Re: RB2011UIAS-2HND-IN completely dead

Wed Aug 28, 2019 10:55 pm

Here's one i repaired, the primary Dc/Dc controller chip fried, and since i hadn't the correct one to replace, i replaced the PSU stage as a module.

It takes +24v from the BIG capacitor, and delivers 3.3 (actually, 3.45-ish) to the small cap.
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synth
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Re: RB2011UIAS-2HND-IN completely dead

Thu Aug 29, 2019 3:50 am

Thank you for your help root and guipoletto,

I think I'm in luck. I measured the Electrolytic Caps and got 24 V on the big 330 μF one, and none on the two smaller 220 μF. On a visual inspection these two seemed fine, but i knew that they are positioned directly beneath two spools that seem to get very hot during operation, leaving the characteristic "baked dust" as I knew it from past hifi-repairs. Most Caps with these marks degrade rapidly faster then caps in "cooler" spots of the Boards, even if they are from the same brand and type. So I changed the Caps and well, it works!

Desoldering the defective ones is very frustrating by the way. After applying and sucking of solder about 20 times with no major effect i simply snipped them off. There are plenty of surface-pads that can be used if you cut cut the leads of the new caps to size and then bend them 90° to the sides and solder them on the pads.

I will also replace the 330 μF Cap, already ordered a fitting Nichicon, so it's an Upgrade too.

I'm very happy, maybe this helps someone else with the same Problem, as these Caps will degrade nonetheless, as the RB2011 is getting older.

Thanks again for the help. :)

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