Cisco WS-C3560CX-12PC-S PoE Repair

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hk92doom

Member
Jun 4, 2020
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Our workplace was getting rid of older network devices. One of these seemed perfect for my home office. Quiet and plenty of 1Gb PoE ports. Unfortunately, they didn't provide any power, although the switch otherwise worked perfectly. I took it apart, trying to figure out what parts it uses to find replacements.


C3560CX-12PC_PCB4.png


The power supply is manufactured by Delta Electronics, model: DPS-300AP-89. It provides three voltage outputs

54V 4.48A
12V 5A
3.3V 0.7A

While looking for a replacement, I found another model that may be a suitable replacement: DPS-300AP-97. Luckily, mine was not damaged.
Delta Electronics was not the only vendor of power supplies for the C3560CX series, later models also feature power supplies manufactured by Lite-On, such as the PA-3301-2B2
For both power supplies, Cisco uses the same part number: 341-0675-02. They are shared by the same family of switches

WS-C3560CX-8XPD-S
WS-C2960CX-8PC-L
WS-C3560CX-12PD-S
WS-C3560CX-8PC-S

There is almost no information on fixing PoE problems, but there is a general consensus , that PoE controllers are responsible for most problems. I followed this lead and decided to replace both controllers.
The Si3458B03-IM controllers (U4701, U5001) were manufactured by Silicon Labs, now acquired by Skyworks Solutions. Although there is no datasheet for the Si3458, there is one for the Si3459, which has the same number of pins (56 QFN) and modes of operation to manage 8 PoE ports.
Other switches may use PoE Controllers made by Texas Instruments: TPS2388RTQ

The controllers use N-channel MOSFETs as switches to provide power to PoE devices. The MOSFETs, FDMC3612 labeled Q4801-04, Q4901-04, Q5101-04 on the board, are manufactured by ONSEMI.

PoE_Controller_before.png




PoE_Controller_after.png


Replacement of the controllers was not necessary. When I took a measurement, 54 V was present on the 12 MOSFETs, as well as on the input to the Ethernet jacks, but not on the CAT6 connected cable. Only then did I start looking for more information about these type of RJ45 connectors. The 2x2 port mag connectors are manufactured by the Bel Fuse/Stewart/TRP holding companies. In addition to the RJ45 connector, they have built-in magnetics. MAGJACKs Part number: 0854-2x2J-GY-F are no longer manufactured. Potential replacements are manufactured under the TRP brand: 2250210-1, 2250211-1, 2250121-1, 2250139-1 but I could not find any vendor having them in stock.

Again, Cisco has found an alternative supplier, which is Molex. The 2x2 Ethernet connectors use part number: 172611-1000


C3560CX_Magjack2.png




PEP101-5841_58E1_pins3.png

A 58V quad TVS is used to protect PoE devices from line overvoltages. Part number PEP01-5841, marking 58E1, manufacturer: STMicroelectronics. On the board marked as CR4801, CR4901, CR5101.
After opening the rear metal shield of the MAGJACK, I found 8 burnt fuses, two per connector (1.5A 63V, Slow Blow/Time Delay, size 1206). After replacing them, the PoE devices immediately got power.


MagJack_0854-2x2J-GY-F_fuses1.png

Repairing the switch turned out to be much simpler than I had originally anticipated.
 
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klui

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Feb 3, 2019
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Simple for a EE or electronics technician. Not so simple for a SW guy like me.

Did only the fuses inside the jacks need replacement? What do they look like? Could you link to a part number? Thanks!
 

hk92doom

Member
Jun 4, 2020
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In my case, only the fuses needed to be replaced. My switch passed diagnostics, it behaved as if PoE was available, except there was no power from RJ45.
Measurements showed 54V on input pin #12 of the MAGJACK, so I suspected something burned inside (like a coil or fuse).
In the previous post, last picture, the fuses clearly have a melted center.

fuse.png
They can be purchased from several sources such as ebay, amazon or typical electronic parts suppliers such as digikey.com, jameco.com, newark.com or arrow.com.
Search for surface mount fuses and narrow down by current = 1.5 amps, voltage = 63 volts, size = 1206 and type = Slow Blow / Time Delay




fuse2.png
 
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klui

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Feb 3, 2019
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Thanks. I didn't know what to look for. I thought it was that black "thing" in your original post's last picture. Looks like these fuses are ~$1 each and each port is protected by one two.

Excuse the noob question about cost from your link: why would SF-1206S150-2 cost $0.53 when 046801.5NRHF costs $1.33? The only significant difference is the costlier one operates at -55 C vs. -20 C, but the cheaper one's high range is 105 C vs 90 C.
 

hk92doom

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Jun 4, 2020
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The price most likely varies due to the materials used, arc suppression characteristics and manufacturing process, besides other operational parameters. The low-priced model has a simple coating sprayed on the top.
 
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OrlyP

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May 16, 2023
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Interesting topic.

I myself use a non-PoE Cisco 3560G for inter-VLAN routing at home. Been thinking of switching to a proper PoE switch but I only have one UAP-AC-Pro that can take advantage of it at the moment. My other APs (older versions of the UAP-AC-LR) only supports 24V passive PoE. All UAPs are powered using their own individual PoE injectors, 48V and 24V, respectively. I also have a couple of Cisco SPA525 IP phones. But they're WiFi-enabled and are powered independently from a wall wart.

Then again, I might run into used PoE switch with a similar failure mode. Thank you for sharing this repair info.
 
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