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Old 11-19-2012, 04:14 PM
Radiolab Radiolab is offline
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Default Cisco WAP321 - broken transistor repairment

Hi guys!

I have Cisco WAP321 working without any problems for couple months. Suddenly AP has gone away - no radio, no ping. Only LAN LED blinks according to broadcast network activity. I've opened AP and discovered that the problem caused by broken transistor Q1 in circuit of core (?) voltage DC/DC. This transistor is in SOT23-6 case and marked as 187G. There is no any info about partnumber. Also it's impossible to get any info about this circuit due to DC/DC controller is a part of Broadcom SoC and any datasheets are available only with NDA.

I've blown away this transistor and applied voltage directly from HP lab powersupply. Slowly increasing voltage and restarting AP I've made it to work on 1.8V (1.6V on the pcb due to wire dropout) but it's not stable. I think i should add more volts to get stable work, but it's a little bit dangerous.

So I want to ask somebody to help me. Please turn on your AP without top cover and measure the voltage between market point A and B (see attached picture). So I can put external DC/DC tuned to appropriate voltage and bring AP back to life.



Sorry for my English. Best regards. Dmitry.
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File Type: jpg ps_voltage.jpg (38.2 KB, 5 views)
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Old 09-23-2013, 02:00 PM
beny beny is offline
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@RadioLab I don't it's advisable to use external DC-DC unless you're completely sure that you're replicating the original signal exactly. Download the SMD code book, find out what the transistor code stands for. If it's a simple NPN transistor in SOT-23 package you can find any NPN transistor from either Fairchild Semiconductors or Motorola from farnell. It's easy to replace. If you don't have much soldering experience you can go to your nearest RadioShack and find someone to do it or you. It's better to get a simple OST-23 transistor replaced then having to deal with a board with multiple components malfunctioning.

pcb layout

Last edited by beny; 05-16-2014 at 07:02 PM.
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