A customer presented this out-of-warranty router as a "can you have a look at this ... ?". Symptoms: when power applied, all LEDs blink in unison about twice a second, no other functionality. History: had worked great until a thunderstorm, was on a APC UPS at the time.
We opened it up and - apart from lots of nice Nichicon caps - there were two evil CapXon 6800/6.3V with characteristic bulging. ESR measured 1.4 and 1.5 ohms, so replaced them with Panasonic FM's. (All Nichicons were close enough to ESR spec.) No change in behaviour.
The board has a 5A fuse on the 5V input, which is intact. Stuck the CRO on the 5V rail and found it wasn't getting up. It would get to about 2.7V and then collapse, repeating as per the LEDs. This router is supplied from a dual voltage brick, rated 5.2V @ 4.4A and 12V @ 650mA. Independently loaded up the brick and it was smooth as, no signs of distress. The inference is that the board is overloading the SMPS brick.
So somewhere on this board is effectively a dead short. But with schematics of Cisco gear being unobtainium sheltered behind NDA's in their service depots, it's doubtful I can progress this.
(I have ensured that the owner knows which is his left shoulder, so he knows where this eventually goes.)
Have attached a couple of pics of the power area of the board. Any comments?
We opened it up and - apart from lots of nice Nichicon caps - there were two evil CapXon 6800/6.3V with characteristic bulging. ESR measured 1.4 and 1.5 ohms, so replaced them with Panasonic FM's. (All Nichicons were close enough to ESR spec.) No change in behaviour.
The board has a 5A fuse on the 5V input, which is intact. Stuck the CRO on the 5V rail and found it wasn't getting up. It would get to about 2.7V and then collapse, repeating as per the LEDs. This router is supplied from a dual voltage brick, rated 5.2V @ 4.4A and 12V @ 650mA. Independently loaded up the brick and it was smooth as, no signs of distress. The inference is that the board is overloading the SMPS brick.
So somewhere on this board is effectively a dead short. But with schematics of Cisco gear being unobtainium sheltered behind NDA's in their service depots, it's doubtful I can progress this.
(I have ensured that the owner knows which is his left shoulder, so he knows where this eventually goes.)
Have attached a couple of pics of the power area of the board. Any comments?
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