Palo Alto PA220 reverse polarity fault - Page 1
Forum section: electronics / repair

author: corsair6
author_rank: Newbie
timestamp: September 28, 2022, 10:23:30 pm
content: Hello,I have a Palo Alto PA220 firewall that has suffered damage from reverse polarity.Now, when 12V DC power is applied to either input, the corresponding input LED lights but there is no further sign of life. The current draw is 70mA. Interestingly there are no signs of any damage (burned components etc).I have uploaded pictures of the whole PCB as well as closeups of the power supply section of the board.I'm wondering if someone experienced would be able to help me troubleshoot.Thanks,Peter

author: fzabkar
author_rank: Super Contributor
timestamp: September 28, 2022, 11:15:10 pm
content: I can't understand why there was any damage. The 12V input should be protected from reversed polarity via dual diode D15. This diode also serves to isolate the two redundant supply inputs, J2 and J3, from each other.SS10P2CL, Vishay, 20V, 5A x 2, Dual Common-Cathode Schottky Rectifiers, marking S102CL, TO-277A (SMPC):https://www.farnell.com/datasheets/39560.pdfWhat voltage do you measure at the cathode of the diode?

author: corsair6
author_rank: Newbie
timestamp: September 28, 2022, 11:19:36 pm
content: I did look that part up and thought that might be it's purpose.I'm getting 11.7V at the cathode.Thanks.

author: TheMG
author_rank: Frequent Contributor
timestamp: September 28, 2022, 11:21:06 pm
content: D15 is a dual Schottky diode, looks like it might be used to diode-OR the two power supply input, but that would also have the effect of protecting against reverse polarity.Start checking the voltage on the output of each of the DC-DC regulators, maybe one of the regulators is not working and thus a critical supply voltage is missing.

author: corsair6
author_rank: Newbie
timestamp: September 28, 2022, 11:32:17 pm
content: I think you may be right. I have uploaded a couple of photos which I believe to be of the regulator section. Looking closer, there is damage to the TPS53513 chip on the very left regulator which I missed earlier.I would like to understand how this was possible given the presence of diode D15.

author: fzabkar
author_rank: Super Contributor
timestamp: September 28, 2022, 11:36:46 pm
content: Test for shorts between ground and each of the inductors L1 - L4. I expect these supplies are the Vcores for the main processor, so the working resistance would normally be low.

author: corsair6
author_rank: Newbie
timestamp: September 28, 2022, 11:49:05 pm
content: I'm hoping this is what you are after. These are the readings using ground as a reference:L1 top 89.8ΩL1 bottom 89.7ΩL2 top 20.2ΩL2 bottom 20.3ΩL3 top 100.3ΩL3 bottom 100.4ΩL4 top 36.0ΩL4 bottom 36.0Ω

author: fzabkar
author_rank: Super Contributor
timestamp: September 28, 2022, 11:54:17 pm
content: Those readings look OK to me, but perhaps others could confirm. You might get away with replacing the damaged converter.I'm wondering whether there was an overvoltage from an incorrectly rated power adaptor rather than a reverse voltage. That said, the maximum recommended Vin is 18V, so an overvoltage seems unlikely.https://www.ti.com/lit/ds/symlink/tps53513.pdf

author: corsair6
author_rank: Newbie
timestamp: September 29, 2022, 12:04:03 am
content: I'm also wondering about it being over voltage - I wasn't present when the damage occurred so I can't really be sure.Would this be a suitable replacement? (Selecting the TPS53513RVER option) I'm not really sure about the best places to source components.https://www.aliexpress.com/item/1005004729499156.html

author: fzabkar
author_rank: Super Contributor
timestamp: September 29, 2022, 12:11:34 am
content: I would stick with Farnell, Digikey, Mouser, RS Online. Chinese sources are contaminated by fakes.

author: corsair6
author_rank: Newbie
timestamp: September 29, 2022, 12:22:55 am
content: Thanks. I'll check out those sources.