Just curious....but is the 5v USB fan mod on these gridseeds that have the failed USB ferrite bead? It could be the added current usage of the fan stresses it enough over time to the point of failure as I'm sure the USB circuitry wasn't designed with the load of the fan in mind. I'm not saying it can't handle it, because there is plenty of power from the USB port for a fan, but given the build quality of these things it really wouldn't surprise me.
Accidently overheating the FB while soldering the + fan wire to it can cause pre-mature failure. It only takes a few seconds of too much heat to burn one up, I am sure.
Besides the fan is only pulling 78mA, if that while running and maybe 140mA startup which lasts less than 2 seconds to spool up and stabilize.
By the way, I forgot to mention that I revised the 5V USB Fan power mod recently. Only days ago actually. So I'm late posting it. Sue me!
On the last few batches of pods, the fan + is now connected to and powered by 12V input via 5V regulator on the PCB.
See pic.
You can make the change easily if you wish to. I've been powering 6 of my miners via 5V USB for months now, for hundreds of hours straight now. No problems with the FB's!
Just be very careful not to overheat the components you are keeping on the pcb.I know I didn't overheat any of them when soldering to them. It takes me less than a second to solder the wire to the tinned connections.
All is well.
By the way, all 20 were the latest plain aluminum colored pods. All heat sinks were evenly touching their respective chips. No components were on a different plane i.e. higher than the 5 main uP chips. Looks like they got the components mounted right on this run.
See pic.
Overheating could be a big factor. just curios thoose that have blown FB how are you running them? wiht 5v fan mod?, wiht no fan? top heat sink removed? its possible that the 5v fan mod isnt providing enough air flow for the FB causingthem to overheat. likewsie if there is no fan. if it overheating though lack of air flow, take all facotrinto account, ie climate, room temperture humidity, location of grids .
I know runnign them wihtout the top sink can cause them to overheat, i was testing them had top heat sink off, and fans (120mm) running next to them, which got knocked and i didnt notice and im pretty sure i fried a few grid chips, tried reflow to no use. the chips are recongised by cpuminer all of them but only 2 are hashing. anyone know where i can get a few grid chips from to replace the cooked ones?