Topic: Cheap and not simple repair of S7 hash board - page 2. (Read 2224 times)

$1.8 for a single S5 chip? Wow.

Well heck, that almost makes it too easy.

Of course, there is always the option of https://shop.bitmain.com/productDetail.htm?pid=00020160416053348855GEgP3cx0067E

Which I didn't realise at the time.

All? No, of course not, that would be silly

However, the nice people at Bitmain put nice, high-current connectors on the back of each chip in the chain. So, power up 1 set of 3 (the set at ground - .666v). If it starts hashing at the right rate (you can also test clocks, which appear to come up with the 3.3v supply) those are not likely to be faulty. Power up the next set, and so on. Move on down the board until you get a failure. At that point, you can guess that one of those 3 chips is faulty.

When you know the faulty set, you can follow the clock through and isolate the individual faulty ASIC or board section.

Desoldering them on the target board isn't too bad - just don't try and remove until the solder is fully molten (you don't care about the chips you are removing here). You do need to care about the decoupling caps, but you can test those after you have the chip back on and the heatsinks still off.

The Bitmain boards are one of the best I have worked with for a long time - the board its-self is quite high-temperature capable. This would all be easy if it wasn't for RoHS

The source board is a problem, since you DO care about the chips - so you need to heat up using a quite controlled profile, but even so, as you said, these chips are fragile. Hence the need for a test socket...

This is assuming that the level shifters never fail, but I've not seen that yet.

I'm intending to write all this up and probably Youtube it, not that it helps many people as you've said - since it requires quite an insane level of luck, skill and equipment to do. That is, if I get time to do it, which is in rather short supply.

I certainly see why Sidehack doesn't want to touch these chips. You wouldn't think that .1mm is all that different, but... Ugh. And that damn black goop!

Cheers,

Allan.

They do make actual QFN test sockets.  Kinda pricey, especially for 0.4mm, but if you lurk on eba+aliexpress long enough one should come along for under $50.  Or else make your own using ENIGold PCBs from eg OSHPark.

But... why?

I mean are you going to desolder all the chips from your PCB, test them individually, then solder them back on?  The SMT pads are incredibly fragile, even a very skilled operator with the right equipment will damage the board ~5% of the time in a multi-cycle rework operation like this.  Multiply that by 45 chips/board and you're not likely to end up with any more working boards than you had to start with.

So, there's sensible use of time, then there's this. Test socket for bm1385 chips. Not quite sure if anyone else has done this yet, they're only 0.4mm pin pitch... still not sure if it will work. The 'connector' is most of an hdmi mini plug. The tricky bits are going to be local decoupling, xtal and and the power connection, I think. That and the 1.8v IO voltage, but I think I have a trivial solution to that (at least for testing).

https://i.imgur.com/yrrWbzO.jpg

Anyone else been down this rather painful route before?

Cheers,

Allan.