Hi all,

Can anyone share some techniques/tips on how to swap chips on these hashboards.

I have a pile of donor boards and I'm trying to take some bad boards and make then good boards by swapping the good chips in.

But my technique apparently sucks ass -- it generally looks like i cant get enough solder on all the pads to make good contact.

My success rate is like 5% - terrible.

I use a hot-air at 400C to get the top heatsink off (thermal adhesive)
I preheat the bottom - use a hotair at around 250C to pull the chip.
I have no problem getting the chip off nicely, and also removing the rest of the thermal adhesive.

From that point ive tried all various combos of fluxing the PCB pads and putting solder down, trying to flux and re-tin the IC pads, not using flux, etc.
It always looks "too dry" around the pads and I'm sure they aren't making contact correctly.

I'm not really sure what else to do - perhaps my solder and flux are not correct?
I am using leaded solder 60/40 Sn/Pb and Amtech VS-213-A-TF flux

Will send sats for good tips!

I am starting to learn how to fix these boards, hope this is the right subforum

I'm hoping someone can give me a pointer where to look next. I feel like something is messed up with a 1V8 line *somewhere* but I can't really pinpoint it.

Symptoms (Hashboard 63 V1.9) :

• Board is not detected - I believe the kernel log showed "can't find sensors" and it hangs there.
• I measure .772 V to the base of Q86 (The 1V8 -> 3V3 level shift transistor for RX)
  This is ~1.7 V on a good board.
• Audible clicking from the power supply section. (Assuming one of the switching supplies - but don't know which.) Both 14V (14.32) and 9V (9.2 V) appear.
  Makes me believe something is loading a supply somewhere.
• I am reading .464 V on the RI testpoint near IC 2. (The third one in the chain - on what I believe is the 1st voltage domain).
  

  IC	Good	Bad
  0	1.6 V	0 V
  1	1.6 V	0 V
  2	2 V	.464 V

Does this pinpoint IC 0 & 1 as dead? When I compare RI resistance to ground I get roughly 200k on both good and bad.

Side question: Where the heck is 2V5 generated?

thanks for any nudge in the correct direction