Electronics > Repair
TEKTRONIX DPO 6GHz scope issue - broken BGA ball connection?
ZBIQ:
The reballing process went also quite smooth. One or two BGA pads from the PCB were missing, but they were dummies. Some other lost a bit of soldermask so I applied a bit of UV mask as well.
I applied 0,4 mm balls to the chip with the help of a standard BGA screen. This time, however, I used SnPb balls so I had an idea to lower the profile temperatures by 15 deg. Unfortunately, this caused the chip to not solder properly. Only one side of the chip got a proper reflow... So I had to do this again, with the v5 profile. I was a bit scared that I might overheat the chip or delaminate the PCB. Also, the flux might have been activated before, so there was a bit of room for an error. But, luckily, the chip got fully soldered this time:)
BTW. I used NC-559 flux. Original one. Good stuff.
ZBIQ:
3. Final touches
After reballing I tested DPO for about 30 minutes and it showed a perfect behavior at any settings :) No more glitches and perfect 6 GHz pulse response! BUT, after some more tests, DPO died. It couldn't boot for sever times, but I knew this behavior from last time I used this scope. Apparently, after digging some time in the HDD and motherboard area, one of the RAM chips showed no response. After removing it, and working at half the memory, it boots every time. Happy to catch it :)
The final touch was to apply some thermal adhesive to the analogue chips. I used two-part MG Chemicals 8349TFM.
And this is it. DPO now sits in my rack and it is ready to measure some stuff!
inse:
Thats a real crime story!
Thumbs up for solving that cold case
ZBIQ:
I also captured two reballing attempts: too cold one and proper, final reflow.
CaptDon:
I admire the effort you were willing to put into this project!!! Sadly, at the company where I worked, sending that scope to Tektronix for repair would have ended in 'Not worth repair' since they probably would have charged 50 to 60% of the cost of the scope when new. They may perhaps offer a 'trade up' program giving us about 30% of our scopes original purchase price as credit toward a new scope with a much higher purchase price. Way back when the outlandish pricing of a Tek scope came with the benefit of owners manuals, programming manuals and service manuals with in-depth verbal descriptions of every circuit and waveforms and voltage test points for practical repair. Although one of the biggest drawbacks of Tek products were the custom hybrid I.C.'s which became un-obtainium about a year after the product went to market. Today the insane pricing of Tek products becomes a financial risk to small companies when our supply of 'highly degree'd engineers' who absolutely suck when it comes to their technician and troubleshooting skills can blow up a $6000.00 probe or destroy a $150,000.00 scope with a simple 'ooopps' "I forgot that part of the circuit was mains referenced". Yes, we still get college educated engineers trying to measure the source impedance of an operating power supply with an ohm meter or measure voltage while switching the DMM through the amps range! Common sense, caution and troubleshooting are not taught at the university level anymore. Sadly, 90% of our blown up stuff just goes in the dumpster. Glad I was able to snatch and repair a TDS644A and a TDS644B from the dumpster!!
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