Electronics > Repair

TEKTRONIX DPO 6GHz scope issue - broken BGA ball connection?

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ddrl46:

--- Quote from: ZBIQ on October 20, 2023, 09:09:43 pm ---Hi Folks!

I started to dig a bit more into DPO debugging and I have a short question. Where I can find extended selfcal/test files of the DPO 7k series? One of the colegues pointed, that I should look for c:/TekScope/calibration, but there is no such folder in my device.
My scope is running one of the latest software versions on win7, so probably files architecture has changed...

Cheers,
Mateusz

--- End quote ---

Did you enable "show hidden folders" in explorer? From what I can remember from the Windows XP units it should be there.

ZBIQ:
Hi guys, it took me almost 2 years but I finally repaired my DPO :) I will try to summarize it shortly how I did it.

1. Careful diagnose.
As I mentioned before, the faulty BGA connection was under one of the HFD204 chips. I was probing the PCB very carefully with the power on and off. It was clear that this was the only chip affected as one of it differential lines were showing >200 Ohms while others showed <100 Ohms (measured deferentially).

It is important, however, to provide adequate cooling for the PCB, as Illia from Xdevs told me:
"There is no thermal protection and all those chips burn lot of power during operation. I know of a cases when people opened up scopes, ran them for "quick" testing for maybe 20 minutes to do some minor issues testing and then ended up with broken ACQ board because damn ADC blew up from overheating since there was no adequate cooling airflow. Scopes are designed to have air pulled by fans with all covers in place."
I placed a large cooling fan directly blowing on the ICs. It made the job.

ZBIQ:
2. BGA rework
The main PCB is approx 400 mm x 400 mm, >32 layers and 5 mm of thickness. It requires a big and reliable reworking station, since replacing PCB, as well as getting another chip, is not an option. I currently live in Switzerland and for sure I would find the proper workshop. Unfortunately, reworking this PCB would cost me for sure >1..2 kCHF. BUT, 1 year before I moved to CH I purchased for myself in Poland a Chinese BGA reworking machine - LY HR-506C. Quite a decent one, but I knew nothing about BGA rework...

So, I started to train and learn how to reball PCBs. I reballed couple of PCBs found in trash, but the main learning came from a large PCB: 400 mm x 400 mm but only 2 layers and 2 mm of thickness. Probably behaves way different from the DPO PCB, but better this than nothing. I purchased 4 point thermocouple sensor/logger which helped me a lot during my research.

ZBIQ:
I made 5 trial runs with different profiles, but actually simple ramping, soaking and reflowing was good enough - see pictures.

ZBIQ:
Then it was time for the real game. I noticed that my test PCB flexes a lot during reflowing thus my DPO PCB got a stiffening frame. It was built from 15x15 mm2 V-slot construction profiles. I though it might be an overkill, but during the process, PCB bent no more than 2 mm. I truly recommend doing so for any large area PCB.

I also protected other components with aluminum and silicon foil. I didn't want to stress other ICs on the board.

In the end, IC removal was quite smooth and I did it on the first shot  :)

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