Products > Test Equipment
RTO2000 RAM Artifacts
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Harry_22:
Hi Jjoonathan!

In the meantime I made an extension for the front panel. With a length of 20 cm a slight moire is noticeable in the image.
Connector brand Amphenol 88946-102LF and 70233-111LF.

PS
Waiting for the good news.
jjoonathan:
Nice! Yeah, having an extension cable for the screen is a godsend. I'm glad they built one in on the RTO2000 and I remember it being a real pain on the RTO1000 so congrats on building one of your own!

The news right now is that I am waiting for thermal paste, which will arrive tomorrow  :D
jjoonathan:
This story has taken some interesting twists and turns, here's an update!

Swapping DDR2 Chips

The replacement chips arrived from China, but they had gray crusty oxidized balls. I swapped them for fresh ones using the cheapo direct heat stencil kit that gets sold everywhere, which was straightforward from my practice with the DDR4. I should have ordered one of those heat-resistant pads with chip-shaped depressions to hold the chips while I beaded and wicked away the crusty old solder, but upside-down tape worked OK and I wound up with a bunch of chips with shiny silver balls and a melting point of 190°C rather than 220°C. Heat was still a struggle at this point so the extra 30°C of margin was welcome: I could copy the settings and thermocouple numbers that sufficed to remove the chip and be relatively secure in the assumption that it would do an OK job of melting the fresh BGA onto the board.

This went well! Old chip out, new chip in, booted up, problem looked fixed! And then it returned. More RAM artifacts  :( Different time offset, but same amplitude as before (8*LSB). Did another RAM chip suffer a failure on the same exact ball? It seemed unlikely, but maybe the heat flow or stress patterns conspired to kill Channel 2 bit 3 on multiple chips? I shotgun-replaced another 4 chips, going for the entire group of them in case I had caused this second failure by heating without reflowing and pushing the neighboring chip to maximum stress. I booted back up and... oh no, the problem was still there. And one of my induced glitches had become un-fixed when I bumped it with the soldering iron during the shotgun replacement. That was an easy fix, but left me back at square one: the 600ps 8*LSB glitch was still there. New hypothesis: the 8*LSB glitch never shifted in time, but I was upset enough to see it return that I forgot to carefully follow my own procedure and zoomed in before stopping the scope and *that* shifted it in time. The whole shotgun replacement had been a wild goose chase.

I took the 600ps RAM chip off and poked Channel 2 Bit 3 with the multimeter in diode mode. No diode. Uh-oh. My "steel wool" trick for hidden trace hunting didn't work here because the exposed ends of the vias were so small, so I injected a tone into the floating trace and hunted it out with an active probe. No contact. I would have to deal with the big chip after all. The bad joint wasn't under the RAM, it was under the big 1296 ball chip. Nooooo!

jjoonathan:
Exorcising Demons from Intel PCH

And then the screen went red. Lol. Why did the screen go red? Demons? In my oscilloscope?

Well, I found the display datasheet and probed the LVDS lines with a diff probe. It turns out that the common mode on one of the LVDS lines had gone from 1.2V to 0V. Shout out to R&S ProbeMeter for making this a one step check rather than two step! According to the datasheet, the LVDS line in question carried the bottom 5 bits of the red signal, which explained the red tint.

I was hoping the LVDS line would lead to an easy-to-swap driver chip, but it led right to the Intel Platform Control Hub, a 989 ball 0.6mm pitch BGA. Ahhhhh!

Well, I removed the PCH with minimal fuss thanks to dialing in the preheat plate, but I did knock off a few unlabeled 0402s. In my defense, I did try to protect the 0402s, but I had just switched to a new roll of Kapton tape that was thinner and shriveled up more quickly than I expected. Fortunately, there weren't many strays, and though 2 of them were ambiguous the datasheet was available and got that sorted. These resistors were calibrating the DMI termination (DMI is the CPU-PCH interface, "PCI express but a little faster so that it can encapsulate at full speed"), so I'm VERY glad the datasheet was available.

I went a bit nuts with replacement solder mask for reasons that will become clear next post, but I have to say that I really love this stuff. It's easy to apply by dipping the end of a wire, it hardens quickly under UV, it doesn't smell, and after cured it's easy to sculpt with a knife or remove/try again.

I put on the new PCH, crossed my fingers, booted up, SUCCESS! COMPLETE SUCCESS!

Not bad for my first 989 ball 0.6mm BGA replacement. Which is only my second major BGA replacement, if you group together the 5 RAM chips and count them as the first.
jjoonathan:
EDIT: the forum software seems to be dropping a random subset of uploaded images, so there's some churn on these posts.

Here's a template I made so that I could draw alignment marks for the PCH. The RAM chips and big R&S BGA came with alignment marks in the copper layer and solder mask, but the PCH was just plopped into place by a trusty machine that didn't need no registration marks so I had to score some marks for myself into the board with an xacto knife.

I also tried to use solder mask to make registration bumps, but they were less effective than hoped, probably due to all the other solder mask hitting other bumps and making the tactile landscape complicated. Fortunately it didn't make matters worse. Even though there was only about 0.3mm between board and package, the solder mask bumps were only about 0.1mm tall so there was plenty of clearance.
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