Products > Test Equipment
RTO2000 RAM Artifacts
nctnico:
You are excused. Amazing work... :-+
jjoonathan:
Haha, thanks!
Continuing with the story: I put the mainboard on the preheat plate, put thermocouples on both sides, and heated until the top was about 120C. I globbed on a ton of flux, carefully put the RTC chip in place, came in with the 800W hot air, pushed it up to 230C, and let it cool. High resolution, fast, responsive temperature readings from the DMM7510 were amazing. I'm sure you don't need a DMM7510 for these, but coarser/slower reading on the JBC station was by comparison almost completely useless to evaluate the temperature transients caused by angles/gestures/etc. I'm sure you don't need a JBC station either, my point is that you should invest in a fast and accurate thermocouple reader because it made waaay more of a difference than I thought going in. The reading on the hot air station bore little resemblance to the thermocouple reading, even if I stuck the thermocouple right at the tip of the nozzle, and the solder followed the thermocouple not the station. I don't know if this is a problem with my station or if air is just that bad at conducting heat and surface thermocouples are therefore much more necessary than I guessed, but there you go. Invest your money in a good thermocouple reader (I'm sure they can be had for far less than my repaired DMM7510, I didn't plan this just observed it) and invest your time in placing the thermocouples.
I checked the power rails and... ohmic short. Dammit. I suspect I know why, though: the globs of flux bubbled quite a bit while heating and when the solder balls melted and "schlurped" the chip down it was a rather violent event that ejected flux out the sides. I am not surprised that something bridged. Well, nothing to do but remove it, reball it, and try again with less flux. This time I painted the flux on with a brush immediately before putting the reballed chip in place. The balls melted, the chip aligned, and the ohmic short on the 1.2V rail disappeared! Yay!
I booted it up and... leafblower mode |O
jjoonathan:
Ok, debug time. The RTC chips have a 312.5MHz clock input that wasn't present if I powered the mainboard alone, because it turns out that it is derived from the 100MHz main clock sent up from the frontend board. Once I powered the boards together, 312.5MHz was visible on the input to both RTC chips.
The 312.5MHz clock is very familiar from this patent, which almost certainly describes the ADC/RTC interface: https://patents.google.com/patent/US7720108B2 . Also, this interface is AC coupled so at least the frontend board was protected from my DC mistakes.
Both RTC chips get 312.5MHz in, but only the non-replaced RTC chip sends a 400MHz clock to its DRAM. Hmmm. It has a current consumption profile that looks different, but this is probably just because it starts first. I don't like the way it drifts up, but that's hardly definitive.
What *is* definitive is the voltage monitoring. The R&S board designer really outdid themselves here: they brought every sundry power rail, even the little jellybean LDO rails, into a pair of 32-way AD muxes and they left a file in the firmware that records the names and nominal values of each one. Nice! The numbers even match up in the logical way, and they make it very quick to check all of the little rails. If you can boot the scope you can check through PCI Express, and I'm sure there is a UART backdoor or something, but even without knowing any of this you can just go from resistor to resitor on a multimeter and they are sorted in order of ascending voltage so you can tell when one is 0 and shouldn't be. How nice is that?
In any case, a 0.9V DDR termination rail wasn't coming up so that was the next thing to chase.
jjoonathan:
So the 0.9V DDR termination rails are fed by these wacky little special-purpose LDOs TI 51100 with a 5V power rail that they don't use for power, pins designed to interpret sleep states from laptop 5V logic signals, a 1.2V power rail that they do use for power, and two 0.9V outputs, one of which terminates DDR command lines and one of which serves as a reference for the RTC chip to compare logic levels to.
The short was on the RTC side (uh-oh), so I disconnected the LDO and had my power supply feed 1A/100ms pulses (0.9V limit) into the shorted rail and had my multimeter report max voltage between cursors at about -1 and -3 seconds. I am sure there are short-hunting solutions out there with higher quality and lower price, so I'd be interested in hearing from anyone with more experience here, but my setup did produce the classic short-hunting dog-leg pattern, which I repeated from both sides to resolutely point the finger at a single short pad. I then removed the chip, masked off the short pad, reballed, and reinstalled. The 0.9V aux rail was no longer short, but its resistance didn't quite match the sibling rails (700 ohms, 700 ohms, 700 ohms, 400 ohms). Not good. Still, I applied 12V/12A to the mainboard + frontend and the 0.9 rail came up! Yay! But the 400MHz RAM clock didn't appear and the scope app stalled out waiting for the GB receivers.
I'm thinking this RTC chip is dead. When I reflowed it and bridged some of the balls, I must have pulled power through the chip and slagged important silicon. I didn't mention it before but there was discoloration next to the shorted pin that hints at some past excitement.
Fortunately, I accounted for this possibility. Remember earlier when I said "the seller made it right"? Well, I sent out a quote to R&S for a replacement mainboard some time ago, the quote came back, and for once it turned out that I had actually asked for enough money! My partial refund will cover the replacement mainboard.
jjoonathan:
Bringing us to the point. There are two versions of the RTO2000 mainboard (at least). I have the old version with less memory. According to the declassification guide, there is a new version with more memory. I would like to quote this one too, because I want it >:D but I don't know the material number. If anyone has a RTO2000, especially one with the 1Gsa memory option, could you go to File>Maintenance>Mainboard or Menu>Settings>Maintenance>Mainboard and tell me the Material Number? Here's mine (attached).
Also, I couldn't help but notice that a bunch of the numbers on the RTC chip match up exactly with those on the RTO1000. This is giving me some very bad ideas. I mean, how different could two custom silicon chips possibly be if some of the numbers on the package match up? Ebay prices are enough to knock some sense into me, but if I rummage around in the budget there is still a $400 difference between my ebay refund and the replacement mainboard quote, and if there are any other RTO1000 (or RTE) enjoyers out there with a half-dead mainboard that might contain a working RTC that they might be persuaded to part with for what is admittedly not a good price, perhaps we could see together where this dumb idea goes. Probably not, but I had to throw it out there.
That's all for now. I have video of most of this but gee, it was long enough in written form. Maybe once this has had a chance to settle I'll cobble something together and post it.
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