Hey TonyG,
Thanks for weighing in!, Happy New Year to you and all the HP fan boys on the EEVBlog forum.
Nope, Santa’s delivered nothin’ but coal lumps so far. But learning has still been happening. On the cap testing, I hear you, I’d considered the same things. My resistance readings were with a DMM, but I also have a decent LCR meter that I’ve been using to test caps as well, both in and out, of circuit. What I learned from just slapping a DMM across those caps was that things were pretty consistent across the board. Call it a “qualitative measurement”. The circuit was definitely influencing the readings, even if I don’t really know how, precisely. It was just a data point, even if a marginally informative one.
First impressions sure can fool you sometimes. I’ve realized that my initial conclusions about the power rails on this guy were a little bit “slap-dash”. This has screamed power problem from the very beginning, I just didn’t look close enough. The bottom line at this point, is that when all connections are hooked up as intended, the +5V rail becomes +1.8V, and it only does that when pin 2 of the J2 connector is connected into circuit. I’ve looked at the string on sheet 14 pretty closely at this point. I’ve tested the tantalum caps out of circuit, (they’re bang on), and really doubt any of the ceramics are the problem, so I’m moving onto sheet 15, following the 5V distribution. I’ve determined that I do not have the 5V at chips U29 and U33 per the schematic. Interestingly, with the wire from J2 disconnected, I got essentially no voltage on those chips, but with it connected, I got low voltage, 1.6V and 1.7V respectively. The interesting part is that's really close to the 1.8V faulty rail reading observed previously on board A10.
Following other points on sheet 15 where the 5V should be, has led me to the only resistor network on the board, R9. There are 9 - 3.3Kohm resistors in the package. I’m currently doing some investigating of that package and pondering a way to test it. Not sure if I’ll find a diagram anywhere that shows how all those resistors are hooked up inside the package, but it certainly seems like a possible culprit. Great, I suspect that part will be unobtainable in its current form, but we’ll just have to see if it’s got a bum resistor in it somehow. The package has 10 pins.
So, nothing insightful to report unfortunately. This Bodger is still just poking around in discovery mode. More later with any progress....
JRH