Hello FreeCalypso community, Yesterday I got another batch of FCDEV3B boards from the assembly shop, this time using RoHS solder and newly-bought Calypso, Iota and Rita chips which are exactly the same versions as what Openmoko used. This board assembly run was another installment in the series of experiments seeking to shed light on the very mysterious sleep mode bug, and the results are:
* The sleep mode bug is still there, totally unchanged from the previous board builds which were done with SnPb solder and chips from 2013. This result means that the chips from 2013 are not at fault, and that the slightly higher electrical resistance of SnPb solder is not at fault either. * There are a total of 4 boards in this batch, but I was only able to test the RF tract (with the CMU200) on 3 out of the 4: one of the boards did not get the Q401 dual PNP transistor part populated (part shortage, more parts are on order), and without those transistors the Tx path cannot be turned on. And on all 3 tested boards there is a problem in the RF Tx path: * On two of the boards the high band Tx path (DCS and PCS bands) works fine, but when I turn on Tx for the low band (900 MHz), the output power levels are way low. The Rx path is good for all 3 bands. It is exactly the same behaviour as was seen on one of the boards in the very first batch, and points to a problem in the Tx path for the low band, the most likely suspects being the RF3166 PA (has separate internal paths for low and high bands) or the antenna switch (has to have separate paths for each Tx and Rx by the very nature of the switch business). * On one of the 3 RF-tested boards the high band Tx path exhibits the same problem as the one for the low band: the power levels that come out are way low. Furthermore, on that same board there is an oddity in the Rx path for the 1900 MHz PCS band: the measured "magic gain" (GMagic) is 181 half-dB units, whereas the expected value is around 200. That is a 10 dB difference, i.e., we've got 10 dB of extra unexpected loss somewhere in the PCS Rx path on this board, which does not happen on any other board or in the other bands (including the almost-identical DCS Rx path) on the same board. The finger of suspicion points to the antenna switch. It is certainly strange that all 3 of the RF-tested boards from this batch of 4 exhibit almost the same breakage in the RF section, while we haven't had too many problems in this area on our previous board builds: the first batch had two defects in this area (one board with similar low dBm output in the low band, and one with totally dead RF, likely bad Rita chip), and the second batch had no defects at all. The most likely explanation that comes to my mind is that either the RF PA or the antenna switch (more likely the latter, given the PCS Rx path strangeness on one of the boards) did not like the higher heat of RoHS soldering, or perhaps some handling requirement was accidentally violated. I will talk to Technotronix folks about it later, but my primary focus right now is on the sleep mode bug. As for the sleep mode bug, the next relatively easy experiment I plan on trying is to remove the Spansion S71PL129NC0HFW4B flash+RAM chip from one of these boards and populate Openmoko-matching Samsung K5A3281 in its place. I call this experiment relatively easy because my friends at Technotronix have a BGA rework station and they seem to have no difficulty with using it - otherwise it would be near impossible. I am hoping that we'll be able to perform this memory IC swap experiment some time next week. Hasta la Victoria, Siempre, Mychaela aka The Mother _______________________________________________ Community mailing list Community@freecalypso.org https://www.freecalypso.org/mailman/listinfo/community