We now began shipping QMX Rev 2 PCBs. The PCBs have the following minor changes, which are mostly about making the construction easier. There is no major performance or functionality enhancement so nobody?needs to upgrade from a Rev 1 PCB to a Rev 2 PCB. These are just minor improvements, not a major revision! There are always some people who get all panicked about PCB revision changes - please don't, these changes are so minor. I often make these kinds of minor changes each time I do a new PCB batch, just to incorporate customer feedback and observations on improving it. But they're usually MINOR. Just ongoing product improvement.?
1. Move trace that's under the screw for the PA heatsink
There's a?+5V trace that goes under the bolt of the PA heatsink. I have never heard of even one instance where someone over-tightened the bolt, causing the solder mask to be scratched off and a short from the?+5V trace to ground. However it seemed wise to move the trace a little just to sleep better.?
2. Use only half the BPF MUX switch
As per Steve K1RF's suggestion and discussion on this forum; now only half the IC402 74CBT3253 MUX switch is used for BPF switching. See attachment. This slightly reduces losses (due to the non-zero ON resistance of the switches) and reduces parasitic capacitance due to the capacitance of the switch inputs. As I mentioned yesterday, I have not seen any particular benefit from this change yet, I wasn't able to see any difference at all; but I will keep looking.?
3. Add 5.1K resistors at USB CC pins
People using a USB-C to USB-C cable reported this issue where the host computer also uses a USB-C connection, and in some cases the host computer tries to test the attached equipment, to find out whether it should supply power or not; it also decides to determine whether the thing at the other end is going to be the bus master (host) or bus slave (device). The USB specification is not very easy to understand but this does appear to be a correct interpretation. So on the Rev 2 board there are now 5.1K pull-down resistors on the USB-C connectors CC pins.?
4. Move capacitor C204 that is near the mounting hole for the left SMPS board
Just a small distance move to reduce the risk of damaging that capacitor C204 which is near the mounting hole (though I have never heard of an instance of this).?
5. Make 0.6mm wire holes larger on binoculars
On Rev 1, the wire holes are a little tight on the 0.6mm sized wire; so I made the holes a little larger to make it easier to install the 0.6mm sized wire.?
6. Enlarge some 3.5mm jack holes very slightly to make it easier to adjust their position
The 3.5mm jack connectors don't want to sit square with the board edge naturally, something about the Eagle CAD library component differing very slightly from the actual device; so I enlarged the pad holes slightly just to make it easier to precisely align these connectors square with the board edge.?
7. Move part of the power connector +12V pad to avoid nearby short
The 12V power connector center pin (+12V) is rather close to the 2x4-pin SMPS connector, and it is possible to create a short between the supply connector pin and one of the SMPS connector pins. I can't now move the SMPS at all and neither is there space to do so anyway, but I was able to shape the copper pad of the 12V pin to increase the distance and make a solder bridge much more unlikely.?
8. Make the ground connections of the rotary encoder pins easier to solder
Soldering the rotary encoder pins, particularly the ground pins, has been rather tricky; the reason for this is that although the ground pads in the design all use the normal good practice "thermals". which means there isn't a solid connection from the pin pad to the ground plane, there's a gap except for four traces at 0, 90, 180 and 270-degrees; the problem with the 6-layer board is that 6 x 4 = 24 and those 24 traces still conduct plenty of heat away. That combined with how close the rotary encoder pins are to the board edge, and to the body of the rotary encoder itself, made this part of the assembly a bit tricky. So I disconnected the ground pins from the ground plane except for one single trace; it makes them easier to solder now.?
9. BS170 holes slightly larger
BS170 pin pad holes were enlarged slightly, just to make it easier to clean out the holes if you do find yourself needing to replace BS170 transistors.?
10. Possible SMPS short area: moved transistors further apart slightly to avoid risk
The famous Q103/Q104 transistor short on the 5V SMPS board! This is not a practical issue for a few months now, not for you, because once the problem was known, we started testing all the boards here for the short, and when found, I corrected them all to remove the solder bridge. But on Rev 2 the transistors are a little further apart so there isn't a chance for the solder bridge to accidentally form during the assembly process. Well anyway we are still testing for the Q103/Q104 short too, just to make double sure.
11. C204 was 100n now 1n
This is in case it becomes desirable to make faster measurements of the supply voltage.?
12. Move MIC leads a little apart
The electret microphone on the controls board, is slightly different from its Eagle CAD library model, meaning during installation it was necessary to spread the mic legs a bit. On the Rev 2 board, I put the holes a little further apart just to make it easier to get the mic in.?
13. Tidy up spacing of C401/2/3/4
Just purely cosmetic, the four capacitors were unevenly spaced and I found it unsightly (as did Ross EX0AA who reported it!).?
