Control Board Assembly. No sweat this time...

Busy at work today.  I decided to "go for it" on the control card.

Three soldering irons and a hot tweezers?  Yup.  Now I still need a hot air rework station...

I think I might have to do family stuff tomorrow for New Year's Eve though I'm dying to build most of the DSP board (minus the right angle connector.. sigh..)  But I did get about 4 hours tonight uninterrupted to get the control board done-- which is difficult.

Okay.. well.  I went really slow and mostly followed the instructions step by step.  The exception to this was rearranging the mounting screws for the LCD screen as discussed on the SDR-Cube Yahoo group mailing list.  Using all eight fillister head screws on the LCD and panheads on the rest of the standoffs was the correct way to build these with the parts supplied-- it looks good that way.

Anyway.. here is a picture showing the TSSOP level buffer IC's.  It's obvious how they mount but there is no picture of it on the SDR-Cube site instructions as they are covered up on an assembled control board by the LCD panel...

Top of the board prior to mounting the LCD panel.

Note the orientation of the IC's and how they should look properly tacked on and "flow soldered" and properly cleaned.  I also mounted the contrast pot on the back side of the board.  George N2APB stated this is optional because contrast only has to be set once.  I could see no reason NOT to do it this way especially since the potentiometer faces one of the switches.. it would be harder to get to if on the front of the board and couldn't later be easily adjusted...even if later adjustment isn't necessary... why not mount it in the easier to get at location?  I considered also putting the I/Q balance potentiometer on the back.. but it's not that hard to get to and who knows if it will get in the way of something.  The physical design of the cube is such you cannot assume anything will fit right if you change something.

All of the unmounted parts are the DDS option and the Si570 option.  I think a DDS option might be in my future.. but retrofitting this board to add the additional parts shouldn't be too bad...

Here is the back of the board at the same state.  It looks pretty good all washed up like that.  I'm now using Denatured Alcohol since my beloved chlorinated hydrocarbons (Trichor) isn't available anymore.  I suppose it is just as well.  This is the first kit I've built that has had plastic parts that started to melt with the Trichor.  (The Philmore audio jacks on the I/O board seem to be sensitive to Trichor and so does the buzzer.)  The Denatured Alcohol works well except on the dual row through hole connectors since the alcohol seems to need a little scrubbing.  The Trichor didn't really need any scrubbing.

Anyway.. the next step was to mount the LCD.  With the commentary on the Yahoo SDR-Cube group it was easy to figure out how to mount.  I'm a little disappointed with the flex cable.  I'm used to cables made out of Kapton which are better quality.  This will be adequate for these boards and are a better idea/solution than using yet another connector on the boards.

Here is a detail of the flex cable being folded "inwards" as is in the build instructions.
Make sure the fold in the cable isn't rubbing against anything.  Mine barely clears everything.

Starting to look like a radio here, eh?  Another view of the board with LCD mounted.

Anyway.. the next step here would be to put on the standoffs.  The standoffs apparently are a tad bit too short so the instructions have us putting a 2-56 nut on and then the standoff.  This works and puts the LCD up flush against the cutout in the case.  One thing I think you should do at this point that was not in the instructions is to test mount the board in the case.  I'm actually storing my board that way as well.  Yes, I will have to take it apart and take off the screen protector prior to final assembly.. but it'll have to come apart anyway probably to test out the final "smoke test".

It looks like it fits.  It's really starting to look like a radio now.

The "proper screwdrivers" mentioned in the instructions are a small jeweler's common for the four potentiometers.  The shaft encoder knob goes on after the board is in the case in the final assembly (so it will need to come off when I do the final "smoke test").  The "proper screwdriver" in this case is a 1/16" Allen wrench (hex wrench) for the encoder knob.

The four potentiometer knobs need to be brought out as much as possible.  Unfortunately, they cannot come out as much as I like due to the short shafts on the knobs.  The knobs go though the case which is an odd mounting.  The other odd thing is there is a "indicator" on the plastic shaft of the potentiometers.  The marking needs to be 180 degrees out of phase from the markings on the knobs to properly work.  But it seems right and looks alright if you carefully space out the knobs so they are still firm on the shafts and line up properly.  It takes a little while to get them right.  Luckily they go though the front panel so this only needs to be done once.

The knob on the encoder has to be raised up enough so you can push in and still turn the knob while pushing in and not have it rub on the case.

OK.. you knew this was coming... <SOAPBOX>

The other thing I've noticed on these boards, by they way, is that the solder mask on them is nothing to brag about.  On my Control Card above.. in a "blank area" under the LCD there was a light spot on the masking that actually had (nearly) no mask on it.  One spot on the back of the control card has a extra thick spot of masking on it.  This is poor quality control at the board house.  These boards are obviously from China.  Usable and probably necessary to keep costs down for us, but special care should be taken.

On the I/O board, the small amount of rework I did to remove the stubbys of the connector I trashed in a few places stripped off the mask.  I mention this as on the flowing of the SMT IC's having good mask it vital.  I'd be careful around the IC's until they are completely and properly mounted.

One other complaint and I think this is a biggie.  When rigging up the box.. I was going to take a picture with the I/O card set in the box.  I dropped the I/O card (the damn thing is cursed) about 1 foot on to the table.  Just that amount of "shake" or "vibe" broke off one of the leads on the switching module.  Those leads have to be the most brittle I've ever seen on an electronic device.  But that's not the complaint.  The mass of that switching regulator module is too big to be held on only with solder leads.  I imagine on final assembly we will need to also use that double stick tape to tape it to the aluminum subchassis.  That's not good enough for shock though.  So it looks like I'm going to have to design and build a bracket to mount that to the PCB and also probably tie wrap or bracket it down somehow to the subchassis.  I've done this sort of work enough to tell you that, in my humble opinion, if you don't do this and you backpack or use it mobile long enough, you'll eventually have the switching module broken off in the bottom of the box.

I didn't mean to be critical of the design, though.   Likely (and I'm guessing here.. no insider knowledge) that the original 'Cubes used a 7805 and that drew too much current for battery (or ran too hot or both) so this module was a simple retrofit.  What should have been done is that a switching regulator circuit should have been designed on the board or at the very least the whole (retrofit regulator) device should have been tacked down (with the tabs on the top too) to the PCB.

I'm predicting that regulator to be a major failure point of the radio in the field.

Once I come up with a good mechanical solution I'll let everyone know here.  I re-soldered on the broken lead and re-"smoke tested" the board and we are still good to go.

</SOAPBOX>