Thursday, February 28, 2013

Dangerous Prototypes QFP breakout board tips

Today was my second attempt at using the Dangerous Prototypes QFP 0.5mm pitch breakout board to solder  LQFP-64 IC.  My first attempt was messy due to a slight misalignment of the pins. Today's attempt was more successful.

Almost everyone agrees the general workflow is to tack down two opposite corners with a soldering iron and when alignment is verified use your favorite technique to solder the remaining pins in place. But getting the IC perfectly aligned (and keeping it there while tacking the corners) is tricky.

Two things I figured today:

1. The solder mask can act as a physical alignment guide. Put the IC approximately in place and then firmly push down on the IC and attempt to slide it up and left (assuming the normal orientation). You'll find that when the IC's pads reach the solder mask there is resistance to this sliding motion. At this point the IC should be perfectly or nearly perfectly aligned. [Update 4 Mar 2013: this worked just fine with an Analog Devices ADAS1000 but I just tried this with a smaller 32 pin package and noticed the IC's pads were shorter so this tip didn't work: so this is very much package dependent.]

2. Next while keeping the IC pinched firmly in place I used a washing line peg to clap it in this position. I found the peg applied enough force to keep it reliably positioned, yet it was still possible to nudge it slightly should the alignment need adjustment.

I then tacked two corners, removed the peg and soldered the rest of the pins.

Wednesday, February 20, 2013

DeLonghi Cafe Treviso (BAR14F-E) Repair

(Note: I wrote this blog post back in February 2013, but for some reason never I published it. Fixing that now.)

In the last week my low cost coffee machine (DeLonghi Cafe Treviso BAR14F-E) clogged up. Turns out (as I suspected) it was a build up of limescale.  I’m writing this short blog post to aid anyone else who might have the same problem. I suspect many appliances like this are dumped and replaced, when a 1-2 hour repair is all that’s needed to prevent more e-junk entering the world’s landfills.

Usual disclaimers apply: this worked for me, if you try it yourself you do so at your own risk. If your device is still in warrantee  it most likely voids it. There are exposed live mains contacts all over the insides of this machine: disconnect before opening and use common sense.

I got some helpful tips from this write up. Not the same model, but there were several useful tips (eg using a regular flathead screwdriver to remove the security screws).

I suggest you photograph everything before disassembling. In that way if you can’t remember what goes where, you can refer to your photos.

Warning: this is a mains appliance. Inside there are many live contacts. Disconnect before opening (I suggest physically unplugging and keep the plug in view so that there is no doubt that it’s unplugged).

I originally hoped I could perform the entire repair by accessing from the top without removing the mechanism, but found during re-assembly I needed to remove the entire mechanism. So best do this from the start.

Remove the water reservoir.

The top and bottom covers use security screws Torx screws (T20H), however it seems a regular 2.5mm flat head will get sufficient purchase to loosen without causing any damage to the screws.

Remove the bottom cover. Remove the mains lead retaining clamp from the external case by sliding it down. This will facilitate separation of the mechanism from the case.

Remove the top cover. You will need to remove the screw covers (use a knife to pry open). You will also need to remove the steam valve by pulling upward (moderate force is required).

Remove the steam hose from the pressure vessel by clenching the retaining clip with a pliers.

Before this next step carefully note the positions of the electrical contacts to the switches (eg take a photo). Remove the contacts from the switches (some of the spade connectors have a tiny clip which you need to depress to remove). Remove the switches and the element indicator neon (that took a little bit of fiddling).

Remove 3 x cross head screws which secure the pressure metal chassis to the plastic outer case. At this point it should be possible to separate the mechanism from the case.

Remove the 4 x hex bolts which fasten both halves of the pressure vessel and secures it to the chassis. You should now be able to separate the top and bottom half of the pressure vessel. Clean out. Also clean the flow valve as described in Step 19 in this write up.

Reassembly is the reverse of what was just described. Take care not to damage the rubber seal between the two halves of the pressure vessel. If it gets dirty clean it before reassembling. Make sure the seal is good and tight.

Misc notes: There was a manky fiberglass wool like thermal insulator keeping the incoming mains wires separated from the walls of the pressure vessel (which I’m sure gets quite hot). Probably because of it’s age it was falling apart and quite dirty. I thought about using some cardboard instead, but because of the temperature and live voltage operating within mm of this I thought it was too much of a fire hazard. So I opted to leave out that insulator when I reassembled. I’m not sure this is a good idea, I guess I’ll find out soon.