[Clutz]

So I tried your suggestion diablo9, and I'm not sure if it was successful. I lined up all the pins between the pcm2702 and the pcb, put lots of flux on both the pcb and the board, tinned up my soldering iron with lead, and pulled it across at a fast but steady pace. I got a few bridges, but they were easy to fix by either pulling the soldering iron across it again OR by using a bit of think solder wick.

However, I think the 2702 chip became slightly misaligned on the one side of the board. It looks fine on the left side (towards the USB connector), but a little bit off on the right... So I don't know. I don't have the time to finish soldering the other bits on right now, and my electrolytics aren'there yet - so I'll probably have to wait until next weekend to finish.. but if it doesn't work, I'm not sure what to do. Order a new chip and pry off this one? There is anelectronics technician in the department I work in - might he be able to help me get it soldered in place?

Anyway, I'll go and find my magnifying glass and see if I can get a better look. If I get a chance to, on Monday I'll take a picture of it with a microscope and post it.

*crossing fingers*

Clutz

 

[DaKi][er]

Take a look under a real close light source pointed on the board like a desk lamp or something, you should easily be able to see if anything is bridged without any magnification as long as you have 1/2 decent eyesight

and diablo9 probably missed out one of the most important steps, setting your chip up square to begin with, by soldering one outer corner pin to the board and then the diagonal opposite one after that then adjusting to make sure it is perfectly square before soldering the rest of the pins

 

[Clutz]

So, if I have missoldered it (i.e. it's not quite square), how can I adjust it - or do I just have to scrap the chip? I'm not sure it's not square though.. I don't have ahlf decent eye sight.. ;(

Thanks though, I'll try again if I can't get it to work.

Clutz

 

[dsavitsk]

You should go to your local photography shop and buy a cheap loupe (8x is plenty) which will help you see the connections.

I think you are making this process too hard. You should put the chip on the board, tape it down with some scotch tape, and solder down a couple of pins on one side. When you are convinced that the chip is straight, solder everything and use some desoldering braid to suck up the excess. There is no reason to try to do a chip with tight spacing pin by pin, or to try to get it right without desoldering. These chips are built to take a ton of heat and it is very unlikely that you will overheat it.

Anyhow, I doubt you can adjust it. By the time it is hot enough to move you won't be able to touch it with wnything but tweezers, and you are unlikely to be able to accurately adjust it with those. The only way I know to get a chip with a lot of pins off of a board is to hold the board upside down and hit it with a butane torch until it falls off ... then get a new chip ... and maybe a new board.

 

[Francis_Vaughan]

SOP to remove a SMD chip is to cut all the legs off and then take the individual legs off the board with solder braid. At least that only sacrifices the chip. The only alternative is a mega expensive specialty tip for a rework station. The tip alone costs more than the entire DAC project.

(This from my EE brother who learnt this from the rework lab at a military electronics contractor he once worked for.)

 

[diablo9]

use a magnifier to check the pins, as long as you can see ANY contact between the pin and PCB pad, there shouldn't be any problem. alignment is important, too, but as long as the pins are all soldered onto the pad, a little bit mis-alignment is just cosmetic issue.

 

[Clutz]

Quote:

Originally Posted by dsavitsk You should go to your local photography shop and buy a cheap loupe (8x is plenty) which will help you see the connections.

Thanks - I'll do that. i had a friend look at it (he has better than 20/20 vision without glasses), and he said that it didn't look like the pins were connected to the incorrect pads. I don't think it looks like they're connected incorrectly either.

Quote:

These chips are built to take a ton of heat and it is very unlikely that you will overheat it.

This is what I was worried about - frying the chip. At least I have a second 2702 lying around and a second board to try it out with if all else fails.

I'm going to get the loupe and check it out. If all looks good, then I'll go ahead with assembling the rest of it and hope for the best. If it doesn't work, then I'll try the second board out with my other chip - and I'll order myself a few more of the 2702s from digikey.. or somewhere.

Quote:

OP to remove a SMD chip is to cut all the legs off and then take the individual legs off the board with solder braid. At least that only sacrifices the chip. The only alternative is a mega expensive specialty tip for a rework station. The tip alone costs more than the entire DAC project.

I hope it doesn't come to that, but thanks for the tip!

Quote:

use a magnifier to check the pins, as long as you can see ANY contact between the pin and PCB pad, there shouldn't be any problem. alignment is important, too, but as long as the pins are all soldered onto the pad, a little bit mis-alignment is just cosmetic issue.

My concern at this point isn't that I don't have contact between the pin and the PCB pad, or that I have bridges, it's that I may have a pin connected to two PCB pads - but my friend who looked at it said he didn't think so. I'll try to see if a local photography shop is open tomorrow.

Thanks,
Brad

 

[DaKi][er]

If you can't see any bridges then it is safe to say that it should be fine how it is

Seeing you used lots of flux, solder just doesn’t form bridges very well at all and if it does you will clearly see them as you have pointed out when you used too much solder and got rid of them just fine

If you've given it a proper scrub and cleaned off the flux and you cannot see anything with your eyes then it is fine

 

[dsavitsk]

Quote:

Originally Posted by Clutz I'll try to see if a local photography shop is open tomorrow.

They'll try to sell you something expensive (and you can spend hundreds on a loupe if you want) but the $7 ones are good for your purposes. Here's a good example: http://www.bhphotovideo.com/bnh/cont...goryNavigation

Good luck.

 

[Clutz]

Quote:

Originally Posted by Alf My suggestions: * Do your own listening tests for CL/CR. Try different capacitors. You should be able to get away with 0.47uF. Therefore film capacitors could be an option – fitting them could be tricky but worth a try.

How about a .56uF Solen film cap? The orange drop spragues that are 0.56 are about $5 each at a local supplier, and they are freaking huge... Bigger than my baby finger.

 

[dsavitsk]

Quote:

Originally Posted by Clutz and they are freaking huge...

Usually a good sign for a cap. One thing to be careful of with the orange drops, some of them have steel leads (I don't remember offhand which ones, so test with a magnet.)

The Solen's are fine, but they are so cheap that you might move to slightly higher capacitance.

 

[Clutz]

The solen's at the shop I've seen them at are not inexpensive, and they had poor variety - the only capacitance level they had two in were 0.56. They had some other pretty big ones, but only one. They also had WIMA box caps, but I don't think they'd work - leads are too short.

I'll probably start with the Blackgates then when they arrive. The local shops around here all suck.

 

[Clutz]

I made a mistake when I ordered some parts from digikey- I ordered 1.5Ohm resistors instead of 1.5KOhm resistors for R4. I don't have any idea where I can source them locally or I'd just do that. I'd be happy to paypal you a $1 (or a 1 pound) for one or two of the SMD resistors and the cost of postage - I don't really want to spend $8 shipping + $6.50 handling fee (for small orders) to buy like $2 worth of parts, and since they don't have any other parts right now that I'm in need of, I'd appreciate the assistants.

At the same time I found out that digikey made a mistake in the order and didn't send me the 1MOhm resistors and the 1N4004 diodes.

I'm so annoyed with myself.

 

[Clutz]

What the...!! I don't know how to get this thing to solder in place. I made the mistake of putting L1 in place first (eep!), and second - I don't know how to tell which way D1 should be pointing - either on the board, or looking at the part D1 itself. It has no visual references on it to indicate polarity!

 

[Alf]

Quote:

Originally Posted by Clutz What the...!! I don't know how to get this thing to solder in place. I made the mistake of putting L1 in place first (eep!), and second - I don't know how to tell which way D1 should be pointing - either on the board, or looking at the part D1 itself. It has no visual references on it to indicate polarity!

The diode should have tiny stripes on one side. The marked side must point to the capacitor. The unmarked side must point to the inductor.