exxos's Atari, Amiga & retro forum

foft wrote: 08 Apr 2023 10:07 So I just ordered some copper tape to try to fix these in a few weeks. A little bit of scraping of the adjacent vias and a bit of high temp Chemtronics CR2500 epoxy and it'll be golden. Or at the very least frustrating enough to drive me :mad:

That's the way I do it... Time consuming but worth the effort.

Bigger pads are always easier to repair though.

(Please keep a non repaired for me 8-) )

foft wrote: 07 Apr 2023 21:39 Arg, built another one and it would have worked except... I got a little blob of solder under the surface mount socket. These are really tricky to remove, I think because they hold a lot of heat and ... melt!

So I tried to remove it with hot air, then gave up. Then decided to cut it off and desolder bit by bit. Now 14 pads are gone. :( Oh well, live an learn. I think my mistake was to use paste for the SMD header, I'll hand solder it on the next try, like on the first one.

Oh well, off for Easter hols and forget about it then I'll try again! Its all good practice and there are still enough PCBs for the 3 in line.


CTPCI_no2_bottom.JPG

I desoldered such things using Wood's alloy (melting point 70C), you need to dilute the tin on the soldering pads with this alloy and then lightly heat it with hotair ...

markus0321 wrote: 11 Apr 2023 10:28 I desoldered such things using Wood's alloy (melting point 70C), you need to dilute the tin on the soldering pads with this alloy and then lightly heat it with hotair ...

Thanks this sounds super-useful. Which one do you buy? I see Wood's itself has toxic vapours, are the various similar low temp alloys the same - i.e. need extra ventilation vs simple soldering?

HigashiJun wrote: 08 Apr 2023 12:13 (Please keep a non repaired for me 8-) )

Of course. If I sell the repaired one I'll be very clear with whoever is getting it... More likely I'll sell mine and keep this one for me.

I'm back from Easter holidays and just started to build the remaining three ones. So far the PLX chips are on all three and looking good. I did these (+CPLDs) after the birdseed the first time and it made some pins hard to access.

I'm going to take my time with these so it'll be a few weeks before I finish and test them I think.

foft wrote: 19 Apr 2023 21:48 Of course. If I sell the repaired one I'll be very clear with whoever is getting it... More likely I'll sell mine and keep this one for me.

I'm back from Easter holidays and just started to build the remaining three ones. So far the PLX chips are on all three and looking good. I did these (+CPLDs) after the birdseed the first time and it made some pins hard to access.

I'm going to take my time with these so it'll be a few weeks before I finish and test them I think.

Many thanks !

No worries for the schedule, take your time.

foft wrote: 19 Apr 2023 21:48

markus0321 wrote: 11 Apr 2023 10:28 I desoldered such things using Wood's alloy (melting point 70C), you need to dilute the tin on the soldering pads with this alloy and then lightly heat it with hotair ...

Thanks this sounds super-useful. Which one do you buy? I see Wood's itself has toxic vapours, are the various similar low temp alloys the same - i.e. need extra ventilation vs simple soldering?

So it's better to have good ventilation. I still used low-temperature tin, but it is twice as high a temperature needed to desolder the elements. I use Wood's alloy only in such "difficult" cases and not very often. I recently bought it from our Allegro auction site, but I also see it on ebay.

markus0321 wrote: 21 Apr 2023 13:13 So it's better to have good ventilation. I still used low-temperature tin, but it is twice as high a temperature needed to desolder the elements. I use Wood's alloy only in such "difficult" cases and not very often. I recently bought it from our Allegro auction site, but I also see it on ebay.

Wouldn't field's metal be less dangerous and maybe more appropriate for this task ?

It contains much more less bismuth and its melting point is also lower.

The other three I'm building are going well so far and getting closer:
PLX, Xilinx, all resistor arrays and 8k2 resistors are fitted. Just a few more resistors, caps and headers then I can clean and test these. Hopefully later this week or next weekend.

My gluing of the damaged one didn't go so well. I cut copper pads and stuck them on. Many seem solidly glued and others ... move around rather too much! I probably need to re-glue the problematic ones, before trying to wire up the new pads to the broken traces.

foft wrote: 30 Apr 2023 21:42 My gluing of the damaged one didn't go so well. I cut copper pads and stuck them on. Many seem solidly glued and others ... move around rather too much! I probably need to re-glue the problematic ones, before trying to wire up the new pads to the broken traces.

If the heat applied to the CW2500 epoxy - once cured - is too high, the pads will tend to move.

IIRC, the maximum heat supported is 315 degrees Celsius for 1 minute, but I always try to use the lowest one possible.

Three(*) more built and drying from the ultrasonic.

Now, do they work...


Still not been brave enough to try again with the broken pads one.

*: Yes I know there are four here, I cleaned my original one again because I did some soldering after the original cleaning.

Looking good !