Did I ruin my computer?

[Carrie Marie Piazza]

Hi there!

I always dreamed of having a real relay computer! Silly dream, I know,
but I always loved watching them in action I was so excited when I saw
this and had to get one! I bought this last year I finally got it all
put together!

I started it up, set the address to 10 and it started running! Then it
stopped. And now I can't get it running again :( :(

It seems that the program counter simply doesn't increment work
properly like it did the first time. I'm new to these kinds of
projects and I might have bitten off more than I could chew :(

In my soldering, I ended up with a bit of flux on the back of the
board, I was afraid that this might be conducing some electricity and
messing with things, so I decided to clean the back of the board. I
bought some of this:
https://www.amazon.com/Chemtronics-Flux-Off-Concentrate-Flux-Remover/dp/B007XIKL9M

However, all it did was make the board super sticky! I'm so worried I
ruined the board!!!!!

Try as I might I couldn't get it clean and I ended up using the entire
can. Is there any way I can fix this poor computer or did I ruin it?

[Francis Bauer]

I haven't had much success with canned Flux removers, they do seem to leave boards sticky, so I've stopped using them.

Flux on the board doesn't usually cause problems, unless you are dealing with very high frequency boards (This board is not high frequency, I'm talking RF/Microwave frequencies).

Even though your board is now sticky this shouldn't be the cause. But it is possible that some conductive bit of metal or other particle may have been stuck to your board because of it being sticky. Look over your board closely and make sure there is nothing conductive shorting any pin together.

If you have used sockets for the relays and ICs, be sure that everything is well seated. If the partially cleaned flux migrated to the front of the board, it is possible that some of it has gotten into the sockets and is causing intermittant connections. You may want to remove each socketed part and inspect their pins to make sure they are clean.

[Jim Bailey]

I had the same problem and dreaded cleaning THIS board, as it’s so big with a lot of narrow channels. This time I tried a different technique that had worked better for me:

I used MG Chemicals - Flux Remover for PC board (and it does leaves a light residue of while flux behind, if you let it dry). I used with a somewhat soft horse hair brush which didn’t scratch the solder mask.

This time I held the PCB at approx. 30 degrees from vertical and cleaned the “bottom” side facing toward the ground using the horse hair brushed liberally coated with the Flux Remover. I start at the “highest” side of the board and brush only in the direction of the lowest side of the board. I keep reloading the brush with Flux Remover so that the PCB gets very wet, which helps move the flux towards the bottom.

Every so often I use some MG Chemicals - Super Wash, to "rinse" any area I have thoroughly brushed before the flux remover before it has a chance to dry… “let it flow like water”.

Then once the brushed and rinsed area is dry I check to see if any residue remains (and repeat the flux remover brushing and “rinsing” until its clean). Once the upper area is clear and start the whole process again just below the “cleaned” area.

While this takes time but it’s not too hard to do and you don’t need a lot of detailing afterword. It beats trying to scrub the white residue from the board by hand with q-tips or such..

Anyone else have a better technique, I am happy to barrow it 

[Jim Bailey]

If you look at my procedure from above, I can confirm this did not appear to harm the computer. As I was able populate the chips, power it up and run the test program today. even across a few power cycles.