Omega Race PCB repair #5

[omegaman]

Another set arrived a few days ago. This set belongs to YODAinMN.

The board looks fairly clean but on closer inspection needs a lots of work replacing all the sockets.

Fresh out of the dishwasher

 

[omegaman]

I did the usual Ram/Rom/CPU check first. Half of the Ram are dead, the CPU is good and the program Roms are fine....But...2 are the same even though they are marked as being different.

I need to fit new Ram and video Rom sockets then burn some new Roms first.

Will update once I have it ready in a day or so.

Right back to set #4......

 

[omegaman]

You can see the state of the sockets now.

It's always best to remove the plastic top leaving the pins exposed when you have corrosion like this, that way you can add fresh solder top and bottom if needed to remove the old pins.

 

[YODAinMN]

looking good so far!

 

[YODAinMN]

Bumping this thread up since there's been another older inquiry thread rehashed. How's it coming along Simon?

 

[ajcrm125]

It's always best to remove the plastic top leaving the pins exposed when you have corrosion like this, that way you can add fresh solder top and bottom if needed to remove the old pins.

+1

I usually toss the PCB in a PCB vice at this point, vertically. Use tweezers on one size and the soldering iron on the other and pull the pins out one at a time.

 

[kb0jjn]

What do you use to neutralize the acid? I was thinking something like a base baking soda maybe?

 

[That80sGuy]

50/50 mix of water and vinegar. I took my boards and removed the socketed chips, cleaned the board with a toothbrush.. then submerged it in a shallow plastic tub for a couple hours. Then rinsed it off .. dried it off.

 

[omegaman]

White Vinegar and Salt, spread it over with a toothbrush then give it a very good clean, dry and clean again with PCB cleaner/flux remover.



A side note on fixing these boards. If anyone is working on one and needs to disable the watchdog timer then you can do so like this

 

[omegaman]

Bumping this thread up since there's been another older inquiry thread rehashed. How's it coming along Simon?

Not had much time on it as yet, started removing the bad sockets. Will update soon.

You may need to Ctrl F5 this page as I updated the picture with larger text.

 

[kb0jjn]

Where did you get such great looking schematics? I want a set like that.

 

[omegaman]

They are in the Omega Race manual, you can pick them on on ebay for $20.

 

[omegaman]

I should get more time on this board this Sunday...working day and night in my job right now so have so little time for anything. The board is running and reporting video ram problems now. A lot of traces were bad around the Ram and Rom area. I will update with pictures in a day or so.

 

[YODAinMN]

Any updates there Mr. Work-o-holic Simon?

 

[Robotron]

I love these threads. This is some good stuff. Keep up the good work Omegaman!!!

 

[omegaman]

Hi Guys. So sorry my business has been so busy! working 7 day weeks trying to get everything finished. Spending today catching up on emails etc. I have spent a little more time on this board, will download some pics from my phone and update the thread today.

 

[omegaman]

Just updating a few pics on this set.

New sockets installed....corrosion was worse than expected, I needed to add some jumper links under the sockets.

Ram and Roms fitted, ready to fire up.

The board was in constant reset when I powered it up. The problem turned out to be the custom Proms between the address lines and the CPU. I swapped out a pair from one of my working sets and it went into self test. It has no video yet but is reporting bad vector Ram and Rom. I found the video Ram/Rom buffer was bad 74245

Please please....after PCB#4 let this be an easy one!!

Nope here we go again!

 

[omegaman]

And another bad chip

Still reporting bad Ram/Rom......this is where I'm at now. I have to check continuity the hard way pin to pin on all the Video Ram and Rom before going any further, address and data lines.

 

[Robotron]

These chip failures, do you think its from the acid damage, or is it age related?

 

[omegaman]

On this board acid for sure. Usually the chips that are soaked in that area fail.