Help repairing Superboard II

[nfogel]

OK, so I pulled my Superboard II out of the basement after 30-something years it was lying there.
Had to replace the old power supply with a new one, here they are side-by-side -

And the video cable needed some soldering, here it is -

Now is my next problem which seems a bit more complicated.
Once I turn it on, this is what I get on the screen -


Screen is frozen and no reaction to keyboard.
Would be very grateful to get some suggestion here.

Thanks
Noam

[dave]

Hi Noam,

Welcome to the board! Glad you got out the superboard, and found this site. You have video, so that's half the battle already. Now you've got to start troubleshooting the microprocessor section. There are several resources listed on the top of the osiweb.org page. Check out Prof. Mark Csele's web site, where he goes through the process of getting a machine up and running. You should try re-seating the chips on the board. Oxides can form on the pins over the years, degrading the contact in the sockets, and re-seating them produces a wiping action that can remove the oxides. Sometimes that will fix the problem. If not, then you will have to start at the beginning, checking the clock line, then the data and address lines for activity.

What tools to you have available? Do you have any test equipment or a soldering iron?

It looks like the picture didn't post, but since you emailed me a copy of the picture, I'll include it here:

IMG_20120211_123024.jpg (153.97 KiB) Viewed 6342 times

The way to upload a file is to use the "Upload Attachment" file at the bottom, and then when the image is uploaded, click the "place inline" button.

Best regards,

Dave

[nfogel]

Thanks Dave,

I didn't see that it was possible to upload an attachment so I tried to use the IMG tags with image URL. This apparently didn't work.
Anyway, I do have a soldering iron and a digital multimeter, that's about it.

I will try the stuff you suggested and will post back.

Noam

[nama]

I'm not really an expert, but I've fixed many old computers and video game boards with nothing more than persistence, luck, lots of help from more knowledgeable folks and a $10 logic probe. I highly recommend finding a cheap logic probe as these are great for basic testing.
As Dave said, reseating chips is often all that is needed, but it that doesn't work then next I'd see if the the RESET line on the 6502 CPU (pin 40) is getting the reset signal when the reset button on the keyboard is pushed. Testing the voltages coming into the board may also be a good place to start.

Phil

[nfogel]

Sorry for the noob question, but what's the best method for re-seating the chips?
They seem to be stuck in their sockets quite firmly and I am afraid to pull too hard. Is the any tool or recommended method for that?

[nama]

Great care has to be take in removing chips from their sockets. You have to make sure that you ease up one end a little (one millimeter), them do the same to the other side, then repeat, moving from one end to the other until the IC just pops out.
What I do is use a thin flat head screwdriver and gently slide it under one end of the IC, then I twist the screwdriver which raised the chip. then I do the same at the other end, then repeat. Just be sure not to put to much pressure from one end, as he chips have a tendency to suddenly lift, and if it does from one side only, then it'll bend and break the pins on the other end...basically just take your time. Be careful to remember the orientation of the chip.
I use a slightly abrasive eraser to clean the black oxide from the legs. Then carefully put them back, make sure all the legs are going into the socketed holes before applying pressure.

Finally, and this may sound silly, but don't try removing IC's that aren't socketed

[billdrom]

I usually don't completely remove the chips.
Just loosen each end a little bit then push the chip back into the socket. The motion of the chip legs against the socket pins is enough to clean the contact.
This is especially helpful on memory boards where there are so many chips. Of course if the chip pins look very, very dirty to the naked eye, you may have to remove it to properly clean it.

Bill D

[dave]

Hopefully, the above excellent descriptions helped you re-seat the chips. I, too, use a thin screwdriver to help lift up the chips in a controlled way. I slide it under each end and use it as a lever to slightly raise up the chip part-way in the socket, then push it down. Try to avoid lifting up with your fingers--it's hard to control the force, and you may end up with bent pins, and a tetanus shot.

I second Nama's recommendation for a logic probe. You can get one for less than $20 new, and it will help you test logic circuits much more quickly than a multimeter, and also, will help you detect logic pulses that a multimeter will miss.

If you you are able to get access to any kind of oscilloscope, that is even better. It doesn't need to be fancy--an old, slow analog scopewould be fine, and you should be able to find one used for under $100, or free. If you don't have much space, one of those new DSO nano scopes, or similar would be fine for debugging older computers, and are less than $100.

After re-seating the chips, if the system is not responding, then you can start by checking the clock lines on the 6502 chip with a logic probe (or preferably a scope). If that's pulsing at 1MHz, then look at pulse activity on the address and data pins.

Dave

[nfogel]

Thanks for all the help here. I am going to get me a logic probe and move ahead as advised.
Will keep posting until I get this thing playing