Another Superboard II Rev B repair

[Sideburn]

Some more info...

I noticed on the bottom of the board pin 12 and 18 are jumpered together. Is this for the original 2708 eprom?

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I am bypassing that and routing it to U18 pin 3...

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Also there are cuts on the top of the board:

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The other longer wires are just going to spare pins on j2

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Maybe I should just remove all the wires I can that are clearly not participating in anything (going to connectors etc...)

Here's a photo of the terrible rats nest on the under side of the board. Probably literally a 13 year olds work

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[Sideburn]

Sorry guys.. LAST POST in a row for today...

I have a thought and need your opinion. Should I just dive in and remove ALL of the bodge wires, piggy backed ram, PROTO chips and then hunt down and bridge all of the cut traces and bring this board back to bone stock and take it from there?

Top of the board:

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Cut traces:

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PROTO chips:

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Extra VRAM:

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[dave]

It would be a shame for you to undo the modifications. Whoever had that machine did one of the screen doubling upgrades, which seems to be working well. That makes this a special machine.

The issue you are seeing is almost certainly unrelated to (at least most of) the rats nest of mod wires, and most likely just a ROM/EPROM configuration issue.

The 600 board did not use a 2708, so if you received it with a 2708, then pins 18-21 of may have been re-jumpered for the 2708. This could cause incorrect addressing of your 2716. You should check what is connected to pins 18-21, especially jumpers W6, W7, and W8 (see the 600 Board Schematics). Pin 21 should be jumpered to Vcc (+5V). I think pin 18 should be jumpered to GND (pin 12) for a 2716, but someone will correct me if I'm wrong.

You are almost there!

Dave

[Sideburn]

OK I will leave the mods.. here what I am doing now...

I removed the wires coming off of the monitor rom pins that were going to the J3 connector. That left me with two bodges and cut traces that I think were done to get the 2708 to work.

That being pin 12 jumping to pin 18. I will remove that.

Then there's pin 20 jumping to U18 pin 3. I will remove that. It looks like in stock condition this pin was going to U55 pin 11 and those traces have been cut so not sure if I should put that back or not. I assume so... unless the 40 column mod changes things... And pin 20 on the 2716 is the output enable... maybe I should send this to the phi-2 clock?

I will then put pin 21 to +5, and 18 to u18 pin 3.

Does this sound right for a 2716?

[Sideburn]

We have success!!

I did the rework on the MON wiring for a 2716 and pulled pin 19 high and bam!

Here's a video link of it getting into the monitor: https://youtu.be/Iikr4KRpWhM

I then got into BASIC and wrote a hello world test! --> https://youtube.com/shorts/DQwJLW4sQwE?feature=share

The only issue now is its split across the screen... some kind off wrapping going on..

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[bxdanny]

Congratulation!

I made up a ROM image for you to burn into your monitor EPROM that should fix the way the screen is being utilized. Both halves of it are the same, so it would have worked even with the board the way it was, but it will still work now as well.

Since uploads here have to have one of the supported file extensions, I chose .ini, but it is just a straight binary ROM image.

[Sideburn]

Awesome! I have been going through the chips trying to figure out how the video works and was suspecting I need a custom monitor ROM to get the columns working right.

I will try your rom right now! Thanks!

I have since cleaned up the board some and wired U13 correctly for a 2716..

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[Sideburn]

Congratulation!

I made up a ROM image for you to burn into your monitor EPROM that should fix the way the screen is being utilized. Both halves of it are the same, so it would have worked even with the board the way it was, but it will still work now as well.

Since uploads here have to have one of the supported file extensions, I chose .ini, but it is just a straight binary ROM image.

Its FIXED!

So awesome thank you! And everyone else for helping. I can't believe it is working!

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*** some questions:

The 8T28's are getting pretty hot. Is that normal?

[Sideburn]

Hey all, now that the board is working I plan on diving more into how it works and see if I can save/load off the serial interface (the ACIA I believe). I also need to figure out exactly what all of the glue TTL chips are doing (u20 - u23, 53 - u70 etc.)

In addition to the board itself, The box my friend dropped off for me includes a case that his father made for him out of wood, two PSU units, one with a DB25 female connector and a connector that plugs into J2. Also the original manual.

I am curious why there are two power supplies. Anyone know what that is about?

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[jbtech]

Hi again, The Superboard II originally just requires a %V supply which connects to the red and black power wires which emerge from the PCB near J3.

As your machine was previously modified, for some reason (Don't ask me why!) a 2708 EPROM appears to have been used for the monitor ROM position instead of using a 2716.

The 2708 requires +12V and -5V supplies in addition to +5V so it seems an additional power supply was added to provide those Voltages via some previously unused pins on connector J2.

Since you have already replaced that 2708 EPROM with a 2716 the additional power supply Voltages should no longer be required and it will most likely be possible to leave that off, just using a 5V supply and the original power input wiring.

Congrats on getting it running, the modifications look messy but the 48 character display is impressive compared to the original 24. Regards, John.

Edit: just as an afterthought, the DB25 connector is probably for RS232 so your board most likely already has the additional components fitted to support that. It may also use that extra power supply to provide a negative Voltage for the RS232 interface which the Superboard didn't have by default.