OSI 600D Superboard Build

[rubber_jonnie]

I've got 40 SN74LS76AN on my shelf if you need more. I bought a good job lot a couple of years ago. I got a bit OCD about 74X at the time

Much appreciated.

I do have some coming, but will give you a shout if I run into problems, thanks.

[rubber_jonnie]

Quick update, I put together a quickie video buffer that slots into the 2 unused sockets at the top of the board, and picks up 5v & GND to power it.

IMG20240401160112.jpg (307.36 KiB) Viewed 11751 times

Video out on my LCD is pretty nice from it and I now have 2 outputs, one for CRT and one for LCD

IMG20240401160702.jpg (235.75 KiB) Viewed 11751 times

[stephen_usher]

[HigashiJun]

[rubber_jonnie]

Well, my 7476's arrived and it's made no difference to the tape output. Hmm

What's weird though is that pin 11 outputs to R56, a 100K resistor, and on the IC side there is a signal, but on the other side of the resistor, that connects to pin 9 of J2, there isn't. t

Pin 9 of J2 connects to pin 7, the cassette out, via a voltage divider.

The resistor measures fine, however there is a capacitor, C13 between the output of R56 and GND. Could I have got this cap wrong as well? So I need to check that and see if lifting one leg changes what I see on pin 9 of J2.

It should be 0.01 uF. I can at least check that, though for now further testing has to go on hold as an LS163 in my video circuit has died and guess what? I don't have any spares!!!

I have, I'm sure, nearly every 74 series IC ever made (Maybe I'm exaggerating ), but I never have the one I actually need. So the OSI will have to wait a couple of days.

More and more I'm thinking I accidentally powered my bench PSU on at 8.5v and that's why so many have died. Meh!

[stephen_usher]

Grrr.... Silly chips.

Do you see a signal if you lift the non-chip side of the resistor and/or remove the cap?

[rubber_jonnie]

Grrr.... Silly chips.

Do you see a signal if you lift the non-chip side of the resistor and/or remove the cap?

Annoyingly I didn't get that far before the LS163 in the video circuit decided to go bye bye.

I will probably pull one leg of the cap to check the value at least, and I may be able to blind type to see if I get anything with the cap lifted/removed.

Just wondering if I've filtered myself again...

[rubber_jonnie]

One other thing I'll be doing once I have this up and running again is to fix the problem of the display being shunted 2 characters to the right, which is very noticeable on the LCD.

So I have modded the ROM file at location $7E0 after discussing over at OSIWeb, and once I have some new ROMs (My current ROMs aren't erasable) I'll flash it.

It just requires that value to be changed from $65 to $63, which will shift it 2 columns left. Increasing the value moves it a column to the right, decreasing moves to the left. Apparently you can also add or subtract $40 from that value to move the bottom left corner up or down too, however that's not necessary for me.

I'll report back on the results.

[stephen_usher]

[rubber_jonnie]

Well I lifted a leg on the cap and tested it, it is indeed the correct value, 0.01uF. I'll leave the leg lifted until I can get the video fixed and will look at it again then.

The LS163's are from a supplier who I trust so I expect them to be here in the next few days.