OSI 600D Superboard Build

[rubber_jonnie]

Actually, thinking about it, 1.5A at 5V is only 7.5 watts. It just seems a lot.

I suppose the last time I looked at an ST it was just shy of 3A with a real FDD running, so not terrible, but like you say, it seems a lot

[rubber_jonnie]

@stephen_usher I just checked and the build manual for the 600D states:

Screenshot 2024-04-09 at 14.20.01.png (55.96 KiB) Viewed 8075 times

So 1.5A is pretty OK. With the original build it did have all the 5v regulation circuitry, so that may have added additional load?

[stephen_usher]

How are you getting on with the tape interface?

[rubber_jonnie]

How are you getting on with the tape interface?

Well, not got any further, I replaced the IC but no different.

I lifted a leg of the cap and no difference, and the cap was the right value.

I also lifted the leg on the resistor before the cap and the value is correct and with the leg lifted the signal passes through the resistor.

However that signal is just the 1.2khz signal from the LS76, and is unaffected by the data coming into the LS76.

Much headscratching has ensued since the data does leave the 6850,it does pass through an inverter and arrive at the 74LS76, which is the last stop before the output to cassette.

There are jumpers that need to be set for the cassette to work and I've set them and checked but I'll check again.

[stephen_usher]

Sounds like something isn't clocking in the data on the 74LS76, or the clear is being kept low. That would be my next point of investigation.

[rubber_jonnie]

Sounds like something isn't clocking in the data on the 74LS76, or the clear is being kept low. That would be my next point of investigation.

I did check all the inputs and I'm sure clear was OK, but certainly worth another look.

[rubber_jonnie]

A quick aside, one of the guys over on Osiweb.org has created a new monitor ROM that allows for 48 columns as well as 24, selectable at boot time.

As well as the new ROM, there is a small bodge, represented by a jumper wire here:

IMG20240411085229.jpg (325.3 KiB) Viewed 8024 times

And the results are great:

IMG20240411085334.jpg (273.28 KiB) Viewed 8024 times

IMG20240411085225.jpg (305.7 KiB) Viewed 8024 times

And I think I'll be keeping it, so need to do a more permanent change underneath in place of the jumper wire.

[stephen_usher]

Oh, that's so much more usable.

[rubber_jonnie]

Oh, that's so much more usable.

It is isn't it

[rubber_jonnie]

And the 24/48 mod is now permanent

IMG20240411111203.jpg (377.46 KiB) Viewed 8014 times

And working great