Stuff and Things.

[cmorley]

That damn mobo socket is so easy to get wrong

I don't know what happens if you plug one of my EPROM emus 1 pin off in a 42 pin socket... it might survive or kill one of the buffers, I'm not sure. Best not to try

[rubber_jonnie]

That damn mobo socket is so easy to get wrong

I don't know what happens if you plug one of my EPROM emus 1 pin off in a 42 pin socket... it might survive or kill one of the buffers, I'm not sure. Best not to try

Yep, I will be double checking and making damn sure it get's plugged in the right way round and into the correct pins!!

I will let you know, the mobo is currently in our airing cupboard drying out, so can't do anything until later.

EDIT: Orientation confirmed 100%

[Tomswork]

Do you have a tl866 ii ? The adapter kit should have the 40 to 42 pin adapter.

Tom

[rubber_jonnie]

Do you have a tl866 ii ? The adapter kit should have the 40 to 42 pin adapter.

Tom

I do have a TL866 II Pro, but don't think I have a 42-40 pin adapter, but I'm sure I can either make or buy one If I need to. I will try @cmorley's emulator if my ROM still doesn't work, but I presume I could use the 40 pin 27C400's to replace the ROM if it is bad.

Any suggestions welcome!

[Tomswork]

@rubber_jonnie

Ebay item 183888405810 from poland

Tom

[rubber_jonnie]

@Tomswork thanks

[rubber_jonnie]

Ok, so on the off chance I have kille the ROM in my Mac Classic, I have an adaptor for my TL866 Pro on the way so I can burn a new one, plus before that I will likely try going down the route of trying the ROM emulator from Mr Morley.

I also ran into an interesting feature, in that I thought I'd found a short in a little 8 pin voltage regulator, but it turned out to be a blind alley.

First you have to ask the question "When is GND positive?"

Answer is simple when you get down to a bit of research - When the voltage is negative. Turns out the data sheet for the regulator even shows it in an example configuration. The polarised capacitor has + connected to GND and - connected to -5v and the schematic for the Mac shows exactly the same configuration.

It took a little research, but nice to know that it isn't a short. Better keep digging I suppose!

[exxos]

First you have to ask the question "When is GND positive?"

It's all relative

split-rail-power-supply-circuit.gif (13.7 KiB) Viewed 2844 times

[rubber_jonnie]

@exxos Indeed it is:

negativeispositive.jpg (10.13 KiB) Viewed 2840 times

[JezC]

When I used to have to design circuits with ECL logic (especially when interfacing with TTL/CMOS logic) it was a nightmare working out what signals were active (and what polarity that was)...no chance of the logic analyser sorting it out, so we had to rely on a 'scope!

At least the majority of modern electronics (and I'm generously including the ST and Amigas in that category!) don't have that pesky-5.2v supply to confuse things further!
Even just using PECL made a world of difference...