PhilCs blog / the latest things hes broken(fixed)

[PhilC]

Not much of an update on this recently.

I've actually been either busy with work, real life or fixing computers and have forgotten to post about it.

So I just thought I'd share a little fix I've just finished in case it helps some of you out.

On the desk I have a BBC B Issue 7 with extra rom, ram etc etc. Anyway, it had a keyboard fault, essentially the only keys that would work were on the right hand side of the keyboard and even then by work I mean they would print characters on the screen, just not the correct ones.

The Keyboard ribbon was checked as were the header pins, which were a little crusty to begin with. There are four chips on The BBC B keyboard, the two middle ones are the ones primarily to do with the keyboard. A 7445N which is a BCD to decimal decoder, this one is responsible for detecting the individual key presses and then transmits it over to the 74LS163 which then decodes the data and resends it off again in a format that the 6522 VIA chips can understand. (or that's how I think it works ;))

With the scope I verified that the 7445 was receiving the correct keypresses but there seemed to be nothing b being sent out to the 74LS163. It turned out that 3 of the 4 inputs on the 163 were not working and pulling the signal low for some reason.

I removed the very rusty 163 and upon trying to put it into the TL866 to test a couple of its legs fell off.... OOoops, I guess we know that's dead then :lol:

Replaced the 74LS163 and put it all back together and whoop whoop I now have. working BBC B.

[mrbombermillzy]

Good job. :)

[rubber_jonnie]

Not much of an update on this recently.

I've actually been either busy with work, real life or fixing computers and have forgotten to post about it.

So I just thought I'd share a little fix I've just finished in case it helps some of you out.

On the desk I have a BBC B Issue 7 with extra rom, ram etc etc. Anyway, it had a keyboard fault, essentially the only keys that would work were on the right hand side of the keyboard and even then by work I mean they would print characters on the screen, just not the correct ones.

The Keyboard ribbon was checked as were the header pins, which were a little crusty to begin with. There are four chips on The BBC B keyboard, the two middle ones are the ones primarily to do with the keyboard. A 7445N which is a BCD to decimal decoder, this one is responsible for detecting the individual key presses and then transmits it over to the 74LS163 which then decodes the data and resends it off again in a format that the 6522 VIA chips can understand. (or that's how I think it works ;))

With the scope I verified that the 7445 was receiving the correct keypresses but there seemed to be nothing b being sent out to the 74LS163. It turned out that 3 of the 4 inputs on the 163 were not working and pulling the signal low for some reason.

I removed the very rusty 163 and upon trying to put it into the TL866 to test a couple of its legs fell off.... OOoops, I guess we know that's dead then :lol:

Replaced the 74LS163 and put it all back together and whoop whoop I now have. working BBC B.

:girldance: :girldance: :girldance:

[PhilC]

IMG_2753.jpeg

Well that’s just plain annoying, next time I fire up the Beeb and the 74LS273 before the teletext chip decides to fail!

PhilC's stock of said chips? Big fat zero. Oh well,

It’s actually fine in any mode other than mode 7 btw.

[rubber_jonnie]

IMG_2753.jpeg

Well that’s just plain annoying, next time I fire up the Beeb and the 74LS273 before the teletext chip decides to fail!

PhilCs stock of said chips? Big fat zero. Oh well,

It’s actually fine in any mode other than mode 7 btw.

I thought I had a LS273, but I have 373s & 374s, so not much help. Pretty much every time I have to replace some LS IC or other I never have the one I need in stock.

I really do need to tidy up my IC stock...

If you get desperate and need a Teletext chip, I have an SAA5050 here.

[PhilC]

@rubber_jonnie I actually thought it was the teletext chip at first but after changing it its not (I did have a spare of that!)

I've ordered some 273's and have so much more to keep me busy in the meantime but thanks for the offer anyway.

Next up was a Sharp MZ-711 with a popped Rifa and fuse in the PSU. That's at least fixed now, although I. certainly now don't need two of those either :lol: Anyone wanna buy a Sharp MZ?

[rubber_jonnie]

Next up was a Sharp MZ-711 with a popped Rifa and fuse in the PSU. That's at least fixed now, although I. certainly now don't need two of those either :lol: Anyone wanna buy a Sharp MZ?

Stop enabling me...

[PhilC]

Next up was a Sharp MZ-711 with a popped Rifa and fuse in the PSU. That's at least fixed now, although I. certainly now don't need two of those either :lol: Anyone wanna buy a Sharp MZ?

Stop enabling me...

LOL, actually wasn't thinking you :lol:

[rubber_jonnie]

Stop enabling me...

LOL, actually wasn't thinking you :lol:

Of course you weren't :)

[PhilC]

I managed to locate a few 74LS273s and popped a new one into the beeb and hopefully not tempting fate this time, I have a fully working BBC Model B once more.

I also picked up a couple more computers this week and have been slowly working my way through fixing them up.

I’ve been having a bit of fun doing this when I can and by reselling them once they are fixed I’m hoping to make my retro computer hobby pay for itself. With any luck I’ll be breaking even by the next millennium.

I’ve got a really nice Sharp MZ-711 , a nearly new looking TI-99 that’s too nice for my collection, another MSX and another Acorn Electron finished so far if they are of interest to anyone?

Also did a couple of Spectrum repairs for another forum user this week as well, so been pretty productive over all.