BBC Model B No2. Will it live again!

[rubber_jonnie]

And in typical fashion, I just found the 4816 datasheet by tweaking around with my Google search terms :)

[rubber_jonnie]

So, pinout for the 4516 and 4816 are identical, bar the NC pin 1 of the 4816 is used for refresh on the 4516.

However the RAM is automatically refreshed on any RAS operation on the 4516 anyway, so it looks like they are pin compatible.

However, and I need to check this, with pin 1 of the socket showing as NC for the 4616, and pin 1 of the 4516 showing as active low, I am wondering if that pin is actually floating and not behaving as it should.

Also, if pin 1 is held low on the 4516's, then that may also be causing problems. Multimeter time I think.

[Tomswork]

@rubber_jonnie

Can you use a 4164 in place of the 4816 it only has a a7 on pin 9 that should have nc on the 4816 ?

Tom

[rubber_jonnie]

@rubber_jonnie

Can you use a 4164 in place of the 4816 it only has a a7 on pin 9 that should have nc on the 4816 ?

Tom

In theory I guess you could with a small adapter or bodge wires, however since I last posted I've had a conversation with exxos and discovered that pin 1 can be left disconnected on the 4516 if you don't intend to use it.

Of course leaving it floating may cause problems, but I think for now, having pulled all the RAM last night with no difference to the symptoms, that I will look at other areas. I suspect the ROMs or master clock at the moment.

[rubber_jonnie]

Based on fixing the stuff I have parts for, I've made a start replacing sockets, as the existing ones are very old.

ROM sockets are done, no difference, though it could be the OS ROM is bad, I can't tell right now, but have an offer to send them to somebody, including my RAM, for testing, an offer I will consider if I get nowhere with the re-socketing.

I have tried a new CPU and system 6522, but no difference either, and removing the RAM makes no difference either.

Damn thing.

[rubber_jonnie]

So a bit of socket surgery ongoing here:

IMG_20210511_152600.jpg

The plastic frame can be pulled off easily, then the pins are heated and pulled out with tweezers.

As you can see from the next pic, the wipers from the socket have really bad oxidisation, so I think regardless of it fixing the problem, the sockets have had their day.

IMG_20210511_152551.jpg

Just need to wait for some more solder wick so I can clean up the holes and get the new sockets in.

[exxos]

They do look really bad indeed. I've had the pins break in between the socket and the board itself, very difficult to diagnose because when you put the meter on the pin it checks out, but it is actually broken :roll:

[rubber_jonnie]

They do look really bad indeed. I've had the pins break in between the socket and the board itself, very difficult to diagnose because when you put the meter on the pin it checks out, but it is actually broken :roll:

I actually had a few pins break, some apparently before I pulled them, so very possible it's similar to your experience.

[rubber_jonnie]

Well, more socket removal done. All the 40 and32 pin sockets are off and as soon as I have some de-solder wick I'll get the holes cleaned up and the sockets fitted.

Doing all of this with minimal tools has made me think I might have todo a small article on a minimalist workshop, so just what you can use for basic repairs on a budget.

One other discovery whilst doing socket removals was that this board belongs to Bob:

Bobs.jpg

As found under the CPU socket.

[stephen_usher]

So, when it starts working, "Bob's your uncle"?

(Or, if you're a Blackadder fan, "Bob's your aunty".)