exxos's Atari, Amiga & retro forum

rubber_jonnie wrote: 25 Apr 2021 21:58 Do you know of a good source for datasheets that show all pin connections on the chips?

For off-the-shelf stuff that's still available, it's often easiest just to search for the components in question on Mouser or Farnell and download the datasheets from them. Otherwise I generally just use google, which often seems to land me on alldatasheet.com.

derkom wrote: 26 Apr 2021 05:11

rubber_jonnie wrote: 25 Apr 2021 21:58 Do you know of a good source for datasheets that show all pin connections on the chips?

For off-the-shelf stuff that's still available, it's often easiest just to search for the components in question on Mouser or Farnell and download the datasheets from them. Otherwise I generally just use google, which often seems to land me on alldatasheet.com.

That's where I usually get my datasheets from too, I was just hoping the Beeb schematic would show the power & gnd pins like the ST schematics do, and they do for some, but not for all. The Beeb has a lot of chips and didn't want to look them all up if the schematic showed them.

I have now found a troubleshooting book that describes my problem exactly, and goes into more detail, so I will follow that. It's also possible one of the chips is dead as it is supposed to have a heatsink and it's missing. Video chip I think.

I don't think that should stop it booting though.

The chip with(out) the heatsink is the ULA. The original Ferrari ones ran hot and die if the heatsink is missing.

stephen_usher wrote: 26 Apr 2021 09:28 The chip with(out) the heatsink is the ULA. The original Ferrari ones ran hot and die if the heatsink is missing.

Even with the heatsink, mine ran very hot & all the blacks would start to turn into a noisy red pattern...with the newer video ULA it ran fine for hours with no obvious issues

rubber_jonnie wrote: 26 Apr 2021 09:22 I have now found a troubleshooting book that describes my problem exactly, and goes into more detail, so I will follow that. It's also possible one of the chips is dead as it is supposed to have a heatsink and it's missing. Video chip I think.

I don't think that should stop it booting though.

The ULA generates all the clocks for the model B. If it is dead you will get nothing.

cmorley wrote: 26 Apr 2021 09:35

rubber_jonnie wrote: 26 Apr 2021 09:22 I have now found a troubleshooting book that describes my problem exactly, and goes into more detail, so I will follow that. It's also possible one of the chips is dead as it is supposed to have a heatsink and it's missing. Video chip I think.

I don't think that should stop it booting though.

The ULA generates all the clocks for the model B. If it is dead you will get nothing.

This is the frustration, I want to check the clocks, but my oscilloscope is in storage :(

Looking at the ULA, it doesn't appear to have ever had a heatsink on it. No glue residue, nothing. Plus it had a green QC sticker on it, though that's since fallen off!! The one that I'm referring to is IC6, which according to the schematic is the video processor, and that shows no signs of a heatsink ever being attached to it.

It's an issue 4, and of the photos I can find, some have a heatsink on IC6, some don't. None of the issue 7 board photos I can find show a heatsink on IC6, so it is feasible that IC6 was replaced with a later version that doesn't need a heatsink. If I'm honest, it looks newer than the rest, and no signs of any gunge that would have held a heatsink on.

I think I'll have to pull the ULA, clean the pins up and check for power too, and I'll follow the troubleshooting guide which suggests my symptoms point at a problem with IC36.

The original Ferranti ones need a heatsink. The later VIA ULAs do not.

cmorley wrote: 26 Apr 2021 10:13 The original Ferranti ones need a heatsink. The later VIA ULAs do not.

ULA is Ferranti, so wondering why no evidence of a heatsink..... If that is dead then all bets are off for now. Really wish I had my other Beeb here.

IC6, the video processor is a VIA.

I really ought to do some work I suppose!! But this is more interesting!

The serial/cassette ULA (SERPROC IC7) never had heatsink & never needed one. Only the Ferranti made main ULA (VIDPROC IC6).

cmorley wrote: 26 Apr 2021 11:15 The serial/cassette ULA (SERPROC IC7) never had heatsink & never needed one. Only the Ferranti made main ULA (VIDPROC IC6).

Ahh, right, I think I was misunderstanding on account of being used to Sinclair machines with a single ULA.

So two ULAs then, and my VIDPROC IC6 is a VIA ULA so that's a good start, I'm getting to know the geography of the board a bit better.

Are there any other ULAs I should know about?

:dizzy: