Olivetti Prodest 128s

[1ST1]

Hello, I got a Olivetti Prodest 128s computer. This is (mostly?) the same as the BBC Master Compact. I am not familar with that computer but I want to try it and learn a bit about it. I haven*t powered up it yet as I have bad experience with that without first checking some things. So this is my frist question, do I need to check something on that machine first, like power supply capacitors?

And I need manual for the Olivetti version, ( found the Acorn manuals on Archive.org) - are there any differences the Acorn original machine and the Olivetti, I don't have interface pinouts yet so I also don't know how easy it will be to connect it to one of my PAL monitors. I have Commodore 1084, 1084S and a Philipps which I can use for my Commodore 64, Amiga, Atari ST and the Olivetti Prodest-PC1 and others.

[1024MAK]

As I understand it, the hardware is the same as the Acorn Master Compact. The differences are the case, keyboard and the ROM.

It has the same TTL level RGB outputs on a DIN socket. Hence a BBC to SCART lead (which are available from a number of sellers on eBay) will work.

Any monitor that supports TV frequency video RGB inputs will also work. But you may need to include in line resistors if the inputs on the monitor are expecting normal analogue video level signals.

Yes, in the box that has the PSU and the floppy drive, it is wise to see if the PSU has Rifa X2 capacitors. If yes, it's strongly recommended that these are replaced. Rifa capacitors are well known for self destructing and in the process making a nasty mess complete with very smelly smoke...

There is at least one member on here who also has an Olivetti Prodest 128s.

Mark

[1ST1]

Ok, so the video output is TTL-RGB, similar to CGA and Commodore 128 2nd video out. My Philips monitor has analog/TTL switchable input, and my NEC Multisync CRT as well. Do you have the pinout of the video connector?

[Pernod]

Ok, so the video output is TTL-RGB, similar to CGA and Commodore 128 2nd video out. My Philips monitor has analog/TTL switchable input, and my NEC Multisync CRT as well. Do you have the pinout of the video connector?

See https://chrisacorns.computinghistory.or ... AN/238.pdf for RGB port pinout.

[egel]

Yes, I have two and a Master Compact.
The only difference I found on the motherboard is that the SAA5050 (Mode 7) chip is a smaller chip on a daughter board, but no difference in use.

[Pernod]

The only difference I found on the motherboard is that the SAA5050 (Mode 7) chip is a smaller chip on a daughter board, but no difference in use.

That's different, haven't seen that smaller version before and don't think it's common for Compacts.

[1ST1]

Ok, so the video output is TTL-RGB, similar to CGA and Commodore 128 2nd video out. My Philips monitor has analog/TTL switchable input, and my NEC Multisync CRT as well. Do you have the pinout of the video connector?

See https://chrisacorns.computinghistory.or ... AN/238.pdf for RGB port pinout.

Thanks, so it's this one...?

monitor.jpg (9.98 KiB) Viewed 233 times

So thats RGB-TTL with Composite-Sync... I am quite scared... No CGA compatible monitor has composite sync.

[1ST1]

Ok, I did some research, found the schematics, the machine has a 6845 video controller.

That one has separate H- and V-Sync signal on pin 39 and 40.

It's even used somewhere in the video logic. So I can grab these signals and create my own CGA compatible output connector on a DSUB9. To be on the safe side I do some buffering of the H- and V-Sync.

That machine is really a strange design, it has desktop chassis, but the computer is in the keyboard, funny routing of the floppy cable through the bottom of the chassis, it has raw pins of a user port at the right side (which could be short-cutted by anything metal laying on the desk), it has CGA-composite-sync, let's find out the next strange things...

[DaveLecky]

Hi there,

I reciently got a Master Compact without a base unit, Here are some links I found useful,

https://www.nightfallcrew.com/25/09/201 ... ?nggpage=3

https://beebwiki.mdfs.net/Paged_ROM#Master_Compact

http://www.8bs.com/incompmapped.htm

Hope this helps a little….

Dave

[1024MAK]

Some monitors that have separate H and V sync inputs will work if you feed a composite sync signal to one or both sync inputs.

Mark

[egel]

The only difference I found on the motherboard is that the SAA5050 (Mode 7) chip is a smaller chip on a daughter board, but no difference in use.

That's different, haven't seen that smaller version before and don't think it's common for Compacts.

A little search through my house and the internet seems to hint that low serial numbers have the normal SAA5050 and high serial numbers have the small SAA5050T. And that half or more have the small SAA5050T.
https://www.stardot.org.uk/forums/viewt ... 70#p423270

[paulb]

That machine is really a strange design, it has desktop chassis, but the computer is in the keyboard, funny routing of the floppy cable through the bottom of the chassis, it has raw pins of a user port at the right side (which could be short-cutted by anything metal laying on the desk), it has CGA-composite-sync, let's find out the next strange things...

Well, the casing came from another machine, the Acorn Communicator, which was designed as a smart network terminal of sorts. Although the thinking behind the design of the Compact isn't really known (to my knowledge, at least), it seems like Acorn were aiming to do a reduced size version of the Master 128, somewhat in the spirit of the Electron, but retaining as much core compatibility as possible. (It was known as the Baby B, apparently.)

At some point, someone must have realised that it was a bit late in the day to be making a machine that would be loading software from tape (as the base Master 128 did), or maybe they decided straight away to omit the tape interface, but that then necessitated the provision of a separate unit to hold the disk drives. That unit used the casing from the Filestore, which was a network storage appliance, complementing the Communicator but also available more generally for networking Acorn machines.

Indeed, you might be justified in thinking that the Compact was Acorn's way of repurposing manufactured items that were unlikely to be used for their original purpose, although they probably also needed to release a machine that appealed to a broader audience, too. One can dispute whether it was really a success in that regard, however.

[baz4096]

That's different, haven't seen that smaller version before and don't think it's common for Compacts.

I had one go faulty on an Issue 2 Master 128. They're a pain to desolder intact, the carrier board is very delicate.