GCC SAM Coupé upgrade project

[HEXdidnt]

One of my friends from the Greenford Computer Club recently acquired a SAM Coupé and, having tested it at last night's meet, will be embarking on an upgrade project.

The machine came with no floppy drives, just the stock 256K RAM, a keyboard missing its metal backplate and... ROM 1.0 - AKA the one that really didn't work. We tested it out with my keyboard and floppy drive, but didn't get very far as I foolishly neglected to bring any SAMDOS disks, only BDOS, as I've got plans for my old ATOM interface, and was hoping to demonstrate it on the newly-acquired SAM.

The proud new owner is looking to upgrade it with the mechanical keyboard, ROM and RAM upgrades, and the floppy interface from @Quazar, so hopefully we'll be revisiting it early in the New Year.

Photos from last night's meet should be up on Facebook by the weekend.

[PeterJ]

@HEXdidnt,

How nice to have a retro computer club near you. The photos on FB look great too!

[HEXdidnt]

@PeterJ I'm embarrassed to admit that I used to live even closer - my parents are just down the road, and I have dinner with them every time the Club meets - but only learned of its existence from an advert in the Crash 2018 Annual.

All the more frustrating, their first RetCon event had been on my birthday that year!

Still, it's a great club with no overt biases toward any particular machines, and some fascinating projects on the go. Really glad to have found it.

[HEXdidnt]

As an aside to the main SAM recovery/update project, I've taken another few steps with my old ATOM interface. It was originally supplied with a small yellow LED on the end of a couple of long wires, intended to be fed through the drive bay cover plate to show disk activity. I'd never liked it, and so never modified the bay cover to fit the LED, but one of my friends at the Club had a selection of spare LEDs from various Amigas, and let me have a rectangular green one, to match the LED in the floppy drive I currently have installed.

On its short edge, it measures much the same as the indented rim of the bay cover, so I figured I'd just cut out a small section and then basically wedge the LED between the bay cover and the main shell, with the option of using a bit of hot glue if the need arose. Of course, attaching an LED to the case would mean another link between the shell and the motherboard, so I decided to add a plug/socket at one end of the wires feeding the LED, to make it more easily removable.

At first, I attached a pair of pins to the ATOM board itself, but quickly discovered that wouldn't work: that part of the board is right under the vented strip behind the SAM's keyboard, so there's not enough vertical space. A quick bit of soldering later, the wires were reattached to the board, with the other end attached to a 2-pin socket, into which the LED can be plugged. The LED itself is affixed to the inside of the drive bay cover with hot glue for the moment.

The end result looks pretty good (unless you were to examine my pitiful soldering - I should probably invest in some reading glasses before I do any more detail work like that!).



This is mainly just a test, since I use the Trinity interface for mass storage, on an SD card... but this could be useful for future RetCons, so I don't have to worry about any external interfaces. It could also be used to keep a handy backup copy of some of my old graphics disks.

[HEXdidnt]

Had a notification the other day that the new SAM owner has put in his order to @Quazar:

• V3 ROM
• 256K RAM upgrade
• Floppy interface (planning on installing a Gotek)
• Mechanical keyboard
• Replacement PSU

It's going to be a lot of fun watching this develop, but I probably won't see any of it till the New Year, as the Club won't be meeting again till then. Pictures will no doubt appear on the Club's Facebook page, as before, but I'll try to remember to take a few photos myself, to share them here as well.

[HEXdidnt]

Small supplemental addition: the new SAM user has now also acquired a +D interface for his Spectrums. Since SAMDOS is backwardly-compatible, I might actually end up getting my Empire Strikes Back material onto a real Spectrum, as opposed to having just a MODE 1 demo on the SAM...

[HEXdidnt]

First GCC meet of 2024, and I took the opportunity to open up the new SAM and snap a few photos:


It turned out that, while his SAM originally still had ROM v1.0, we both had the v1.1 motherboard (probably not that surprising - not sure how many versions there were, to be honest!). His upgrade to ROM 3, the 256K memory upgrade, floppy disk drive interface and mechanical keyboard all arrived from @Quazar before Christmas and were already fitted ahead of the meeting. He'd also done the reflection fix, giving him a lovely clear picture, and replaced all the capacitors as a precaution. Next on his list is 3D-printing some drive bay covers, and retrobriting the case and keyboard.

Rather than use a traditional floppy drive, he has installed a Gotek, and had a selection of SAM software - including some of my BASIC SCREEN$ demos from the 1990s - though we couldn't get my Trinity interface working on his SAM. My current setup has the Trinity running alongside the ZX-Ecutor in its Trinity Boot ROM setting, connected via a SAMBUS. With these plugged in, his SAM wouldn't even switch on, presenting a black/blue chequerboard pattern... Nor would it work with the SAMBUS alone (blank screen, I think), or with the ZX-Ecutor alone (animated screen corruption!). Worked with the Trinity alone, but he didn't have BDOS on his Gotek's memory stick, so we couldn't make use of it.

One rather cool addition he made was to attach heat-sinks to some of the key chips... Nor something I'd have thought of as necessary, but we'll see how it affects the machine's longevity.

Once he's satisfied that he's done all he can to bring the machine back to life, he'll be passing it on to another member, who wants to work on a networking project. He's already got a Spectrum and a Spectrum Next communicating via Interface II, a Spectrum and a QL, and a Spectrum and an Enterprise... The SAM is the next logical step... I can't remember the specifics of his plan, but he's not intending to use the MIDI ports as he felt they were somehow compromised.

Whether this leads to, for example, a simple network game that runs between the Spectrum, Next, QL, Enterprise and SAM Coupé, only time will tell... but it's certainly an interesting thought. Cross-format Net-Chaos at a future RetCon?

While working on my own machine, I noticed that the reflection fix applied was a wire running parallel to inductor L5 rather than replacing it. Ended up taking a pair of wire clippers to the inductor to remove it entirely, and I may end up going back in and de-soldering its pins, then re-soldering the wire directly to the board.

[flatduckrecords]

He's already got a Spectrum and a Spectrum Next communicating via Interface II, a Spectrum and a QL, and a Spectrum and an Enterprise... The SAM is the next logical step... I can't remember the specifics of his plan, but he's not intending to use the MIDI ports as he felt they were somehow compromised.

This sounds very cool! I think the MIDI/Network ports are fixed at MIDI speed (31250 baud) so it's not particularly fast and I've had some trouble getting non-MIDI devices to communicate reliably at that speed.

Instead I've been thinking about getting one of @Quazar's RC2014 bus interface cards and using an RC2014 SIO/2 serial module to give SAM two proper serial ports. (I still like the idea of getting some use out of the onboard ports though!)


Quazar's four-way RC2014 bus interface for SAM


An RC2014 SIO/2 serial module

While working on my own machine, I noticed that the reflection fix applied was a wire running parallel to inductor L5 rather than replacing it. Ended up taking a pair of wire clippers to the inductor to remove it entirely, and I may end up going back in and de-soldering its pins, then re-soldering the wire directly to the board.

Yeah, My SAM had terrible ghosting but replacing L5 with a wire link made a huge difference. Did you notice any further improvement after removing the inductor?

[HEXdidnt]

...been thinking about getting one of @Quazar's RC2014 bus interface cards and using an RC2014 SIO/2 serial module to give SAM two proper serial ports. (I still like the idea of getting some use out of the onboard ports though!)

Thanks for that - I'll pass the suggestion on to our resident networking enthusiast!

Yeah, My SAM had terrible ghosting but replacing L5 with a wire link made a huge difference. Did you notice any further improvement after removing the inductor?

Not so far, to be honest, but the screen I was using last night wasn't great... I'll give it a try at home over the weekend, though - haven't unpacked my bag yet today.

[flatduckrecords]

Rather than use a traditional floppy drive, he has installed a Gotek, and had a selection of SAM software - including some of my BASIC SCREEN$ demos from the 1990s - though we couldn't get my Trinity interface working on his SAM. My current setup has the Trinity running alongside the ZX-Ecutor in its Trinity Boot ROM setting, connected via a SAMBUS. With these plugged in, his SAM wouldn't even switch on, presenting a black/blue chequerboard pattern... Nor would it work with the SAMBUS alone (blank screen, I think), or with the ZX-Ecutor alone (animated screen corruption!). Worked with the Trinity alone, but he didn't have BDOS on his Gotek's memory stick, so we couldn't make use of it.

Strangely enough I had the same symptoms this weekend. I normally have my SAM set up in the same configuration, (Trinity, SAMBus and ZX-Ecutor) but it started to behave as you described. The addons would work independently, so I suspected a bad connection with the SAMBus. I gave it a good blast with some contact cleaner and that seems to have restored it.


Note: it's WD-40 branded but not actually "WD-40"!

It's non-conductive but do switch off and let it dry out before applying power again.

The SAMBus itself was in a sorry state when I got it—the internal battery had leaked a fair bit; so that's something to look out for as well.

[HEXdidnt]

I gave it a good blast with some contact cleaner and that seems to have restored it.

That's a very good call - hadn't thought of that... which is strange, considering how often someone at the GCC recommends spraying something with contact cleaner. I'll have to invest in some, I think.

The SAMBus itself was in a sorry state when I got it—the internal battery had leaked a fair bit; so that's something to look out for as well.

Oh, same... Those Varta cells have a terrible reputation. One of the first bits of advice I got at the Club was to check all my old kit for any Varta-branded batteries, and get rid of them ASAP, regardless of what state they appeared to be in.

One of these days, I should probably stick a new battery on... though it's only for the clock, which I don't tend to make use of.

[flatduckrecords]

That's a very good call - hadn't thought of that... which is strange, considering how often someone at the GCC recommends spraying something with contact cleaner. I'll have to invest in some, I think.

Hahah, I can imagine. Yeah it's a bit expensive, but worth it if you own older equipment I reckon. In fact I've promised to take my can with me next time I'm in the office as I've a couple of colleages with jittery rotatary-encoders on their kitchen equipment that could do with a skoosh, but they didn't want to shell out for a whole can of the stuff!

One of these days, I should probably stick a new battery on... though it's only for the clock, which I don't tend to make use of.

It's one of the reasons I got an original one! It's supported by Trinity but I started playing with Master DOS and Master BASIC and I quite like having the correct timestamps there too. And it keeps not-too-bad time either! But if you're not worried about all that @Quazar makes a nice modern alternative (although I'm sure you knew that anyway!):


Available as 2-way or 3-way

[HEXdidnt]

But if you're not worried about all that @Quazar makes a nice modern alternative (although I'm sure you knew that anyway!):

Yeah, if the contact cleaner doesn't work and the SAMBus continues to cause problems I may well pick up one of those... Be a bit of a shame, though, as @Quazar made me up a 3.5mm jack to USB adapter, so I can put 5v into it from pretty much any spare phone charger plug I have laying around, rather than having to get a specific 5v PSU, since I'd had some odd performance issues with some other peripherals plugged in.

[HEXdidnt]

Some cool news from last night's meet: there's another new SAM at the Greenford Computer Club.

There was a posting recently in the SAM Users' Facebook group from Pamela Martin, regarding her late son's machine. After chatting with our Club principle, Steve Bennet, she decided to donate it to the Club, with a view to getting it fixed up and ensuring it gets used rather than sold on for profit. Steve brought it along to last night's meet, and we got it up and running without too much trouble.

The Good News:

• ROM 3.0 (though not the sort of chip I'd expected - see photo below)
• 512K RAM
• 1x Original Citizen slimline floppy drive + manual (drive needs a new belt though!)
• Original power supply in good working order (though the buzzing started to give me a headache, just like my own!)
• Additional keyboard membrane (the original MGT one has broken traces, but could be recoverable)
• Reflection fix already applied
• Original box and foam inserts
• Mouse (Atari/Amiga switchable, analogue), mouse interface and Parallel Printer interface (Format Publishing 'branded' with dot-matrix printed labels)
• Other bits included: SAMDOS disk (copy), MasterDOS disk (copy), Issue 3 Technical Manual, Flash! manual, SAMPaint manual, ProDOS box and manual, The Secretary disk (copy), Prince of Persia (original)

The Bad News:

• Absolutely no screws in the case, both the keyboard and the floppy drive were loose
• Drive belt had turned into putty (as expected!)
• Quazar SCART lead note, but no lead (and I'd forgotten to bring mine!)
• Users' Guide is the 30th Anniversary reprint (hardback) with loads of OCR errors
• 2nd drive bay cover missing
• Software with no manuals and manuals with no software

It has black feet rather than blue, the keycaps are all cool grey rather than the warm grey of mine, its serial number starts 0708 and it displays "SAM Computers Limited" at startup. I'm assuming it was one of the machines scooped up and sold by Format Publishing after SAMCo's demise and, aside from some yellowing of the shell and the previous owner's name and address scratched onto the bottom, it's in great condition. So that's three SAM Coupés within the Club now.

I installed the replacement keyboard membrane, but figured we might as well keep the original, as we hopefully just need to trim off the tips of the leads where the traces are broken.

On the whole, it's in a far better state than we had any right to expect, so we shouldn't have too much trouble getting it ready to appear at RetCon in June. A replacement drive bay cover is already on its way, and Steve is planning to recap the floppy drive and replace the belt... but he's also considering fitting a Gotek at some point in the future.

[HEXdidnt]

The Plot Thickens!

I had to miss the Club meet on 28/3 due to illness, but I'd loaned my SCART cable to Steve at the previous meet, so he could wire up his own cable to match. He reported that, having done so, he got no picture on any TV he tried, using his own cable, or mine. At this point, my instinct was that there had to be something wrong with the SCART socket on the SAM - dry solder joints, dodgy pins, etc. - and it turned out I wasn't too wide of the mark. We started investigating at yesterday's meet and, just to be sure, I tried his cable on my SAM. It worked perfectly.

The true source of the problem is actually visible in the motherboard photo I posted on 1st March, but here's a close-up:


Pins 2, 6, 8, 16, 18 and 20 have been cut. Most aren't important, but 16 is CSYNC... which probably explains why there's no picture. He's now ordered a replacement SCART socket, so hopefully that'll be installed by (or at) the next meet.

He's got the parts needed to refurb the floppy drive, but hasn't yet had a chance to tackle that. However, to make life all the more fun, he's been sent an Atom interface and a 4Gb CF Card.


Had to transfer my floppy drive over to test it, but he already had a BDOS disk, same version I have for the Atom - 1.5a. There were a few bits already installed on the CF card, but we couldn't get some of it working - the BDOS record and one with some games on returned an 'invalid record' error, but the other two/three were OK. I figured we might as well reformat and start again, and I'd brought a few disks that I could copy over to give him something to use once he's sorted his floppy drive. Here's where things got 'interesting'... Because literally nothing I copied over would work. It either failed to load (blank, black screen) or reset the SAM.

I'd brought my own Atom along, just in case, and stuck my 256Mb CF card into his interface... and that worked perfectly. Pretty certain everything on my card got there by copying over from floppy disks, all of which had been created by copying from records on my Trinity's SD card...

Tried my Atom in Steve's machine... and it didn't even pick up the CF card. Couldn't figure out what was going wrong until I took a closer look at the interface itself this morning, and found this:


So now I either need to get a new Atom (Steve's is far more compact and tidy, to be fair!) or solder on a jump wire to replace the blown trace. I've borrowed the 4GB card but, obviously, I need to sort out the interface before I can do anything with it.

Other interesting things... I mentioned previously the black feet, cool grey keycaps and nonstandard ROM... Apparently this is something 'new', particularly with its SAM Computers Limited startup screen:


Anyone have any ideas?

[HEXdidnt]

Haven't yet fixed my old Atom interface, but I was at least able to use SAMDisk to transfer a few extra bits and bobs to Steve's 4Gb CF card ahead of this week's meet... But not a single thing worked.

RECORD correctly listed all the disks I'd transferred over.
RECORD [number] didn't encounter any 'Invalid' records.
BOOTing any of them led to either a blank screen (most), a corrupted loading screen and then nothing (Bubble Ghost), the appearance of loading but a blank screen on starting the game (Pang) or a corrupted title screen and the machine locking up (Battlezone).

One of the other members kindly donated another 4Gb CF card to try out, and here's where it gets interesting. The CF card that came along with the Atom (Transcend '133x') reported something in excess of 4,800 records when formatted. The new one (SanDisk Extreme III) reported 5,018 records when formatted. I know some CF cards can be a bit fussy, and not all machines get on with them, but I've never encountered a situation where the capacity is so wildly different between two cards that are ostensibly the same size... 200 records worth of difference seems crazy.


I'd neglected to bring much by way of software this time, as I packed in a bit of a hurry, so wasn't able to test anything but the software on the disks that came with the SAM, but the few things I tried copied over perfectly (one floppy disk error, but that's to be expected), loaded and ran without any problem. I brought the new CF card home with me to try adding all the other software to it... Hopefully that'll be a bit more successful.


In other news, Steve had fitted a replacement SCART socket, which was working nicely with his cables. Apparently removing the old one was pretty difficult, as it's a very tight fit. Likewise, installing the new one was tricky because the pins and tabs didn't seem to line up precisely with the SAM's motherboard and, having pushed it in, Steve felt like he wouldn't be able to get it out again without damaging the board.

He also gave the motherboard a deep clean - the righthand side seemed to have been literally bathed in flux - and is planning to recap the motherboard, but hasn't yet sorted out the SAMDrive, so we had to use my floppy drive again this week. It's coming along nicely, though.

One cool little extra - which he gave me the honour of unwrapping - was 'The Art of Selling SAM', the marketing booklet put together for vendors. To call it an optimistic interpretation of the state of play around the time SAM was released would be... er... generous, to say the least. It makes several claims - particularly around the machine's software support - that just weren't true, but it's a neat insight into the hopes MGT had for their last creation.