Wrecked Master Compact ADD04 base unit

[jms2]

I have a working Master Compact, but the base unit as I received it is in a heavily compromised condition (wrecked is overstating it, but there's not much left!) Specifically the following parts are missing:

- The front fascia
- The floppy drive and whatever support structure was present originally (there's just a void now)
- One of the feet

When I got it, my plan was to restore these missing bits as and when the opportunity arose. Needless to say, it never has! The key item is the fascia really, because obviously the drive(s) could be replaced quite easily.

So does anyone have a use for this fairly useless object (in which case I'd be happy to send it to you for the - substantial - cost of postage), or alternatively some suggestions as to how where I could source the missing bits.

[tricky]

I would be interested, but in all honesty, I would probably only get around to using the PSU unless a fascia came along, then I would take it to shows.

[jms2]

I had better test it out - I am pretty sure it does work because I used it when I first got the machine, but whenever I use the Compact I just use an ordinary 5V power supply.

[1024MAK]

John, is this an item for sale?

Or are you after the missing bits?

Mark

[jms2]

I'm actually not sure Mark!

If someone has a fascia panel that they'd be prepared to sell, then I'd possibly buy it and restore the base unit to something close to its proper appearance.
Alternatively (and I think this is more plausible) , if someone else has a workable plan for it (such as using the psu, or maybe making the whole thing functional but without a fascia) then they can have it for nothing.

What I am trying to move on from is the current situation of "big lump of metal doing nothing and with no plan for getting fixed"!

Incidentally, in a similar category I have a non functional Spectrum and PSU which I am definitely seeking to give away. The Spectrum has a broken lower case and I think the ULA is also dead... but I'm not certain.

[1024MAK]

Which issue board does the Spectrum have? I may be interested in it.

I have a base unit for a Compact that is incomplete myself. I forgot it’s actual condition. I’ll have to go and find it if you are interested in it.

Mark

[jms2]

Its an issue 3b.

[rharper]

I have a Master Compact with a free standing floppy, no base unit, so I could make use of this base unit if no one else needs it.
Ray

[tricky]

That sounds more legitamate than my use.

[jms2]

That sounds more legitamate than my use.

I’m not looking forward to being the judge of “who has the most legitimate use!”

Seriously though I need to test it and put up some pictures so people know what they’re dealing with. This is going to be delayed a bit because I’ve had to rush off on a bit of a family crisis

[jms2]

I dug the base unit out of the attic today with a view to testing it and making a proper list of what's there and what's missing. It's condition was pretty much as I reported previously, and (as I thought) the PSU works. However (and this isn't in any way a negative reflection of anyone on here) I have decided that I'm going to hang onto it after all.

The reason is, I have realised that all but one of the missing bits are actually pretty easy to source. The main exception, of course, is the front fascia - which I previously assumed was impossible. However two things have changed my mind about this:

1) I have realised that the rear fascia is actually very similar in all its key dimensions to the front fascia. So by measuring that, I can recreate the front fascia as a 3d model quite easily (* in theory).

2) My daughter has become super-keen on designing things in 3d and is being encouraged to get into 3d printing at school.

So I have decided that I've got a fair chance of restoring this machine to (Gotek-based) working order and with a reasonable cosmetic appearance. I might be looking for some guidance when it comes to 3d printing from those people who've tried it though!

[steve3000]

Might be worth checking with CJE. A couple of years back I saw they had a Master Compact second drive upgrade kit listed in stock which included a drive and the modified 2nd drive facia...

[jms2]

Might be worth checking with CJE. A couple of years back I saw they had a Master Compact second drive upgrade kit listed in stock which included a drive and the modified 2nd drive facia...

That's a good idea! I did check their online price list actually, and its not on there any more. But it could be worth an email.

[jms2]

I decided recently that with all the stress and upheaval of the Coronavirus pandemic, it's nice to have something reassuringly Beeb-like to read on Stardot as a form of escapism. So I decided to contribute a story of my own, which is all about my ongoing attempts to restore the drive unit from my Compact. As I explained above, most of the steps are easy enough, with one very hard final step involving 3D printing (or, just possibly, CJE coming to the rescue!). As far as I can see, very little has been written about the details of these machines so I thought it might be useful for other people to see how they come apart (and possibly how they fit back together again).

One thing that I didn't account for is computer fatigue - if you're working at home in front of a laptop all day, you don't really fancy typing things up of an evening. This has meant that my actual progress is somewhat ahead of my typing on here, but is beneficial in one way - it means my posts should hopefully lack some of the sense of jeopardy that they often have!

So... the base unit. Here is a general view from the front:

It's very obvious that the front fascia and both drives are missing. What's not so obvious is the missing foot, which gives the whole thing a drunken lean. In addition, the paintwork on the top is blistering and rusted, and (I later discovered) the top panel is actually fitted the wrong way round - the grille is supposed to be at the back, over the PSU.

Here's the back:

No major problems round here, and crucially the rear trim is present. I discovered (by looking at photos) that the rear trim is essentially identical to the front trim except the front has no grilles and instead a recess for the drive bays. It also has a full-width "apron" underneath. However, it is possible to get all the key measurements from the rear piece in order to model the front piece in 3D.

One other point of interest is that Compacts often seem to have this rear trim missing - I have found two pictures online of otherwise perfect machines which are minus this item.

[jms2]

One of the most helpful documents I have found is the Service Manual, which is available online at Chris' Acorns and elsewhere. This contains, among other things, advice on how to get the base unit apart. I was worried that I would almost certainly destroy the remaining plastic by attempting this, but actually it is pretty easy - the clips on the top are really small and don't go in very far, so all you need to do is pull outwards on the top whilst at the same time lifting slightly. The trim then kind of hinges down on its lower clips and then they come away from the sides.

You only need to remove one "end" (ie, front or back) piece of trim in order to slide the lower part out of the upper part, after removing four screws. Inside, there's this:

So... practically nothing, then. All those things at the back are for PSU sockets, a switch, and a fuse. There are holes for mounting the drives, and that's about it. But on mine there were also quite a few rust spots, like this:

It was pretty evident that this machine had been left out in the rain for a while, or at least somewhere pretty damp. Under the PSU there was an even worse area:

Immediately underneath the PSU is a thin transparent plastic sheet, which is to prevent anything live touching the base. The water appeared to have crept underneath this, leaving a large area of corrosion:

I was able to remove all the corrosion using vinegar and a toothbrush, plus a bit of gentle abrasion from a scouring pad. At the end of the process, it looked a lot better, like this in fact:

I was pretty happy with that - it's not perfect, but the residual damage can be regarded as "patina"!

[jms2]

The next thing I wanted to sort out was the missing foot. The original feet are rubber, 18mm diameter and 18mm tall. They are secured to the base with a screw and washer.

Although loads of rubber feet are available on Ebay, I struggled to find 18mm ones of the right shape. However, I did manage to find some black plastic ones which match and seem to work well. The wobbly case was really annoying, so its good to have sorted it.

The next things was the capacitors. They had not exploded, but all those cracks suggest its only a matter of time...

I had a capacitor kit for a BBC B PSU, and I planned to use the Rifa capacitor out of that, but the Compact uses a physically larger capacitor, albeit of the same rating. This one has a lead spacing of 20.3mm. It's easy enough to get a replacement, although the "Rifa" brand has now changed to "Kemet" and the designations have changed a bit. This is the new one alongside the old one:

...and installed in the PSU:

I also changed this other electrolytic capacitor, based on a previous post on here by Col:

[jms2]

Next, the painted metal case top. The existing paint finish didn't look too bad from a distance, but closer up it's a different story. There are some bits that have flaked off, plus some nasty blistering. Basically manky.

I decided that the only way to fix this was to sand all of it off and respray it, using 2K cellulose paint in RAL1015 Satin, as recommended on here by Remklep. Sanding it off was fairly easy, but I was intrigued to see that there appeared to be a fine layer of rust over the entire surface, not just the blistered parts. The paint seemed to be really well adhered to it, so I reckon the case was rusty all over when it was originally made. You can see the rust under the paint in this picture:

This is the final result, after a coat of grey primer and a couple of coats of the satin beige. Actually, I need to give it another coat actually because the paint takes several days to go really hard, and like an idiot I rested the keyboard/CPU unit on it for a while and the rubber feet managed to mark the paint. Doh! Still, it's a massive improvement:

[jms2]

Next - the drives. The base unit of the Compact is not strictly necessary, and has been viewed (including by me) as pretty useless. However, the availability of Gotek drives changes things a bit, because they need to be powered and the Compact's PSU can of course do that neatly. In fact just one 13A plug can power two drives, the main unit and the monitor - so it's potentially quite a tidy solution.

My plan is to fit a Gotek and a real 3.5" floppy, to allow easy transfers. However the Gotek that I bought is currently stuck at my office, quarantined due to the Coronavirus!

The Service Manual shows how to mount the drives. It's a lot easier than I first thought, with no bracketry involved, only some 35mm hex pillars and M3 screws:

The drives stick out a bit at the front, but this is of course shrouded by the front fascia. The original drive is a Sony F63W, which has quite a distinctive fascia, but these seem to be unobtainable. Instead I have used the common Sony MPF920. These are only 25mm high, whereas the original drive is taller (32mm). I'll have to take account of this in the design of the new fascia.

The Compact drive cable is... odd. For some reason, Acorn decided that they did not need to use the full-width 34-way ribbon cable, but instead a 25-way ribbon cable with a DB25 connector. This maintains the main disadvantage of a ribbon cable (ie being a bit cumbersome), but adds the further disadvantage of being non-standard! MDFS.net explains how the DB25 connector is attached; basically lines 1-7 and 33-34 are simply not present. However a further oddity is that line 3 is locally connected to line 4 next to the drive, like this:

I'm not sure why this is necessary. It ties the "Drive in use" signal to ground, but I don't really know whether this is necessary (or what it means).

This is how the cable looks when connected up to the drive. The key is on the top, and pin 1 to the left. I made a mistake here: the back of the drive has key slots at both top and bottom, meaning that to all intents and purposes it isn't keyed at all. I only noticed the slot at the bottom, so I installed the cable upside down. It was easy to simply turn it the other way up though.

I have made up a dual drive cable which is essentially the same as the single cable, but with two connectors. As yet, I have only tested it with the one drive, so I'm not sure if it is correct. We'll see.

[1024MAK]

However a further oddity is that line 3 is locally connected to line 4 next to the drive

I'm not sure why this is necessary. It ties the "Drive in use" signal to ground, but I don't really know whether this is necessary (or what it means).

Some drives have an input which turns on the “in use” LED. Most drives either don’t support this, or don’t need this pin to be driven. Some have a link/jumper shunt to select if this input is used or ignored.

To find out for certain what effect (if any) connection of this pin has, you need to find the floppy drive manufacturers drive specifications...

I have made up a dual drive cable which is essentially the same as the single cable, but with two connectors. As yet, I have only tested it with the one drive, so I'm not sure if it is correct. We'll see.

The Shugart like interface used by Acorn has the second floppy drive connected in parallel with the first (straight through cable). However that does require each drive / device to have a selection link/jumper shunt or equivalent to enable the drive / device identity to be selected. When the computer wants to access any drive, all the drives power up their motors (some only if they have a disk inserted). More modern floppy disk drives made for use in a IBM compatible PC have all drives set to one device number (one if you count from zero to three, two if you count from one to four). Then a twist in the cable swaps two signals (motor on and device/drive select) so that the two drives respond to different device/drive select signals. And each drives motor is individually controlled.

Mark

[jms2]

To find out for certain what effect (if any) connection of this pin has, you need to find the floppy drive manufacturers drive specifications...

Whilst I couldn't find the F63 datasheet, I was able to find the equivalent for the F53, which looks physically the same. It says that the drive does require the "in use" pin to be held low in order for the LED to light:

inuse.JPG (7.59 KiB) Viewed 1930 times

I doubt this is necessary for the modern drives that I'm using.

The Shugart like interface used by Acorn has the second floppy drive connected in parallel with the first (straight through cable). However that does require each drive / device or have a selection link/jumper shunt or equivalent to enable the drive / device identity to be selected. ... . More modern floppy disk drives made for use in a IBM compatible PC have all drives set to one device number (one if you count from zero to three, two if you count from one to four). Then a twist in the cable swaps two signals (motor on and device/drive select) so that the two drives respond to different device/drive select signals.

Thanks Mark, that's what I thought. I've gone with the Acorn-style "flat cable and jumpers" method. The Sony drive is pre-set to DS1 and can't easily be adjusted, but that's OK because I want it to be Drive 1 anyway.

[jms2]

I found the floppy datasheet on Bitsavers, along with a couple of other useful documents - the product brochure for the range of floppy drives used on the Compact (which shows the F63 is just a faster version of the F53), and also a Chinon datasheet for the double-sided version of the drive used in the Electron Plus 3. So it does exist! (The drive that is, I think all Plus 3s were single sided only).

Sony_Micro_Floppy_Drive_Brochure.pdf

(3.75 MiB) Downloaded 25 times

Chinon_F-354C_135TPI_Double-Sided_3.5_In_Specifications.pdf

(917.86 KiB) Downloaded 25 times

[jms2]

The next step is to get a front fascia 3D printed. My daughter kindly modelled it in Sketchup - I didn't really know how to get started, but now that she's done all the hard work I find I am competent to take measurements off it and make minor tweaks. This is what the final model looks like:

I have sent this off to made in Nylon (PA12) using the Multi Jet Fusion (MJF) process. I'm hoping it turns out OK!

In the meantime, is there anyone with a Compact who could take a high resolution photo of the logo on the front? My keyboard has the logo, but it is drastically faded. Also - photos of the base unit suggest that the finish of the dark bit on the front is glossy and possibly black (as opposed to brown). Does anyone know what colour/finish it really is?

[1024MAK]

A quick snap. Is this what you are after?

Master Compact drive unit logo

If you want a higher resolution photograph taken during daylight, I’ll try to do that tomorrow.

Mark

[jms2]

That's perfect Mark, thanks! I guess the higher the resolution the better, so if you can improve on it, that would be great. But if you can't manage it, I'm sure I could work with that image.

Is the background the same gloss level as the bit around the keyboard, or shinier? It seems very glossy on some photos, but that might be an illusion.

[1024MAK]

It’s not the same as the keyboard. I would not describe it as a full gloss finish.

I’ll take a better photograph tomorrow, and I will attempt to describe the finish in more detail when I am sat in front of it.

Mark

[1024MAK]

Poor light today due to heavy rain

I'll try again tomorrow.

Mark

[jms2]

It was lovely up here! I think we must be getting the rain tomorrow.

[CMcDougall]

rain?? What is that...

Glad you liked my post about sorting caps out a few year ago!

Nice job on its spray job

Here is mine, off crap mobby camera:
So keyboard surround is more of a Matt black (even brown'ish) & PSU unit is shinny gloss on metal strip & smooth like a mirror, left little bit is different not on metal, bit like normal beeb keyboard surround colour

[jms2]

It's metal? I didn't realise that!

My solution will still be a vinyl sticker, but it's useful to know that painted metal is what I need to emulate.

[1024MAK]

Okay, high resolution photos attached.

I would describe the metal front of my PSU/Drive unit as satin black. It's a very thin metal strip (it bends). Colin's is different to mine. The piece to the left of the drive is the same as the piece with the logo on it.

The keyboard surround I would describe as very dark brown. In the areas where it's not worn, it's textured.

Mark