cpc472 schematic?

nocash · 21:25, 31 March 10

Hi, does somebody have a cpc472 schematic? Most sources say that the extra 8K RAM is not connected. But after seeing this article, http://www.cpctech.org.uk/docs/cpc472.html, it seems as if it is connected in same way.

Here's a description of the two keyboard versions, http://perso.wanadoo.es/amstradcpc/cpc/cpc472.html

Here are some photos of the top/bottom side of the daughterboard, http://www.zonadepruebas.com/modules/smartsection/item.php?itemid=591

As the author of the schematic/drawing stated, "it is not easy to see the source/destination of some connections", so the drawing is probably full of mistakes. Anyways, no matter if they are wrong, there seem to be connections.

Does somebody have a cpc472? It's difficult to see the conections under the white paint, but with a multimeter it'd be super-easy to test which pins are connected with each other.

---

Some ideas about if/how it could work: To me, the schematic looks a bit too complicated to be a totally useless fake. On the other hand, there seem to be no RAS/CAS signals for accessing the DRAM, so it'd be difficult to access the whole 8K, but at least a few bits might be accessible.

Gryzor · 08:40, 01 April 10

Very interesting... thanks for bringing it up.

For all we know, maybe it was connected in a way that it did exactly nothing, so as to not be so obvious that it was a fake...?

Bryce · 09:02, 01 April 10

If they went to the bother of making a daughterboard etc, you would think that it must have been connected in some way. Maybe it just wasn't accessable due to it having standard 464 Firmware? Or was there a 472 Firmware version? The screenshot suggests otherwise.

The other question is how it would be addressed. If I recall correctly, the bank switching works with 16K banks, so the extra memory would have to be:

A) connected to the PAL somehow?
B) addressed as "half of a bank" ?

No?

Bryce.

Gryzor · 09:16, 01 April 10

Well, I guess they *had* to make a daughterboard. They couldn't just plug the extra chip into a random position on the motherboard, could they?

But this makes me wonder: how much was the tax anyhow, so that they saw it more convenient to design and add all this thing to the machine? Any Spaniards in here?

ukmarkh · 09:33, 01 April 10

It was a null connection... i.e. no connection to the main CPC motherboard.

Gryzor · 09:34, 01 April 10

Soooo that ribbon goes... to nowhere???

arnoldemu · 09:42, 01 April 10

Quote from: Bryce on 09:02, 01 April 10
If they went to the bother of making a daughterboard etc, you would think that it must have been connected in some way. Maybe it just wasn't accessable due to it having standard 464 Firmware? Or was there a 472 Firmware version? The screenshot suggests otherwise.

The other question is how it would be addressed. If I recall correctly, the bank switching works with 16K banks, so the extra memory would have to be:

A) connected to the PAL somehow?
B) addressed as "half of a bank" ?

No?

Bryce.

The cpc464 or cpc472 as far as I know don't have the PAL.

The daughter board is connected into the same location as the original 32K ROM is connected.

So it seems (unless there are additional connections under the pcb) that the the small PCB only has access to the signals the rom has.

ukmarkh · 09:43, 01 April 10

The extra 8K was just a tax dodge, the 8k was non funtional. I think the 472 came in two different versions though? Maybe I'm wrong, but the early models didn't feature the 'N' key, where later models did. Maybe the later model connected the extra memory?

Quote from: Gryzor on 09:34, 01 April 10
Soooo that ribbon goes... to nowhere???

Gryzor · 09:56, 01 April 10

Yes, of course we know all that. But the matter here is, if it was non-functional indeed, how come there are connections? That's what we're asking.

Bryce · 10:29, 01 April 10

Quote from: arnoldemu on 09:42, 01 April 10
The cpc464 or cpc472 as far as I know don't have the PAL.

Oh yeah, sorry hadn't booted my brain this morning before posting, was thinking of the 6128.

Quote
The daughter board is connected into the same location as the original 32K ROM is connected.
So it seems (unless there are additional connections under the pcb) that the the small PCB only has access to the signals the rom has.

Indeed, it would need something to switch the Chip enable / output enable when the right bank / address was chosen.
Unless it was being initialised with ROM0 access, but using different addresses?

Bryce.

nocash · 13:42, 01 April 10

>> It was a null connection... i.e. no connection to the main CPC motherboard.
> Soooo that ribbon goes... to nowhere???
That detail isn't visible on the photos, too. But I think it's safe to say that the ROM chip is connected to the motherboard :-) The question is if the RAM chip and the two logic chips are connected, too. There are wires on the daughterboard, so they seem to be connected -- or are they dead-ends, ie. do the wires end shortly before reaching the soldering points?

Mapping the RAM to address 2000h (for example) would require more complex address decoding, mapping it to a larger region like 2000h..3FFFh would be possible, but then important areas of the ROM would be unusable. So, the two logic chips are probably not capable to map the RAM to memory - though they might map it as I/O ports.

The ribbon cable has 28pins, but the ROM uses only 27pins (pin1 is NC). So the extra wire could be used as /IORQ. Though that'd additionally require a small modification of the mainboard - the photos don't show the mainboards solder side, nor the region under the daugherboard - so one can't say if there's such a mod.

> But this makes me wonder: how much was the tax anyhow
Good question. Does somebody know details on that?

No matter of the tax. I wonder if the daughterboard with the three extra chips plus the rebadged case with 472 on it was actually cheaper than changing the letters printed on the keyboard.

> I think the 472 came in two different versions though?
Yup, the one with english keyboard (with the avoid the tax trick), and the one with spanish keyboard (when the trick no longer worked). The latter one could have been renamed back to 464, but for some reason they stayed with 472... either Indescomp had produced a lot of 472 cases & daughterboards that they needed to get rid off... or they thought that spanish users got familar with 72K machines, and won't buy lousy 64K computers :-)

ukmarkh · 17:57, 01 April 10

Well, somewhere out there on the tinternet or in a Retro Gamer mag is an interview with Roland Perry or William poel where they actually mention that the memory was not usable, but was made to look as if it were. Don't forget guys, this is Alan sugar we're talking about, he used to buy equipment and re-badge it with the Amstrad logo. In his younger days, he was selling tv's from his mums house, and each customer would trundle into his bedroom only to be told it was his own tv, and he was selling it because he needed the cash. As soon as the guy had bought the tv, he'd put another one out and start all over again. The guy was a trickster, and a good one at that... fooling people was his game.

nocash · 21:05, 01 April 10

Which interview? Do you mean this one: http://perso.wanadoo.es/amstradcpc/interviews/roland.html or this http://amstrad.cpc.free.fr/amstrad/poel_e.htm ?
In that interviews, Roland Perry and William Pole both say that they never heard of the CPC472. As far as known, the daugherboard was made by Indescomp (spanish distributor), not by Amstrad (and thus nothing to do with Alan Sugar).
Anyways - the interviews don't say that the RAM is nonfunctional.

PS. Here was a cpcwiki user owning a CPC472, http://cpcwiki.eu/forum/index.php/topic,202.0.html unfortunately the other people in the forum were kidding (?) him and told him to pour destilled water on the mainboard, and to spray compressed air on it. Not so nice to scare people like that, but okay it was funny :-) the downside is that Tom left the forum after that suggestions, so we can't ask him about details. Does somebody else have a 472?

PPS. From http://amstrad.cpc.free.fr/article.php?sid=12 translated to english: "To avoid this tax, it was decided to add a module for 8 KB (which serve absolutely no purpose and are not even visible from BASIC) thereby increasing the machine to 72 KB of RAM."
That only states that the RAM isn't visible from BASIC, not that it'd be nonfunctional.

PPPS. Here http://www.zonadepruebas.com/modules/smartsection/item.php?itemid=1058 is some spanish text, saying that the fee could range from 15,000 to 300,000 Pesetas per unit. How much would that have been in dollars or euros?

Gryzor · 07:52, 02 April 10

I'm not quite sure how we were "kidding him" when we advised him on how to clean the mobo. Both methods suggested are time-honored ones, and they work. Why would that scare anyone, and why would it be funny?

nocash · 15:55, 02 April 10

Oops, that wasn't joking? Compressed air sounded a bit surreal... like buying spray cans or air compressors... of course, cleaning a board with a small brush, and then blowing away the dust is the best solution. Just calling your lungs an air compressor sounds a bit mechanoid. And destilled water - if that idea isn't scary!

It's an interesting method though - as far as I understand, destilled water is non-conductive, so it can't produce shortcuts? But if you pour it on a dirty board, then you would get conductive dirty water, wouldn't you? And if you wait until it has dried completely, then you could as well have used normal water... or does that "rot" the soldering points? Anyways, I am feeling fine with dusty electronics, but pouring liquids on them - even if it'd be harmless - that's scaring me :-)

For the 472, I've checked the history of the cpcwiki article. The not-connected info seems to come from Mcleod ideafix, I've sent him an email, maybe he can confirm if he verified the info himself, or tell where the info came from. I guess he knows what he's talking about, though the sentence "difficult to turn the daughter board over and reveal the trick" is confusing me - since the photo of the turned board doesn't actually reveal anything.

Gryzor · 17:02, 02 April 10

Surreal??? You mean you have never seen an air blower for PC case cleaning? Or the air sprays they sell at computer stores? No, shire, not surreal at all!

Distilled water is, I admit, a bit more bizarre, but I have done it, and I know professionals who do it. You have a point about the dirty water being conductive, but I guess that if you make sure that whatever it is that you're cleaning has no charge you're on safe ground... Distilled water, however, is needed not for its non-corrosive capacity, but because you need to make sure it doesn't leave anything behind - that is, salts. So arguably you could use whatever liquid has no salts, like pure alcohol - it's just that water is much cheaper

Bryce · 18:31, 02 April 10

We often clean PCBs at the place I work with distilled water with some alcohol added (dries quicker supposedly) and then blow dry it with compressed air. I can confirm that it works perfectly, we've never had a problem with this process. It has to be distilled to avoid salt (and other impurities) in the water getting left on the board, which would corrode the board over time. Obviously the board needs to be rinsed until there is no dirty water left over or it would (as nocash suggested) possibly cause short circuits or at least cause an unwanted resistance between solder points. I suppose we could use pure alcohol instead, but it might evaporate too quickly, or maybe they are just worried that the engineers might drink it

Bryce.

Cholo · 23:50, 02 April 10

I recall a thread about washing your mobo/graphics cards in a normal washing machine and weather or not you should add extra stuff or not. Cant recall how it ended tho, but made me chuckle a bit. Still nothing wrong with the shower and hairdryer method i hear.

What is the other thing pro people do ? Ultrasonic bath or something?

Anyways, personally ive just used a compressed air can (same can for like 5+ years) and that is probably what most normal people do with eletronics.

Gryzor · 07:15, 03 April 10

Yeah, I guess you can put stuff in the washing machine - heck, while you're at it, put your cat and dog in there, too. They'll come out all clean. Maybe in pieces, but clean pieces.

Ultrasonic bath is a great way to remove grime, as it makes all dirt go loose. Many cameras use ultrasonic waves to clean the lenses. Where to find such a bath though, and at what prices, is another story...

nocash · 22:59, 11 April 10

Got some brandnew CPC472 super pictures from Mcleod ideafix - see here, http://cpcwiki.eu/index.php/472. They revealing how it "worked" quite well. He's also thinking about a way to remove the white paint completely, with chemicals or so.... I think best would be scraping or using sandpaper...?

Also changed some other things on the CPC472 page. I hope I got the timeline correct? There were four different 464/472 models in spain? And can somebody fill-in the "how much" pesetas/euros values?

Gryzor · 11:45, 12 April 10

Wow... see, you learn something new every day.

My question remains - how much did that ruse cost, especially against the cost of paying the tax?

ukmarkh · 15:54, 12 April 10

Quote from: nocash on 21:05, 01 April 10
Which interview? Do you mean this one: http://perso.wanadoo.es/amstradcpc/interviews/roland.html or this http://amstrad.cpc.free.fr/amstrad/poel_e.htm ?
In that interviews, Roland Perry and William Pole both say that they never heard of the CPC472. As far as known, the daugherboard was made by Indescomp (spanish distributor), not by Amstrad (and thus nothing to do with Alan Sugar).
Anyways - the interviews don't say that the RAM is nonfunctional.

PS. Here was a cpcwiki user owning a CPC472, http://cpcwiki.eu/forum/index.php/topic,202.0.html unfortunately the other people in the forum were kidding (?) him and told him to pour destilled water on the mainboard, and to spray compressed air on it. Not so nice to scare people like that, but okay it was funny :-) the downside is that Tom left the forum after that suggestions, so we can't ask him about details. Does somebody else have a 472?

PPS. From http://amstrad.cpc.free.fr/article.php?sid=12 translated to english: "To avoid this tax, it was decided to add a module for 8 KB (which serve absolutely no purpose and are not even visible from BASIC) thereby increasing the machine to 72 KB of RAM."
That only states that the RAM isn't visible from BASIC, not that it'd be nonfunctional.

PPPS. Here http://www.zonadepruebas.com/modules/smartsection/item.php?itemid=1058 is some spanish text, saying that the fee could range from 15,000 to 300,000 Pesetas per unit. How much would that have been in dollars or euros?

I'll need to get back to you on this, but I read it some years ago now. Apparently Alan Sugar was a bit of a trickster, and used a similar technique in his early range of Hi-fi models. I think it was something to do with him selling a hi fi model with 3 inbuilt speakers, and someone noticed at curry's that one of 'em wasn't actually wired up. It was a dummy 3rd speaker, put there to fool the public.

nocash · 16:43, 12 April 10

> It was a dummy 3rd speaker, put there to fool the public.
Cool :-) That hints towards Amstrad, maybe he told his devrs, "if somebody asks: you've never seen this 472 model, got that?" though maybe Indescomp knew something about trickery, too.

I guess the tax applied to all computers, not only imports. So it could be imported without tax, and modified it in spain before selling it. Indescomp seems to have purchased the 464 together with 664 ROMs from Amstrad, so Amstrad should have at least noticed that something strange was going on.

For the cost of the daughterboard: The two logic chips aren't too expensive. Though the 64Kbit RAM may have been a bit more valueable back then. And it might have been necessary to mount the daughterboard by hand. My guess would be around $5. And don't know how much $5 would be compared with 15,000 pesetas.

ukmarkh · 15:45, 13 April 10

More info on Indescomp:

I'm not sure if you guys are aware of Indescomp, but basically a chap called Jose Luis Dominguez run this small outfit. He originally contacted Bob Watkins and asked if he could become Amstrad's distribution network seller in Spain, Watkins told him Alan Sugar wasn't interested in Spain and that Amstrad wasn't yet ready for such a thing. Dominguez had already approached Sinclair, but they told him no! Later he agreed a deal with Acorn, but the 2000 machines he purchased off them didn't sell. This left Dominguez on his knees with little money and no where to turn. This guy was basically a sales man, a one man band trying to seek his fortune.

He called Bob Watkins once more, in an act of desperation and asked if he could meet Alan sugar. Watkins told him to stop wasting his time, and reaffirmed that Amstrad wasn't yet setup to launch in Spain. Just before Dominguez contemplated putting down the phone, Bob Watkins said "Unless you have a game for us, sugar wants games?" Dominguez quickly remembered a game an associate of his was working on, and said "yes we have a game, but I'll need you to send me a CPC in order for me to modify it to work on your system". And with that Bob sent the CPC and agreed for Dominguez to meet up and demo the game to Alan sugar. When Dominguez finally met up with sugar, he recalls how rubbish the Amstrad building was, and how horrible Alan Sugar came across. The demo didn't go well either, the game wouldn't load, and sugar apparently moaned about Dominguez being a time waster. But he tried again and the game loaded.

Sugar and Watkins were happy with the game, and Sugar offered to pay him there and then, but Dominguez refused payment and instead offered the game to Amstrad as a gift. Sugar had never experienced this before, and asked Dominguez what he really wanted? Dominguez basically asked if he could sell Amstrad CPC computers in Spain. After a heavy conversation, Sugar agreed to loan and send Dominguez 4000 CPC's direct from Japan, with a 60day return on investment, but with it under the condition that Dominguez and his outfit would release ten games for the CPC. Dominguez accepted and the rest is history.

Gryzor · 08:36, 14 April 10

This is a great post. I knew some of the info, but not all of it... Btw, have you noticed that all this is not in the wiki article? (hint, hint!)

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cpc472 schematic?