Amstrad Module MP-1 Refurb and Mods 

Very interesting. I remember the Christmas we got our CPC464 in the year it came out - me and my brother were wondering if we would even get one as it was a LOT of money for my family and many others. It was the era where the UK had home catalogs (like Grattans, Kays etc.) where you could buy things and pay them off over time. I think the stores in the UK typically sold with the Green or Colour monitors - but - in the catalogs you could buy the machine with MP-1 (a cheaper option for many families I guess) - a good way of them trying to keep competitive with the prices of the Sinclair Spectrum and C64 machines. Santa came and we could see 2 big parcels for us - on opening them one was the CPC - and the other was the colour monitor 😮 - we felt so very very lucky - and my mum and dad still got to use their TV LOL. Both myself and my brother have had 20+ year careers as software engineers and its entirely as a result of these awesome 8-bit machines - movnig on from those to 16-bit machines with C and 68000 assembler meant by the time I went to university I was already fluent in quite a few languages. Who would have thought that learning Locomotive BASIC and z80 would have lead to this. Somebody once said if your job involves something you love - you'll never work a day in your life. We are so very very lucky - thankyou for bringing all these memories flooding back Jan ! 🤗

The 2 diode centre tap FW rectifier dates back to the days when vacuum tube diodes were large and relatively expensive. The split configuration needs twice as much copper in the secondary winding of the transformer than the single tap 4 diode FWR circuit but the cheapness and simplicity of the double-diode arrangement made the trade off worthwhile. Designers in the '70s grew up in the vacuum tube era and the 2 diode split secondary arrangement was habitual for them, even though the trade off of fewer diodes no longer applied with solid state devices.

I think the modulator mainly existed because green screen systems were sold, and they were a cheaper way for people to experience the system in colour on a TV than to buy a new monitor.

We had a colour monitor but we took the CPC and one of these units on holiday to Denmark for Christmas and played games with my cousins all Christmas on my Grandparents' TV.

Man oh man, when someone already admits that he has done something wrong. It just makes you likeable and honest. 👍

That's some great self-reflection and learning experience, Jan. I think we can all take something from your experience. Danke Dir!

I always appreciate the transparency in your videos, Jan. This was a great video. I always watch with the hopes that I'll improve my abilities with hardware, so I don't expect perfection. In fact, this helps me learn.

My first computer was a Commodore VIC20, but my second ever computer was an Amstrad CPC 464, with the green screen monitor, we weren't rich enough to afford the colour one. Ahhh, memories.

That center tap configuration of the rectifier would have confused me as well. I'm glad you shared the mistake, so I (and other's possibly) don't do the same thing you did, which I very well could have done...

One fun fact about the UK and our plugs, at the time this Amstrad product was sold, they often came without plugs fitted, so you had to fit your own, and most people just bought an off-the-shelf plug with a 13 Amp fuse (Ceramic, sand-filled jobs, not glass) fitted and went with it (My Spectrum Plus came like this!!!), this was common across pretty much all appliances from a lamp to a fridge freezer, so, had anything gone wrong with the transformer, that's about 3.1 Kilowatts of power flowing though that cable, so lots of smoke and fire probably... :S

Another great video as always, Jan! Ups and downs are all part of the fun. 👍

I added an RGB scart socket to mine, used a panel mount connector and made a nice job of it. The image is excellent quality!

I reallllllly wish I hadn't sold our Amstrad CPC464 at a garage sale back in the late '90s :( You just can't find them here in Australia that much anymore. We had the CPC464 + greenscreen monitor + over 200 Amstrad magazines that came with code that you could type into the computer, plus a whole stack of games. Mum bought the 464 around '84/'85 when I was like 2, so these days I am absolutely kicking myself. It was the first computer I learnt to do stuff on in like '86 when I was old enough to touch it.

Un lavoro fantastico al modulo mp-1,sei impeccabile Jan

I remember my MP add ons. I could only afford the mono monitor at the time so used my colour tv. This was actually better than getting the colour because I then had the choice. The mono monitor was great. I’d would have removed the modulator and fitted fuses in that spare area.

Great video nothing wrong some extra protection with the Diodes simple yet effective

Thanks! Learned something new today by reading the Wikipedia page for center tap transformers besides your video.

Thx so much for your informative content, Jan 👍

PCBWAY is the way

I think your idea of using a Mean Well power supply will work out very well.

Great video Jan. Now you need a DDI5 Expansion cartridge.. just as I do on my CPC 464.

With the RF modulator removed, you could have fitted a RGB to HDMI there with the original CPC RGB cable! :D

Happy Septamstrad! :D

Yes, that 10VA transformer is way underrated (not slightly), so you should have checked its output under load. 7805 regulators are not LDO, so if their inputs get too close to their rated outputs, they start behaving unexpectedly. What you need on their inputs is at least +2V over their rated outputs, in your case 5V+2V=7V absolute minimum. If your transformer drops its output due to load, you might not get this.

For use with Scart my CPC 6128 came with a contemporary DIY power supply which according to the original owner "was made by a friend who studies electrical engineering". That thing sounded like a swarm of angry bees and was vibrating so much that it was prone to walking off the desk

Als du den Brückengleichrichter eingelötet hast, hats du den Minus Anschluss des Gleichrichters an den Mittelanschluss das Transformators angeschlossen. Damit hast Du in der einen Halbwelle die eine Transformatorwicklung kurzgeschlossen und in der anderen Halbwelle die andere Transformatorwicklung. Eine Transformatorwicklung war schneller kaputt als die Andere, die dadurch gerettet wurde. Du hättest als am Brückengleichrichter den Minus-Anschluss offen lassen müssen. Dann hätten zwei Dioden des Gleichrichters den Pluspol gerichtet. Aber dann ist es sinnlos einen Brückengleichrichter statt zwei Dioden zu nehmen. Auch den Mittelanschluss zu entfernen macht keinen Sinn. Mit den beiden äußeren Anschlüssen hast du die doppelte Spannung und den halben Strom, den du brauchst. Die 7805 hätten eben 20 Volt Vorspannung und nicht genug Strom mit beiden Wicklungen in Reihen. Mit der Mittelzapfung zwei Dioden Gleichrichtung werden beide Wicklungen abwechselt parallel geschaltet. Also ca 10 Volt vor dem Regler und Stromfestigkeit höher. Oder gleich ein 5 Volt 2 Amp Powersupply nehmen.

I think that transformer will hang in there. From memory, the CPC used just under an Amp @ 5V. It's probably just on the borderline but im sure it will work. Accessories plugged into the CPC definitely wouldn't be recommended though. Love you video's, Jan. Keep up the awesome work.

Like other posters, we had a mono monitor CPC464 and got this so we could use it in colour. The big downside was this thing ran very hot indeed, you had a smell of hot plastic to go with your games!

I would try to include a small automatic fire extinguisher. 🤪 Seriously, love your videos I'm almost ready to begin working on my own retro computers.

The MP-1 was to allow you to connect to a TV if you'd bought a green screen monitor, allowing you to have a colour display.

awesome

This would be a neat case for a PC/104 computer.

Dear Mr. Jan, the transformer failed because you fitted the rectifier bridge which resulted in overcurrent in the secondary winding. Because during an alternation (eg: positive alternation in the secondary), one of the diodes (from the rectifier bridge) will take the voltage from winding 4-5 and rectify it, the other diode will take the voltage from winding 5-7 (which has a negative voltage relative to the transformer pin marked 5, which is connected to ground) and which tends to reduce to 0.7V, what it represents diode forward voltage (without the existence of a current limitation on this electrical path) which leads to the appearance of a very high current in the secondary, in winding 5-7, implicitly overcurrent in the primary, which leads to rapid overheating of the windings and failure of the transformer. The 1A fuse was large as it allowed up to 220 watts into the transformer and did not protect the transformer from overheating. Greetings and all the best, Marius.

33:43 In my time "Repairing" dead electronics, I tend to find that if a device has a transformer, that's the most likely thing to be dead. I "Repaired" an old fiber optic Christmas tree for my brother a few months ago. "Repaired" in that it was the PSU that was dead, literally nothing more than an AC transformer in a plug-top box. So I found another old transformer (Wasn't plug top, plug was on a wire) with the same value, cut the plug off the end of each cable, and made a soldered joint. It worked, it was safe enough (used heat shrink with hot melt glue inside it), and he was happy with it.

Well done Jan. To mount the power supply I would have just used MB or Drive Spacers, the Hex type brass spacers. Bigger the better. But I guess cable ties are an option. ;)

Just add a fuse of 2Amps with the 6v protection diode. Also when you connected the center tap of the transformer to the negative output of the Bridge, I exclaimed Noooo! . The two diodes were used to enable cheaper lower current transformer to be used by adding two outer windings of the center tap of the 9v out was a common and reliable method, shame about the transformer they are/were very reliable. Infact those modulators were good Astek were the best available at the time, replacing the caps was a good move. The MP-1 was prone to bad solder joints and cable damage, I only recall replacing one set of regulators and that was due to a customer shorting the DC cable when he tried to repair the lead. Leaving the Bridge in place and disconnecting the Negative would have been acceptable. Personally I would have left the diodes alone if the tested ok, or at the very least replaced them with 1N5407/8 which are the same diode at 800v/1000v not 100, just because it's easier and cheaper to order one type rather than several.

Got one of these with a CPC6128. My original colour monitor failed and couldn't get it fixed at the time!

Correction: You get about ~0.8A before you exceed the VA rating of the transformer! This is linear PSU so the linear regulator and bridge rectifier "burns" of the excess voltage as heat, most of this is done on the semi-stable peak-voltage side so you can get an approximate ampere very safe rating by dividing the transformers VA rating with that peak voltage (12.7V). Actually, it might be even lower since it'll probably be rather peaky which amplifies the VA number but I suspect it's probably OK up to that. There's way to calculate this but it's complicated and I'm not confident I would get the correct result. Also, starting with 9V AC means the linear regulators will need to get rid of a lot of voltage and thus heat, the bridge rectifier and linear regulators will burn ~15W at 2A load, this comes in addition to whatever heating happens in the transformer. So the PSU will generate more heat than the entire machine. Based on your measurements the original design probably used a 6.5V AC transformer, this makes sense given that this appears to be about as low you can go and still be guaranteed a "regulated" 5V DC output assuming a full bridge rectifier (FBR) using standard diodes and a 7805 or compatible linear regulator, they actually had slightly more safety margin since the dual diode centre tap design only incur one diode voltage drop instead of two. I'd suggest seeing if you can find a 7V AC transformer, if you use a 6.5V AC transformer it might be fine but I'd probably use a Schottky FBR (much lower voltage drop) for a bit of extra headroom even if it "should" be fine without AFAIK. I think all 7805 models are specified to be capable of handling least 12V DC input so using a 9V AC transformer should be safe if you provide enough cooling (the FBR will drop it below that). Some model are specificed up to much higher voltages but they quickly becomes veritable heating elements if you draw any noticeable current - the 2A ST L78S05C for example is rated up to 25V! which would result in 40W power dissipation in the regulator alone to deliver 5V @ 2A (10W)... Ouch, not sure that's coolable in that form factor without using "exotic cooling".

Cool to see a UK Amstrad in Germany instead of the Schneider.

About original transformer. Some transformer have a embedded current/thermal fuse. If transformer is a single voltage input, and have a three terminal, the fuse bridge between two. PSU don't have a fuse, so can have a embedded one.

The only thing to really do with an MP-1 is open it, throw all the insides in the garbage and use the case to fit a new open frame switching power supply. No need to play around at the component level.

The transformer has four taps with tap 2 to 5 being maybe 15v apart. Then from tap 4 to 7 is maybe 8-9. For the 12v the simplest version of rectification which is a single diode is used. The diode blocks the voltage on the negative side giving just the bumps above 0. That then gets regulated to 12v using the zener. The 5v is using two diodes to to block either side in turn producing a very dirty “dc” output which is then smoothed by the three quite large caps. Then the 5v gets regulated with the normal 3 pin 7805s. The transformer is a multi tapped secondary transformer rather than centre tapped. If I were doing that board I would add the voltage for the floppy too. I can’t remember what voltage it needed off the top of my head. There is nothing inherently wrong with half wave rectification and those diodes were overkill from the start. I do look forward to your videos. It was only after I started making my own that I realised just how hard it is!!

Nice video, did a fantastic job sorting that out. The fuses in a UK plug are sand filled ceramic not glass fuses :), and people love to stick 13 amp ones in everything. 3 5 and 13 are common in the UK . You used to be able to get 1 an 7 too but they are much less common ( even tho for much stuff today (like phone chargers ) a 1 amp would be more than enough).

I remember having the tuner that turned the colour monitor into a tv

Off topic, but in the background I see the pokes for screen and border colours have gone, and the Defiant and Voyager have taken their place :-)

For people considering replacing the diodes with a bridge (because they have one) just don't connect the negative terminal. That way you'll just be using half of it, but it will be in the configuration as originally designed. The diodes in the negative side will block each other because their common point (-ve terminal) is not connected to the transformer. If you connect the negative to ground and disconnect the centre tap of the transformer, you'll be getting twice the voltage you expect on the capacitors, which could be troublesome! I don't think Jan damaged the transformer unless he plugged it in before removing the connections to the transformer, which he clearly said he didn't. Transformers kept in lofts and garages can get damp and critters in them and burn out on their own when people try them out. The final mod with the sealed transformer looks like a good job that will last..

Hi Jan, from the video I don't understand how you connected the bridge. If you left the center tap (black wire) disconnected and connected the two orange wires to the bridge AC pins e the + - terminals to the capacitors then you will have twice the dc voltage input to the 7805s; if, on the other hand, you connected an orange and the center tap (black) to the AC pins while leaving an extreme pin (orange) disconnected then you will have half the available current.

AFAIK the MP-1 was an option for people who didn't want to get a monitor. Since the power supply is normally in the monitor, you need some kinda special brick to otherwise use the CPC.

I remember distinctive smell of this modulator. The smell of my childhood. 🙂 But the RF output was very bad.

In the good old times two diodes costed more then some copper in a transformer. Back then it was useful to save money on the bridge. Nowadays they look different to this matter. Now the copper wire is more expensive. The money was spoiled in the past, you can't correct that. But, improvement would always be welcome. In the transformer with two secondary coils (three wires) in combination with two diodes, half the time half does nothing useful. If it would be possible to disconnect the common wire and make two separated secondary coils (four wires) then these wires could be differently connected, then a bridge rectifier could be used and then the result would be that there would be more efficiency, a slightly higher current could be drawn from it. Then all the time both secondary coils would be in use all the time. Everybody happy! So, going to the bridge would be great if also the transformer could be reconnected. By the way, I would add as many capacitors as could be stuffed inside. A flatter direct current is better than "Hong Kong"-style power-supply with only as mutch capacitors as needed and nothing more.

I had put a simple USB connector into the CPC, connect a simple USB power supply and called it a day. The only thing to check in that case ist If the supply can deliver enough current. May be even USB-C, that might even fit the barrel plug hole in the case. Such connectors with soldier connectors are easily obtainable over AliExpress for example :)

get rid of internals, add a swtching psu and a mod for videoe circut

I had one of these as a kid it released some magic smoke and died after about a year. It was the 1st thing i owned that went pop.

just ordered myself an MC1377P so I can finally build a clone of the MP-1 thanks to your teardown ;-) the original ones are horribly expensive and hard to get, so i've been using RGB via Scart before, and have stowed away the CPC for some time now since my new TV doesn't do RGB anymore. now I can get it to work again - thanks a lot! How did you manage to get 5.27V from an 7805 though? Those usually regulate to better than 2%.. I don't think I've ever had one deviate above 5.1V unloaded. Is there a bad ground connection maybe?

Doesn't Reichelt have a nice 5V/12V Meanwell PSU that could, theoretically, fit inside here? Wouldn't that have been an option?? My reasoning for that is higher efficiency. Linear Power Supplies have a very high voltage drop. If you have a Mega Drive power supply, I encourage you to measure the 9 or 10V DC PSU. ANd you'll be surprised that it ain't 9V AT ALL. By todays Standards its 12V for the Mega Drive - and its very similar to lightly and heavily loaded. Though the Ripple might be an issue. Though we're talking about less than 20W though...

43:13 I'd definitely refit the modulator. It will at least have more of its originality preserved & it'd also be interesting to see what the RF output looks like. I for one have only ever seen a CPC display on its dedicated monitor. ↓↓EDITED TO ADD↓↓ With this you could at least connect your CPC to the big telly in the living room … and probably get better sound too if the RF signal carries audio.

Peak opposite is trough :)

If the transformer is speciefied to 10 VA and 9V, you will not get more than 1.1 A at 5 V with linear regulators. The rest is dissipated as heat. :)

Faul, wie ich bin hätte ich die alte Technik sofort aus dem coolen Retrogehäuse gerissen und ein nettes 5A Meanwell eingebaut, keine Extra Sicherungen oder heiß werdende Trafos und vor allem Power. Wäre aber ein deutlich öderes Video geworden als deins. Ich hätte ja gerne den HF Modulator in Aktion gesehen, aber ich denke, der ganze Ärger um den Brückengleichrichter bzw. den abgerauchten Trafo hat dich zu lange aufgehalten...

The rf output was really bad. I had a cpc464 with colour monitor. But a friend had one with the rf. Looking at it after using it with the monitor, it was almost un-usable for me

does this require a smoke test ?

The fuse isn't glass in a UK plug. it's not transparent.

That’s almost a whole new PSU, (Triggers broom) but no better than the original and actually worse. Meanwell is definitely the way to go. Enjoyable as always though.

There was a MP-2 model that provided the12V required for the 6128's floppy drive. Thing is, this model also needs to provide 12V to the modulator. Yes, a floppy drive sure enough draws more power that a modulator, but still, I don't understand why two models existed instead of producing one that would cater for all CPC models. Why Amstrad, why?

Edit: Sorry, I commented when you were still at minute 45 without having seen the whole video.

If that transformer is the same kind that I've used in the past, they're really annoying! They use 5 mm pin spacing, so they don't fit into standard 2.54 mm prototyping board.

Change the awful euro mains sockets to UK one jan :p

Maybe add a RGB Out to the MP-1 (MD 2) to upgrade it from RF.

I'd love to know why the Schneider people did away with the colours for their version. Was it like "Sis is too colorful, ve cannot take sis serious, computers are serious business, not colorful play"?

I thought most motors are 12V

Keeping the mistakes in makes for a better video imo.

I bought a used CPC464 and threw it away, converted the monitor to connect to my Amiga. Apologies to all Amstrad Fanboys, but #Amiga!

It was invented because most people had the green screen monitor and after a while they wanted colour

Er, yeah. Modifying power supply circuitry when you don't know what you are doing is not the greatest idea. Amstrad was notorious for producing the cheapest, most cost-reduced products possible so as to get able to undercut the competition and still have a healthy profit margin. It is not at all surprising to see a primitive PSU design in one of their products.

Get rid of the old shit, and replace the internals with a meanwell power supply.

toilet paper