Amstrad ACL-386SX laptop computer.

[santosp]

Hi,
I would like to introduce the internal mainboard which is a totally redesign "all in one" mainboard, in relation with its monochrome brother ALT-386SX.

In the differences included also the main memory which here is 4 MB on board versus 1MB in monochrome model, which can increase at 6MB if someone solder the rest 4 memory chips in the empty places.

Another difference is the non existed VGA card. In this implementation has built on board, using 3 ic of "CHIPS" corp.
It have total video ram 256KB using 2 ic with 128KB each. This is fast page dynamic ram.

Looking at the processor seen that the speed has increased to 20 MHz vs 16MHz in monochrome model.

The BIOS and also the VGA BIOS included in one eprom ic, 27C1024 type. "CHIPS" VGA controller can have access in specific addresses in main eprom in order to extract the data it needs.

Memory expansion remain the same as the previous monochrome model, with two differences. Is integrated on mainboard (not in a card form), and autosense who means not need configuration switches.
In any case the new 1MB 30pin sims must placed with a specific series if not all will placed!

Description of ic follows...

1. F82C411 (CHIPS) Flat Panel Color Palette/DAC
   
2. F82C457 (CHIPS) Flat Panel/CRT VGA Controller
   
3. F82C401 (CHIPS) Flat Panel/CRT Clock Synthesizer
   
4. V53C664K-10 (VITELIC) VGA Dynamic RAM 128KB * 2 = 256KB
   
5. VL82C331 (VLSI) ISA BUS Controller
   
6. VL82C320 (VLSI) System Controller / Data Buffer
   
7. VL82C106 (VLSI) I/O Combination Multi CHIP which include....
   
   Serial Port, Parallel Port, Real Time Clock, IDE HDD Controller, KBD/Mouse PC/AT & PS2 support, BIOS RAM Keeper
   
8. DP8473V (National) Floppy Disk Controller PLUS-2
   
9. NG80386SX-20 (Intel) 386 CPU @ 20MHz
   
10. M27C1024-15 (Mitsubishi) 128KB BIOS + VGA BIOS
    
11. M514400A-70 (OKI) Dynamic Ram 524KB * 8 = 4MB Total.
    
12. GM80C51 (FUNAI) Intel microcontroller. Keyboard Internal Matrix / External DIN 5Pin
    
13. Empty Socket for 80387SX-20 Coprocessor
    
14. LT1137CS (Linear Tech) RS232 Driver / Receiver
    
15. 3.6 Volt / 400 mAh (Yuasa) Ni-Cad Battery (Not leak after 31 years!!) I am very lucky!
    
    

 

[ajacocks]

Welcome to the forum @santosp !

That’s a heck of a detailed motherboard description. Are you planning to do more?

- Alex

 

[santosp]

Thank you Alex,
I really don't know. The reason who I share these info (they will follow more) is because this specific "color" model is a very rare laptop PC, and the information is minimal if not non-existent, anyywhere on the web.

 

[santosp]

Part two

Rubycon RPS-1205 PSU

As every computer a Power Supply Unit exist ever! Here Amstrad trusted the Rubycon corp.

I must to note here that even if in the past have repair many electronic devices, first time in my life (I am 50 now) see an exclusive manufacturer of capacitors to make complete power supply units. But as they say... for all things there is the first time.

Of course because of Rubycon, all the capacitors who have been placed there is from the same manufacturer and all has a leak! A very bad leak!
The board of PSU was in very bad condition from this leak, so it washed off using isopropyl alcohol and next deionized water.

I took measurements for every one of those capacitors with my capacitance meter, and I must to say that the capacity in all those was almost right!
But the ESR (internal resistance) was incredibly low, almost 0 Ohms.
So I was replace all of them.
I used Nippon Chemi-Con at 105 C as replacements.

Next I changed the old dried up thermal paste in all the metal heatsinks in semiconductors, voltage regulators and rectifiers.

Last I was setup the two main output voltages +5V and +12v using the two trimmers in the right end onboard. In my case only +12v was minus a bit.

I must note here that even if this PSU work "in the air" only with mains voltage, the output voltage settings must be done with it connected to the rest computer under load!

After the end of all this repair and during the time of putting back this PSU on the computer, you start to realize that something is buzzing in your ears. Yes I am talking about the cooling fan! It is noisy! It really have enough annoying sound!!

The fan is a 40*40*10mm small fan working with 12volt at 100mA. In reality its main work is to cooling the rectifiers, regulators and semiconductors, which are placed in the two large metal heatsinks.
Rubycon have design the point with such way (placing a metal cover over the heatsinks) so that a tunnel is created between them, and thus the heat that is abducted through them is pushed towards the environment through the small fan. It clever...

As is understandable this fan must has worked many many hours all these years, so this have as result wear and tear.
I found as new replacement a same dimension model from Sunon Corp. This have a better bearing, and speed selection (upon purchase) so that it is quieter. I was choose the "Medium speed" model.
Part number is MF40101V2-1000U-A99

Below is a list with all the capacitors of this PSU.

AC Line Polypropylene
C1 100N/275VAC Caution is X2 Class capacitor!
C2 220N/275VAC Caution is X2 Class capacitor!

Electrolytic
C10 180/400V (Booster Capacitor. It can used instead, 220uf value)
C21 1000/35V
C22 1000/35V
C23 10/50V
C25 470/35V
C26 470/35V
C27 1000/25V
C28 2200/16V
C29 2200/16V
C30 47/35V
C31 10/50V
C37 100/10V

One last thing is worth noting, is the existence of some vertical circuit boards as to the main circuit board. This is a method used by manufacturers in the past to keep the main board as much as possible "within the original design".
They usually covered these circuit boards with a resin coat as an anti-theft measure, so that the circuit inside is not visible.
The strange thing is that while they have done it to one of that, the rest are completely naked!?
See photos below.

 

[santosp]

The rest of pictures...

 

[santosp]

Part Three

HDD & Floppy Disk.

One more difference here versus the monochrome model was the HDD.
ACL-386 was coming with a Conner CP30104 type HDD, with 19ms average seek (very fast for 1992) and 120 MB capacity.
I don't know if some from the owners of this laptop they would have the luxury to have more than a HDD to change between them, but the disk here was came removable in a plastic manger!
For my luck Conner was in perfect working and hardware condition "the surface of the plates" after 31 years! In this maybe was help its option to go in sleep mode after 2 minutes during the work of laptop, in case which the system not need to accessed.
So HDD not work all the time, but only when it really needed!
A very helpful tip here is the type that must be declared in BIOS as to work. Is "40".
In any other case BIOS report it as "not a system disk" and look like damaged.
This is useful in case this laptop have lost all the BIOS settings because of dead backup battery.

The floppy drive is a 3.5 inch Citizen brand, 1.44 MB capacity. Two more differences here from the monochrome ALT-386 model.
First is that it come without plastic façade, because is built (part) of the bottom plastic shell of the laptop. Maybe this was a way for the Amstrad to procure more economically the floppy drive mechanisms.
Second, is its electric interface. This is an older style of 26 pin connector, versus the standard 34 pin. Because of this it use only 5 volt via 3 points in ribbon cable to work.

In my case floppy drive it does not worked at all, and although I was disassemble it and change the 3 smd capacitors which was leak and the drive belt, the status remained the same.
So I decided to replace it with a newer Gotek floppy emulator, as to be easiest for me to load any floppy image within a USB stick feed from my today PC. I don't even have to worry about the type 360 or 720 or 1.44, 3.5" either 5.25"of image of floppy disk, since it supports them all!
Below I share the conversion from the Citizen 26pin to the standard electric interface of 34pin.
Was a "trial and error" method for me and many hours of research on web on those ancient interfaces, as to find what finally work.

Note
At this time I have a almost fully working computer, and this saga on this very rare laptop will finished soon with the adaptation of the new color TFT screen, which will arrive in some days. That will have the last part which I will describe about the ACL-386.

26pin>>>>34pin Citizen U1DA-71A
-=====--================--============-==-
1 > 5v Power
2 > 8 Index
3 > 5v Power
4 > 10 Drive Select 0
5 > 5v Power
6 > 34 Ready
7 > 12 Drive Select 1
8 > N/C
9 > N/C
10 > 16 Motor on
11 > 17 Ground
12 > 18 Direction
13 > 19 Ground
14 > 20 Step
15 > 21 Ground
16 > 22 Write Data
17 > 23 Ground
18 > 24 Write Gate
19 > 25 Ground
20 > 26 Track 0
21 > 27 Ground
22 > 28 Write Protect
23 > 29 Ground
24 > 30 Read Data
25 > 31 Ground
26 > 32 Side 1 Select

 

[santosp]

Complementary.. The Battery

Battery in this model it huge, internal, with capacity 5000 mAh, versus the smaller, externally detachable, with capacity of 2500mAh, at the monochrome model.
I think that this happen mainly because of the new color TFT screen with which it is equipped.

So the model is 10KR-5000DL from Sanyo. It use 10 * 5000mAh batteries connected in series, with two thermistors as a safety measure against the overtemperature.
One of that send a reference back to power supply unit, and the other it work just as a simple mechanical breaker.

Those thermistors came from Klixon manufacturer, and use as electrical breakers at 115 Celcius. The manufacturer say that the circuit continuity restore at 41 Celcius.

I will not intend to make a new battery for this laptop, because I will use it mainly in my desk.
But I did a rough sketch looking the internal, just for reference.