MPT/100 microNOVA

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Restoration Progress

Just arrived (Jan 2019) as (hopefully) my second project this gorgeous DG Enterprise MPT/100 desktop computer which sports a microNOVA CPU under the hood. It’s a little dirty but in good shape and no screen burn. I am attempting to find schematics, Field Engineering and User manuals and 5.25″ floppy disks with MP/OS or MP/DTOS DIAGS before I do much with this unit.

This is exactly as I picked it up, its dirty and needs a good clean!

Once I source the correct size socket I will post images of the internals as well……..

So, having sourced a small imperial socket set I am now able to open the MPT/100 up and see what’s under the hood. PCB Part Number 005-15542 contains the keyboard and associated logic and PCB Part Number 005-16560 is best described as a single board microNOVA computer which utilises the following Integrated Circuits:

mN602 (DG)
mN615 (DG)
FD1791A (Floppy Disk Controller)
P8035HL (CPU (Intel 8048 based)- Suspect Keyboard Processing)
2651 UART(s)
4116N DRAM(s)

The overall condition inside is dirty in places but generally ‘as new’ 🙂 The only sign of any kind of damage is some minor oxidisation on both of the DG Integrated Circuit caps and some oxidisation on the legs of both of the Signetics 2651 UART’s.

One thing that is immediately clear though is that I will not be able to isolate the Power Supply Unit (PSU) to test it in isolation (I would normally do this to protect the logic from a failed PSU outputting something it shouldn’t!). So a very close visual inspection along with through PSU component testing will be in order before any power is applied to it!

I am going to park it up for now and continue work on my MV/9800 restoration. I will dismantle it to visually inspect and component test and I will document my findings at a later date. 

I am VERY keen to obtain schematics for this PCB (005-16560) as it will be far easier for me to check for possible faults prior to power up with drawings in hand. If you have or know where I might be able to obtain schematics or manuals for the MPT/100 please let me know by using the contact form here.

Here’s whats under the cover:


So after a very long time on the shelf (unintentional) I have started the work required to bring this MPT/100 to life. It is now on my bench and is in the process of being completely stripped down, cleaned and visually inspected.The first step in this restoration is to disassemble and inspect each component part within the MPT/100 to the point where the chassis does not contain any component parts and can be thoroughly cleaned.

Warning: This device utilises a CRT (Cathode Ray Tube) and there are very high voltages present inside the device which remain present after the device has been turned off. If you are not familiar with safe working practices for CRT devices seek advice from a professional BEFORE you venture inside your device. 

Floppy Drives: The design of the MPT/100 is such that the Floppy Drives can be removed using a large paper clip pressed in to the small hold located between each floppy drive on the on the right hand side. This dis-engages an internal latch which holds both drives in place and the individual floppy’s can be pulled forwards and removed from the chassis. 

Upon removal a visual inspection is performed along with a moving parts assessment. Sadly these floppy disks have been left (unused) for so long that the belts have adhered to the pulley! Slowly rotating the pulley shows the belt being dragged by the pulley at the top. 

The Data General part number for the Floppy Disk Drive is 005-015163 and there were two versions of floppy drive referred to as Model A and Model B. My example appears to be a Model B variant manufactured by Tandon (Model TM100-2A) I believe Model A was manufactured by Qume.

We will return to the floppy drives later. 

Keyboard: Next to be removed is the keyboard; this unit is comprised of a single PCB (005-015542) which locates into moulded recess posts at the front of the chassis. Removal is a very simple process of un-plugging the PCB connector ribbon (005-014541) and lifting the keyboard PCB up at the rear by approx 30 degrees and lifting the PCB out of the recesses by moving it towards the rear of the MPT.

We will return to this PCB later for inspection and cleaning: 

Chassis: The chassis is hinged at the rear (moulded plastic) which allows it to be propped open using an internal rest and also allows the seperation of the two halves for maintenance. 

I carefully unplugged the AC, deflection coil, floppy power, floppy signal cable, floppy 5v cable, fan power and grounding plugs from the main PCB and pulled the tube end connector off the CRT. The only remaining connection was for High Voltage and even though its not been powered on for years I still ensured any residual voltage was discharged to earth before I attempted to remove this.

With everything unplugged I was able to extend the chassis up to a point where the hinge exited the lower section thus separating the two half’s:

Here are some close-ups of the hinge parts:

Main PCB: The main PCB is held in place by two bolts towards the back of the PCB, four retaining posts across the middle and four retaining clips at the front as illustrated below:

To remove the PCB from the chassis, undo and remove the two retaining bolts at the rear of the PCB, then carefully pull each of the plastic retaining clips at the front of the MPT forward just far enough to release the PCB from the latch – don’t pull the PCB up, just let it rest on top of the retaining clips whilst you release the other three latches. 

Once the four front retaining latches have been released, gently pull the PCB towards you (forward and not up) to release it from the central retaining posts. 

You are now ready to lift the PCB our of the chassis.

Caution: The PCB construction is delicate and the weight distribution across the PCB is uneven. Because of this you can easily flex the PCB and risk damaging the PCB through stress (cracked tracks). I found that if I placed one hand on the front and then held on to the large capacitors at the rear this provided a good balance and I was able to lift the PCB clear without physically stressing it. 

Here it is out of the chassis:

Not only do you need to exercise caution not to bend the PCB when handling it, be advised that the underside (solder side) has lots of long component legs that can easily be bent into each other. On initial inspection of my PCB I can see a couple of very close encounters:  

Lots more to follow………….

Interesting historical insight courtesy of Bruce Ray

The MPT series consisted of the MPT/85, MPT/87 and MPT/100. Although they used the microNOVA chip set, they were not technically part of the microNOVA, MP/100 (or MP/200) micro-products.

You will note that the MPT series evolved over the 1978 – 1985 time frame, starting with the MPT/80 and ending with the MPT/100. Different models were added and dropped depending upon sales and marketing (and embarrassment). These systems were also given the non-unique name “Enterprise” when DG attempted to sell them to select business and general consumer markets as an alternative to the Apples and early IBM PCs(!).  Yes, Data General even had its own retail stores. For a while.  😉

The MPT/100 uses a proprietary format (i.e. PC compatible) for the 5.25″ diskettes so must have “special” hardware to format, create and copy diskettes.

MP/OS is not AOS, nor even MP/AOS. Again, insignificant to outsiders but substantially different when working with DG. MP/OS was designed to be resilient to hardware problems and also minimise disk[ette] accesses. 

MP/OS had different names during its gestation and public release: Mikron, Micron (and I believe Ozmos), before the MP/OS name was finally determined. Different trademark conflicts kept DG (and other vendors) busy during those dynamic times trying to come up with non-conflicting names. Different manuals/sales literature had different names on them during this time just depending upon the name-of-the-week used.

MPT/100 Documents and Pictures

6 thoughts on “MPT/100 microNOVA

  1. Hi, my name is Thomas and i’m from Switzerland.
    I’m very pleased to see that some of the MPT/100 still exist’s.
    I have a fully working MPT/100 and a fully working mainboard.
    Also i have MP/OS and some Diskettes (Pascal and MP tools)
    I’m very interrested to share technical informations.

    Kind regards,

  2. Nice machine. I found a mN615 chip in a lot of chips I purchased and after lots of searching I ended up here. If you find out what it does or if yours is bad let me know!

  3. Hi I worked for DG from 1983 until 1992 at the European repair center in the UK, The first product I worked on was the MPT series (known affectionately as Muppets), I will give you a word of caution about these machines, the power supplys have a habit of spectacular failure, (I ran them at 220V), a ‘cure’ was found by retro fitting a resistor in line with the mains input but I cannot remember anything more about this (sorry). I will see if I have anymore information about these machines.

  4. I used one of these in the early 80;s to develop the software for the Nimslo 3D photograpic printer. MP/OS was burned into EPROM along with the control code. I used MP/Pascal and assembler. The control code ran on an MP/100 SBC.

  5. If one does not have the knowledge handle a CRT (Cathode Ray Tube) all one has to do is find any television repair book from the 90’s and previous decades, it is not rocket science. It is nice to be cautious but there is no need to scare people from the task either.

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