Category Archives: Retro Tech

Starlet part 2

IMG_20150421_175215684In part 1 I talked about the NEC Starlet. Now, a bit more.

Software.

The  Starlet  comes with a number of programs that run from  ROM.  MicrPro’s Wordstar and CalcStar are included in their mobile, “To  Go”  forms.  WordStar was the de-facto word processor back in  the  day and so it’s inclusion here is logical.  In addition, there is a terminal emulator and personal filer.

Telecom.

The terminal emulator is worth a special mention. It emulates the  DEC  VT-100 terminal.  This is one of the most popular  terminals  and being emulate one allows the Starlet to communicate with most  available systems of the time.  In addition to emulation, Telecom  offers  file  transfers both as plain text or with  modem7/xmodem  protocol.  There  is even a switch on the file that allows it  to  convert WordStar files on the fly as they are being  transferred.  This must have been quite a boon at the time.

Add-ons.

The  Starlet had a variety of add-ons available there was a  3.5″  floppy  disk drive,  a CRT/disk adapter,  a 32K RAM cartridge.  I  don’t have any of these so can’t really comment but they look  to  be well thought out.

NEC Starlet

NEC Starlet.

IMG_20150421_175215684The NEC PC-8401A-LS also known as the Starlet is an interesting
little machine. I don’t remember this from way back in the mid 1980s when it was released but I suppose laptops were not too common as far as I was concerned and so I might have missed it.

Specifications.

The 8401 features “a Z80 compatible” processor. I believe it is
an NEC V20, 64k RAM, 96k ROM an 80×16 character LCD and a full
travel keyboard with full sized keys.

The processor is a bit intriguing as I thought the NEC V20 was an
8086 compatible processor with an 8080 mode. I’ll need to clarify
that one.

Outside.

IMG_20150421_175040891_HDRThe case is a selection of browns and beige and feels very well
screwed together. It is sturdy and feels like it can stand up to
the rigours of portable life. The screen folds down over the
keyboard when not in use as you would expect. The screen itself
is typical for the period but by the standards of the 2010’s is
sadly lacking contrast and there is no back-light. I understand
that it’s monochrome and that’s fine but the contrast is not
great, it is very prone to reflections and with no back-light,
finding a good position for typing and a good angle for the
screen is critical. We get so used to the good displays we have
nowadays.

On the right hand side of the case are the on/off switch and a
contrast control. At the rear there is a DC input, a reset
button, and serial, parallel and cassette ports. I am interested
to know how well the cassette works with a C/PM machine. In
addition there is a phone line in and a modem out port and a
300/1200 baud switch. The ports are protected by small plastic
covers that have to be removed to use the ports. These will
easily get lost and I’m sure my machine is unusual in the all are
still present.

The left hand side reveals a spring loaded flap covering the
system slot into which various expansion modules could be
slotted.

Keyboard.

IMG_20150421_175151043As I mentioned above the keyboard has full sized keys with full
travel. It’s a very nice keyboard and pretty typical of the age.
I’m writing this piece on the machine as I try to do with my
portables and it’s one of the nicest keyboards to type on.
However, having just read back my writing so far there have been
a lot of mistakes. I am probably not used to it yet.

The keyboard has the conventional keys as you would expect. In
addition it has five function keys along the top which can be
combined with the shift keys to give ten (obviously). There is
also a “Stop” key. Unusually, the caps lock key locks in each
position. The cursor keys are a group of triangles arranged in a
square are pointing inwards. You will find a locking “NUM” key on
the left hand side of the space bar. Pressing this makes a number
pad out of the U I O J K L and M keys.

 

That will do for now, I’ll write more in the next post.

Grant Searle’s Multicomp

IMG_20150403_144747337I have just screwed the lid down on the machine you see to the right. This is my self built Multicomp.

Grant Searle has been prolific when it comes to modern builds of retro computers. On his web site you will find examples of Z80, 6502 and 6809 based machines. All with schematics and details on how he built them.

His work has inspired other to have a go at building a simple machine with the minimum of parts (The Z80 uses 7 chips).

The only problem you really face is which to build. He has a solution. Build the Multicomp. This machine is based on a cheap FPGA board that uses free tools from Altera to build a machine that emulates any of the above processors and wraps a machine around them.

The word “emulates” is a bit of a grey term here as the machine is implemented in hardware. This is not the same as running a Spectrum emulator on your WinPC. The logic needed to “be” a Z80 is programmed into the FPGA at build time and there it sits, being a Z80. There is no other software “tricking” a Spectrum program into running. The only software there is  running on the bare metal.

IMG_20150403_145227272_HDRMine all mine.

Mine has been built as a Z80 with 2k of RAM (this saves an external chip but upto 64kb can be accessed). I have two serial ports and a VGA port. These can’t all be accessed at the same time but it’s very easy to reprogram it to use whichever of the port you need.

I’ve used a small piece of blob-board to sit on the FPGA boards I/O pins to give me something to work on. The serial outputs of the FPGA are not at RS-232 levels and so I bought two, cheap, level converters built into 9 way D-type sockets.

IMG_20150403_145144622_HDRThe whole thing is packaged into a box previously occupied by a digital TV decoder that went “POP” in a stylish fashion.

Get out there now and build your own. Please.

Screenshot from 2015-04-03 14:54:31

BBC. What next.

I’ve moved the game on a game a little in the last few days.

When I first tried the machine I tried to type in a four line program to output numbers so I could see if the machine was hanging or if the keyboard interface PIA was failing. At first I couldn’t type it in before the machine hung. I determined that this was overheating and found a cause.

Now I can type in the program but when I run it it crashes with changing errors. Sometimes it reports a bogus/ill formed error message. Sometimes it just hangs. If I press “Break” the machine restarts. I then type “OLD” and the program is still there. When I run it I get the same result.

I’m thinking dodgy a RAM chip. About half of the DRAM has been socketed.

Bit by bit.

I have made some progress over the last couple of days.

I looked at the power rails before and after the hang and nothing to report there really. At bit of hum (about 40mv) but it says constant.

I found that IC 69, the 6522 was getting too hot to touch. Cooling it kept the machine running a little longer. I looked at the circuit diagram and IC69 is connected to the outside world via an 8 bit buffer. I pulled the buffer and the temperature went right down. Looking at the buffer, its pins were filthy and so I cleaned them up with a pencil eraser and then some IPA. When I put the chip back in the 6522 stayed cool. Result.

I think the buffer wasn’t getting powered properly because of the dirty pins and so was taking “Phantom” power through it’s I/O lines. I’ve seem something similar before.

Now the machine is running for a few minutes before hanging. Much improved.

My plan now is to work through the rest of the chips making sure that they are not just seated well but also cleaned :-)

BBC. Closing in?

I have asked for clues on the StarDot forums, a valuable source of BBC knowledge.  Within hours some very good ideas were suggested.

So far I have tried cleaning and re-seating the socketed chips and swapping the 6522s but to no avail. I have measured the volages on the supply rails before and after the hanging but they don’t change.

I also tried putting a spot of IPA on the back of the chips to see which was getting hot. The hottest should evaporate the IPA quickest. I couldn’t tell but I thought the machine stayed running for longer because of the cooling effect but I’m not sure.

I’ll keep trying.

BBC Micro. So close.

Spoiler alert. If you don’t want to know what happened, don’t read the title of this post. Too late.

I got home tonight to find that the new keyboard cable for the BBC Micro had arrived. I plugged it in and just a long beep. Doh!

I then did a lot of looking and checking and found that the left most pin on the motherboard had been bent over at some point. I bent it over and tried again. This time, beep, beep and a banner and prompt.

Yea!

IMG_20150311_184500250However. It hands after a minute of so. A restart and it only lasts seconds and so I’m convinced that it’s thermal. More investigation needed.

 

BBC Micro. Fix first bit.

As I said in my previous post, the BBC micro was showing some signs of life but wasn’t booting. I sent off for capacitors for the PSU and they arrived. In with the screwdrivers.

IMG_20150310_192638665[1]Just three screws from the back and the PSU is on the bench. The unit itself is a little trickier to take apart but not difficult.

Be aware there can be high voltages on the board even when it’s out of the computer and disconnected from the mains.

The easiest way is to pop out the switch and external power connectors first. A flat bladed screwdriver will let you press the springy plastic lugs down and then they push out. Look out for the two green earth leads bolted inside.

Then the unit is out.IMG_20150310_193434344[1]

I think two of the caps had already been changed which just left the electrolytic at C9 (IIRC). This looked bad and was bulging so out it came.

I reassembled the machine but to be honest I wasn’t expecting a change as I think the fault is caused by the keyboard cable and not the PSU. Changing the cap was a safety measure. Hopefully the cable will arrive in the next day or two.

IMG_20150310_211215630[1]

BBC Model B micro

IMG_20150308_165922022Now be honest. Is there anyone aged between 35 and 55 in the UK who hasn’t used a BBC micro? This little machine was massive over here. They were everywhere, Rugged, dependable, terrific BASIC interpreter, in-line assembler. The list goes on and on.

This machine came to me from my friend Tris. He is another retro-computer collector but unlike most of us, knows when enough is enough and decided the his BBC Master would be enough and gave me this non-functioning unit.

Under the lid.

An Issue 4 mother board.
An Issue 4 mother board.

The machine has an Issue 4 mother board. I think this is a bit unusual. From memory I think Issue 3 and Issue 7 were the most numerous. Another thing it has is a lid lined with aluminium foil. Curious. I wonder if it gave out too much interference for the TV or somesuch.

Aluminium foil inside the lid. RFI problems perhaps. Or just to keep it fresh?
Aluminium foil inside the lid. RFI problems perhaps. Or just to keep it fresh?

Power up.

When power is applied, I here one beep. There should be two. With a monitor connected there is a nice raster on the screen and a flashing cursor. Nothing more.

The keyboard connector has seen better days.
The keyboard connector has seen better days.

A look inside shows that the keyboard connector is very tired, with a number of connections broken. I tried to reconnect the broken ones. There was a brief bit of activity as the words “BBC Micro…” started appearing on the screen. _VERY_ Slowly. I tried a reset and things got worse. The beep didn’t end.

Now I’ve seen that the machine is close to working and so my strategy is this.

  1. Replace the keyboard cable – I have one on order.
  2. Replace the capacitors in the power supply – It won’t hurt.
  3. Re-asses the situation.

 

 

Sharp MZ-700

Sharp MZ-700.

I’ve been tinkering with my recently aquired Sharp MZ-700. I’ve solved the problem of getting programs into it by playing it WAV files from another machine using a cheap car cassette adapter and it’s working like a good’un.

Sadly a couple of the key switches are broken and to my surprise they aren’t individual switches. I’m on the lookout for bits and bobs to fix it.