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Hi from Lew - Lew - 29-01-2021

Hi all,

I have some old Microbees in the basement, and I suddenly got interested in whether any of them still work.  However I couldn't find a power supply, and I was very excited to find this forum in my quest to figure out the power supply requirements and the polarity of the plug.  The latter was very elusive, and I only found that out by studying an image of a plugpak on the Microbee Technology web site!   Then I found some useful information about the voltage and current requirements in a post by "someone" on this forum.   Thank you!

So far I have established that one computer and one monitor works.  The thrill of writing and running a 3-line program last night was still the same!

A standard Microbee 16k was my first computer, and I have fond memories of learning to use it to write simple Basic programs back in the 80's.  It does not seem to work, but it does draw 1 Amp at any voltage between 9 and 12 Volts DC, so something is working!   I'm not sure what I am going to do with any of these computers, but I'd like to get this one working for the sake of nostalgia at least.  You may hear from me again about that.

And now some information to introduce myself.  I am a radio amateur, and am interested in building UHF repeater systems using vintage Philips FM828 radios.   They are comparable in age to the Microbees and are a lovely old two-way "taxi radio".   Recently I have also become quite interested in Micromite computers (see  https://geoffg.net/micromite.html or go to Silicon Chip magazine for projects using the Micromite).  Like the Microbee, they are programmed in Basic, and therefore much easier for me to use than Arduinos.   A 28-pin Micromite is possibly more powerful than a Microbee 16k!  But that's not the point of course...   I like old things.  After all, I are one!


RE: Hi from Lew - ChickenMan - 29-01-2021

Hi Lew and welcome to the forum Smile

You say you found some Microbees in the basement, how many and what variety of Microbee are they? One is a 16k Microbee, thats great, not a lot of those are around today and their biggest issue is corrosion on the pins where the coreboard plugs into the mainboard. Try reseating all the socketed chips and cleaning those coreboard pins.

We should have all the Manuals, Schematics and software you would need in the Repository also.

RE: Hi from Lew - Lew - 29-01-2021

Hi ChickenMan,

Thankyou very much for your welcome to the forum, and for your advice about repairing the 16k.  I will try that.  I have a few operating manuals, but no servicing manuals or schematics, so I will look at the Repository with great interest.

I have four in total.  Here is what I know about the other Microbees at the moment:

Number 2 is the one that is working.  It is not labelled but it has the expansion socket and it comes up with Colour Basic 5.22e, 1983.  I don't know how much memory it has.  Is there a way to interrogate that from the command prompt?  Of course I will get some clues when I open it up.  There's a backup battery floating under the baseboard in a plastic bag, so I need to get in there and clean it up!  This unit only draws about 0.5 A at 9-12 V.

I also have a twin disk unit, which may work with the unit above. 

Number 3 is a B-ETI Serial Terminal.  I have found this morning that it does seem to work, but seems to be sensitive to supply voltage, and only seems to boot up when I change that (between about 10 and 12 V DC).  This might just be a capacitor issue.  I'm not sure how much use a maximum 4800 baud terminal would be these days - it's seems so much easier to use a program on a PC.  Maybe this unit could be reprogrammed as a Microbee?


Number 4 is very old.  It has a metal chassis with a T0-3 voltage regulator on the bottom, and a thin black one-piece plastic cover over the top.  I see no indication of the model.  Like number 1, it draws about 1 A at 9-12 V DC, but it does not boot up.  It also has three AA cells soldered together as a backup battery, and they have not leaked.  They must be at least 20 years old, and they look new!


I have 4 monochrome Microbee screens.  The two rounder ones, which look newer, both seem to work, but one gives 16 V DC on its power socket and the other gives 0.2 V DC, so both need to be investigated.  The other screens two are more square in shape, and look older.  I haven't tested those yet.



RE: Hi from Lew - ChickenMan - 29-01-2021

Your Number 2 if it boots to Basic 5.22e then its an early 16/32k model, probably an IC. The expansion socket (50 way ?) would be typically for a ROM Expansion board.

Number 3 as a B-ETI, well these are almost unknown and would be surely collectable. I know of only 1 other and it was missing its top cover so would love to get a picture or scan of the top cover badge.

Your Number 4 is an early Kit bee and rare as hens teeth, but when you get it going, would be most interested in the version of Basic that you have in it.

I assume your No 1 matches with your twin floppy drive unit. Does this unit have a 50way or 34way cable ?

RE: Hi from Lew - someone - 29-01-2021

Welcome aboard Lew!

Someone is also also a ham and is happy to help you get the microbees up and going again.
Just send someone a PM and we can exchange callsigns.

The metal based microbee is the most interesting.  Do you know what BASIC revision is written or printed on the ROMS?
They might range between 4.9x to 5.00  Are they ceramic purple Hitachi ROMs by any chance?

The metal based microbee runs on about 10VAC @ 50Hz. Back then, plug packs read higher open circuit voltages than when under load.
The TO-3 regulator is rated at 1.5A. AC was used so that a -12V voltage source could be used on the RS232 signals. 
Subsequent models used 10VDC after finding out that most RS232 equipment worked without the negative voltage swing (i.e. +10V to near 0V transition was sufficient).  The change from AC to DC also remedied many 50Hz AC hum issues.

The 3 x 1.5AA batteries replaces the original 4.5V camera battery.

Just ensure that the voltage past the rectifier diodes reads a voltage higher than the dropout voltage of the 7805/LM309K voltage regulator and microbee power good sensing circuit.

If you've got an oscilloscope it'll make things much easier to fix.
(Back in the 1970's to early 1980's owning an oscilloscope with sufficient was just a dream. - Someone didn't have the dosh to afford a 60-100MHz one).
It also pays to use the probes correctly so that you're not seeing distorted signals.


RE: Hi from Lew - Lew - 30-01-2021

Hi ChickenMan,

Thanks for your very helpful reply.  Here are some answers to your questions:

#1:  The 16k model has 8 x 6116P-3 RAM chips.  It does not have a 50-way or 34-way cable.  From what you have said, I don't think any of my machines will work with the twin disk drive unit.  I have just seen that it has WBE and WBF EPROMS. I seem to recall using Wordbee with this computer.

#2:  I have now opened.  I can see that it has 32k or RAM (6116P-3 x 16).  It has BASICA and BASICB  ROMS v5.22 as expected, and a third ROM C v1.10.   Does that confirm that it is an IC?  The expansion port is 50-way.  It does not have a 50-way or 34-way cable either. 

#3: The B-ETI serial terminal does have its top-cover badge, but it has some deposit on it, possibly the remnants of a plastic cover that was not peeled off for a long time.  I have cleaned it up a little for the purpose of photography.  I won't go any further with that until I am confident in proceeding in manner that does not damage the lettering, which is totally OK at this stage.  I have taken a couple of photos, but I haven't figured out how to embed them in this post - please let me know how to do that.


#4:  The very old unit has a blue coreboard.  I have also taken some photos of that.  I'm looking forward to being able to tell you the BASIC version!




Hi someone,

Thanks to you also for your helpful reply. 

It's good to know that you are also a ham, and thanks for your offer of help.  I will send you a PM.

#4: Unfortunately the metal-based unit does not have any version numbers on its 4 BASIC EPROMS, which are labelled A, B, C and 250, in pencil, whatever that means.  From the logo,  think they are Hitachi chips.  They have a white layer sandwiched between the top and the bottom.  I guess that means that they are ceramic.  I wouldn't call them purple, but I think they have a bluish tinge.  I will post some photos when I know how.

I had read some of your posts, and I was wondering whether this model was designed for an AC supply.  I have only tried it with DC so far.  Would that stop it from working, or would it just compromise the serial output?  I will check the voltage at the input of the voltage regulators.

I do have an old Oscilloscope with divide-by-ten probes, but it's certainly not a 60-100 MHz model.  It's OK at 10 -20 MHz on the x10 time-base setting.



RE: Hi from Lew - ChickenMan - 30-01-2021

#1 Yes the eprom is Wordbee Smile

#2 The eprom with 1.2 is also Wordbee version 1.2.  Check the crystal speed, its on the mainboard just above the 9 key.  If its 13.50 then an IC or Series 2 running at 3.375mhz.  If 12.0 then its an early Series 1 running at 2mhz.

#3  You can add the pic in your existing post.  Click Edit Icon bottom right of the page, it the first Icon and select Full Edit.  Then the page opens and go to the very bottom of the page and next to the New Attachment, click the Choose Files and browse to the file on your HD.  Then click Add Attachment and finally click Update Post button.  Done Smile

#4 They didn't write what version of Basic on the early models, and would assume its version 5.0 or 5.1.  We currently do not have a copy of ver 5.0 although it has been recently found and will be made available soon.  Looking forward to your pictures.

RE: Hi from Lew - ejwords - 30-01-2021

Hello Lew & Welcome to the forum.

You have a very nice collection there.. In particular of interest to me is the B-ETI!
Can't wait to see a photo of that one.

If you need assistance in getting any of these going, feel free to ask, or, if you are in Victoria,
drop into the Microbee Technology shop.

RE: Hi from Lew - ChickenMan - 30-01-2021

Thanks for the pics of the B-ETI and your Kit bee which I have included in your post above. Both look in good condition Smile

RE: Hi from Lew - Lew - 31-01-2021

Hi ChickenMan,

Thanks for the additional information about my Microbees. The crystal on the mainboard of #2 is 13.5 MHz, so it is indeed an IC.

Thanks also for putting up the photos of the B-ETI and the Kit bee. I've been doing some work on #1 (Series 1: 16k), and will leave the Kit bee until last.

I will endeavour get a copy of the EPROMS in the Kit bee for the archives.



Hi Ewan,

Thanks for your welcome to the forum., and offer of help. It makes me sorry that I'm in Sydney!

You will see a photo of the B-ETI above. Don't hesitate to ask if you would like any other photos.

Best wishes,