Restoring my Microbee

dinotron · 12-02-2022, 01:35 PM

Hi all,

As mentioned in the Intro thread - I just acquired a Bee - ready for restoration.

I used a Bee as a kid - though didnt really do much except learn to write BASIC apps - it was only 16K and I never got the chance to upgrade it or play with much software.

I picked it up last night - and have discovered the following:

1. Despite the listing saying 16K, (as noted in the intro channel) the unit has been upgraded to PC85/colour. So from what I can see, the top board - its got 32K ram and a bunch of ROMS (and another spare rom stored inside the case!)

2. An extra board underneath the main board, which I assume is the colour expansion

3. The monitor I got - I guess is just a B/W monitor with composite only. It doesn't seem to be able to connect to this Bee (maybe it was used prior to the upgrade)

4. The battery on the top board had begun to leak - I removed it -- doesn't seem to have cause any tracks to fail.

I do have some questions if I may:

1. The colour expansion board, seems to me, to be attached with pin headers -- also seems to have a wire soldered from it to the main board. Is this removable? And is it the colour expansion?

2. Is the 15 pin connector from this board the video out? I think i was reading this morning that its an RGBI/CGA video signal. Is that correct?

3. The monitor is a bit of a mystery to me. As I don't think it can connect to the Bee - as there is no matching port. I guess it might have been connected to it via a composite signal, before the colour upgrade was done. Unless the 15 pin connector also has composite?

4. General visual inspection of the boards seem fine - just the usual dust and grim. Will re-seat the ROM sockets. I didn't see any caps that look bad --- Is it recommended to re-cap these boards? If so, any guides on what caps etc?

5. To get colour output, I guess I need to get a converter setup to feed into my VGA LCD monitor - found this https://www.insentricity.com/a.cl/220/br...uit-layout I have plenty of the GBS-8200 RGB to VGA converters. How do people typically connect their Bees to LCD screens?

6. Tech/schematic/pinouts: I haven't had a chance yet to search for - I assume the repo has images/docs to help in restoring the unit. Any recommendations?

7. Also noticed that the `colour` pins dont seem to be soldered (see attached pic) - is that normal?

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Thanks
Dean

***ChickenMan*** · 12-02-2022, 04:42 PM

A nice looking Microbee, congrats Smile

To answer your questions,

1. Yes thats the Colour expansion board. The smaller board is the Viatel board. But you have ROM H which would of been the Viatel ROM replaced with the EDASM rom.
2. Yes its CGA out, for pin out see the file microbee_colour_socket_connections.pdf in the Repository in the MbeeTech\Microbee\Documentation\Articles\Technical folder.
3. If the monitor is Composite, then its connected to the Bee via RCA plug on the grey lead with the 5 pin DIN plug at the one end.
4. No caps need to be replaced specifically though the small Tantalum caps can explode and/or catch on fire when powered up. So replace if they do. Normally the ones near the voltage regulators on the top core board or the ones under the left & right sides of the keyboard.
5. I use the CGA to VGA unit sold by Microbee Systems - CGA to VGA Video Converter - Microbee Technology - The home of the Microbee computer - Online Store though it appears hes out of stock at the moment.
6. Yes all the Schematics etc you need are in the Repository.
7. Pins not soldered, hmm I have no idea why not as one of my boards are the same, I think they are there to help line up the other pins that actually connect to the board.

someone · 12-02-2022, 05:38 PM

Yay! and Yikes! in the same breath! A colour microbee in good nick!
However, they're bastards to work on! (Cut PCB tracks and a bunch of spaghetti wiring!)

From the photos:
a. Those unsoldered DIP pins are normal, they're where the wirewrap sockets from the baseboard mate with the colour board.
(Yes, you can remove the colour board if you really want but it is fiddly.)

b. Thank goodness you removed the leaky NICAD battery!

c. You can construct your own composite cable to connect to the colour port.

d. Power up the microbee using a lower input voltage (lower is better!).
A suitable variable DC power supply is ideal where you vary the voltage from 8V to 12v.
It's a great sign if you can power it up and get a beep!

If you don't - no don't fret.
Please place and update post once it's powered up (beep or not).

dinotron · (This post was last modified: 12-02-2022, 06:22 PM by dinotron.)

Thanks ChickenMan and Someone for the advice Smile

, especially regarding power

I will try and figure out the monitor/cable connection. Will do a bit of reading/reviewing to figure it out.

But as is the usual - I am very time poor at the moment - probably not gonna get to it until March - ho -humm

Will update here when I do the first power on test - will shield my eyes in case a cap goes bang! Sad

Dean.

I just had a closer look at the cables - stupid me - yeap there is a 5 pin din connector - with a barrel connector - which appears to be for power, an RCA - guess that's the comp video, and 2 3.5mm sockets - guess there for cassette. A red and a blue one - dont know which is input/output though - so i guess i can connect this to the Monitor - but for colour i would need to get the CGA interface going

So how does the colour output work ... Is it 2 completely separate systems? and you switch from one to the other? Or does the composite include the colour signal?

Maybe I might find a little bit of time tomorrow to do a power on test.

***ChickenMan*** · 12-02-2022, 07:06 PM

Both the Colour port out of the 15pin socket and the mono Composite out of the grey cable both work at the same time, you can use either or both.

CheshireNoir · 13-02-2022, 11:22 AM

What an amazing system! the previous owner obviously loved it enough to do a lot of upgrades.
As you have mentioned you're time poor, I am loathe to mention this as a good solution, but one solution to get CGA into modern colour LCD is NecroWare's MCE Adapter (https://github.com/necroware/mce-adapter). That'll get your CGA up to suitable signals for an VGA style monitor. (I use one with my Comm0odore 128 for 80 column mode)
Unfortunately it's only half the battle, as you'll need some way of handling the 15KHz signal coming out of your Microbee. I have two different solutions that I use. The first option is to have a monitor that supports 15KHz natively, which is my primary solution. (http://15khz.wikidot.com/ and https://15khz.net/. I have an Acer V226HQL and I love it very much. I use it with my Amiga, C128, Amstrad CPC, Atari ST and Acorn systems). My secondary solution, and I believe it's built off the same technology as the CGA to VGA adapters above is a GBSControl. It's a modified GBS8200 with a few extra chips added for a rocksteady upscaler for a very reasonable price, but very DIY :-D https://github.com/ramapcsx2/gbs-control
I will admit to NOT having a colour 'bee, so I just use composite on a little LCD telly I have.

Chesh

dinotron · 13-02-2022, 06:22 PM

Hi ChesireNoir,

I am informed, that the previous own was a bit of a collector - he passed away a few years ago - and his daughter is managing the sale of his old computers. There is also a commodore 128 and an Ollivetti M24 with 2 CRTs from the same seller (https://www.ebay.com.au/sch/red55shoes/m...pg=&_from=)

The Microbee has its original box, receipts and a few manuals and publications -- If I can get it operational - I want it to be fully functional, and displayed nicely - should be able to make it quite visible in the background for zoom meetings as well ---- will become quite the conversational piece i think.

Thanks for the link to the mcd-adapter - looks interesting - I see its using a PLD - I assume its much the same as the one I linked to - but they replaced the 2 chips into 1 PLD to reduce size - not a bad idea - will certainly check it out.

For the upconverting to VGA frequency - I have some GBS8200 (and also a OSSC) --- i know they work - due to my other retro activity (been playing with RC2014 kits and extending it with full MSX compatibility - its a lot of fun exploring Japan's take on the Z80 (https://hackaday.io/project/175574-msx-c...for-rc2014) - that was my pandemic distraction. Now retro computing has become more of an obsession!

I have previously looked at the GBS-control mod - but so far I have not needed the extra quality/control - but I would like to do the mod one day!

I was reading thru the repository last night - and found the original schematics for the colour boards (there is some really cool stuff in there) -- there were 2 schematics I found. I don't really know too much about video stuff, but it seem to me the Microbee colour is more EGA than CGA - as it has an intensity signal for each colour - not just the single intensity. Also there appeared to have been 2 versions --- one where the RGB analogue signals are also suppled -- no idea if both were made, and what version would be in my machine.

I did attempt to power on the machine this afternoon - just a quick test -- unfortunately no speaker sound on powering - but also no smoke or other scary things happened. I really feel I want a full day -- take my time with it - next month should have a bit more time.

Dean.

***MbeeTech*** · 13-02-2022, 07:56 PM

The original colour boards had (essentially) 2 bits per R,G & B with no intensity signal.
There were also 2 versions of the board - the first version required an external circuit to combine the 2 bits per colour into an analogue
output, whereas the 2nd version of the board included that circuitry on the board and the resulting signals fed out other pins of the DB15
connector. Both versions of the board provided COMPOSITE sync out only (ie, Separate Horizontal and Vertical Sync signals were not available
at the output connector.
The colour scheme with these boards was 26 Foreground colours with 8 Background colours.
This differs from when the Premium series came out as it had standard digital RGB + Intensity that was
compatible with the IBM CGA 9 pin connector.

someone · 17-02-2022, 08:42 AM

A historical tidbit: The change to use standard IBM CGA interface came from the development of the Alpha plus baseboard where there was space for a D9 connector and not the D15 connector.

***MbeeTech*** · 17-02-2022, 09:45 AM

(17-02-2022, 08:42 AM)someone Wrote: A historical tidbit: The change to use standard IBM CGA interface came from the development of the Alpha plus baseboard where there was space for a D9 connector and not the D15 connector.

It was a good move anyway, to move to a more common standard, and also to not have 2 of the same connector for different purposes (parallel port / colour port)