New Microbee with a 1217 colour board

[someone]

Someone had one of the original colour microbees.
The colour bee was designed to connect to the TAXAN/Kaga Denshi & monitors which had analog signal support.
VSYNC and HSYNC rates retained their standard settings for 50Hz monochrome output so that with the use of a modulator it could be connected to a standard PAL TV.

Rather than just use the limited 16 colour TTL colour CGA standards, it output analog levels to make use of the monitors' analog capabilities.
If you look at the marketing literature, you can see the additional colours.

This was scheme was dropped on the Alpha Plus (Premium Series) to use a smaller connector so it could fit on the base board.

[CheshireNoir]

Someone,
Is there any documentation on this model? I assume it was something with a new baseboard, rather than the "tacked on" feel of the 1217.
(BTW got the 'bee booting today. All it needed was the 4700uF capacitor downrated to 470uF and it's happily loading software).

John

[someone]

It's good to hear your system is booting.
The original kit microbees were powered using a 12VAC plugback to provide a negative voltage for the serial port and hence had a large filter cap and diode bridge on the baseboard to derive the 10VDC. This was changed to a 10-12VDC power supply to minimise 50Hz mains hum affecting the video output signal with the serial port losing its negative voltage. This new configuration meant that a smaller mainboard filter capacitor could be used because the main filtering cap and the diode bridge was in the external power supply. When switch mode power supplies are used the filtering cap may be further reduced as not to present transient short circuit upon power up. The single 1.5A TO-3 voltage regulator was replaced with 2 x TO-220 1A regulators which used the keyboard bracket as a heatsink.  The single 5V rail on the baseboard was split into 2 separate ones - one for each voltage regulator.  The diode bridge was replaced with an inline polarity protection diode. (These days we could use a MOSFET)

Someone didn't have much documentation on the Colour board.
The colour daughter board was just a tacked on the baseboard using wirewrap sockets, a few PCB mods and patch wires.  (Not dissimilar to how the S100 TCT PCG was tacked on to the S100 DG640 VDU).
It is a horrible thing - particularly to repair.

In addition to colour capability, a video memory contention circuit was added to remove the annoying black flickers however this introduced CPU wait states so the firmware needed the appropriate adjustment for bitbashed functions such as Tape, Serial and Spaker. (The colour contention circuit was later redesigned twice - once as a motherboard revision for standard bees and another for the Alpha Plus (Premium Series).  Implemented with Monostable Multivibrators with an RC network, the trimmer resistors are adjusted so the flickers disappear. 

MW Colour BASIC also introduced a new COLOUR/COLOR statement but it isn't actually implemented as a tokenised keyword. It's handled in a quite different manner and can handle either spelling.

[Ernest]

Hi John,
There were four versions of the "below Mainboard" colour add-on's.

MB1217 - Standard (original)

MB1217 - Analog (fuse in the ground line to pin 14/15 of the D15 output connector) also a three level (analog RGB) output was added to pins 13,11 & 12.

MB1217 -3-01 The fuse was moved to the +5 Volt line instead of the ground and the fused +5 Volt was routed to Pin 9 of the D15 output connector.

MB1217 -4 01 The final version before the Microbee design moved to the Premium mainboard which integrated the Colour onto the Main board. This version was designed to work with the MB1248 Rev6 Mainboard.
As this new mainboard had a Deglitch circuit integrated into it's design, the deglitch circuit was dropped from the last Colour adapter board reducing the parts count and the number of interconnections between the two boards.

All four of these diagrams should be in the schematics section of the Repository.

Ernest

[CheshireNoir]

Thanks Someone and Ernest,
I'm still learning so much! There's so many interesting pieces of history here. My board has the following markings: DRG 1217-4-06 followed by 1217-54-07W.

Next weekend I'll see if I can get colour out of it :-)
(Need to wait for a pay cycle. I also need to pay off a third party for the 3 x Microbee Disk System units he sold me for what I thought was a very reasonable price)

John

[Ernest]

Hi John,
Do you have a monitor/TV with a SCART input? if so you can borrow my adapter to get you under way till you sort your own interface, just call or sms.

Ernest

[CheshireNoir]

Thanks Ernest,
I won't take you up on that as I won't have any spare time between now and the weekend anyway. My current project "on the bench" is actually an Atari ST project :-)

(I also need to save up so I can buy one of Ewan's keyboard conversion kits)

Cheers!

John

[CheshireNoir]

I should probably add that the 4700uF Capacitor, when removed from the mainboard has a distinct rattle when gently shaken. Methinks it may have been my root cause of issues.

John

[Ernest]

If you are using a switched mode power source you don’t need the hulking big 4700uF, a 470 uF will be fine in that case.

Ernest

[ChickenMan]

I have changed most of my 4700uF caps with 1000uF caps in Microbees but to 4700uF in power supplies.