A visitor from Sweden!

[Crud3]

Progress! 

I managed to write some diskettes and after swapping out (and rejumpering) the two drives I got it to boot!



I was also then able to check on the commandline which keys that worked and which that didn't! It turns out there are only a few that are actually dead so that is a great start...
I will probably end up desoldering all of them in the end anyway but I thought I would initially do just a few to get my bearings! 
Another interesting thing was that I got convinced that the keycaps of the special Swedish keys were placed in the wrong spots as the keyboard layout in the Monitor and in CP/M are not the same! 
Turns out they are in the right spots for use in the OS!

I am in the process of setting up my solderstation and desoldering gun at the moment so will probably start the keyboard refurb next week! I found mentions of two different versions of the key switches and the ones in mine have a white shaft so will try to find some instructions for those keyswitches specifically!

[ChickenMan]

Thats fantastic, all looking good then There is a Keyswitch repair guide in the Repository in the MbeeTech\Microbee\Documentation\Articles folder called microbee_key_switch_repair_guide, worth checking out

[Crud3]

Finally!

Since the last post I have managed to refurbish the keyboard to complete working order... a lot of desoldering and resoldering of keyswitches!

As a sidenote I would like to point out that the keyboard repair guide mentions that you can exchange the resistor network at RN1 from a 10 pin SIP 3.3K one to a 10 pin SIP 10K one and change IC3 from a 74LS151N to a 74HC151N and see if that helps before starting desoldering and refurbishing the keyswitches! I think that the correct chip to change should be IC4! On all the schematics and my motherboard IC3 is a 74LS157N while IC4 (next to RN1) actually is a 74LS151N...

I also managed to find an original Microbee monitor and recap the powersupply in the screen! It had a small crack in the bezel which is now repaired!
The only thing still to do is to respray the bezel matte black where the crack was but it is now to the point where I am prepared to call it finished!



Thank you so much for all the great tips and feedback from you guys!

[ChickenMan]

Thats great that its finally up and running as it was originally intended.  The amber monitor looks great and is the same as I used back in the 80's as well.  Now you need a few games to play

[Crud3]

Yup will get some diskimages with games downloaded and written! Any recommendations?
Also am I correct in my assumption, mentioned above, that the instructions in the keyswitch repair guide refer to the wrong IC, IC3 instead of IC4?

[ChickenMan]

Start with arcade 1 & 2 as outlined here https://microbeetechnology.com.au/forum/...php?tid=14  The 56k DS40 images should work still on your bee.  Yes I believe it should be IC4 rather the IC3, expect to find many more errors in the tech docs and schematics, unfortunately.

[someone]

The 74xx151 is either IC3 or IC4 depending upon the microbee mainboard model.
As for the resistor network, this value can be tuned according to your circumstance - e.g. low resistance or high resistance key switches.

These tunings are bodges made to accommodate the high resistance switches.

Even with brand new sealed bag old stock keyswitches have developed the unwanted high resistance.
It's probably due to the chemistry used for the carbon pills.

It's performance being not dissimilar to the fault stolen electrolyte formula for electrolytic capacitors.

[Crud3]

Got some 74HC151N and 10K Resistor Networks coming from Mouser in a few days and will try to use those to fix a Microbee with Basic that I have picked up as well but that had been relegated to the corner while I focused on getting the Disk Microbee refurbished! It has an even worse keyboard response with even fewer keys working than the Diak one... so if swapping those components out does the trick then I am happy!

Also I had to clean up the bottom of the case but luckily not the mainboard after the 4.5V battery memory backup that had leaked and in its place fit a battery holder for three 1.5V AA batteries instead! It now boots to the Basic screen but the keys... well they do not cooperate! I have measured the resistance levels and they seem really high compared to the Disk Microbee so I hope that replacing the new IC4 and RN1 will do the trick! If not then back to desoldering and refurbishing keys again!

[ChickenMan]

An alternative could be a permanent fix for the keys, check out https://www.facebook.com/MicrobeeTechnology

[Crud3]

Purchased two of the keyboard replacement kits today! One as an "insurance policy" for my Microbee 128k SBC shown above! The other for a recent pickup of a PC85 32k Series 3 with the battery backed up Basic!

That last one has a weird issue when it boots up and shows the startup message! As soon as the > basic prompt is displayed it acts like someone is pressing the 1 key. The line fills up with 1's and just keeps going.

The guy I got it from had tested the fix from the keyboard repair guide and replaced IC4 with a LS74HC151N and RN1 with a 10K one instead of the 3.3K original! I think he might have gotten the wrong resistor network type! He got a 10 pin (which it is) resistor network with 9 resistors! Is that correct or should it be a 10 pin with 5 resistors?