Introductions

beeingdavid · 26-10-2024, 05:42 PM

Hi, I have recently joined this forum.
My first Microbee was a Series 1 16k machine, which I later upgraded to 32k at Software 80 in Brisbane.
I later acquired a disk-based Bee. I still have both these examples.
In 2012 I bought a Premium Plus kit. It has been sitting on a shelf, but I am about embark on its construction.
I have just powered up my series one. For a few days in a row, it happily powered up with the friendly beep. I didn't have a composite video monitor, but I did get confirmation that the machine had booted to the Microworld prompt by plugging the video into a Y input. It wasn't syncing obviously, but in amongst the hash was the occasionally readable Microworld prompt.

I powered down, purchased an av lead for my TV, and powered it up again today (only one day later) and it failed to beep or produce a video signal. Nothing had been physically disturbed since the last time it booted up.
I removed the original plug pack from the setup and connected a variable power supply. I raised the voltage to slightly above 12 volts (measured by DMM), but still no beep or video.

The only thing I can think of is that the humidity is much higher today.

I'm going to open it up, check the boards, and see whether there is anything obvious wrong, and see whether re-seating the upper board makes any difference.

Bear in mind it was working when I disconnected the power yesterday.
There have been no explosions or smoke signals.

If anyone has any ideas about what might have changed overnight, I would appreciate any information.
Cheers,
David

***ChickenMan*** · 26-10-2024, 08:05 PM

Hi David, welcome to the forum and back into the Microbee world Smile

Remove and re-insert the top coreboard a number of times generally helps. Same for any removable chips. I wouldnt raise the voltage above 12v in fact I'd lower it to 10v as the Tant caps near the voltage regulators tend to fail. Have you checked the output voltages of the voltage regulators?

Looking forward to your Premium Plus kit construction story. I have one and is simply the BEST Microbee ever made.

beeingdavid · (This post was last modified: 27-10-2024, 05:54 AM by beeingdavid.)

(26-10-2024, 08:05 PM)ChickenMan Wrote: Hi David, welcome to the forum and back into the Microbee world

Remove and re-insert the top coreboard a number of times generally helps. Same for any removable chips. I wouldnt raise the voltage above 12v in fact I'd lower it to 10v as the Tant caps near the voltage regulators tend to fail. Have you checked the output voltages of the voltage regulators?

Looking forward to your Premium Plus kit construction story. I have one and is simply the BEST Microbee ever made.

Hi Chickenman, thank you for your encouragement. I have reseated the core board a few times, but unfortunately it is still being passive aggressive. No beeps for me. I have checked that there is voltage to the board, and I am getting around five volts at one of the voltage regulators. I haven't yet reseated any of the ICs. Next I will probably replace the filter capacitor. When I was using the variable power supply, the Bee wasn't beeping till it had at least 11 volts. If something should have happened it ten suggests that there was a bit of a drain that shouldn't have been there. so I had thought 12 volts would give it a bit of a margin. The plug pack is marked 12 so I thought it was safe, but now I note that the actual voltage from the original plug pack is closer to 11. I suppose I should move this discussion to another thread "people who gaze sadly at their silent machines" or something!I haven't done any circuit fault finding for decades, so I'm hoping the diagnostic flywheels will eventually come back up to speed, though I'm more familiar with audio and radio. Is there a diagram anywhere showing expected voltages or signal shapes at different parts of the circuit? Though I'm heavily suspecting the power section.
All the more motivation to get on and build the kit!

***ChickenMan*** · 27-10-2024, 09:39 AM

Yes, some of the Technical manuals have wave shapes etc, all the Repository so just apply to access it - https://microbeetechnology.com.au/forum/thread-15.html

Yes, time to start on the Premium Plus, you wont regret it.

CheshireNoir · 27-10-2024, 01:36 PM

Hey Beeingdavid,
This group can certainly help with advice and encouragement on the fixing front. They've all helped me plenty of times, and now I get to help other people.
The "Microbee Hardware" channel is where I put most of my plaintive meepings :-)

BTW, My course of action for fixing your board would be as follows:
1) Check what voltage you're getting across one of the 74 series chips on the core board. If not 5v, investigate.
2) Clean the connectors between the main (lower) board and the core (upper) board. These are a common source of failure. Some deoxit on the sockets and an ink eraser on the pins should help.
3) Check the reset signal. If you have a fast multimeter, or a logic probe, this will help. An oscilloscope is very useful, and these days they have got ridiculously cheap, and will make light work of it. Check pin 18 of the right hand connector. It should stay low, then go high. (I had a world of pain with a bad reset circuit on one of my 'bees)
4) See if any chips are getting excessively hot, especially RAM chips. You can risk your fingertips, or get a contactless thermometer. If you have access to a thermal camera, this becomes trivial. Of course, it only helps with the core board chips.
5) At this point I would go and get some riser cards from someone. These allow you to lift the core board up and out of the way of the main board, and allow you to star looking at signals on the main board. Very useful things to have! You're in deep diagnostics territory here. Thank fully there are a lot of resources available to help diagnose. Test ROMs and the like.

Also, enjoy building up the Premium Plus. I love building kit computers now (I have built three computers, a console and two different core boards for my Microbee) and hope to pick up one of Ewan's new ones when they become available. So much fun, even when they don't work.

Cheers!

John

beeingdavid · (This post was last modified: 29-10-2024, 06:44 PM by beeingdavid.)

(27-10-2024, 09:39 AM)ChickenMan Wrote: Yes, some of the Technical manuals have wave shapes etc, all the Repository so just apply to access it - https://microbeetechnology.com.au/forum/thread-15.html

Yes, time to start on the Premium Plus, you wont regret it.

Thanks for this!

(27-10-2024, 01:36 PM)CheshireNoir Wrote: Hey Beeingdavid,
This group can certainly help with advice and encouragement on the fixing front. They've all helped me plenty of times, and now I get to help other people.
The "Microbee Hardware" channel is where I put most of my plaintive meepings :-)

BTW, My course of action for fixing your board would be as follows:
1) Check what voltage you're getting across one of the 74 series chips on the core board. If not 5v, investigate.
2) Clean the connectors between the main (lower) board and the core (upper) board. These are a common source of failure. Some deoxit on the sockets and an ink eraser on the pins should help.
3) Check the reset signal. If you have a fast multimeter, or a logic probe, this will help. An oscilloscope is very useful, and these days they have got ridiculously cheap, and will make light work of it. Check pin 18 of the right hand connector. It should stay low, then go high. (I had a world of pain with a bad reset circuit on one of my 'bees)
4) See if any chips are getting excessively hot, especially RAM chips. You can risk your fingertips, or get a contactless thermometer. If you have access to a thermal camera, this becomes trivial. Of course, it only helps with the core board chips.
5) At this point I would go and get some riser cards from someone. These allow you to lift the core board up and out of the way of the main board, and allow you to star looking at signals on the main board. Very useful things to have! You're in deep diagnostics territory here. Thank fully there are a lot of resources available to help diagnose. Test ROMs and the like.

Also, enjoy building up the Premium Plus. I love building kit computers now (I have built three computers, a console and two different core boards for my Microbee) and hope to pick up one of Ewan's new ones when they become available. So much fun, even when they don't work.

Cheers!

John

Thank you for this advice. I'm thinking of putting my energy initially into building the Premium Plus kit and then returning to the restoration of the old Bees. I also have a BBC model B but I'm not touching that until I've re-capped the power supply. Too many reports of blue smoke from that PS! Can't wait for the new kits to be released!