PC85 - Joining the conversation

[CheshireNoir]

Well, I got the PC85 'bee "sort of" working...
https://ilike8bits.com/2021/08/19/2-bee-or-not-2-bee/
Currently (After some additional work from the above post) I have it reliably booting into the Boot Menu ROM (PAK5?)
Unfortunately WORDBEE seems to have stopped working, and I'm not sure which ROM I should be checking. It's usually PAK0? Is that correct? So that would be IC15? (I want to read the contents and see if I can compare it to ROM images)

So I have a couple of questions, if that's OK? (Maybe I should move this to a different part of the forum?)
1) What ROMs would have shipped with these normally? I have 3 empty sockets, and the only app onboard, other than the Menu seems to be WORDBEE.
2) Am I missing something obvious that might have failed that I should be checking?
3) Is there a source of cases, other than buying something gutted from a dead system?
4) What ohmage should the speaker be? This one seems to have a 50Ω speaker, but my other one has an 8Ω speaker. Could this be why the speaker doesn't work?
5) Should I be seeing colour on a PC85? I'm assuming "no".

Thanks everyone! This one has so much nicer picture than the last one. I'm really tempted, if new cases aren't available, to swap it with the guts of my Personal Communicator. That'd be the last resort of course.

[ChickenMan]

Arr some success at last, looking good

1. Your missing the Telcom 3.21 rom, that will also give you the Monitor. Next rom is the Calculator and Self Test.  You can them put in a couple game eproms in the other sockets.
2. The coreboard connector pins & main board sockets, good idea to replace them with gold plated units.
3. No cases commercially available, maybe you could draw one up from the artwork in the repo and get them 3D printed, but easiest would be get a gutted unit.  Also, check out the Super-80 Google Group as it uses the same keyboard and they are making new cases. Totally different to the Microbee case but its still a case that should work.
4. Speaker should be 50 ohm, Microbee Tech has stock if one is needed.
5. Monochrome only unless a colour option has been fitted.  Only the Premium series units had colour built in.

We have also posted the CoreLift files here from wizged and will use your pic showing their use, if thats okay ?

EDIT: The First 2 eproms on the left are BASIC, next is Wordbee (IC15) and next is Telcom (IC20) and next Calc/Self Test (IC25)

[Ernest]

Looking at the picture on the I Like 8 Bit's site the TELCOM ROM looks to be present (the one marked D) lower centre of the Coreboard. This ROM also contains Calculator, Self test and the Monitor. ROM IC25 is the Command help for Basic.
It's possible the TELCOM ROM (IC20) is faulty or there is a problem with the decoding.

Ernest

[CheshireNoir]

We have also posted the CoreLift files here from wizged and will use your pic showing their use, if thats okay ?

No worries at all :-)

Arr some success at last, looking good

1. Your missing the Telcom 3.21 rom, that will also give you the Monitor. Next rom is the Calculator and Self Test.  You can them put in a couple game eproms in the other sockets.

As you posted later, they are in there. It's just all not very reliable. I also don't know enough about the system to use all the features yet. It did come up by accident once.

2. The coreboard connector pins & main board sockets, good idea to replace them with gold plated units.

Sigh. Not looking forward to that. I might try ordering a bunch of Machine Pin sockets and pins, for long term reliability. So much desoldering!

3. No cases commercially available, maybe you could draw one up from the artwork in the repo and get them 3D printed, but easiest would be get a gutted unit.  Also, check out the Super-80 Google Group as it uses the same keyboard and they are making new cases. Totally different to the Microbee case but its still a case that should work.

I'll keep my eyes open for a solution once I get this working.

4. Speaker should be 50 ohm, Microbee Tech has stock if one is needed.

Huh. I've fitted a pin header in that spot to make it easier to add and remove the speaker. I'll order one of those next pay.

5. Monochrome only unless a colour option has been fitted.  Only the Premium series units had colour built in.

I figured as much.

EDIT: The First 2 eproms on the left are BASIC, next is Wordbee (IC15) and next is Telcom (IC20) and next Calc/Self Test (IC25)

I see I have much work ahead of me. Thankfully with this much working, I have some momentum to keep going.


Cheers!

Chesh

[ChickenMan]

I assume you have removed the BASIC, Wordbee, etc eproms and cleaned their pins and re-seated them. If not I would be doing that as a priority.

[CheshireNoir]

I assume you have removed the BASIC, Wordbee, etc eproms and cleaned their pins and re-seated them.  If not I would be doing that as a priority.

I have. I have also now replaced the connectors between the Base and Core boards, and replaced the socket for IC27 (PAK 5, aka the Menu).
It's still unreliable. I checked the contents of the ROMs and they seemed "sane". I'll compare them to a dump to see if there are major differences.
If there aren't, I suspect it's time to pull out the scope and see if there are noisy traces or the like.

Thanks for the help!

Chesh

EDIT: I just compared the ROMs to PC85 ROMS from "outside sources" and A-E ROMS are identical. I ROM (IC27) seems different but dropping the different version onto a ROM and running it gives me a system that flashes up the menu then crashes.

[ChickenMan]

There were 2 version of the PC85. The pic of your Menu shows it is the first version. The second version, generally referred to as PC85b, has extras included in the Menu and had an updated coreboard. I tried the PC85b eprom IC27 (PAK 5, aka the Menu) in my PC85 (same as yours, the 1st version) and it crashed also.

[CheshireNoir]

Thanks ChickenMan.
That makes sense. I'll need to see if I can find the correct ROM.
I did find something interesting tonight, that may help pinpoint some of the issues. I burned a 16k "double rom" of kilopede in the lower 8k and microspac_invaders in the upper 8k and dropped it in IC24 position. If I run PAK2, I get kilopede. If I run PAK10 I get the option not installed message, which suggests it may be not switching ROM banks properly. I might desolder the chip in the slot nearest the damage (IC36) and see if it's OK.

Chesh

[Ernest]

PAK5 should be called SHELL not MENU as there is a separate MENU ROM used in the PC85b, this ROM actually resides at PAK 10 position.
So even if you do hid correct decoding you can't access ROM 10 as it is reserved for the MENU ROM.
That's the reason the "PC85b eprom IC27 (PAK 5, aka the SHELL)" crashes is that it tries to switch in the MENU at PAK 10 position and doesn't find it there.

That all said as Chickenman stated, there is two versions the PC85 and the PC85b.
The PC85 can only address PAK ROMs 0 - 7. PC85B adds and extra data line to the HCF4042 Latch and this latched output is used to bank switch the PAKs to decode ROM PAKs 8 - 15.

The board revision that enabled this was Rev 6, you have the Rev 4 board, but still doable if required.
However I would get it working in it's present form first before launching into any upgrading.

Ernest

[CheshireNoir]

PAK5 should be called SHELL not MENU as there is a separate MENU ROM used in the PC85b, this ROM actually resides at PAK 10 position.
So even if you do hid correct decoding you can't access ROM 10 as it is reserved for the MENU ROM.
That's the reason the "PC85b eprom IC27 (PAK 5, aka the SHELL)" crashes is that it tries to switch in the MENU at PAK 10 position and doesn't find it there.

That all said as Chickenman stated, there is two versions the PC85 and the PC85b.
The PC85 can only address PAK ROMs 0 - 7. PC85B adds and extra data line to the HCF4042 Latch and this latched output is used to bank switch the PAKs to decode ROM PAKs 8 - 15.

The board revision that enabled this was Rev 6, you have the Rev 4 board, but still doable if required.
However I would get it working in it's present form first before launching into any upgrading.

Ernest

Thanks Ernest!

I was looking at the core board description here and it seemed to suggest this core board supported the 27C128 series ROMs. If this revision doesn't support the double density ROMs. that explains some of the issues I was seeing.

I found a fried signal diode near the corrosion and replaced it, but it still hasn't come good. My next plan is to socket the ICs near the corrosion so I can test them separately out of circuit.

What is getting me is that once it's stable, it's stable for quite a while. I've had no end of fun playing Kilopede and games off "tape", so once it gets into BASIC it works quite well.

Never been able to get the NET command to work right and it's pretty random as to whether it boots to the Shell (Most of the time, at which point BASIC and WordBee usually work), BASIC (At which point WordBee usually works) or just WordBee (At which point you're usually just stuck)
This makes me think it's an issue with the line select logic, which, looking at the schematics would seem to be mostly tied to IC28 and IC31, if I'm reading things right?

Anyway it's gone into the "naughty corner" until next weekend as I want to work on other stuff until then.
Thanks for everyone's help here! It kept me investigating for a lot more of the weekend than I initially planned :-D

Chesh