Upgrading A310 RISC OS 2 to 3.11

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rharper
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Upgrading A310 RISC OS 2 to 3.11

Post by rharper » Wed Sep 11, 2019 4:21 pm

I have an A310 with an issue 2 motherboard & RISC OS 2 that I want to upgrade to 3.11.
I have the Acorn ALA32 upgrade and ROMs.
There is link 12, molex pins not fitted and no tracks between the pins.
Instruction 6, Figure 1, says cut a track at LA18 with a issue 1 board so I did not do that.
I soldered the 3 wires to LA18, 19 & 20 as described, attached the board and roms.
At power on the video was slow appearing and just before I could power off the tantalum bead capacitor at C37 between the 0v and 12v connectors blew. :(
By a small miracle I have replaced the capacitor and restored it all to its RISC OS 2 status and it is still working.
I don't want to risk destroying the motherboard with a second attempt without some idea of what I did wrong.
Should the track at LA18 be cut even with an issue 2 board?
Step 7, Figure 3, for soldering the wires shows the track cut but that could be just for an issue 1.
Does the capacitor blowing fit that possibility?
Any help welcome, particularly from someone with a RISC OS 3.11 A310 issue 2 motherboard.
Ray
Attachments
L12.png
C37cap.png
figures.png
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IanS
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by IanS » Wed Sep 11, 2019 4:48 pm

C37 is a common failure on A310's, it's unlikely to be related to the RISC OS upgrade. (search for C37 on *.)

rharper
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by rharper » Wed Sep 11, 2019 5:03 pm

IanS wrote:
Wed Sep 11, 2019 4:48 pm
C37 is a common failure on A310's, it's unlikely to be related to the RISC OS upgrade. (search for C37 on *.)
OK, but this is a new old stock motherboard so the C37 had only been powered twice before.
Ray
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Kazzie
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by Kazzie » Wed Sep 11, 2019 5:09 pm

rharper wrote:
Wed Sep 11, 2019 5:03 pm
IanS wrote:
Wed Sep 11, 2019 4:48 pm
C37 is a common failure on A310's, it's unlikely to be related to the RISC OS upgrade. (search for C37 on *.)
OK, but this is a new old stock motherboard so the C37 had only been powered twice before.
Ray
Components can still age and degrade without being used. (Think of leaky batteries, for example!) And you can have components fail on their first use, too:

Image
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rharper
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by rharper » Wed Sep 11, 2019 8:01 pm

Fair enough.
Unless someone says I should cut the track I'll give it another go tomorrow.
Ray
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by rharper » Thu Sep 12, 2019 8:39 am

On reflection, although I don't understand the motherboard tracks, it doesn't seem to make sense to split the L18 track so that it continues on the motherboard and goes to the ALA32 board.
Cutting seems right.
Ray
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by Kazzie » Thu Sep 12, 2019 9:47 am

rharper wrote:
Thu Sep 12, 2019 8:39 am
On reflection, although I don't understand the motherboard tracks, it doesn't seem to make sense to split the L18 track so that it continues on the motherboard and goes to the ALA32 board.
Cutting seems right.
Ray
Reading the instruction extract you've posted, it states that you need to cut a track because LK12 isn't available on issue 1 PCBs. But you said yours is an issue 2 PCB, and your photo shows a position for LK12 (albeit not fitted). My first impression is that you shouldn't need to do any cutting of tracks, though something may need to be done at LK12.

I don't have anything older than a 420/1, so I don't have any first-hand experience of this upgrade, but I'm happy to act as a second pair of eyes and a sounding board. Could you point me toward a full copy of the instructions you're referring to, so I can get properly up to speed? Thanks.
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by Kazzie » Thu Sep 12, 2019 10:14 am

Here's an extract of the circuit diagram for the A300 series:
a310-lk12.png
LK12, connecting LA18 to pind 2 or 24 of the ROM sockets
LA18 comes in to LK12 on pin 3, and pin 2 is grounded. By putting jumpers either north-south or east-west on LK12 (when fully fitted) one can choose whether LA18 is connected to pin 24 of the ROM sockets, or pin 2. (The other will be grounded.) This appears to be for the purpose of supporting pinouts of different types of 28-pin ROMs: 27C301 vs 27C101. The default appears to be connecting LA18 to pin 24 (A16 on a 27C301 or 27C1000), with pin 2 grounded.

Cutting LA18 on an issue 1 board would leave A16 floating, with a carrier board taking control of it instead.

My personal preference would be to fit some pins to LK12, and control things with jumpers there. It would make life a lot easier if you ever wanted to remove the ALA32 board and re-fit the RISC OS 2 ROMs in the future (for testing, or whatever).

Before doing that, I'd suggest using a multimeter to check whether there is already continuity between locations 1&2 and 3&4 of LK12. Those would need to be cut before fitting pins to LK12.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
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rharper
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by rharper » Thu Sep 12, 2019 11:11 am

Thanks Kazzie.
The fitting instructions are here http://chrisacorns.computinghistory.org ... ctions.pdf
The ALA32 board contains a replacement LK12 and has the jumpers set for RISC OS3 but can also be set for RISC OS 2 ROMs & EPROMS.
If LK12 is supposed to take control shouldn't LA18 be cut regardless of the board issue?
Ray
Last edited by rharper on Thu Sep 12, 2019 11:15 am, edited 1 time in total.
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Kazzie
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by Kazzie » Thu Sep 12, 2019 11:39 am

rharper wrote:
Thu Sep 12, 2019 11:11 am
Thanks Kazzie.
The fitting instructions are here http://chrisacorns.computinghistory.org ... ctions.pdf
The ALA32 board contains a replacement LK12 and has the jumpers set for RISC OS3 but can also be set for RISC OS 2 ROMs & EPROMS.
If LK12 is supposed to take control shouldn't LA18 be cut regardless of the board issue?
Ray
Thanks for the link.
LK12, when fully fitted, allows you to isolate or redirect LA18 however you wish.
From the documentation, the functionality of LK12 is replaced by LK5 on the expansion board.
The advice given in the fitting instructions for an issue 2 board mean you will effectively be cutting LA18 at LK12, either by removing the jumper if fitted, or cutting the default track if it isn't.

Cutting LA18 elsewhere, as advised for an issue 1 board, should achieve the same effect on an issue 2 board, but I'd suggest following the instructions given for an issue 2 board, rather than experimenting with your own hybrid solution.

Note in particular instructions 3 and 4 (as your board doesn't have molex pins fitted):
3 If the LK12 position is available but the Molex pins are not
fitted, check for tracks between pins 1-2 and 3-4. If these tracks
are present, you must cut them.

4 After cutting the tracks, fit Molex pins, which enable the
machine to be returned to its original state. You do not need
shorting links here, unless you intend to return the board back
to its original state (that is, using 1Mb ROMs without the upgrade
board).
I suggested above that a good way to check definitively whether there are tracks between 1-2 and 3-4, is to do a continuity check with a multimeter when the machine is off. But the Mk1 eyeball is the tool Acorn advise. ;)

Step 4 is technically optional (you don't need it for the expansion board to work), but it'd be just as well to do it while you have the machine disassembled and ready for soldering.

After that, you can skip instructions 5 and 6 (as they aren't relevant) and continue from instruction 7 onwards.
Last edited by Kazzie on Thu Sep 12, 2019 11:39 am, edited 1 time in total.
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM, ZIDEFS with 512MB CF card
Acorn System 1 home-made replica

rharper
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by rharper » Thu Sep 12, 2019 6:55 pm

Yeh! RISC OS 3.11 is up and running :D
The problem was relying on eyesight rather than technology.
It looked like there were no tracks at LK12 from pins 1-2 & 3-4 but they were covered by the white paint.
Checking continuity with my multimeter before & after cutting the tracks solved the problem.
Thanks Kazzie for good advice.
Ray
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Re: Upgrading A310 RISC OS 2 to 3.11

Post by Kazzie » Thu Sep 12, 2019 7:06 pm

rharper wrote:
Thu Sep 12, 2019 6:55 pm
Yeh! RISC OS 3.11 is up and running :D
The problem was relying on eyesight rather than technology.
It looked like there were no tracks at LK12 from pins 1-2 & 3-4 but they were covered by the white paint.
Checking continuity with my multimeter before & after cutting the tracks solved the problem.
Thanks Kazzie for good advice.
Ray
Great news! :) =D>
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM, ZIDEFS with 512MB CF card
Acorn System 1 home-made replica

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