A3000 restoration

Arc/RPCs, peripherals, RISCOS operating system & ARM kit eg GP2x, BeagleBoard
markdryan
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A3000 restoration

Postby markdryan » Sat Aug 26, 2017 12:45 pm

The A3000 found in my dad's garage has now been restored. I'd like to take the credit for the restoration but to be honest my father did most of the work. My contributions were limited to making the tea and chronicling his endeavours.

The A3000 was bought in September 1990 and was heavily used for about 2 years. It was put into storage but was used for a few months in 1996. It then sat dormant for 8 years. I turned it on briefly in 2004 and found that I needed to boot holding down R to get to the desktop. Sadly, this was long before I discovered stardot and was unaware of the evil nature of CMOS batteries, so I played a game of Zarch and then put it back in the garage with its battery still in place.

Fast forwarding to Tuesday, the machine still booted but did not retain CMOS settings. The battery had leaked as can be seen in the first picture (taken through a magnifying glass, which is why it looks a bit warped). We removed the battery, cleaned up the board and connected up a single AA battery seated in battery compartment following the instructions here (http://www.waitingforfriday.com/?p=701# ... he_battery). The cleaned up motherboard with the wires (and diode) leading into the battery compartment are shown in the second image.

The machine booted up but did still not retain its CMOS settings. It turned out that the connection between the battery and the R7 resistor was corroded. We replaced it with a small piece of insulated copper wire, which fixed the problem. The machine now seems to be working fine although it's a little difficult to test fully until I get a compatible monitor.

I'm planning to upgrade the OS from RiscOS 2 to 3.11 but to be able to really use the machine I'm going to need some sort of hard disk and a compatible monitor.

My understanding is that I can connect it up to a BenQ 912 without any modifications to the machine. Is this correct or do I really need to get a VIDC enhancer?

What are my options for connecting a hard disk to an A3000 in 2017?
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badbattery.jpg
goodbattery.jpg

RobC
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Re: A3000 restoration

Postby RobC » Sat Aug 26, 2017 2:06 pm

Good job =D> :D

markdryan wrote:My understanding is that I can connect it up to a BenQ 912 without any modifications to the machine. Is this correct or do I really need to get a VIDC enhancer?

I believe you can just connect up the monitor as it will scan down to 15KHz but others will know for sure.

markdryan wrote:What are my options for connecting a hard disk to an A3000 in 2017?

You'll need an IDE or SCSI podule. Unfortunately, they are increasingly difficult to find and are therefore very expensive when they turn up (particularly the internal/mini podules).

Some IDE podules are better with modern storage (e.g. CF/SD cards) than others. The Castle mini-podule is particularly fussy but things can be improved by soft-loading Wizzo IDEFS. I've found that DOMs work well and sometimes turn up on eBay for very reasonable prices.

On the SCSI side, I use SCSI2SD in my R260 and that works really well. >2GB mechanical drives sometimes turn up at reasonable prices.
Last edited by RobC on Sat Aug 26, 2017 6:24 pm, edited 1 time in total.

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danielj
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Re: A3000 restoration

Postby danielj » Sat Aug 26, 2017 3:56 pm

You can use all the standard TV modes with the BenQ, but not sure if it'll cope with the A3000's pseudo - VGA. A vidc enhancer will give you proper VGA frequencies.

d.

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paulv
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Re: A3000 restoration

Postby paulv » Sat Aug 26, 2017 11:17 pm

danielj wrote:You can use all the standard TV modes with the BenQ, but not sure if it'll cope with the A3000's pseudo - VGA. A vidc enhancer will give you proper VGA frequencies.

d.


I've only got an A3000 out at the moment and it's got a VIDC Enhancer with just a 25.175MHz clock on board as opposed to the traditional 36MHz VIDC Enhancers because it's an ARM2 processor and MODE 31 really pushes the capabilities of the machines unless an ARM 3 is fitted.

The pseudo VGA screen modes kind of work with the BenQ 912 as that's what's attached to my A3000 but without adjustments the display is a good inch away from the left hand side of the screen. As soon as the VIDC Enhancer driver loads up (I have it in the ROM on my IDE board), the display switches over to the correct position and all is well and the display requires no adjustments at all.

I really need to pull my finger our and get the stack of VIDC Enhancer boards I have built up at some point. Things just take a lot longer than I expect for me to do these days so the boards don't get the attention they deserve :(

Paul

markdryan
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Re: A3000 restoration

Postby markdryan » Fri Sep 01, 2017 9:27 pm

A quick follow up.

The BenQ 912 monitor arrived this morning and I was able to test the restored A3000 properly for the first time. And by test I mean playing Elite and Populous for a couple of hours. Everything seems to be working fine.

I have a follow on question about the BenQ monitor. I think I read in a separate thread that someone had got this working with a BBC. Could anyone tell me what sort of cable I'd need to connect a BBC master up to the BenQ 912? The master is currently connected to a old Samsung 40inch LEDTV which is taking up a lot of room on my very small desk. Replacing it with the BenQ 912 would free up just enough room on the desk for the A3000.

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danielj
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Re: A3000 restoration

Postby danielj » Fri Sep 01, 2017 9:45 pm

You'll need to make something the equivalent of the RGB-SCART cable with the resistors in it to reduce the level of the signals to something the monitor can take:
http://mdfs.net/Info/Comp/BBC/Monitor/BBCtoTV.htm

Then it's a question of taking the R,G &B to the relevant pins on the VGA connector:
http://pinouts.ru/Video/VGA15_pinout.shtml

I think the c-sync should go to pin 13.

d.

markdryan
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Re: A3000 restoration

Postby markdryan » Fri Sep 01, 2017 10:30 pm

Thanks for the info.

I was sort of hoping there would be some sort of scart to VGA connector I could use with my existing RGB to scart cable. I've had a look online but haven't been able to find anything suitable. Does anyone know if such a thing exists and would work with a master and a BenQ 912? If not, I'll have a crack at making something. It looks like it might be fun.

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1024MAK
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Re: A3000 restoration

Postby 1024MAK » Sat Sep 02, 2017 5:36 am

Apart from one I made up (DIN to VGA), I have only seen such a cable once, but can't remember where. Buy a normal VGA cable chop one end off the VGA cable, use a meter to work out which cable core goes to which pin, then wire to the appropriate plug. Don't forget the resistors.

Mark
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danielj
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Re: A3000 restoration

Postby danielj » Sat Sep 02, 2017 5:40 am

(ha! Snap! :D)

The easiest thing is to lop the end off a VGA cable, use a multimeter to identify the r-g-b, ground and sync wires, solder the resistors in to the relevant din plug, then solder the wires to the other ends of those (I don't have a picture to hand, but hope this makes sense) ideally stick some short lengths of heat shrink over the wires which you can then pull down over the resistors to prevent shorting.

The biggest pain is wiring up the VGA connector, so using an existing cable makes it a bit easier and provides a length of cable! :)

Failing that I'm pretty sure Mark at retroclinic would build you one at a reasonable price.

d.

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trixster
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Re: A3000 restoration

Postby trixster » Sun Sep 03, 2017 7:37 am

Mark at retroclinic will definitely be able to supply you the correct cable... because he's already supplied me with three! :mrgreen: =D>
A3020 | A3000 | BBC B + 128K RAM/ROM + 20K Shadow + Pi0 + VideoNuLA
BBC Master Turbo + DC | Atom | A1200 060 | A500 | Jaguar | A420/1
A4000/040 060 | Atari Falcon 060 | Saturn | PS1 | SNES | CPC6128 | C64 | 3DO | MD

markdryan
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Re: A3000 restoration

Postby markdryan » Sun Sep 03, 2017 7:52 am

Thanks. That's good to know. I'll order a cable from retroclinic.

markdryan
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Re: A3000 restoration

Postby markdryan » Tue Sep 05, 2017 1:51 pm

Sad news I'm afraid. The A3000 is unrestored. I turned the machine on last night and it booted to desktop without any problems. I spent about five minutes typing things at the comand prompt after having pressed F12. However, when I returned to the desktop the machine crashed. The desktop screen sort of appeared but it was corrupted. I rebooted the machine but it only rebooted to supervisor. Now no matter what I do I can't get it to go back to the desktop, even when holding down R or DEL during the boot. I don't seem to be able to change any CMOS settings and when I type modules I only see one utility module listed. The keyboard is working fine.

Reading other threads this seems to be indicative of a dead CMOS chip. Does this seem like a reasonable diagnosis? I was hoping that it was just one of the connections to the CMOS chip but they all appear to be good. Assuming I order a new CMOS chip are there any instructions for removing the old chip and fitting a new one? Also what tools would I need to remove and fit? I used a multimeter today for the first time so replacing a chip on a motherboard is really stretching my skills here. However, as the machine is useless right now, I might as well give it a go.

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DutchAcorn
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Re: A3000 restoration

Postby DutchAcorn » Tue Sep 05, 2017 2:32 pm

That's bad news :(

Have you checked that the CMOS chip is getting power when the A3000 is switched on? And are you sure the DEL key works perfectly?

2 x yes and judging from the first photo you posted I'd say a failed CMOS chip is likely. It is a through-hole chip. For instructions how to remove this video may be useful.

A solder pump, desoldering braid and sharp small pliers will make life a lot easier...

Also note that the old solder may not flow well because of the battery alkali. Some solder flux will help if you have it, otherwise you could try to add a little fresh solder.

Good luck!
Paul

markdryan
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Re: A3000 restoration

Postby markdryan » Tue Sep 05, 2017 4:01 pm

> Have you checked that the CMOS chip is getting power when the A3000 is switched on? And are you sure the DEL key works perfectly?

I haven't checked that the CMOS chip is getting power but I have checked the keyboard. All the keys are working fine, including delete and R. I'll follow these instructions http://stardot.org.uk/forums/viewtopic.php?f=16&t=9436#p109644 tonight.

Thanks for the video link. If I do need to replace the chip it will help a lot.

steve3000
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Re: A3000 restoration

Postby steve3000 » Tue Sep 05, 2017 5:33 pm

It does sound like a dying chip, but as well as power, also check continuity from all other pins on the cmos RAM chip - the tracks for data c0 or c1 and the clock circuit often corrode before power tracks and lead to spurious errors (although usually accompanied by POST error of cmos RAM unreadable).

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DutchAcorn
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Re: A3000 restoration

Postby DutchAcorn » Tue Sep 05, 2017 6:01 pm

markdryan wrote:... I'll follow these instructions http://stardot.org.uk/forums/viewtopic.php?f=16&t=9436#p109644 tonight..

In addition to that you can measure that pin 5 of the CMOS chip connects to IC13 pin 44 and pin 6 connects to IC13 pin 45. Those are the two data lines Steve refers to.
Paul

markdryan
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Re: A3000 restoration

Postby markdryan » Tue Sep 05, 2017 9:03 pm

I've verified that the CMOS chip is getting power and I've checked all the tracks between the pins and whatever it is they directly connect to. Everything seems to be okay.

> In addition to that you can measure that pin 5 of the CMOS chip connects to IC13 pin 44 and pin 6 connects to IC13 pin 45. Those are the two data lines Steve refers to.

I haven't done this yet. If I understand correctly, this will involve removing the motherboard in which case it's more of a weekend job.

In anticipation of having to replace the chip, could someone recommend a suitable replacement? I found some recommendations here (http://www.retro-kit.co.uk/page.cfm/content/Acorn-BBC-A3000-Battery-Maintenance/) but they seem to be discontinued.

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danielj
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Re: A3000 restoration

Postby danielj » Tue Sep 05, 2017 9:07 pm

Mark Hayesman (retroclinic) definitely has a stock of the through hole ones that you need for the A3000?

http://www.retroclinic.com/

d.

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DutchAcorn
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Re: A3000 restoration

Postby DutchAcorn » Wed Sep 06, 2017 6:39 am

markdryan wrote:...I haven't done this yet. If I understand correctly, this will involve removing the motherboard in which case it's more of a weekend job...

It is the square chip just north of the column of RiscOS roms. You should be able to access it without removing the main board but in all fairness, I have not opened my A3000 to check. Pin 1 on this chip is the middle pin of the 17 pins on the right side of the chip. It is marked as "1" on the pcb. Pin counting is counter clockwise; the pin above pin 1 is pin 2.
Paul

markdryan
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Re: A3000 restoration

Postby markdryan » Wed Sep 20, 2017 9:03 pm

Mark Hayesman (retroclinic) definitely has a stock of the through hole ones that you need for the A3000?


In the end I sent the entire computer off to retroclinic who promptly fixed it and sent it back. For the record the issue of the machine only booting to supervisor was fixed by replacing the CMOS chip. There were a couple of other issues with the mouse and the clock that were also fixed. I've used the machine for about 5 hours over the last week and it's still running fine. Thank you Mark!

The return of the A3000 marks an important milestone in my stardot membership. It means I'm now at liberty to post my beeb setup.


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