A5000 repair and the origins of ctrl-g

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DutchAcorn
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A5000 repair and the origins of ctrl-g

Post by DutchAcorn » Thu May 05, 2016 4:20 pm

Recently I bought an A5000 with battery damage and today I managed to get it working again (mostly).

The excellent information on the Retro-Kit site was very helpful in getting it back to life. The main issue was my developing soldering skills :oops: .

In the end all the south pads of IC58 came loose. I restored two of them using IC feet through the conveniently nearby holes in the PCB (pins 5 and 6).

Some of the things I found during this process:
- the monitor type is set to auto if the CMOS chip can't be read. So you can use a normal VGA display to debug.
- the floppy drive does not always flash error codes
- it can take 34 (!) seconds for the Supervisor prompt to appear with a failing CMOS chip
- sound is can be off with a defective CMOS chip - don't rely on ctrl-G or a start-up beep.

In other words: the machine can appear completely dead with a CMOS chip issue, wait at least 34 seconds before thinking about other causes.

The state before:
before.jpg
And after:
after.jpg
To my surprise I did not need to fix the connection to R281 from IC58, it seems to be redundant.

At some point in the process I had a chip that had constantly changing cmos values giving random results. One of the start-up screens I got was this one:
floppy startup.jpg
The IDE interface does not work. Any suggestions how to find the failing track there are appreciated. Is there a full circuit diagram available for the A5000?
Last edited by DutchAcorn on Fri May 06, 2016 9:15 am, edited 1 time in total.
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Re: A5000 repair

Post by Zarchos » Thu May 05, 2016 4:56 pm

http://chrisacorns.computinghistory.org ... awings.zip

What is Ctrl G for exactly ?
Had never heard of this key combination.

Nice job, board is very clean and soldering looks if not perfect, more than very good to me.

I've got an A5000 I saved after a very heavy battery leakage but like you no IDE working, so if you do the job and help me find which tracks I should check ...(I'd like not to have to change the IDE connector, I don't have the tools to do that properly) it could be yet another fully restored Archie.
=D>

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Re: A5000 repair

Post by paulv » Thu May 05, 2016 5:51 pm

DutchAcorn wrote:Recently I bought an A5000 with battery damage and today I managed to get it working again (mostly).

The excellent information on the Retro-Kit site was very helpful in getting it back to life. The main issue was my developing soldering skills :oops: .
I'm glad the site helped you :D your repair looks nice and neat.

Getting the IDE to work can be a pain I had an issue with the floppy drive due to damaged tracks. The only way to test was to continuity check each pin all the way back to the PC style IO chip to try to find the issue. As the floppy and IDE traces are all closely packed together it can be a tricky task with plenty of false positives so check each line two or three times and any that appear to be broken, double check you're on the right pin and contact for the line.
Zarchos wrote:What is Ctrl G for exactly ?
Had never heard of this key combination.

Nice job, board is very clean and soldering looks if not perfect, more than very good to me.
Ctrl+G = VDU 7 = BEEP

If you hit f12 in the desktop and press ctrl+g the machine should beep. Ctrl+g does not work in the desktop environment though so if you bit a machine without a screen, Ctrl+g can't be used to verify the machine has booted unless you hit f12 first to drop to the command prompt.

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Re: A5000 repair

Post by Zarchos » Thu May 05, 2016 6:38 pm

Ah ok thanks for this info.
One a day and one day I'll fully understand how an Archie works, who knows ?
I'll have to remember Ctrl+G with 'G' for Grunt, I'll assume (Woops I hope Peter N. isn't reading :twisted: ).
'S' was too easy after all, it could have meant 'Sound' so at Acorn, they had to find something more cumbersome.
#-o

OK I leave, see the avatar. :wink:

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Re: A5000 repair

Post by paulv » Thu May 05, 2016 6:49 pm

Ctrl+G predates Acorn entirely as it forms part of the 7-bit ANSI character set and I'd just one of many control codes available.

https://en.wikipedia.org/wiki/ANSI_escape_code

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Re: A5000 repair

Post by 1024MAK » Thu May 05, 2016 9:10 pm

For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
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Re: A5000 repair

Post by paulv » Thu May 05, 2016 9:29 pm

Indeed :D =D>

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Re: A5000 repair

Post by DutchAcorn » Fri May 06, 2016 8:55 am

paulv wrote:...Getting the IDE to work can be a pain I had an issue with the floppy drive due to damaged tracks. The only way to test was to continuity check each pin all the way back to the PC style IO chip to try to find the issue. As the floppy and IDE traces are all closely packed together it can be a tricky task with plenty of false positives so check each line two or three times and any that appear to be broken, double check you're on the right pin and contact for the line.
Thanks Paul, do you have access to a circuit diagram? I could trace the data lines to IC37 and IC49, ground pins are ok and found and fixed one issue but there are still some pins I have trouble tracing.

It now only recognises IDE drive 2 but that produces all kind of errors (SWI call errors, window size does not fit, broken directory).
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Re: A5000 repair

Post by s1paulr » Fri May 06, 2016 9:09 am

I believe that CTRL+G or BEL predates ASCII and goes back to the 5-bit Baudot days of the 19th century.

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Re: A5000 repair and the origins of ctrl-g

Post by 1024MAK » Fri May 06, 2016 11:05 am

BEL does: https://en.wikipedia.org/wiki/Baudot_code#Western_Union
Not sure about CTRL+G

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Re: A5000 repair and the origins of ctrl-g

Post by s1paulr » Sat May 07, 2016 6:29 pm

You are quite correct Mark. I should have said "The origins of CTRL-G or BEL, as it is referred to in the ASCII table, predates ASCII and goes back to the 5-bit Baudot days of the 19th century, as the name and function is derived from the original Baudot BEL name and function although the coding is of course different as ASCII is 8-bit and Baudot is 5-bit".

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Re: A5000 repair and the origins of ctrl-g

Post by 1024MAK » Sat May 07, 2016 6:42 pm

No worries :D

Reminds me that a lot of terminology and the words and terms go back to telegraph and the telephone system. And the various systems that then were developed from these. In my job, (well before my time, I hasten to add :lol: ) the systems used branched off and different areas then had their own ideas, procedures and systems (as normal, that's what happens with private companies, some of which were competing directly, or indirectly with each other).

But despite that, ideas were borrowed, and eventually some standardisation started to happen.

And now, ASCII which became more or less the standard in the mid to late 1980's has been replaced by Unicode.

But we still have a lot of things where the history dates back a lot further than people think :wink:

Mark

PS, so some of the history bits of computer studies that I did from 1983/1984 has come in useful :shock:
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Re: A5000 repair and the origins of ctrl-g

Post by DutchAcorn » Sat May 07, 2016 7:44 pm

Right, so I found and fixed 2 broken tracks, but still no joy. I suspect pin 28: drive select. But I can't find any tracks going to pin 28 on the PCB. Without a circuit diagram it is like finding a pin in a haystack.

Any chance on a picture with the IDE connector removed anyone? Or else a reference to the component pin 28 of the IDE connector is supposed to connect to? [-o<
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Re: A5000 repair and the origins of ctrl-g

Post by JonC » Sat May 07, 2016 8:11 pm

I found these on my HDD, any help?
Attachments
Acorn_A5000TRM_MainPCBCircuitDiagram4of4.pdf
(375.57 KiB) Downloaded 37 times
Acorn_A5000TRM_MainPCBcircuitDiagram3of4.pdf
(590.9 KiB) Downloaded 37 times
Acorn_A5000TRM_MainPCBCircuitDiagram2of4.pdf
(915.82 KiB) Downloaded 36 times
Acorn_A5000TRM_MainPCBCircuitDiagram1of4.pdf
(821.45 KiB) Downloaded 40 times
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Re: A5000 repair and the origins of ctrl-g

Post by steve3000 » Sat May 07, 2016 8:50 pm

JonC wrote:I found these on my HDD, any help?
A5000 circuit diagrams are also available on Chris's Acorns here:
http://chrisacorns.computinghistory.org ... s.html#TRM

The all important A5000 tech ref manual I scanned last year should still be available here (let me know if not):
viewtopic.php?f=16&t=8026&p=108059&hili ... ce#p108059

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Re: A5000 repair and the origins of ctrl-g

Post by DutchAcorn » Sat May 07, 2016 9:27 pm

Thanks guys, that makes tracing the connections a lot easier! Pin 28 is not connected according to the circuit diagram, no wonder I could not find the track. :roll:
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Re: A5000 repair and the origins of ctrl-g

Post by DutchAcorn » Sun May 08, 2016 1:09 pm

I traced all the connections from the IDE socket and all measure ok now. I can sometimes access an IDE drive but the data is corrupted:
image.jpeg
Next suspect is the IC49 buffer chip; it was also somewhat green from the battery leakage so it may have been affected.
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Re: A5000 repair and the origins of ctrl-g

Post by 1024MAK » Sun May 08, 2016 1:41 pm

As well as testing the tracks for conductivity. Also test for low and medium resistances between them. Contamination on a PCB can cause all sorts of signal distortion, as some contamination partly conducts.

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Re: A5000 repair and the origins of ctrl-g

Post by DutchAcorn » Tue May 10, 2016 8:14 pm

1024MAK wrote:As well as testing the tracks for conductivity. Also test for low and medium resistances between them. Contamination on a PCB can cause all sorts of signal distortion, as some contamination partly conducts.

Mark
Thanks Mark, I have. I've decided to desolder the IDE socket (when time permits) and check the condition there.

While checking for continuity / resistance I documented the places I used to check the tracks and inserted them in a photo of my slightly molested PCB. This may help others checking the IDE connector after battery leak damage. Yellow numbers are the pins on the connecting IC, orange numbers are the pin numbers of the IDE socket. Pin 34 connects to 5V via a 10K resistor.

Because the resistor (R282, 10K) is very close to the IDE socket I chose to find a point to check the track including the resistor.
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A5000 PCB.jpg
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Re: A5000 repair and the origins of ctrl-g

Post by Zarchos » Tue May 10, 2016 8:48 pm

Thanks a lot, Paul.
It's a great work you're sharing, this picture should help a lot of people (including me). =D>

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Re: A5000 repair and the origins of ctrl-g

Post by DutchAcorn » Thu May 12, 2016 4:09 am

Here's a picture of the PCB under the IDE socket showing the tracks. There was no track damage I could find, no improvement yet. :|
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image.jpeg
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Re: A5000 repair and the origins of ctrl-g

Post by DutchAcorn » Sat May 21, 2016 9:27 pm

Replaced IC49 (74HCT245), IDE is now fully working! :D :D :D

Thanks for all the help!
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Re: A5000 repair and the origins of ctrl-g

Post by 1024MAK » Sat May 21, 2016 10:16 pm

Well done on getting it fully working =D> \:D/ =D>

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Re: A5000 repair and the origins of ctrl-g

Post by DutchAcorn » Fri Jun 22, 2018 10:57 am

Yesterday I managed to fix another A5000. This one had more track damage. The tracks damaged by battery alkali are on the top side of the PCB. Many of those tracks have some part of the track on one side and some part on the other side, connected by through-hole points on the PCB. So instead of fixing the track on the top side it is often easier to make the bypass on the bottom side. You just need to find out what through-hole point is connected to what pin on the IDE/Floppy sockets. The tracks run under the floppy and IDE sockets making them harder to trace.

For future reference I made a picture of the underside of the PCB with the bypasses I made to fix broken tracks on the other side of the board. For some I used very thin wire, they are highlighted for clarity.

a5000 IDE Floppy tracks.jpg
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Re: A5000 repair and the origins of ctrl-g

Post by 1024MAK » Fri Jun 22, 2018 12:22 pm

Thanks =D>

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