A5000 freezing and random problems

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steve3000
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A5000 freezing and random problems

Postby steve3000 » Mon Jun 27, 2016 9:40 pm

I have an A5000 which I've been using fairly regularly for the past year and a half, and it has just started failing in a very bizzare way. I wonder if anyone has experienced this type of failure before and any thoughts on what could be causing it...

Before I go into the issue, bear in mind that the CMOS battery was replaced about 2 years ago and the PCB is in pristine condition - there is absolutely no evidence of battery leakage, no corrosion around the CMOS chip, all legs of the surface mount ICs near the battery are shiny and in perfect condition, the ARM3 chip's legs are also in perfect condition... In fact it is probably the best condition A5000 PCB I've seen, since I've been playing with these as retro-computers (and I have seen quite a few A5000 PCBs!) :)

So the issue - a couple of days ago the computer started randomly freezing/unfreezing when in use. The freezes stopped everything including the disc drive access, to the mouse pointer - completely frozen, but the screen was still displayed (so VIDC is still functioning and DMA still occurring). When the computer unfroze (anything from a few milliseconds to a few seconds later) everything was working again until the next freeze. Over time the freezes seemed to get more frequent until the computer would no longer start up...but after leaving the computer overnight it was working again and usable for quite some time until the freezing started again.

Tonight it's been running for an hour so far with no freezes.

I thought the freezing was the only problem, but when thinking more about the computer, and probing a bit more over the weekend - there are a few strange things with this A5000:

1) it boots up extremely quickly - unnervingly quickly in fact - considerably quicker than my A540 (which has a faster ARM3 chip). It's as if the POST is not taking place at all on the A5000... (can this be disabled in the CMOS ram?)
2) (possibly related to #1) switching on holding down Del or R doesn't do anything - computer boots as normal, no attempt to reset CMOS ram or clock [I only discovered this today!]
3) pressing Ctrl-Break doesn't do anything (but Ctrl-Reset does work) - the Break key is working but seems to be acting like an Escape key (I had assumed this was a faulty line in the !Boot file - but today realised the same happens even if no !Boot file is run at startup...)

Any thoughts?

munchausen
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Re: A5000 freezing and random problems

Postby munchausen » Tue Jun 28, 2016 6:29 am

In my experience random freezes like this are caused by capacitor failure. However, I've not got that much experience with acorns.

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daveejhitchins
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Re: A5000 freezing and random problems

Postby daveejhitchins » Tue Jun 28, 2016 6:34 am

Something failing when it get warm would be my guess. Try going round with a can of freezer spray. Capacitors, IMO, are a little further down the list!

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Zarchos
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Re: A5000 freezing and random problems

Postby Zarchos » Tue Jun 28, 2016 8:02 am

Haven't you got some routines relying on the IOC you could use to test this chip ?
Keyboard failures, freezes to me the IOC should be checked.
Have you tried tapping the capacitors around it while the machine is running to see what happens ?

sirbod
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Re: A5000 freezing and random problems

Postby sirbod » Tue Jun 28, 2016 9:28 am

Funny you should mention your A5000 playing up, I switched mine on last week to be presented with a blank screen and no response.

I tried resetting the CMOS, but it looks pretty dead to me. I've not had a chance to look at it yet, but suspect component failure.

JonC
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Re: A5000 freezing and random problems

Postby JonC » Tue Jun 28, 2016 9:31 am

sirbod wrote:Funny you should mention your A5000 playing up, I switched mine on last week to be presented with a blank screen and no response.

I tried resetting the CMOS, but it looks pretty dead to me. I've not had a chance to look at it yet, but suspect component failure.


Mine does exactly the same thing, not had chance to look at it yet. John (Flaxcottage) is also having issues with his..... :shock:
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steve3000
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Re: A5000 freezing and random problems

Postby steve3000 » Tue Jun 28, 2016 10:56 am

Thanks for the responses!

munchausen wrote:In my experience random freezes like this are caused by capacitor failure. However, I've not got that much experience with acorns.

I was thinking maybe capacitors... RobC recently had success with his A4 which was freezing, by cleaning the PCB and replacing a few of the capacitors: http://www.stardot.org.uk/forums/viewto ... 16&t=11382
daveejhitchins wrote:Something failing when it get warm would be my guess. Try going round with a can of freezer spray. Capacitors, IMO, are a little further down the list!

...Yes, before going down the route of replacing capacitors, I really want to rule out any obvious failing components. Will try freezer spray - but typically, as soon as I posted this thread, my A5000 has suddenly started behaving itself again. :roll:
Zarchos wrote:Haven't you got some routines relying on the IOC you could use to test this chip ?
Keyboard failures, freezes to me the IOC should be checked.

:D yes, I've got a rolling set of test routines which I ran for an hour this morning, but the computer was behaving itself... (even Ctrl-Break worked a couple of times, but not any more...)
Zarchos wrote:Have you tried tapping the capacitors around it while the machine is running to see what happens ?

I did tap around the PCB when it was having its last period of repeated freezing and there did seem to be an improvement when I was tapping near the ARM3 and the 50MHz oscillator... Possibly this has lead to the computer behaving itself more today.
sirbod wrote:Funny you should mention your A5000 playing up, I switched mine on last week to be presented with a blank screen and no response.

I tried resetting the CMOS, but it looks pretty dead to me. I've not had a chance to look at it yet, but suspect component failure.

Not a good week for A5000s! :(

I actually have a second A5000 which does exactly as you describe (blank screen, no POST errors, no signs of life) - however it proceeded to reach this state in a gradual failure over a few weeks last year, through random crashes, internal errors on start up, etc. I had no time for a full investigation, so moved to using my spare A5000 (the one which this thread is discussing)...

However, I suspect/hope the cause of the blank screen/completely dead A5000 is something to do with the power-on RESET process. Try switching on, and pressing RESET a few times / holding RESET when switching on / etc. Also try leaving it for 10 minutes then press RESET.

Reason I think this is because I have a RiscPC which failed in a very similar way and pressing RESET would sometimes get it going again. After some investigation I tracked the fault to a failed IC (74HCT14) (from the power-on reset timing circuit) and repaired it - still working fine today. Investigation and repair is documented in this thread: http://www.stardot.org.uk/forums/viewto ... =16&t=9960 :)
JonC wrote:Mine does exactly the same thing, not had chance to look at it yet. John (Flaxcottage) is also having issues with his..... :shock:

As above, for the black screen/completely dead A5000s - check the power-on reset circuit, and try pressing RESET a few times...
Last edited by steve3000 on Tue Jun 28, 2016 11:01 am, edited 1 time in total.

RobC
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Re: A5000 freezing and random problems

Postby RobC » Tue Jun 28, 2016 11:00 am

steve3000 wrote:1) it boots up extremely quickly - unnervingly quickly in fact - considerably quicker than my A540 (which has a faster ARM3 chip). It's as if the POST is not taking place at all on the A5000... (can this be disabled in the CMOS ram?)
2) (possibly related to #1) switching on holding down Del or R doesn't do anything - computer boots as normal, no attempt to reset CMOS ram or clock [I only discovered this today!]
3) pressing Ctrl-Break doesn't do anything (but Ctrl-Reset does work) - the Break key is working but seems to be acting like an Escape key (I had assumed this was a faulty line in the !Boot file - but today realised the same happens even if no !Boot file is run at startup...)

Any thoughts?

The freezing does seem to be similar to what I've experience on the A4 but the other issues lead me to think that there's some issue with the IOC (or supporting circuitry). I'd be tempted to get the scope out and looking at the signals to the CMOS chip and keyboard controller are as you'd expect.

Check the seating of the IOC too - I've had problems with bent pins on my R260.

You can disable some of the POST tests in CMOS RAM - see page 4 here:
http://www.retro-kit.co.uk/user/custom/Acorn/32bit/documentation/RISCOS-POST-AppNote225.pdf and here:
http://www.riscos.com/support/developers/prm/cmos.html.

steve3000
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Re: A5000 freezing and random problems

Postby steve3000 » Tue Jun 28, 2016 11:11 am

RobC wrote:The freezing does seem to be similar to what I've experience on the A4 but the other issues lead me to think that there's some issue with the IOC (or supporting circuitry). I'd be tempted to get the scope out and looking at the signals to the CMOS chip and keyboard controller are as you'd expect.

Thanks Rob.

Good idea, but I'd need to buy a scope and learn to use it first :( However, I do have my handy logic probe :D which has helped me solve numerous issues (including my dead RiscPC issue last year) so once I find the computer freezing again, I'll check the status of various ICs.

I've also started writing a comprehensive interrupt monitor programme which monitors all IOC activity - and displays on screen. This could be useful aid to spotting spurious events or IRQ triggers, and checking that the keyboard input is correct (ref. the Ctrl-Break not working).

RobC wrote:Check the seating of the IOC too - I've had problems with bent pins on my R260.

And as for the IOC itself, in the A5000 it's surface mount so seating shouldn't be the issue, but I will check for dry joints on surrounding components.

Since CMOS reset with power-on + Del / power-on + R wasn't working, I've manually reset the CMOS to 0's and then set up defaults myself. But this doesn't seem to have solved anything - switch on still seems faster than expected, Ctrl-Break still isn't working, and neither are power-on + Del / power-on + R...

Zarchos
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Re: A5000 freezing and random problems

Postby Zarchos » Tue Jun 28, 2016 11:16 am

Yes check all socketed ICs, IIRC I had a machine where the IOC or the MEMC was slightly not entirely into its socket and after pushing it back it worked again flawlessly.

On a more general note, but it won't be the case for Steve, when a machine has had battery leakage and the battery is near the RISC OS ROMs, I remove the ROMs, try to remove the 'dirt' on the sockets with a small screwdriver (flat headed), use a 600 sand paper to clean the pins of the ROM chips, spray some contact spray ( like the F2 by KF http://www.ebay.co.uk/itm/Aerosol-KF-F2 ... xyj4hTIDKK ) on everything, and then plug back the ROMs.

This spray is also quite good to detect if the solders have aged, because there's so little 'product', and the non socketed chips don't have anymore a good contact with the motherboard. (Works well too to detect broken tracks in the CMOS chip area after leakage : if the computer works ok after heavy spraying, at least you know the chip isn't dead, and the issue comes from broken tracks and/or damaged joints and/or vias. I've got an A540 that doesn't boot anymore unless I spray some F2 in the CMOS area. Battery had leaked, I had removed it, but it appears I had not cleaned well enough the whole area, so the battery alkali kept on producing havoc).
Last edited by Zarchos on Tue Jun 28, 2016 11:34 am, edited 1 time in total.

sirbod
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Re: A5000 freezing and random problems

Postby sirbod » Tue Jun 28, 2016 11:30 am

steve3000 wrote:...Yes, before going down the route of replacing capacitors, I really want to rule out any obvious failing components. Will try freezer spray - but typically, as soon as I posted this thread, my A5000 has suddenly started behaving itself again. :roll:

Mine too, just powered it on and it's now working flawlessly.

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Re: A5000 freezing and random problems

Postby sirbod » Wed Nov 22, 2017 12:21 pm

sirbod wrote:
steve3000 wrote:...Yes, before going down the route of replacing capacitors, I really want to rule out any obvious failing components. Will try freezer spray - but typically, as soon as I posted this thread, my A5000 has suddenly started behaving itself again. :roll:

Mine too, just powered it on and it's now working flawlessly.

And now mine is dead again, so any obvious checks I should be doing?

It was working okay, switched it off whilst I worked out a patch for ADFS. Powered back on half hour later and nothing, no POST as far as I can tell. IOC and VIDC aren’t initialised as there’s no keyboard or video output and no floppy light or beep.

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helpful
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Re: A5000 freezing and random problems

Postby helpful » Wed Nov 22, 2017 4:42 pm

steve3000 wrote:I've also started writing a comprehensive interrupt monitor programme which monitors all IOC activity

I was going to suggest running the SWIstat and VECstat programs from the ARMclub, but it looks like you might be ahead of me!
https://armclub.org.uk/free/

Bryan.
RISC OS User Group Of London - http://www.rougol.jellybaby.net/
RISC OS London Show - http://www.riscoslondonshow.co.uk/

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Re: A5000 freezing and random problems

Postby sirbod » Wed Nov 22, 2017 6:46 pm

I believe I’ve found my A5000 issue, two resisters below the ARM chip (R288, R290) are no longer attached to the board!

That’s five machines I now have sitting waiting for reflow work (A5000, A7000, Kinetic, 2xIyonix). I won’t have any working ones left at this rate!

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danielj
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Re: A5000 freezing and random problems

Postby danielj » Wed Nov 22, 2017 6:48 pm

Ouch - battery leak related?

d.

sirbod
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Re: A5000 freezing and random problems

Postby sirbod » Wed Nov 22, 2017 8:39 pm

danielj wrote:Ouch - battery leak related?

Probably, it’s the no.1 killer.

A few more resistors and capacitors fell off whilst inspecting, all close to the CPU. Sadly reflowing them hasn’t fixed the issue.


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