A5000 woes

Arc/RPCs, peripherals, RISCOS operating system & ARM kit eg GP2x, BeagleBoard
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RobC
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A5000 woes

Post by RobC » Tue Mar 27, 2018 6:03 pm

My A5000 has died :(

It was previously working fine but I tried to power it on today and, apart from the power light coming on, it seems to be pretty dead. No POST fault code (or other signs of life) from the floppy and the keyboard lights are usually off but sometimes all come on power up (and then stay permanently on). There's no output on the video either.

There was a tiny amount of battery damage when I got the machine but I neutralised it and repaired a single damaged track. I've checked the CMOS circuit and it all buzzes out, the battery is charged and there doesn't seem to be any other track damage (no signs of bare copper etc.).

I've only had time for a quick look on the scope and there doesn't seem to be much happening but the PSU output voltages are okay.

Does anyone have experience of this happening and any pointers of what to look for?

Thanks,

Rob

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vectorlight
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Re: A5000 woes

Post by vectorlight » Tue Mar 27, 2018 6:27 pm

I had a similar dead A5000 recently with the usual battery damage. The fault with mine was the ACT74 (IC61?) chip that feeds the 25mhz signal was dead. I suppose if you have a scope, you could check the clock pin on the ARM3?
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Re: A5000 woes

Post by SteveBagley » Tue Mar 27, 2018 6:32 pm

Have you tried pressing RESET? Mine, oddly, will sometimes only boot if RESET is pushed…

Steve

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Re: A5000 woes

Post by RobC » Tue Mar 27, 2018 7:32 pm

Thanks both.

I have tried the reset button and I believe the 25Mhz clock was present at the ARM3 but I'll check again.

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lcww1
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Re: A5000 woes

Post by lcww1 » Tue Mar 27, 2018 8:06 pm

Well, I too am wandering in an A5000 related vale of tears - I've got two A5000s (both with socketed MEMCs) showing similar behaviour to your machine. There are signs of life - both produce a video signal, and the keyboard leds light up on pressing reset, but neither machine will boot. I've reached an impasse with both machines. Recently, I checked all the caps using an ESR meter, but found that all the caps appeared to be ok. Most recently, I attached my logic analyser to the test connector (see: http://www.stardot.org.uk/forums/viewto ... 92#p197306) - I was hoping that I might find something related to the floppy POST error message, and whilst I did get an interesting looking signal on D(0), I can't interpret what I'm seeing. I don't have a scope at present, but even if I did, I'd need some guidance as to using it to diagnose my A5000s' ailments. It's frustrating, as I'm sure both of these machines could be got working - their PCBs look ok, and I've not been able to find any problems with broken or corroded traces, so far. ](*,)

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danielj
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Re: A5000 woes

Post by danielj » Tue Mar 27, 2018 8:15 pm


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Re: A5000 woes

Post by steve3000 » Tue Mar 27, 2018 9:49 pm

Sorry to hear about your A5000. I've had exactly the same too, and posted about it a while back: viewtopic.php?f=16&t=9378

Exacty like SteveB has said above, my A5000 would intermittently boot up if you pressed reset repeatedly after switching on, but it got progressively worse and less responsive. I tried various things using my trusty logic probe and multimeter, but without a scope I was struggling to get any recognisable signs of life. So I retired my A5000 until I find new ideas and/or a scope... and it currently resides in the spare bedroom, under the spare bed.

I didn't try IC61 or replacing the 25MHz clock, but that could be a really good place to start, since anything along that front edge of the PCB is easily hit by the dreaded battery damage.

Last time I though about this properly I was considering it could be a dead CMOS RAM chip, as a really dead or missing CMOS chip can hang RISC OS before it gets to POST. I must have a go a replacing my CMOS chip... You mentioned battery damage - did you replace the CMOS chip at the time?

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Re: A5000 woes

Post by RobC » Wed Mar 28, 2018 7:25 am

Thanks Daniel and Steve.

From the looks of things, I didn't replace the CMOS chip or crystal as it worked when I got it. From memory, it just needed a new battery and a charge. I repaired a damaged track but I don't even think it was ever completely broken.

The battery damage really doesn't look that bad but the CMOS chip would have been next in line after the damaged track. I'll replace it and report back.

One other thing I thought about was the hanging issue that affects A4s. This eventually resulted in my A4 being dead until I reflowed the IOC. However, I've tried reflowing all the main chips and that hasn't brought the A5000 back to life :(

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Re: A5000 woes

Post by danielj » Wed Mar 28, 2018 8:20 am

I've certainly seen RPCs that have to all intents and purposes been dead to the world until the CMOS IC was replaced...

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Re: A5000 woes

Post by steve3000 » Wed Mar 28, 2018 12:16 pm

RobC wrote:One other thing I thought about was the hanging issue that affects A4s. This eventually resulted in my A4 being dead until I reflowed the IOC. However, I've tried reflowing all the main chips and that hasn't brought the A5000 back to life :(
Out of interest, did your A4 give any POST error messages when it died? Mine is giving IOC register failed... I've assumed that it needs a new IOC, but wonder if it could be solved with reflowing.

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Re: A5000 woes

Post by RobC » Wed Mar 28, 2018 3:42 pm

steve3000 wrote:Out of interest, did your A4 give any POST error messages when it died?
No - it started freezing more and more frequently and then eventually stopped booting with no POST error (or signs of life).

Definitely try reflowing as it fixed on fibble's too. I just applied some no-clean flux around it and then touched each pin with the iron.

If you do end up needing a new IOC, PM me as I may have a spare...

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Re: A5000 woes

Post by steve3000 » Wed Mar 28, 2018 10:34 pm

RobC wrote:Definitely try reflowing as it fixed on fibble's too. I just applied some no-clean flux around it and then touched each pin with the iron.
Thanks Rob, I'll definitely give that a try :)

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Re: A5000 woes

Post by Andrewcee » Sat Mar 31, 2018 8:04 am

Probably not related but maybe worth checking the 'bleeding obvious'?

Fixed a couple of 5000s recently. Battery in one was a little fury but hadn't leaked, was working fine although now replaced. (Glad I kept it, now a temporary replacement in Risc PC) Swapped out cmos as post reported cmos & rom errors. With hindsight, believe cmos to be okay (kept original in case ever needed) as after short charge of new battery post reported only rom fault. 2nd 5000 arrives,... That's when I realised my mistake. Having removed pcb & throughly cleaned - white fur around links, etc - from memory links 10/11 (?), I'd fitted wrong way round, think they have to be north/south, have to lift lid to check. Anyway, swapped around & correctly fitted, no post errors and both machines working a treat.

Should say, found link error after several hours with scope, dvm, circuit diagrams, etc. Checked clocks, power-up delay, even confirming cmos being read on startup. Ditto all address lines from roms, tracing data lines I learnt each rom carries 1/4 of the 32bits, think it was, ie. All 4 roms needed (obvious statement). All this, and I'd fitted a couple of links incorrectly!

Good luck fault finding, both entertaining & frustrating. I'm working on a RISC PC trying to get IDEFS working.

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Re: A5000 woes

Post by Andrewcee » Sat Mar 31, 2018 8:07 am

Forgot - cmos reads into two lines on I/O chip, difficult to find on circuit diagram. They toggle for maybe 1/2 sec on power-up. Although unable to 'read' the data coming from cmos using scope, I confirmed CMOS being read okay on power-up.

Hope this helps.
Last edited by Andrewcee on Sun Apr 01, 2018 7:20 am, edited 1 time in total.

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lcww1
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Re: A5000 woes

Post by lcww1 » Sat Mar 31, 2018 11:03 am

Andrewcee wrote:but maybe worth checking the 'bleeding obvious'?
Always worth bearing in mind! It took me a little while to notice that the socketed 66MHz oscillator was missing from the non-booting A5000 alpha board that I’m trying to revive....... ](*,) Unfortunately, merely adding an oscillator has not fixed the machine, so the quest continues...............I will eventually fix this machine, though I can see that it may turn out to be a lifelong project :!:

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Re: A5000 woes

Post by DutchAcorn » Sat Mar 31, 2018 12:22 pm

A corrupted CMOS chip can prevent the computer from starting. Instead of replacing the cmos chip, you could just snip leg 8 of the chip (+5V) and see if it starts. In my experience the A5000 will boot to supervisor if the CMOS chip is removed.

The configuration you end up with a dead CMOS chip typically has the video set to "auto". Auto detection does not play well with modern flat TFT monitors (although it may work). No point in trying to "blindly" correct the configuration, it will not be retained. A CRT VGA monitor will eliminate that issue.

It can take up to 40 seconds before the computer shows the supervisor prompt. Don't switch off too soon.

If you want to check the two data lanes (pins 5 and 6 on the CMOS chip) you can check the connectivity to the IO chip but it may be easier to use pins 13 and 14 on the expansion connector (SK9, where the backplane plugs in). You can put a header in there and buzz out the connections. The tracks run mostly on the under side the PCB and have through-hole connections to the other side of the PCB. Relatively easy to find and to fix.
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RobC
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Re: A5000 woes

Post by RobC » Mon Apr 02, 2018 2:43 pm

I've replaced the CMOS chip but, unfortunately, it's made no difference :(

I've also dug out my non-working A5000 Alpha so if the kids don't object too much, I'll try to get the scope out tomorrow and have a big repair session.

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Re: A5000 woes

Post by steve3000 » Mon Apr 16, 2018 8:18 pm

RobC wrote:I've replaced the CMOS chip but, unfortunately, it's made no difference :(

I've also dug out my non-working A5000 Alpha so if the kids don't object too much, I'll try to get the scope out tomorrow and have a big repair session.
Shame to hear the CMOS chip didn't solve it. Did you get any further with your A5000 repair?

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Re: A5000 woes

Post by RobC » Mon Apr 16, 2018 8:34 pm

steve3000 wrote:Did you get any further with your A5000 repair?
Not yet - I've been trying to sort out a few other things for the show on Saturday but I'm hoping to take a good look at it soon.

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