I started working through all my stored computers to remove all the CMOS batteries. Before doing so, I decided to check they all worked still.
All of them did, except the A4. The LEDs light up, but nothing else. I've stripped it down and checked the board. All seems fine, even the tiny batery on the board looks fine.
While it was stripped, I tried to power it up again and that's when I heard a buzzing noise. Seems to be coming from the small vertical board that plugs into the main pcb. It looks like a power board. Is the buzzing normal or are they prone to failing?
Just wondering if it's an easy fix or if I may need to replace this board somehow. Other than this buzzing board, there's no other noises (not even the HDD spinning), is this likely to be the culprit? I don't think it'll be the screen, I bought it from Theo Markettos a while back and the A4's hardly been used since.
Alan James <REMOVEala...@blueyonder.co.uk> wrote: > While it was stripped, I tried to power it up again and that's when I > heard a buzzing noise. Seems to be coming from the small vertical board > that plugs into the main pcb. It looks like a power board. Is the > buzzing normal or are they prone to failing?
That's the DC-DC converter board. Takes 12ishV from the battery or power brick, and makes -24V for the LCD and +5V for everything else. The transformer on it can make a quiet buzzing sound, but if it's loud then that sounds bad.
You can also try running the board from a separate 5V power supply - best to have a current limited one in case you blow something. The DC-DC is only at 3 or 4A so don't go over that.
There isn't a schematic of the DC-DC available - that was bought in from Olivetti (who made it for the Triumph Alder Walkstation). But it isn't a hugely complex board. Make sure you put it on the right pins, and not off-by-one or backwards.
If the DC-DC is at fault you can try repairing it, or arrange an external 5V and -24V supply. If the noise is loud that suggests that the switching frequency is too low, which might be due to dry capacitors. If you have access to an ESR meter you could measure them, or else just try replacing all the electrolytics on that board.
<URL:mailto:theom+n...@chiark.greenend.org.uk> wrote: > Alan James <REMOVEala...@blueyonder.co.uk> wrote: > > While it was stripped, I tried to power it up again and that's when I > > heard a buzzing noise. Seems to be coming from the small vertical board > > that plugs into the main pcb. It looks like a power board. Is the > > buzzing normal or are they prone to failing?
> That's the DC-DC converter board. Takes 12ishV from the battery or power > brick, and makes -24V for the LCD and +5V for everything else. The > transformer on it can make a quiet buzzing sound, but if it's loud then that > sounds bad.
> You can also try running the board from a separate 5V power supply - best to > have a current limited one in case you blow something. The DC-DC is only at > 3 or 4A so don't go over that.
> There isn't a schematic of the DC-DC available - that was bought in from > Olivetti (who made it for the Triumph Alder Walkstation). But it isn't a > hugely complex board. Make sure you put it on the right pins, and not > off-by-one or backwards.
> If the DC-DC is at fault you can try repairing it, or arrange an external 5V > and -24V supply. If the noise is loud that suggests that the switching > frequency is too low, which might be due to dry capacitors. If you have > access to an ESR meter you could measure them, or else just try replacing > all the electrolytics on that board.
-- CJE Micro's / 4D 'RISC OS Specialists' Telephone: 01903 523222 Fax: 01903 523679 ch...@cjemicros.co.uk http://www.cjemicros.co.uk/ 78 Brighton Road, Worthing, West Sussex, BN11 2EN The most beautiful thing anyone can wear, is a smile!
In article <koLHm.74755$zt3.45...@newsfe03.ams2>, Alan James
<URL:mailto:REMOVEala...@blueyonder.co.uk> wrote: > Chris Evans wrote:
> > We have DCD DC units in stock!
> Hmm! Is it returnable if it doesn't fix the problem? ;)
I'm sure we can come to an arrangement, I'll email you.
Chris Evans
-- CJE Micro's / 4D 'RISC OS Specialists' Telephone: 01903 523222 Fax: 01903 523679 ch...@cjemicros.co.uk http://www.cjemicros.co.uk/ 78 Brighton Road, Worthing, West Sussex, BN11 2EN The most beautiful thing anyone can wear, is a smile!
On Sat, 31 Oct 2009 23:25:37 +0000, Alan James wrote: > Just wondering if it's an easy fix or if I may need to replace this > board somehow. Other than this buzzing board, there's no other noises > (not even the HDD spinning), is this likely to be the culprit?
Sadly my TRM's not with me... I think a hard disk fault is a reasonable bet. You could try pulling the drive and then see if it'll start, but I honestly don't remember if the A4 will do anything meaningful without one (although at the very least the buzzing should go away I suppose)
Jules <jules.richardsonn...@remove.this.gmail.com> wrote: > Sadly my TRM's not with me... I think a hard disk fault is a > reasonable bet. You could try pulling the drive and then see if it'll > start, but I honestly don't remember if the A4 will do anything > meaningful without one (although at the very least the buzzing should > go away I suppose)
It will... don't forget 2MB floppy-only A4s were the entry model. You should get a floppy seek noise when you power on if the OS is up. It may have hung waiting for the HD, in which case a power-on Delete should help (think it'll revert to the no-HD configuration). Always test A4s with external monitors, in case the screen output is set to the VGA port.
But you're right, buzzing could also be caused by overcurrent due to a stuck drive, which would probably mean the voltages would drop out. Pulling the drive will tell you.
(My most recent success with a stuck 3.5" drive was to hit it with a hammer until it spun up. Data was perfectly readable after that - and all I wanted to do was wipe it anyway)
In message <Miv*KC...@news.chiark.greenend.org.uk> Theo Markettos <theom+n...@chiark.greenend.org.uk> wrote:
> (My most recent success with a stuck 3.5" drive was to hit it with a hammer > until it spun up. Data was perfectly readable after that - and all I wanted > to do was wipe it anyway)
I've found an A4 floppy drive, boxed from the man, but don't know if it's any good since I don't have an A4 any more. Anyone interested? -- BW Chris F. [ British Iyonix, RISC OS 5.13 & A9 ]
Theo Markettos wrote: > It will... don't forget 2MB floppy-only A4s were the entry model. You > should get a floppy seek noise when you power on if the OS is up. It may > have hung waiting for the HD, in which case a power-on Delete should help > (think it'll revert to the no-HD configuration). Always test A4s with > external monitors, in case the screen output is set to the VGA port.
Don't think I've heard any noise from the floppy at all. I've tried the VGA port, but the monitor stays on standby. Not sure if the A4 can bring it out of standby? I remember problems with my RiscPC until I changed some settings like MonitorType or something.
> But you're right, buzzing could also be caused by overcurrent due to a stuck > drive, which would probably mean the voltages would drop out. Pulling the > drive will tell you.
I tried without the HD when it was stripped down, so can't be that. Once or twice I've heard the HD spin up tho, but that's usually after it's had no power for a few hours or overnight. I keep trying it every so often while crossing fingers!
Apart from the HD, the only other thing that changes slightly is the LEDs. When the power is connected but the switch is off I get the usual PSU light and the battery charging LED (with battery and without!?). When switched on, I get the same 2 LEDs plus the power on LED. The thing that changes is the Num, Caps and Scroll LEDs are sometimes all off and sometimes all on.
I've ordered a DC/DC converter from Chris, so I'll give it a try anyway. I'll probably hold on to it either way just in case I need it in the future!
> (My most recent success with a stuck 3.5" drive was to hit it with a hammer > until it spun up. Data was perfectly readable after that - and all I wanted > to do was wipe it anyway)
Um, it was removed from the computer first, right? ;) I've had success with HDDs and hammers. The hammer is often overlooked by IT personnel, I've been using them since my very first 286 PC! Never taken one to an Acorn machine tho. Not sure if that's out of respect, caution or because they've always generally worked.
Alan H James wrote: > I've tried the VGA port, but the monitor stays on standby. Not sure if > the A4 can bring it out of standby?
Yes if it is producing a valid signal understood by the monitor.
> I remember problems with my RiscPC > until I changed some settings like MonitorType or something.
If the A4 has defaulted to CGA signal, modern monitors wont recognise it as a valid signal. As the A4 doesn't have a numeric keypad, you can't power up holding 4 to select VGA, so you'll have to type blind:-
> I've ordered a DC/DC converter from Chris, so I'll give it a try anyway. > I'll probably hold on to it either way just in case I need it in the future!
This may be OT but once I had an A4 which would only run with all the peripherals removed.
The fault was a diode, which had failed to a short circuit, on the internal DC-DC converter board. I found the fault by testing each component with a multimeter, I replaced the SMD diode with a similar size leaded one and it was all good after that.
Alan Williams <a...@genesis.net.au> wrote: > The fault was a diode, which had failed to a short circuit, on the > internal DC-DC converter board. I found the fault by testing each > component with a multimeter, I replaced the SMD diode with a similar > size leaded one and it was all good after that.
druck wrote: > If the A4 has defaulted to CGA signal, modern monitors wont recognise it > as a valid signal. As the A4 doesn't have a numeric keypad, you can't > power up holding 4 to select VGA, so you'll have to type blind:-
Been messing around again today and noticed something else. This time I completely removed everything apart from the main board and the DC/DC board, ie. no screen, no keyboard and no drives. Just connected the monitor lead in case.
The buzzing seems to change, like there's some kind of strain? I don't have a great deal of knowledge on things like this, so apologies for any bad descriptions I give!
Earlier on today I also noticed a popping from the tiny speaker in the lid. It wasn't constant and I'm not convinced there was a pattern to it either, seemed fairly random and varied by a number of seconds each time. One other thing, it's not easy to tell, but there appears to be 'something' around some pins on the underside of the main board. It's around the transistor Q1 next to the parallel port. It could just be discoloured PCB coating, not sure.
Hmm, just had another quick look to confirm my description above and under the light a dull area of the board caught my eye. Around the headphone socket, there appears to be leakage (or spillage?) in between the tiny silver capacitors. I'm confident it's not spillage, unless it happened before I got the A4 and while in storage it killed something! Moving a thin piece of plastic through it, it seems kinda greasy or oily? Can't really see anything running down the plastic holders for them, but i guess it could be from underneath? Any way to test them? I only have a simple yellow Multi-Meter at hand.
Not sure if any of that helps, thanks for all your replies so far.
Forgot to add that when I read this page I noticed a bit about the flashing battery LED meaning a battery error. Well, the Battery LED on my A4 flashes off and on whether the battery is in or not.
Alan H James <REMOVEala...@blueyonder.co.uk> wrote:
> Apart from the HD, the only other thing that changes slightly is the > LEDs. When the power is connected but the switch is off I get the usual > PSU light and the battery charging LED (with battery and without!?). > When switched on, I get the same 2 LEDs plus the power on LED. The thing > that changes is the Num, Caps and Scroll LEDs are sometimes all off and > sometimes all on.
That sounds like the battery manager and keyboard microcontrollers are up, so there's some kind of voltage there. Though I think the BMU will run off the raw battery voltage (tempered a bit), rather than the regulated 5V.
> I've ordered a DC/DC converter from Chris, so I'll give it a try anyway. > I'll probably hold on to it either way just in case I need it in the future!
I'd try putting it on a current-limited 5V supply if you have one, to test if it's the DC/DC that's the problem. (You could use an un-limited supply - eg an old PC PSU - but if there's a problem on the board you could fry it some more)
> > (My most recent success with a stuck 3.5" drive was to hit it with a > > hammer until it spun up. Data was perfectly readable after that - and > > all I wanted to do was wipe it anyway)
> Um, it was removed from the computer first, right? ;)
Nope :)
Free Pentium 120 PC. 'Buyer' collects from Cambridge ;-)
> > I've ordered a DC/DC converter from Chris, so I'll give it a try anyway. > > I'll probably hold on to it either way just in case I need it in the future!
> I'd try putting it on a current-limited 5V supply if you have one, to test > if it's the DC/DC that's the problem. (You could use an un-limited supply - > eg an old PC PSU - but if there's a problem on the board you could fry it > some more)
Are you able to try a different brick? I have seen more of those fail than DC-DC converter boards.
If the brick output is low then this may well cause the DC-DC converter to struggle and get noisy.
On Fri, 13 Nov 2009 01:56:03 +0000, Theo Markettos wrote: > That sounds like the battery manager and keyboard microcontrollers are up, > so there's some kind of voltage there. Though I think the BMU will run off > the raw battery voltage (tempered a bit), rather than the regulated 5V.
Is this a good point for me to grumble yet again that my A4 TRM is still stuck in storage over in the UK? :-)
Someone else had a copy of the TRM, too - if I remember who it was I'll shout as maybe they coule pore over the schematics and perhaps shed some light on things...
In message <Liv*8-...@news.chiark.greenend.org.uk> Theo Markettos <theom+n...@chiark.greenend.org.uk> wrote:
> Alan Williams <a...@genesis.net.au> wrote: > > Are you able to try a different brick? > > I have seen more of those fail than DC-DC converter boards.
> Good point. You don't need the full brick - about 15V on UMAIN should do > the trick (pinout and specs in the TRM).
Is there a schematic for the A4's external brick anywhere on the web?
Jules <jules.richardsonn...@remove.this.gmail.com> wrote: > Is this a good point for me to grumble yet again that my A4 TRM is still > stuck in storage over in the UK? :-)
Permission granted :)
> Someone else had a copy of the TRM, too - if I remember who it was I'll > shout as maybe they coule pore over the schematics and perhaps shed some > light on things...
Chris Whytehead has scanned the schematics, and Alan Williams the manual. I posted links earlier in this thread. But the bought-in bits (DC-DC, power brick, screen assembly, hybrid LCD riser) don't have schematics.
Alan H James <REMOVEala...@blueyonder.co.uk> wrote:
> Been messing around again today and noticed something else. This time I > completely removed everything apart from the main board and the DC/DC > board, ie. no screen, no keyboard and no drives. Just connected the > monitor lead in case.
> The buzzing seems to change, like there's some kind of strain? I don't > have a great deal of knowledge on things like this, so apologies for any > bad descriptions I give!
> Earlier on today I also noticed a popping from the tiny speaker in the > lid. It wasn't constant and I'm not convinced there was a pattern to it > either, seemed fairly random and varied by a number of seconds each time.
Hmmm... 'something' is going on. Quite what is a bit difficult to tell from a distance.
> Hmm, just had another quick look to confirm my description above and > under the light a dull area of the board caught my eye. Around the > headphone socket, there appears to be leakage (or spillage?) in between > the tiny silver capacitors. I'm confident it's not spillage, unless it > happened before I got the A4 and while in storage it killed something! > Moving a thin piece of plastic through it, it seems kinda greasy or > oily? Can't really see anything running down the plastic holders for > them, but i guess it could be from underneath? Any way to test them? I > only have a simple yellow Multi-Meter at hand.
You sure it's not some kind of glue/rubber gone a bit soft?
I'd try measuring the resistance between power and ground. It's possible one of those capacitors has gone short circuit, and the DC-DC is trying to drive into a short (which might cause some heating/burning, so watch for that). But normally capacitors go open circuit rather than short. If you had an equivalent series resistance meter I would try measuring the ESR of the electrolytic caps as they often go high ESR with age. Unfortunately you'd need to remove at least one leg of each cap to test them.
I'd also try measuring the supply voltages when powered on - if they're very low then that suggests bad regulation or a short.
In article <2fa8c4b950.davehig...@dsl.pipex.com>, Dave Higton
<URL:mailto:davehig...@dsl.pipex.com> wrote: > In message <Liv*8-...@news.chiark.greenend.org.uk> > Theo Markettos <theom+n...@chiark.greenend.org.uk> wrote:
> > Alan Williams <a...@genesis.net.au> wrote: > > > Are you able to try a different brick? > > > I have seen more of those fail than DC-DC converter boards.
> > Good point. You don't need the full brick - about 15V on UMAIN should do > > the trick (pinout and specs in the TRM).
> Is there a schematic for the A4's external brick anywhere on the web?
The only Acorn PSUs [1] that there are circuit diagram/schematic for are the A3010 & A3020 as the PSU is on the main PCB.
[1] Since and including BBC B
Chris Evans
-- CJE Micro's / 4D 'RISC OS Specialists' Telephone: 01903 523222 Fax: 01903 523679 ch...@cjemicros.co.uk http://www.cjemicros.co.uk/ 78 Brighton Road, Worthing, West Sussex, BN11 2EN The most beautiful thing anyone can wear, is a smile!
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