A3000 crackling (right) speaker

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Tills
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A3000 crackling (right) speaker

Post by Tills » Sun Sep 22, 2019 9:41 pm

I'm experiencing a new issue on my recently recommissioned A3000 (repaired battery damage) and I wonder if any board members can shine a light on it.

Today, all of a suddden, the right speaker started crackling like a warm fire. Plugging in headphones gave the same result. It begins the moment I power on (i.e pre-desktop), and in any wimpmode. Deactivating the sound in !Configure stops it.

I've also noticed the screen dipping in brightness intermittently, which seems to be related. I'm wondering whether it's a capacitor issue, perhaps close to the VIDC. I changed C70 out of curiosity (the cap. these days re-wired for the sound mod for the right channel) but no joy. It might be a capacitor closer to the VIDC, or any of the electrolytics on the board. Or something more ominous.

Any suggestions/ideas gratefully received.

N.B. My setup: Issue A, 4MB RAM, Watford Super VIDC Enhancer, 16bit external HD (CF), ARM3 25MHz, Risc OS 3.11
Last edited by Tills on Mon Sep 23, 2019 12:42 pm, edited 6 times in total.

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Re: A3000 crackling (right) speaker

Post by arkleyjoe » Mon Sep 23, 2019 7:59 am

Looking at the schematic, it seems there are several electrolytic capacitors that are exclusively related to the right speaker outlet and a couple specifically inline before the headphone jack branches off.

I'd strongly suspect those.

Your screen dipping in colour may not be directly related but could also be a cap or maybe power supply problem? I'd be tempted to replace all of the electrolytic caps but for the speaker issue specifically I think c97,c70 (done already),c60,c61 would be my first ones to replace.

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Re: A3000 crackling (right) speaker

Post by Tills » Mon Sep 23, 2019 12:15 pm

Thanks. I think so too, and shall be ordering new electrolytic caps for the whole board. It is perhaps instructive that the issue does not manifest itself when the Arc is powered on from cold; only when it's warmed up a little after a few minutes. I think that's meant to be indicative of a bad cap somewhere.

I think the PSU is fine as it reads a steady 4.92 volts on my multimeter.
Last edited by Tills on Mon Sep 23, 2019 12:42 pm, edited 1 time in total.

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Re: A3000 crackling (right) speaker

Post by arkleyjoe » Mon Sep 23, 2019 12:41 pm

Tills wrote:
Mon Sep 23, 2019 12:15 pm
only when it's warmed up a little after a few minutes
Yeah very true, it's almost certainly the caps.

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Re: A3000 crackling (right) speaker

Post by steve3000 » Mon Sep 23, 2019 6:50 pm

Tills wrote:
Mon Sep 23, 2019 12:15 pm
Thanks. I think so too, and shall be ordering new electrolytic caps for the whole board. It is perhaps instructive that the issue does not manifest itself when the Arc is powered on from cold; only when it's warmed up a little after a few minutes. I think that's meant to be indicative of a bad cap somewhere.
My A4000 does this... and it's spread to both speakers.

First started happening in/around 2014, but lack of time and many other projects has relegated the capacitor change to bottom of the pile. After the crackles spread to both speakers it developed a high pitch whistle... I see it as part of its character now... but it annoys the wife, so I'll have to fix it eventually.

It will be great to see if changing the electrolytics works for you :)

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Re: A3000 crackling (right) speaker

Post by Tills » Mon Sep 23, 2019 8:04 pm

I'll try and report back on the weekend, if the replacements have arrived.
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Re: A3000 crackling (right) speaker

Post by markdryan » Mon Sep 23, 2019 8:44 pm

> I've also noticed the screen dipping in brightness intermittently, which seems to be related.

That's interesting. Mine's been doing this for a few months now, although I hear no crackling from the speaker. I'd also be very interested to hear whether the re-capping solves this problem. All I've done so far is to check the power supply which appears to be fine.
Last edited by markdryan on Mon Sep 23, 2019 8:45 pm, edited 1 time in total.

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Re: A3000 crackling (right) speaker

Post by Tills » Wed Sep 25, 2019 1:06 pm

markdryan wrote:
Mon Sep 23, 2019 8:44 pm
Mine's been doing this for a few months now
I am wondering whether the tantalum caps attached to two of the VIDC's supply rails might also be worth replacing. I have a MacBook Pro (2010 model) with a faulty tant on its graphic card's supply rail (a very well-known fault on this model); these tend to blow short, which might explain the intermittent pulsing of the display powered by the VIDC (in the case of the Mac, sudden display failure when they warm up).

So if changing the electrolytics brings no joy, they are my next suspects: C108 and C100, (I think) decoupling Sndvdd and Vidvddd respectively.

Just thinking out loud on this.

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Re: A3000 crackling (right) speaker

Post by arkleyjoe » Thu Sep 26, 2019 8:15 pm

Tills wrote:
Wed Sep 25, 2019 1:06 pm
I am wondering whether the tantalum caps attached to two of the VIDC's supply rails might also be worth replacing.
possible for sure, but much less common.

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Re: A3000 crackling (right) speaker

Post by Tills » Mon Sep 30, 2019 11:34 pm

Well, I have now replaced all the electrolytic caps on the board, except for the five on the serial port (I hadn't ordered enough!), plus the two tantalums attached to two of the VIDC supply rails. I also replaced the six electrolytics in the PSU, because, on closer examination, the two 200v 100uF did show signs of leaking. The Arc has been on now for 2.5 hours without any issues. There is no longer any cracking.

I had actually tested the board straight after servicing the PSU a few days ago (which I did first) and at that stage the crackling had disappeared. I'd left the Arc switched on for several hours. So for those with similar issues, it might be worth exploring that avenue first. Although my supply appeared to be fine on a multimeter, the quality might have been a different matter. Quite why that would affect only one speaker I don't know, but there it is.

Cost for capacitors (decent makes) was about £17, variously from RS (for the big, Nichicon replacments for the PSU, and for the tantulums) and CPC (for everything else). Of that, the PSU caps accounted for £4.20.

Of course, if I have spoken too soon I shall report back! Knowing how technology likes to tease us ...
Last edited by Tills on Mon Sep 30, 2019 11:49 pm, edited 4 times in total.

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Re: A3000 crackling (right) speaker

Post by markdryan » Tue Oct 01, 2019 10:19 am

Has the recapping also solved the screen dimming issue you were having? If so, was that solved by the power supply recap or the motherboard recapping?

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Re: A3000 crackling (right) speaker

Post by Tills » Tue Oct 01, 2019 3:55 pm

markdryan wrote:
Tue Oct 01, 2019 10:19 am
Has the recapping also solved the screen dimming issue you were having? If so, was that solved by the power supply recap or the motherboard recapping?
Good question. All I can say is that the screen dimming issue, which I noticed only in one session a week or two ago, has not materialised since.

As to whether this had been due to the PSU I cannot be sure, as I tested the latter with the motherboard on the bench without a monitor (only the speakers). The intermittent dimming probably wouldn't have manifested itself on command in my case, so I didn't check for it, and as I had intended to recap the whole board as a precaution, I moved straight on to that.

Recapping a PSU for an Issue A A3000 is relatively straightforward, and I think well worth the effort, given the heat those ballast capacitors have endured next to heatsinks, not to mention the deleterious effect of decades of non-use on electrolytics. If you like I can post a short list of the items I ordered from RS (a bonus is they don't charge for postage).

The motherboard, on the other hand, was a bit of a pig with basic tools. But if recapping the PSU does solve your problem, there's no need.
Last edited by Tills on Tue Oct 01, 2019 4:02 pm, edited 3 times in total.

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Re: A3000 crackling (right) speaker

Post by markdryan » Tue Oct 01, 2019 9:14 pm

Tills wrote:
Tue Oct 01, 2019 3:55 pm
Recapping a PSU for an Issue A A3000 is relatively straightforward, and I think well worth the effort, given the heat those ballast capacitors have endured next to heatsinks, not to mention the deleterious effect of decades of non-use on electrolytics. If you like I can post a short list of the items I ordered from RS (a bonus is they don't charge for postage).
The list of items would be very useful, thanks. Was it difficult to remove the glue around the base of the large capacitors?
The motherboard, on the other hand, was a bit of a pig with basic tools. But if recapping the PSU does solve your problem, there's no need.
I'm going to practice on a few, hopefully non-sacrificial, C64s first before attempting to recap my A3000. I did manage to recap one breadbin C64 at the weekend. Amazingly, it still works and the video output is greatly improved, so it was worth the effort (and risk).
Last edited by markdryan on Tue Oct 01, 2019 9:15 pm, edited 1 time in total.

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Re: A3000 crackling (right) speaker

Post by Tills » Wed Oct 02, 2019 1:16 am

markdryan wrote:
Tue Oct 01, 2019 9:14 pm
The list of items would be very useful, thanks. Was it difficult to remove the glue around the base of the large capacitors?
The glue was somewhat brittle around the biggest two, a bit more tacky around the second biggest. A combination of melting one joint and slightly pulling to one side, in alternation, worked for me. The residue can then be scraped off gently with a flat-bladed screwdriver.

I bought two of each:

RS Stock No.739-4510 (pack of 2)
RS Stock No.862-4121
RS Stock No.862-3197

As for the motherboard, unless you have a desoldering gun, or perhaps a heated manual pump, I'd opt for leg snipping close to the board, and combined heating of the joint with removal of legs with pin-sharp tweezers from the underside, because those legs are bent almost 90 degrees over and it's too risky pulling them through by the capacitor body (in my opinion). The manual pump is good for cleaning up the joint afterwards though, heating from the upper side, sucking from under; it makes for a clean hole for the new caps. One thing to look out for is any stray solder debris. A cotton bud with IPA is good for cleaning as you go, with a good lens to hand.

P.S. When soldering new through-hole components, I have found it helpful to add a dab of no-clean flux to the pad on the upper side of the board as well as the lower, to persuade the solder to go up the hole (particularly important where the track is actually on the top or indeed the middle). I mention this only because I wish I'd done this at the outset, and I've seen other repairs where the joints look hollow from above.

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Re: A3000 crackling (right) speaker

Post by Tills » Sun Oct 06, 2019 6:57 pm

steve3000 wrote:
Mon Sep 23, 2019 6:50 pm
It will be great to see if changing the electrolytics works for you :)
Tills wrote:
Mon Sep 30, 2019 11:34 pm
Of course, if I have spoken too soon I shall report back! Knowing how technology likes to tease us ...
Looks like I spoke too soon. The crackling is back.

Very odd that is has been fine for a week. Think I'll focus on all the remaining caps in the right speaker circuit: ceramic and 'MPSTR' (not sure what these are, but presumably any same-rated cap will do?).

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Re: A3000 crackling (right) speaker

Post by philpem » Mon Oct 07, 2019 3:14 am

Does the A3000 use the little "Acorn Sound" hybrid that's used in the A3010?

If so, I found that the pins on the hybrid had started to fail. I ended up soldering on some Harwin pin-strip and fitting the mating connector to the PCB.

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Re: A3000 crackling (right) speaker

Post by Tills » Mon Oct 07, 2019 8:33 am

philpem wrote:
Mon Oct 07, 2019 3:14 am
Does the A3000 use the little "Acorn Sound" hybrid that's used in the A3010?
I don't believe so. It has the sound chip(s) directly on the PCB, and far away from the battery which I understand was the cause of your strife.

A search of internet forums leads me now to suspect the MPSTR capacitors, whose failure is not uncommon in all sorts of equipment. Apparently humidity can be a factor, which sadly applies to my Arc which was stored in a shed and then the loft for the past two decades. I'm assuming the initialism MPSTR stands for metalised polyester.
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Re: A3000 crackling (right) speaker

Post by Tills » Sun Oct 13, 2019 10:30 am

markdryan wrote:
Tue Oct 01, 2019 10:19 am
Has the recapping also solved the screen dimming issue you were having? If so, was that solved by the power supply recap or the motherboard recapping?
An update on this: having the board out on the bench to test the new metalised polyester caps, I experienced screen dimming again. The voltage tested low (4.75v) but wiggling the extension fly-leads I'd set up from the PSU rectified the issue: volts back to 5, and screen stable. Seems a poor spade connection may have been the culprit. I hate these intermittent type faults.

P.S. I should point out that I have a piggy-back connector on the positive terminal which powers the VIDC enhancer. Perhaps worth a look at if you have a similar setup.
Tills wrote:
Sun Oct 06, 2019 6:57 pm
Looks like I spoke too soon. The crackling is back.
Happy to report that the A3000 has been on two whole days now without any issues. I'd say with some confidence that replacing those MPSTR caps on the right audio channel did the trick. For reference (for both L&R channels):

C77, C92: 22nF, >=50v, 10%, metalised polyester, 5mm lead pitch(e.g. RS stock no: 1082340)
C80, C88: 100nF, >=50v, 10%, metalised polyester, 5mm lead pitch (e.g. RS stock no: 1082700)

Not sure about the 'Acorn Sound' hybrid card on the A4000 but at a cursory look at the schematics it might have something similar.
Last edited by Tills on Mon Oct 28, 2019 5:21 pm, edited 4 times in total.

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Re: A3000 crackling (right) speaker

Post by markdryan » Mon Oct 14, 2019 7:52 pm

Thanks for the update. I haven't got around to changing the caps yet (I'm still practicing on Commodores), but my impression is that the screen dimming has improved since I switched memory expansions and replaced the internal 8-bit cf card reader with an external 16-bit one. I do need to spend some time actively using the A3000 to see if this is really the case.

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Re: A3000 crackling (right) speaker

Post by Tills » Mon Oct 14, 2019 8:26 pm

markdryan wrote:
Mon Oct 14, 2019 7:52 pm
Thanks for the update. I haven't got around to changing the caps yet (I'm still practicing on Commodores), but my impression is that the screen dimming has improved since I switched memory expansions and replaced the internal 8-bit cf card reader with an external 16-bit one. I do need to spend some time actively using the A3000 to see if this is really the case.
It may be that in the process of swapping out cards you've nudged the +ve/-ve spade connectors for a better connection. I'd try pulling the leads out and pushing them firmly back in, or crimping if slightly loose. ArkleyJoe is likely right to suggest a power issue. The VGA port seems awfully sensitive to the slightest power fluctuations (as giving the leads a wiggle demonstrated in my case).

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Re: A3000 crackling (right) speaker

Post by Tills » Mon Oct 21, 2019 9:36 pm

steve3000 wrote:
Mon Sep 23, 2019 6:50 pm
My A4000 does this... and it's spread to both speakers.

First started happening in/around 2014, but lack of time and many other projects has relegated the capacitor change to bottom of the pile. After the crackles spread to both speakers it developed a high pitch whistle... I see it as part of its character now... but it annoys the wife, so I'll have to fix it eventually.

It will be great to see if changing the electrolytics works for you :)
Update: The Arc's been on for a week now during the daytime without issue. Seems like replacing just those four MPSTR capacitors has finally sorted out the problem of the crackling audio. I've been running it hard, too, overclocking the ARM3 to 33Mhz (a tidy 16 MIPS) at the same time.

N.B. The 'Audio Hybrid' cards in the A3010, 3020, and 4000 appear to share the same circuitry as the A3000 (but without any values listed in the schematics), and use SMD components instead of radial. Shouldn't be too hard to work out which are which, if one of these models is having the same or similar audio issues.

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