BBC Model B takes up smoking

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richmond62
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BBC Model B takes up smoking

Postby richmond62 » Sat Sep 09, 2017 12:05 pm

As the small chimney said to the big chimney, "If it soots you, it soots me."

So, there I am, having dragged my Model B all the way from GB to Bulgaria; plug the thing in, attach to oldish telly, and turn
on: happy start up ping . . then, after about 2 mins, as I start fiddling around trying to tune the telly, there is a jolly 'pop' and smoke comes
out of the back of the Beeb . . .

The power light remained on . . .

Am I completely bu**erd?

Please advise.

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Lardo Boffin
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Re: BBC Model B takes up smoking

Postby Lardo Boffin » Sat Sep 09, 2017 12:12 pm

Ah magic smoke! From the PSU? These are famous for capacitors failing. Should be an easy fix or various people can fix it for you - I send mine to Mark at Retroclinic.

It shouldn't have caused any permanent damage. I bought one that had done similar and it is fine.
BBC model B 32k issue 4, 16k sideways RAM, Watford 12 ROM board, Retroclinic Datacentre + HDD, matchbox co-proc, Viglen twin 40/80 5.25" discs, acorn cassette
BBC model B 32k issue 7, turboMMC, Opus Challenger 3 512k, Pi 3 coproc, Acorn 6502 coproc

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richmond62
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Re: BBC Model B takes up smoking

Postby richmond62 » Sat Sep 09, 2017 12:31 pm

Thanks!

I'll head out to the sleazy guy who I've been trying to winkle a PULDIN Bulgarian commie computer out of for a year.

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paulv
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Re: BBC Model B takes up smoking

Postby paulv » Sat Sep 09, 2017 12:33 pm

In the short term, if it is the X2 suppression caps, you can simply remove them and it'll still work as these caps are used for noise suppression only.

Paul.

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richmond62
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Re: BBC Model B takes up smoking

Postby richmond62 » Sat Sep 09, 2017 12:35 pm

Um, Err, How would I recognise X2 suppression caps?

And why "the short term" ?

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CMcDougall
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Re: BBC Model B takes up smoking

Postby CMcDougall » Sat Sep 09, 2017 12:58 pm

richmond62 wrote:why "the short term" ?

don't really need them, they where to stop interference with old TV tune in & the FM radio dial.
but since we have digiTV and radio is full of adverts, no one listens to it now anyways :lol:
Caps :
caps.jpg

it's usually the big one that goes pop, easy fix if you wish, or rip them out!
ImageImageImage

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richmond62
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Re: BBC Model B takes up smoking

Postby richmond62 » Sat Sep 09, 2017 1:04 pm

"rip them out"

what? just remove? no replacement, nothing?

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1024MAK
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Re: BBC Model B takes up smoking

Postby 1024MAK » Sat Sep 09, 2017 1:14 pm

Search Google or any other good search engine for "bbc micro x2 capacitors" and you will find stacks of stuff on this subject :wink:

The two X2 suppression capacitors have two jobs. That is they both have two jobs.
Together with a choke (inductor coil) they filter the incoming mains voltage to reduce unwanted interference. They also reduce the transmission back to the mains wiring of the switching frequency that the Beeb PSU generates. This reduces the interference to nearby radios and other electronic devices.

If you live in an area where the mains supply is mainly free from unwanted mains spikes and other interference, and neither you or your neighbours use analogue radio, or other electronic devices that are sensitive to interference (music, TV, wired telephone etc), then you could remove these capacitors and the Beeb would work fine. However, it's not recommended to leave it like that.

Note that they are known as "X2" types after the standard that requires capacitors used in this application (connected across the mains supply) to operate safely.

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
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1024MAK
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Re: BBC Model B takes up smoking

Postby 1024MAK » Sat Sep 09, 2017 1:18 pm

CMcDougall wrote:
richmond62 wrote:why "the short term" ?

don't really need them, they where to stop interference with old TV tune in & the FM radio dial.
but since we have digiTV and radio is full of adverts, no one listens to it now anyways :lol:
Caps :
caps.jpg
it's usually the big one that goes pop, easy fix if you wish, or rip them out!

A malfunctioning switch mode PSU like used in a Beeb can also affect some digital equipment as well as some audio equipment...

And there are still radio amatuers plus other radio spectrum users using analogue transmissions.

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
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1024MAK
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Re: BBC Model B takes up smoking

Postby 1024MAK » Sat Sep 09, 2017 1:24 pm

The parts are not expensive. RetroClinic does a service pack. This is his eBay listing. Or contact him direct and he won't have eBay fees to pay. He's a member here. He is also on Facebook and he has his own web site. His email address is on his web site.

Mark
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richmond62
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Re: BBC Model B takes up smoking

Postby richmond62 » Sat Sep 09, 2017 2:25 pm

As I live in Bulgaria, in the short term, at least, I'll try the machine without the X2 suppressors: the "only" problem might
be that I am connecting it, at the moment, to a cathode-ray tube TV . . .

I have a flat-screen TV connected to my BBC Mater Compact, and I can pick up another one for about 25 quid (bog-basic Chinese knock-off).

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Lardo Boffin
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Re: BBC Model B takes up smoking

Postby Lardo Boffin » Sat Sep 09, 2017 2:30 pm

I think I paid about £20 to have Mark do a PSU for me. Obviously the p&p from where you are will put that up a bit.
BBC model B 32k issue 4, 16k sideways RAM, Watford 12 ROM board, Retroclinic Datacentre + HDD, matchbox co-proc, Viglen twin 40/80 5.25" discs, acorn cassette
BBC model B 32k issue 7, turboMMC, Opus Challenger 3 512k, Pi 3 coproc, Acorn 6502 coproc

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richmond62
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Re: BBC Model B takes up smoking

Postby richmond62 » Sat Sep 09, 2017 2:36 pm

I know a character who inhabits a "cave" full of old machines and ancient components, and if push-came-to-shove
he could probably "do" a PSU for me.

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tricky
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Re: BBC Model B takes up smoking

Postby tricky » Sat Sep 09, 2017 3:11 pm

The caps are quite easy to replace, even with just a soldering iron, but disassembly and reassembly of the PSU can be a little fiddly.
The worst thing about the popped caps and continued use is that it will add a new aroma that you may not want your beeb to have - quite distinctive.
[looks for the smiley for holding your nose?]

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1024MAK
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Re: BBC Model B takes up smoking

Postby 1024MAK » Sat Sep 09, 2017 3:13 pm

Lardo Boffin wrote:I think I paid about £20 to have Mark do a PSU for me. Obviously the p&p from where you are will put that up a bit.

He means Mark of RetroClinic, not me!

Mark
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Re: BBC Model B takes up smoking

Postby Boydie » Sat Sep 09, 2017 3:48 pm

If you have someone who can fit them (it's not a difficult DIY), RS claims they deliver to Bulgaria.

You'll need a 10nF (RS Stock No 311-1024) and a 100nF (RS Stock No 210-500). These have always worked well for me - it's amazing how many manufacturers used power supplies with these fitted, not just Acorn.
They only come in packs of 5 (which comes to about £6 for a pack), but if you've got more than one machine it's only a matter of time...

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george.h
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Re: BBC Model B takes up smoking

Postby george.h » Sun Sep 10, 2017 6:11 pm

The most difficult thing about this "issue" - getting rid of the smell! It lingers for bloody ages! :lol:
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Re: BBC Model B takes up smoking

Postby flaxcottage » Sun Sep 10, 2017 6:29 pm

Boydie wrote:If you have someone who can fit them (it's not a difficult DIY), RS claims they deliver to Bulgaria.

You'll need a 10nF (RS Stock No 311-1024) and a 100nF (RS Stock No 210-500). These have always worked well for me - it's amazing how many manufacturers used power supplies with these fitted, not just Acorn.
They only come in packs of 5 (which comes to about £6 for a pack), but if you've got more than one machine it's only a matter of time...


Just be aware that even a new 100nf capacitor from RS can fail after a few months! :shock: :( And, yes, the smell is disgusting. :lol:
- John

Currently running Level 4 Econet with BBC B, BBC B+ 128K, Master 128K, 4Mb A3000, 4Mb A3020, 4Mb A4000, 4Mb A5000 dual FDD; UK101; HP41CX setup; Psion 3a, 3mx and 5mx; Z88; TI-58c, TI-59 and printer, HP-16C programmer's calculator

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1024MAK
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Re: BBC Model B takes up smoking

Postby 1024MAK » Sun Sep 10, 2017 8:37 pm

george.h wrote:The most difficult thing about this "issue" - getting rid of the smell! It lingers for bloody ages! :lol:

A lot of IPA, a toothbrush and a lot of elbow grease to remove all traces of the gunk that the old capacitor let out does wonders :wink:

Mark
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Re: BBC Model B takes up smoking

Postby dominicbeesley » Mon Sep 11, 2017 12:24 am

CMcDougall wrote:
richmond62 wrote:why "the short term" ?

don't really need them, they where to stop interference with old TV tune in & the FM radio dial.
but since we have digiTV and radio is full of adverts, no one listens to it now anyways :lol:
Caps :
caps.jpg
it's usually the big one that goes pop, easy fix if you wish, or rip them out!


You do need them, if you're not going to potentially upset your neighbours! They have more of an effect at AM/LW frequencies. Some of us DO listen to those. Also, if anyone near you has ADSL and you're any sort of distance from the exchange any noise in the LF,MF,HF frequencies can affect the signal to noise ratio. A noisy PSU can cause all manner of difficulties for your neighbours especially any that are in to old radios, Amateur radio or as I said have ADSL.

The mains wiring in your house is an aerial system transmitting a lot of noise, don't make it worse, please

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Re: BBC Model B takes up smoking

Postby BradBrad » Fri Sep 15, 2017 8:01 am

Hi. I made a video a while back showing how to replace the caps if you are feeling brave. The biggest faff is getting the PSU board out of the housing. The kits are widely available and usually include the 3 capacitors and a couple of cable ties. They are cheap.

I am not sure if there are any bleeder resistors on the caps so don't touch the underside of the PSU board once it is out until you have checked that there is no voltage on the large capacitors or the power transistor. I show all this in the video. Good Luck.

https://youtu.be/YSc9nxHslHI

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Re: BBC Model B takes up smoking

Postby 1024MAK » Fri Sep 15, 2017 10:00 am

There are resistors (R2, R3 & R5) that will discharge the two 200V electrolytic capacitors (C6 & C8 ), but no separate discharge resistor for C1 and C2. However, they should discharge via R2, R3 & R5 if the bridge rectifier (DB1) is okay.

Schematic of the primary side here :wink:

It is always wise to short out the terminals of any high voltage capacitors with a screwdriver (or better still, a 10k 1W resistor with test clips/probes) anyway, just in case a resistor has gone open circuit...

Mark
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Re: BBC Model B takes up smoking

Postby vanpeebles » Fri Sep 15, 2017 12:27 pm

How long could a BBC PSU capacitor hold a charge for? When I did the ones in my Master I left it turned off for a day, flicked switch on and off etc. I'm still very wary of working on electronics.

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Re: BBC Model B takes up smoking

Postby BrianR. » Mon Sep 25, 2017 5:49 pm

This is the state of one of the X2 caps that failed on one of my beebs recently.

As previously stated, the repair is fairly easy, but getting the PCB out of the PSU housing isn't.
A set of replacement caps (C1,C2 & C9) was just £2.00 + £1.20 postage from one of the eBay suppliers (there are several).
Attachments
2017-09-25 18.37.39.jpg

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1024MAK
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Re: BBC Model B takes up smoking

Postby 1024MAK » Mon Sep 25, 2017 6:08 pm

vanpeebles wrote:How long could a BBC PSU capacitor hold a charge for? When I did the ones in my Master I left it turned off for a day, flicked switch on and off etc. I'm still very wary of working on electronics.

In general, there isn't a simple answer to this, as it depends on the circuit, the voltage and the capacity of the capacitors.
As I said above, the primary/ mains voltage side capacitors should discharge within a matter of minutes IF the PSU is in a working condition and there are no component faults and no broken tracks or connections. The secondary / output capacitors may well hold a charge for rather longer if the PSU is not connected to the Beeb circuit board. Again, if there are faults, capacitors may remain charged, but these lower voltages are not normally a problem.

But for safety reasons, you should always discharge (short out) any high voltage capacitors before working on a PCB just in case...

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki‬ - for answers to many questions...

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richmond62
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Re: BBC Model B takes up smoking

Postby richmond62 » Sat Sep 30, 2017 5:22 pm

Sorry chaps, I've been a bit preoccupied lately, so have only just followed your advice and ordered the Acorn BBC Micro and Master Replacement tiddly-poms.

Thanks for the support :D

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Re: BBC Model B takes up smoking

Postby KayjayUK » Mon Oct 16, 2017 10:52 am

flaxcottage wrote:
Boydie wrote:If you have someone who can fit them (it's not a difficult DIY), RS claims they deliver to Bulgaria.

You'll need a 10nF (RS Stock No 311-1024) and a 100nF (RS Stock No 210-500). These have always worked well for me - it's amazing how many manufacturers used power supplies with these fitted, not just Acorn.
They only come in packs of 5 (which comes to about £6 for a pack), but if you've got more than one machine it's only a matter of time...


Just be aware that even a new 100nf capacitor from RS can fail after a few months! :shock: :( And, yes, the smell is disgusting. :lol:


That is so true. I stripped and repaired 6 psu's at one time about 2 years ago, every one of them has now popped. Oh and I used RS parts, I have always believed in their quality but I assume this isn't a quality issue.

Keith
From little Acorns great Beebs grow!

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Re: BBC Model B takes up smoking

Postby vanpeebles » Mon Oct 16, 2017 11:07 am

1024MAK wrote:
vanpeebles wrote:How long could a BBC PSU capacitor hold a charge for? When I did the ones in my Master I left it turned off for a day, flicked switch on and off etc. I'm still very wary of working on electronics.

In general, there isn't a simple answer to this, as it depends on the circuit, the voltage and the capacity of the capacitors.
As I said above, the primary/ mains voltage side capacitors should discharge within a matter of minutes IF the PSU is in a working condition and there are no component faults and no broken tracks or connections. The secondary / output capacitors may well hold a charge for rather longer if the PSU is not connected to the Beeb circuit board. Again, if there are faults, capacitors may remain charged, but these lower voltages are not normally a problem.

But for safety reasons, you should always discharge (short out) any high voltage capacitors before working on a PCB just in case...

Mark


How would you do this on a BBC? :)

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Re: BBC Model B takes up smoking

Postby 1024MAK » Mon Oct 16, 2017 11:49 am

vanpeebles wrote:
1024MAK wrote:
vanpeebles wrote:How long could a BBC PSU capacitor hold a charge for? When I did the ones in my Master I left it turned off for a day, flicked switch on and off etc. I'm still very wary of working on electronics.

In general, there isn't a simple answer to this, as it depends on the circuit, the voltage and the capacity of the capacitors.
As I said above, the primary/ mains voltage side capacitors should discharge within a matter of minutes IF the PSU is in a working condition and there are no component faults and no broken tracks or connections. The secondary / output capacitors may well hold a charge for rather longer if the PSU is not connected to the Beeb circuit board. Again, if there are faults, capacitors may remain charged, but these lower voltages are not normally a problem.

But for safety reasons, you should always discharge (short out) any high voltage capacitors before working on a PCB just in case...

Mark


How would you do this on a BBC? :)

If you know that it has not been powered up for a week or two, then it is safe, as electrolytic capacitors have leakage paths that will slowly discharge them.
Otherwise, be careful when removing the PCB from the metal case. Then use a plastic handled screwdriver (with a uninsulated metal shaft) to short between the two solder connections / leads of each the two large 250V electrolytic capacitors (marked C5 and C8 on the PCB screen print) in turn.
The electrolytic capacitors between the larger of the metal heatsinks and the output wiring/plug are all low voltage, and will not electrocute you.

IMG_5433.JPG
IMG_5434.JPG
IMG_5435.JPG

Cheap mains items from a certain well populated country in the East are more of a hazard.

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki‬ - for answers to many questions...

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vanpeebles
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Re: BBC Model B takes up smoking

Postby vanpeebles » Mon Oct 16, 2017 11:59 am

Ah when I did the Master, it was left for a number of days but I was still a bit weary :) So you touch the points of a single capacitor together?


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