Domesday PSU

discuss both original and modern hardware for the bbc micro/electron
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BeebMaster
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Domesday PSU

Post by BeebMaster » Sun Aug 29, 2010 1:16 am

Following on from the Domesday Error Codes thread, which has been the scene of two BeebMaster fires of 2010, here are the pictures as promised of the power supplies inside the laserdisc players, along with my appeal for help in identifying what's broken and how to fix it.

There are three PSUs from my three Philips VP series players, and they've been swapped about that much over the last couple of months that I'm having trouble remembering which originated where, so for simplicity I've decided to call them PSU A, PSU B and PSU C.

PSU A is the good one that still works, PSU B is the one that's been on fire twice, and PSU C is the rogue one that not only looks different from A & B but is also dead without looking dead.

Here goes, starting with PSU A, the good one, long shot followed by some close-ups for reference purposes:
VP-PSU-A1.JPG
VP-PSU-A1.JPG (816.38 KiB) Viewed 2702 times
The orange mcdougleflump on the left has blown in PSU B, so hold this thought:
VP-PSU-A2.JPG
VP-PSU-A2.JPG (316.71 KiB) Viewed 2702 times
This square one has blown in PSU B:
VP-PSU-A3.JPG
VP-PSU-A3.JPG (249.66 KiB) Viewed 2702 times
There's a similar one of these here if it's any help:
VP-PSU-A4.JPG
VP-PSU-A4.JPG (267.57 KiB) Viewed 2702 times

Now to PSU B, prepare to cringe, this was a working Domesday Player from November 1986 to May 2010 when it went on fire and then decided to do it again yesterday:
VP-PSU-B1.JPG
VP-PSU-B1.JPG (805.25 KiB) Viewed 2704 times
Burnt orange:
VP-PSU-B2.JPG
VP-PSU-B2.JPG (220.5 KiB) Viewed 2702 times
Burnt square thing
VP-PSU-B3.JPG
VP-PSU-B3.JPG (258.56 KiB) Viewed 2699 times
I'm not sure if anyone can see anything else which might need replacing in the first picture from PSU B.

Finally, it's PSU C which is a different layout. This has a slightly earlier revision number than the other two and I can't see any actual damage, but it's pretty much dead as it will power the fan but nothing else:
VP-PSU-C1.JPG
VP-PSU-C1.JPG (889.77 KiB) Viewed 2699 times
I'm not sure if this should be as rusty-looking as it does:
VP-PSU-C2.JPG
VP-PSU-C2.JPG (256.58 KiB) Viewed 2700 times
I've got the service manual, which is about 94,000 pages long but has one of those 94,000 pages missing. By a hilarious irony (I can't stop laughing, honest) the missing page is the one which contains the PCB layout drawing of the PSU and the list of components.

So I could do with a bit of help knowing what sort of capacitors to get, and I hope these pictures are enough for somebody to work it out! I went on Farnell and searched for capacitors, but it said there were 38,713 products and more than one type including aluminium, electrolytic, tantalum, niobium oxide, film, television, ceramic, fine bone china, dishwasher safe, rassilon imprimature, tellurium and pentalian. I don't think the budget (or the likely number of hours remaining in my life) will run to getting one of each of the 38,713 types to test...
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Re: Domesday PSU

Post by station240 » Sun Aug 29, 2010 5:37 am

BeebMaster wrote:
Now to PSU B, prepare to cringe, this was a working Domesday Player from November 1986 to May 2010 when it went on fire and then decided to do it again yesterday:
VP-PSU-B1.JPG
Burnt orange:
VP-PSU-B2.JPG
http://uk.farnell.com/vishay-bc-compone ... dp/1215475

But caution, things don't go up in smoke like that for no reason,
BeebMaster wrote: Burnt square thing
VP-PSU-B3.JPG
Its your standard X2 high voltage smoke machine.
http://uk.farnell.com/panasonic/ecqu2a6 ... dp/1198301
Minimum order is 5, so replace them in all of your 3 PSUs.

BeebMaster wrote: I'm not sure if anyone can see anything else which might need replacing in the first picture from PSU B.
PSU B has a crack in the X2 0.1uf capacitor, this is the exact same one that goes fwoomp in BBC PSUs. Better replace all of them too.

If you don't have any, here is the link
http://uk.farnell.com/panasonic/ecqu2a1 ... dp/1198295

BeebMaster wrote: So I could do with a bit of help knowing what sort of capacitors to get, and I hope these pictures are enough for somebody to work it out! I went on Farnell and searched for capacitors, but it said there were 38,713 products and more than one type including aluminium, electrolytic, tantalum, niobium oxide, film, television, ceramic, fine bone china, dishwasher safe, rassilon imprimature, tellurium and pentalian. I don't think the budget (or the likely number of hours remaining in my life) will run to getting one of each of the 38,713 types to test...

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Re: Domesday PSU

Post by BeebMaster » Sun Aug 29, 2010 11:38 am

You mean it's going to cost £1.68 to replace these caps?

Time to 'phone up BCCI for a second mortgage!

That first one, the orange type, says in the spiel near the bottom it's for surface mount (although it says through-hole earlier on), does that make any difference?

I've never really taken an interest in the goings-on inside the BBC micro PSU before (apart from watching the plumes of smoke escape). I'd always assumed that it was one of the round blue metal drum things that goes up in smoke, not a square one. Perhaps I'll get in a job lot of these if they're the same as the BBC one and maybe one day I'll work myself up to trying to change one.
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Re: Domesday PSU

Post by station240 » Sun Aug 29, 2010 2:44 pm

Yeah the bbc uses the same 0.1uf capacitor, and also a smaller 0.01UF one. Need one of each for every PSU. Also advisable to replace the startup capacitor, I can't remember the value of it at the moment, 220uf at 35V I think

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Re: Domesday PSU

Post by BeebMaster » Thu Sep 02, 2010 6:37 pm

The parts arrived today (well, as many as Farnell will let me have at the moment) but unfortunately the orange one is the wrong type. You wouldn't really have been able to tell from my picture, it looked quite a good match seeing it online but the ones which have arrived are much bigger in reality. I think the one I need is more like this one:

http://uk.farnell.com/vishay-bc-compone ... dp/1166597

The 0.68uF X2 are here, look a bit smaller than the ones on the board but the pins are spaced out about the same so I think it's right. I ordered the other two types for in the BBC micro PSU where one of them is duplicated in the Domesday PSU, so hopefully one day I will work up the nous to try to repair some of my smoky ones. However these are on back order and I'm not getting them till January!

That was slightly better than RS who said I couldn't have them till next June, which was far too close to the Domesday 25th anniversary for my liking!
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Re: Domesday PSU

Post by BeebMaster » Thu Sep 09, 2010 9:32 pm

The new little orange caps arrived and I've put one in, but "PSU-B" is still in the same state as it was before the explosion, ie. it spins the fan for about 3 seconds and that's it.

That suggests to me 1 of three things:

1. I've soldered it in wrong or it isn't connected properly
2. It got too hot whilst I was soldering it in and I've bust it
3. It was the X2 cap which caused the second explosion not (as I'd thought) the orange one.

I'll have to wait till the new X2 caps turn up next year before I can solve that one!
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Re: Domesday PSU

Post by retroclinic » Thu Sep 09, 2010 9:55 pm

BeebMaster wrote:I'll have to wait till the new X2 caps turn up next year before I can solve that one!
Maybe someone on here keeps them in stock, for regularly refurbing PSUs, and could send you some for the weekend?

Can't think of who tho... :^o
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Re: Domesday PSU

Post by BeebMaster » Thu Sep 09, 2010 10:55 pm

That would be handy, except I'm off to Prawns in the Pork first thing in the morning, which also means it's exactly a year since Acorn World in Huddersfield!

I suppose I'm also delaying the inevitable, because I kinda know that even when I put in the new X2 cap it still won't work...
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Re: Domesday PSU

Post by station240 » Wed Sep 22, 2010 6:07 am

BeebMaster wrote: I suppose I'm also delaying the inevitable, because I kinda know that even when I put in the new X2 cap it still won't work...
You'd be right, I just spotted some more fried parts on the board. When I figure out what the correct replacement part is I'll let you know.

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Re: Domesday PSU

Post by elecdrum » Wed Sep 22, 2010 10:46 am

Just a thought here, I have had psus in the past which have just kept blowing and demanding fresh parts etc. There is a cure albeit more expensive than a repair if you are lucky. In the pages of RS are lots of power supplies with +5 -5 +12 -12 all on the same psu. So as long as you dont need stange voltages one of these would make a good stand-in till you can get the psu repaired.

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Re: Domesday PSU

Post by BeebMaster » Wed Sep 22, 2010 11:32 am

I'd thought of that, and it doesn't need anything fancy, just +5V, -5V, 12V and 0V but unfortunately it does need a pretty specific connector. If you look at any of the pictures above which I've called "VP-PSUA1", "VP-PSU-B1" or "VP-PSU-C1" you'll see the connector in the bottom left-hand corner of the picture.

In fact it's two separate connectors side by side, I can't just recall the official name for this type of connector but they're very similar to the sockets for the internal co-pro inside a Master.

I could probably connect wires supplying the correct voltages to the pins inside the player but that risks more explosions...
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Re: Domesday PSU

Post by station240 » Sat Sep 25, 2010 5:13 pm

You'll have to help me better identify these parts. Is that diode (aqua with red + brown stripe) used anywhere you do have a parts list/diagram for. Also is there a wattage rating on that big resistor ? I think its 3w anyway.
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VP-PSU-B2.JPG (338.92 KiB) Viewed 2404 times

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Re: Domesday PSU

Post by BeebMaster » Sat Sep 25, 2010 11:39 pm

Right, I'll have a closer look next time I have this one in pieces. At the moment, I put it back together after I'd changed the burnt orange cap and taped up the switched and kettle lead hole so I couldn't accidentally plug it in. According to Farnell, the X2 cap is due in stock on 4th Oct. so when it arrives I can take it all to pieces again.
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Re: Domesday PSU

Post by BeebMaster » Thu Oct 07, 2010 1:09 pm

The 0.1uF X2 caps arrived yesterday so I've had the dead PSU out again for another session.

First of all, on the additional dead parts:

The "diode" appears to be a resistor, it's shown more clearly in picture VP-PSU-A2 further above.

On the good PSU I got the following readings on my multimeter:

POWER ON
20K Ohm setting: -8.05
2000 setting: -811 to -825

POWER OFF
20k Ohm setting: 4.83
2000 setting: 705

On the dead one, the only reading I could get was with the power on on the 20K setting and the reading was -1.39.

So I think that one's dead. What is it?

The salmon coloured one is also shown more clearly in picture VP-PSU-A2 and is marked "68R +5%", so the good one is giving the following readings:

POWER ON
20K: 0.71
2000: 370

POWER OFF
20K: 0.07
2000: 068

The dead one reads as follows:

POWER ON
20K: -3.64 or +4.23 depending on which way the probes are connected
2000: -241

POWER OFF
20K: 0.07
2000: 068

So I think that one might be OK but perhaps being affected by something else dead (hopefully the other resistor)?
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Re: Domesday PSU

Post by BeebMaster » Thu Oct 07, 2010 1:22 pm

elecdrum wrote:Just a thought here, I have had psus in the past which have just kept blowing and demanding fresh parts etc. There is a cure albeit more expensive than a repair if you are lucky. In the pages of RS are lots of power supplies with +5 -5 +12 -12 all on the same psu. So as long as you dont need stange voltages one of these would make a good stand-in till you can get the psu repaired.
This is a picture of the connector on the main board into which the PSU module plugs:
VPPins.JPG
VPPins.JPG (62.01 KiB) Viewed 2345 times
You may have noticed something amiss in the picture!

Unfortunately, despite my bestest efforts, I haven't been able to straighten them out. There's practically no room to maneouvre with the plastic housing round the pins and the proximity of the connector to the player casing, so I'm afraid the innermost one broke off completely at the board and the outer one has partly broken off but there is a bit left which I've straightened.

I was hoping that these bent pins might be the reason why it still wasn't powering up after changing the orange cap last month but I've tried the dead PSU in the Wonky (But Currently Working) VP415 and nothing happens.

I've also now replaced the X2 cap and changed the orange one again because I wasn't terribly happy with the original job I did. I think my normal soldering technique of leaving the iron in contact for a few minutes till everything is bubbling nicely and the green is starting to lift of the PCB might just possibly have damaged the new orange cap, so I made sure I was a bit quicker this time!

In order to end on a slightly positive note, trying the PSU from the Wonky (But Currently Working) VP415 in the dead one does get some functions working, the fan powers up, the drive door and buttons work, the laser moves but the disc doesn't spin, so I think those two broken pins on the connector must power the disc spinning mechanism. I'm hoping I've be able to replace the pins at some point, once the PSU is fixed.
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Re: Domesday PSU

Post by MartinB » Thu Oct 07, 2010 1:25 pm

Be careful Ian, you shouldn't really use a multimeter on resistance setting when the unit under test is powered. The meter is applying it's own voltage to get a resistance reading and you will not only get meaningless values but also risk blowing the meter.

If you want to do comparisons with power applied, read across the component on a DC voltage range starting high and coming down until you have a valid reading.

For interest, 68R is 68 ohm so that resistor seems to be ok but again, reading in-circuit component values even with power off may not yield the expected absolute value. Comparisons are fine though as long as you use the same probe polarity on both.

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Re: Domesday PSU

Post by BeebMaster » Thu Oct 07, 2010 1:42 pm

MartinB wrote:Be careful Ian, you shouldn't really use a multimeter on resistance setting when the unit under test is powered. The meter is applying it's own voltage to get a resistance reading and you will not only get meaningless values but also risk blowing the meter.
I did wonder about that - can it blow up the board or just the meter?!!

I remember killing Station 112 completely by using the amp setting so I'm not having anything at all to do with amps ever again!
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Re: Domesday PSU

Post by MartinB » Thu Oct 07, 2010 1:47 pm

In a PSU, most likely just the meter but it depends on the amount of voltage that the meter applies which may vary with the selected range. Certainly with more delicate electronics you would run the risk of damaging components.

The 'amp' or current ranges can be pretty much a short circuit (very small resistance) and should only be used in a series connection to a circuit or else yes, carnage can ensue :shock:

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Re: Domesday PSU

Post by station240 » Thu Oct 07, 2010 2:28 pm

BeebMaster wrote: I've also now replaced the X2 cap and changed the orange one again because I wasn't terribly happy with the original job I did. I think my normal soldering technique of leaving the iron in contact for a few minutes till everything is bubbling nicely and the green is starting to lift of the PCB might just possibly have damaged the new orange cap, so I made sure I was a bit quicker this time!
[-X [-X [-X [-X [-X [-X [-X [-X [-X

About 10 seconds is all you really need to solder something in place.
I know your not used to this sort of thing, but the point is to only melt the metal. Starting a fire or lifting the tracks off the PCB isn't desirable.

As for the bent/broken pins, if you heat the pad for each damaged pin you should be able to yank it from the other side. The square pins from a commonly available SIL connector style would do as replacements.

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Re: Domesday PSU

Post by BeebMaster » Thu Oct 07, 2010 3:50 pm

station240 wrote: About 10 seconds is all you really need to solder something in place.
I know your not used to this sort of thing, but the point is to only melt the metal. Starting a fire or lifting the tracks off the PCB isn't desirable.
I was exaggerating slightly. But only slightly! Anyway, the second attempt is a much better job.
station240 wrote:As for the bent/broken pins, if you heat the pad for each damaged pin you should be able to yank it from the other side. The square pins from a commonly available SIL connector style would do as replacements.
I think I should be able to do that without much trouble. The real problem will be getting at the underside of the carrier board. This will involve unscrewing the Domesday sandwich from the bottom of the player. I tried this a while back and it involves putting a star shaped screwhead up a little tunnel. What happened what that the screwhead was a mite too wide and so it got stuck and when I got it out, the magnetic force which was holding the star bit to the screwdriver stopped doing whatever magnetic forces do to hold Pole +A to Pole -A or whatever it is, and so the bit was stuck up the tunnel. In the end I had to superglue it to the screwdriver and break off bits of the tunnel to get it back!

(I was then about to go to a bus stop holding a wooden chair I'd superglued together shortly after trying to bring home a wendy house which was too big to fit through the workshop doors but I thought I'd better not....)

Anybody got any idea what value that first resistor is?
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Re: Domesday PSU

Post by station240 » Fri Oct 08, 2010 3:22 am

BeebMaster wrote: The "diode" appears to be a resistor, it's shown more clearly in picture VP-PSU-A2 further above.
Don't let the coloured bands fool you, many diodes have those instead of numbers. Problem is I decoded the numbers and they are meaningless.

Simple test, if its glass with silicon on the inside (or a fine wire and a block of something) its a diode, if its white ceramic inside its a resistor.

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Re: Domesday PSU

Post by BeebMaster » Fri Oct 08, 2010 11:48 am

OK, here's a new picture from the working PSU, which shows outlined in red the mystery diode/resistor which is dead on the dead PSU, and outlined in blue 4 others in the same area which look identical:
VPUnknown.JPG
VPUnknown.JPG (139.08 KiB) Viewed 2298 times
The other thing I thought of is that there are quite a few fuses on the board, here's an example:
VPFuse.JPG
VPFuse.JPG (92.32 KiB) Viewed 2298 times
There are a couple of these (2A ones, not 3.15A) near that X2 cap which exploded, but I've no idea how to figure out if they've blown 'cos you can't see the filament like you can with the glass ones!
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Re: Domesday PSU

Post by BeebMaster » Fri Oct 08, 2010 12:10 pm

I've managed to extract the pages relating to the PSU from the Service Manual. I'm not sure how much use this is because it relates to the (earlier?) version of the PSU which is shown in the "C" pictures at the beginning. There may also be some pages missing but this is all there is in the scan I have.
VP415 PSU.pdf.zip
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Re: Domesday PSU

Post by BeebMaster » Fri Oct 08, 2010 1:30 pm

I had the idea of comparing PSU "C" with what's in the manual, so I did and the mystery part is definitely a diode, I should never have doubted it! Cross referencing things here and there tells me it's a BAV21 if that means anything.

Assuming I can get one (or more likely, 1000 of 'em) is putting a new one in really likely to bring this PSU back from the dead, or will nothing happen (again) and leave me searching around for the next dead part?

Curiously, whilst I was examining PSU "C", I tried it in the player and it operated the fan but wouldn't bring anything else to life. Last time it was marked as most definitely dead, so a rest has done it a bit of good at least!
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Re: Domesday PSU

Post by station240 » Fri Oct 08, 2010 3:31 pm

BeebMaster wrote:I had the idea of comparing PSU "C" with what's in the manual, so I did and the mystery part is definitely a diode, I should never have doubted it! Cross referencing things here and there tells me it's a BAV21 if that means anything.

Assuming I can get one (or more likely, 1000 of 'em) is putting a new one in really likely to bring this PSU back from the dead, or will nothing happen (again) and leave me searching around for the next dead part?
http://uk.farnell.com/fairchild-semicon ... dp/1700930

minimum order quantity 1, cost £0.056
LOL yeah 5 pence.

One difference between the circuit you uploaded, and the PSUs you have, its the number of transformers on the board has been reduced.

If I'm reading it right T401 is replaced by the CNX82 6 pin IC and some extra components. Now given that some of those extra parts are what went up in smoke, I would assume that CNX82 itself is damaged.

CNX82 is a photo transistor (light triggered transistor) and an LED in the same package, its to isolate high voltages from low voltages. In this case is controls the main power supply.

The fuses you can test yourself.
With the power OFF, use the multimeter to measure the resistance between the two pins, you should get a reading of zero or very close too.

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Re: Domesday PSU

Post by BeebMaster » Sat Jul 02, 2011 11:14 pm

OK, I'm back onto this, I could do with getting this PSU fixed before November. I've checked the fuses with the multimeter at 20K ohms and 2000 ohms and they all read 0.00. I think that's good.

I'll get some of those diodes but I was trying to see if Farnell will sell me one of those CNX82 things, but the Farnell website is dead at the time of writing and Maplin and RS haven't heard of it so I might be struggling.

The other job to do is to fix the damaged connector for the PSU on the VP415 main board. There's a picture of the damage from last year up above and I've also made a new thread about it.

I particularly want to get this VP415 working as I had a smidgen of success reading LV-ROM data off a disc with the player connected up to a Beeb via a host adapter/1MHz bus arrangement instead of the AIV SCSI board last time, so I want to do some more on that once it's working again.
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Re: Domesday PSU

Post by flynnjs » Sun Jul 03, 2011 7:15 pm

Ian, might be worth having a workshop to help you sort some of
your stuff out. You bring tea cakes and LV-ROM drives (and service
manual) and we bring the soldering iron to stir the tea with :-)

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Re: Domesday PSU

Post by BeebMaster » Sun Jul 03, 2011 9:14 pm

This is a good idea, I could perhaps bring it to "the Lass" in a couple of weeks' time, or even have a session back here on the Sunday afternoon, it's only a few miles away.
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Re: Domesday PSU

Post by 1024MAK » Sun Jul 03, 2011 10:25 pm

BeebMaster wrote: I was trying to see if Farnell will sell me one of those CNX82 things, but the Farnell website is dead at the time of writing and Maplin and RS haven't heard of it so I might be struggling.
I had a quick look, but (unsurprisingly) Farnell do not appear to stock it. Here is a list of similar types, one or more of these may be suitable (I have not had the time to compare the specifications) http://uk.farnell.com/jsp/search/browse ... 1%2B203598 .
Attached is a copy of the CNX82 datasheet.
More bad news :( , having worked on switch mode power supplies (SMPSU) before, often a number of components die, so it is very likely that there are more damaged or faulty parts lying in wait. One of the causes is old electrolytic capacitors (the "tall" cylindrical ones). Have a very good look and if you see any bulges (even slight) or any sign of leakage, renew them. Also renew any that live next to other components that get (or may get) hot. Indeed as these are old units, it may pay to renew all the large ones and any small ones that are used for controlling the regulator action.
Mark K.
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Re: Domesday PSU

Post by BeebMaster » Sun Jul 03, 2011 11:41 pm

Thanks for that, I'd had a trawl around E-bay a bit earlier and found somebody selling the exact part. It's quite a bit more than those Farnell ones, but still low numbers (in fact single units) of £Pounds apiece so I've sent off for them. I've also ordered some of that dodgy Diode from Farnell, so with any luck both bits will be here by mid-week and I can give it a go.

Hopefully this and using my bits-of-wires-wrapped-round-holes-and-sticky-tape method of getting round the broken connector problem mentioned in the related thread will have the thing back in working order.

If not, then some of you will have to take a leave of absence from the Up Your Arcadians convention a week on Sunday to come round here and fix it up for me.
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