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Power Supply snap-crackle-pop...


morelenmir
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I bought a cheap 5V, 2000mA wall transformer from ebay - doubtless an old mobile telephone charger - to replace my failing original. It tested okay on the multimeter at about 5.03V. Unfortunately, on plugging in to the A8 and then switching on the thing gave a sharp crack. I instantly switched off again - but in electronics that means nothing of course and even after such a small fraction of a second there was a distinct smell of 'magic smoke'. Worse still, on reattaching the old supply I get... Nothing from the A8; no screen and the power lamp flashes on and off, as do the LED's on the VBXE and the uSwitch.

 

Clearly the cheap phone charger was a dud in some way, suffered a big voltage excursion on power-up and has fried my Atari - not to mention the very real chance my various mod-boards are also toast... Bugger!!!

 

Assuming the absolute worst has not happened, where should I start looking for blown components to replace on the motherboard? I understand the RAM chips are usually the first thing to cook off. Those blinking power lamps also suggest maybe a blown capacitor or diode somewhere, maybe?

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Blinking suggests that the power supply failed (hopefully). Look for a more robust supply than a cheap Chinese phone charger.

 

Sadly the lamps flash when the original Atari supply is plugged in and also when trying the noisy, but otherwise good 5.12V supply I have had for a while. The 'newest' one I got today that caused all the trouble is permanently dead.

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Most of these new compact high amperage power packs are based on a high frequency switching circuit that normally just goes dead upon failure. Not to say that it couldn't have failed with a high voltage output, but this sounds more like what would happen due to a reversed polarity connection. If that were the case, and based on having quite a bit of current available (2 amps) probably nearly all of the chips got fried.

 

- Michael

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Did you verify the polarity when testing the voltage before plugging it in?

 

I did - and at the time i was sure I had it the right way around... But in hindsight - it is certainly possible it was reversed, or perhaps I was reading the pinout diagram backwards. Never try to do fiddly electronics when you are tired! I dismantled the thing last night, so I cannot re-check.

 

Going from what has been said here it sounds like this whole motherboard is pretty much a write off. Do you think the U1MB and VBXE are going to be casualties as well? I'd imagine there is no way to be sure until I buy a new motherboard and try to fit them.

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Look for any caps that have a bubble shaped head, they should be flat but when they go the top expands and as daft as it sounds its always worth smelling the board, you can normally track down some culprits that way. Also if there was a crack there will probably be a mark on the pcb.

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Look for any caps that have a bubble shaped head, they should be flat but when they go the top expands and as daft as it sounds its always worth smelling the board, you can normally track down some culprits that way. Also if there was a crack there will probably be a mark on the pcb.

 

The 'nose test'!!!

 

I'll give that a try - there was certainly an air of magic smoke when I first turned the thing on Paul... Never release the magic smoke, especially from Tantalum capacitors or a CRT trippler ladder!!!

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The magic smoke is normally carcinogenic so not so good :) (don't sniff too much in :) )

 

I lived above a TV shop for a while (the owner was my landlord), poor old Malcolm the owner and TV engineer had a stroke but still tried to carry on working soon after, all you could hear was loud bangs and Malcolm shouting "f#&k". He taught me to stay away from tripplers, mucho KV I'm told..

 

He also liked to do this weird thing of checking if voltage was going through an item by touching it, apparently he had got used to being mildly electrocuted...

 

Very odd man....

Edited by Mclaneinc
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The magic smoke is normally carcinogenic so not so good :) (don't sniff too much in :) )

 

I lived above a TV shop for a while (the owner was my landlord), poor old Malcolm the owner and TV engineer had a stroke but still tried to carry on working soon after, all you could hear was loud bangs and Malcolm shouting "f#&k". He taught me to stay away from tripplers, mucho KV I'm told..

 

He also liked to do this weird thing of checking if voltage was going through an item by touching it, apparently he had got used to being mildly electrocuted...

 

Very odd man....

 

It sounds like your landlord and my father were cut form the same cloth Paul! My dad's favorite way of testing if a valve still worked was to wet his finger and touch the metal cap...

 

The worse thing with old CRT screens was the EHT socket. Apparently even if they had been switched off the grids inside kept a big charge for a good while. It was very easy, having swapped out the tube for a new one to carry it away and while you were lumbering around to let one of your finger ends slip against the recessed contacts... He said he'd thrown more than one CRT across a living room after getting the residue from 30,000 volts running through his forefinger!

 

Anyway - I'm just hoping that a single component or sub-section took all the over-voltage, burnt out and saved the board. At the very least I hope the mods will live to fight another day.

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The worse thing with old CRT screens was the EHT socket. Apparently even if they had been switched off the grids inside kept a big charge for a good while. It was very easy, having swapped out the tube for a new one to carry it away and while you were lumbering around to let one of your finger ends slip against the recessed contacts... He said he'd thrown more than one CRT across a living room after getting the residue from 30,000 volts running through his forefinger!

 

Yes, CRT's have an inner and outer conductive coating usually referred to as the 'dag' coating. Since CRT's are basically a parallel plate capacitor with glass as the dielectric, they form VERY low loss capacitors. So low, in fact, that even once you've discharged a CRT, it can automagically accumulate charge from just sitting around.

 

So, if you ever discharge a CRT and remove the anode cap, you should go ahead and clip a lead onto the anode button, and the other end onto the spring loaded outer dag ground strap.

 

Another thing to note, is that you should connect all grounds of the tube itself before you go to reconnect the anode connection. I had a CRT that had accumulated a charge, and I went to put it back in place. I connected the anode first, then the grounds. Well, at the time I was not in the habit of shorting out the CRT capacitance, so it had accumulated a charge, and thus a voltage across it's two plates. When I connected the anode, I more or less connected the anode to ground, through a bleeder resistor, diodes if the current is flowing the right way, etc. Afterwards I went to connect the ground lug and got shocked, not any worse than your typical static shock, but enough to make me wonder just what I had done wrong there.

 

So PSA: short out your CRT capacitances when working on them, and make sure the grounds are the first connections to make, and the last to break, when installing or removing a CRT.

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  • 4 weeks later...

Having just done a search about the PSU for my 800XL - CO 61763-34 and converting the 5V 7.5VA to watts, am I right in thinking, as per the original post I think, that a decent USB charger can be used to replace the giant ingot?

 

I have a couple of Anker 40W & 60W multi-port USB chargers that can do 2.4A on a number of ports, could I simply hack a USB cable to a 7-pin DIN and use that instead of the brick?

 

If so, it'd be nice to retire the ingots from what I read.

 

Aaron

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Having just done a search about the PSU for my 800XL - CO 61763-34 and converting the 5V 7.5VA to watts, am I right in thinking, as per the original post I think, that a decent USB charger can be used to replace the giant ingot?

 

I have a couple of Anker 40W & 60W multi-port USB chargers that can do 2.4A on a number of ports, could I simply hack a USB cable to a 7-pin DIN and use that instead of the brick?

 

If so, it'd be nice to retire the ingots from what I read.

 

Aaron

 

Yeah - you need between 5.0 and 5.2V at a minimum of 1.5A and better 2A+ to be absolutely sure. I don't know about USB chargers though, the ones I have seem to offer a maximum 450mA but there may be better ones out there. One thing I have noticed from all the wall-transformers I have used though is they seem very noisy - but again I was buying £2-£4 ex-mobile phone units and doubtless a bit more money laid down would improve your chances of a clean supply. I actually wondered about the dedicated 5V LED transformers you can buy for comparatively little - they are switch-mode and also offer at least some degree of variability so you can be certain you are dialled in to 5V on the nose. I'm not in any manner endorsing or recommending them; after my experience I am very PSU-shy right now - but these do look interesting:

 

eBay Auction -- Item Number: 1218299342501?ff3=2&pub=5574883395&toolid=10001&campid=5336500554&customid=&item=121829934250&mpt=[CACHEBUSTER]

 

However, if you take nothing else away from my sad story - do test, test, test; test the output voltage at least 8 times (preferably under a synthetic load if you have something like that handy) and make 20 double checks you have attached the DIN7 plug with the correct polarity!!! The sound of crackling RAM chips is not a happy one...

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Thanks, good info there.

 

I might just try butchering a USB cable and see how it goes with a Maplin 7-pin DIN plug. And quad-check the wiring to the original PSU before putting it anywhere near the 'XL!

 

The PSU you point to looks interesting, may just get one of those to put on the shelf anyway, or be available if I fritz the Anker USB thingy :)

 

Cheers

 

Aaron

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Thanks, good info there.

 

I might just try butchering a USB cable and see how it goes with a Maplin 7-pin DIN plug. And quad-check the wiring to the original PSU before putting it anywhere near the 'XL!

 

The PSU you point to looks interesting, may just get one of those to put on the shelf anyway, or be available if I fritz the Anker USB thingy :)

 

Cheers

 

Aaron

 

This also seemed like a really interesting unit and I umm'ed and ahh'ed for a while:

 

eBay Auction -- Item Number: 1818249981731?ff3=2&pub=5574883395&toolid=10001&campid=5336500554&customid=&item=181824998173&mpt=[CACHEBUSTER]

 

Its more of a bench deal, but I like the look of it with that built-in voltometer and very clean design. I'd still test it first though!!!

 

Also, Maplins screw you through the nose on their plugs like everything else. I picked up these instead:

 

eBay Auction -- Item Number: 1508897969451?ff3=2&pub=5574883395&toolid=10001&campid=5336500554&customid=&item=150889796945&mpt=[CACHEBUSTER]

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I get 5V power supplies at thrift stores... the ones I like are the ones that come with routers. The D-link power supplies seem robust and they are often 5V 2.5A... I've gotten tham for $2. Hey its even worth it if you have to buy the whole router for $5 and then just toss the router.

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I get 5V power supplies at thrift stores... the ones I like are the ones that come with routers. The D-link power supplies seem robust and they are often 5V 2.5A... I've gotten tham for $2. Hey its even worth it if you have to buy the whole router for $5 and then just toss the router.

so you're the reason I can never find the PSU for routers at goodwill :mad:

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If anybody is interested, I will soon have available 30 XL/XE power supplies. They are 5V, 2A and use a Neutrik 7-pin DIN with cast aluminum housing and gold pins. $15 each, $5 will ship one or two in the USA (so $20 for 1 shipped, $35 for 2 shipped).

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If anybody is interested, I will soon have available 30 XL/XE power supplies. They are 5V, 2A and use a Neutrik 7-pin DIN with cast aluminum housing and gold pins. $15 each, $5 will ship one or two in the USA (so $20 for 1 shipped, $35 for 2 shipped).

 

Sounds like nice gear Stephen! Did you put them together yourself? Do you have a photo to share of them?

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Sounds like nice gear Stephen! Did you put them together yourself? Do you have a photo to share of them?

I make them myself - only make a few dollars per unit. Just doing them to get some decent supplies out there. I'll try to get a photo up tomorrow.

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I make them myself - only make a few dollars per unit. Just doing them to get some decent supplies out there. I'll try to get a photo up tomorrow.

 

 

Excellent - good, reliable PSUs are something that is badly needed! Are they switch-mode or linear? Both types have their strengths and weaknesses.

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