Magic smoke escapee

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jgharston
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Magic smoke escapee

Post by jgharston » Sun Dec 15, 2019 11:48 pm

Well, after more then 20 years faithful service, the magic smoke has escaped from my Electrohome monitor:
Image

Shame, as it's a nice solid monitor, with a nice solid display, and a nice square case that things can be piled on top of. Some bit of it was repaired by an ABUGer at Halifax a few years ago, I'm terrible at names, but many thanks. I'll now start looking for a flat-screen SCART display and re-arrange my worktop, and prepare it for electronic disposal.

I've currently got the kitchen door open for ventilation.... ;)

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BigEd
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Re: Magic smoke escapee

Post by BigEd » Mon Dec 16, 2019 8:44 am

Oh, was that an RGB CRT with enough clarity to show 80 columns in comfort? That's pretty good!

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Re: Magic smoke escapee

Post by roland » Mon Dec 16, 2019 11:25 am

I'm sorry for your monitor. But still ... it might be repairable ....
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Re: Magic smoke escapee

Post by topcat96 » Mon Dec 16, 2019 2:16 pm

I feel your pain after recently experiencing a visit from the magic smoke fairy myself. She tapped her wand on my BBC Model B, invoked the spirits then promptly disappeared as the room filled with the smell of burnt electronics ... her maniacal laughter ringing in my ears.
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Re: Magic smoke escapee

Post by jgharston » Mon Dec 16, 2019 4:44 pm

Yes, a nice solid high-res display.

It might be repairable, I haven't looked inside yet so don't know what's gone fizzzzzzpop. Anything other than a clearly scorched fuse will be beyond me. I might bring it to a future ABUG as a donation rather than binning it.

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$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

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1024MAK
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Re: Magic smoke escapee

Post by 1024MAK » Mon Dec 16, 2019 5:41 pm

Fuses generally don’t produce any significant amount of smoke. A glass fuse where the glass ruptures violently (due to a sudden dead short on a high current supply) may break and leave black soot marks in the area.

Capacitors and inductors are the main cause of smelly smoke. Occasionally a defective chip/transistor/diode will fail and may stink (but most don’t create much smoke) or sometimes the defective semiconductor may cause an excessive amount of power to be dissipated in a resistor, it will then overheat and may stink and may smoke.

If there is a dry solder joint in a high voltage section, the resulting arcing can burn a hole in the PCB.

Did the screen image disappear when it failed?

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BigEd
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Re: Magic smoke escapee

Post by BigEd » Mon Dec 16, 2019 5:45 pm

Oh, a repair at an ABUG would be good!

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Re: Magic smoke escapee

Post by rharper » Tue Dec 17, 2019 5:23 pm

Ah yes, excellent monitor.
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Re: Magic smoke escapee

Post by gidandridge » Tue Dec 17, 2019 9:41 pm

Don't throw it away. =; Chances are it can be repaired.

May just be a capacitor. :)
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Re: Magic smoke escapee

Post by BeebMaster » Sat Dec 21, 2019 3:36 pm

Very sad, these are nice monitors. I always thought the colour was better than on a Cub, but they are bulkier.

Yesterday I had a similar episode with a Daewoo television set that must be getting on for 25 years old, although I blame Victor Meldrew in this instance. I was just away cleaning the DVD as I was getting sick of watching the same two-thirds of the same episode repeatedly same two-thirds of same two-th same repeat repeat repeatedly, and when I came back into the room there was an electrical burning smell so I checked everything important and eventually realised that the TV set had gone off, except it wasn't off, it was still on but no picture comes out any more. It only does sound now. No idea how, if at all, that can be fixed. I really will have to engage the services of a TV repair man, I could keep him busy for a fortnight probably.
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Re: Magic smoke escapee

Post by Kazzie » Sat Dec 21, 2019 5:03 pm

BeebMaster wrote:
Sat Dec 21, 2019 3:36 pm
I checked everything important and eventually realised that the TV set had gone off, except it wasn't off, it was still on but no picture comes out any more. It only does sound now. No idea how, if at all, that can be fixed.
Assuming it's a flat TV, the obvious first guess would be the backlight for the LCD. Have you tried examining the screen closely (possibly with a torch) to see if there's any evidence of a picture on the LCD itself?

(I've got the opposite situation myself: a flatscreen TV where the audio processing circuitry is fried. That's a lot easier to deal with: we've diverted the sound to the stereo system instead.)
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Re: Magic smoke escapee

Post by BeebMaster » Sun Dec 22, 2019 3:45 pm

No, it's a CRT - it will be a very long time until my personal T.V. set is anything else, although it has probably just come a step closer!

There's a faint bit of brightness towards the top of the screen but nothing else.
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Re: Magic smoke escapee

Post by 1024MAK » Sun Dec 22, 2019 5:42 pm

From what you describe it could be a number of things. If you can feel static electricity from the screen, the EHT supply must be functional, normally some of the other power rails are derived from the line output transformer (that also does the EHT).

The loss of the supply or any other failure that results in the tube cathode heater going out will give a blank black screen. As will one of the protection circuits cutting in.

If the brightness at the top of the screen that you see is from the CRT, then it can’t be the heater and that points more to the signal processing circuitry.

Mark

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