Author Topic: Spot the problem  (Read 7166 times)

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Offline djos

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Re: Spot the problem
« Reply #25 on: December 13, 2016, 08:59:13 pm »
It could be the somewhat out of focus picture, or my out of focus eyeballs, but isn't the topmost (closest to transformer) diode installed backwards?

It looks like it's installed the same way as the second (from the bottom of the picture) diode, which is not what the silk screen specifies.

I wondered the very same thing in reply #19
The impossible often has a kind of integrity which the merely improbable lacks.

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Online mikerj

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Re: Spot the problem
« Reply #26 on: December 13, 2016, 10:01:53 pm »
I used to see lots of NTC failures in the degausing circuits of old CRT TVs/Monitors, they aren't the most reliable of components.  However sleeving them is not a good idea because it makes them take that much longer to cool down.

Those are PTCs.  :)

Oops, err...well done for spotting my deliberate mistake  |O
 

Offline TerraHertz

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Re: Spot the problem
« Reply #27 on: December 15, 2016, 03:26:21 am »
About that diode - it looks wrong because the stripe paint is mostly rubbed off. But it is the right way round.

The schematic - sigh. Various unexpected chores popped up, and I didn't finish that yet. Almost.

There's another 12V DC supply built into my wiring closet. It's by the same manufacturer, though a lower current. I thought I'd better check the caps in it. They are OK.

Collecting old scopes, logic analyzers, and unfinished projects. http://everist.org
 

Offline TerraHertz

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Re: Spot the problem
« Reply #28 on: December 18, 2016, 07:59:05 am »
Here's the schematic of that power supply, if anyone wants it.
The writeup here http://everist.org/NobLog/20161129_3d_learning_curve.htm#ps
also has a PNG version and the raw SCH file & library. In Protel98 form, ha ha, yes I know, very old tools.
After tracing the diagram in the rough form (very messy, on several sheets of paper) I'd intended to do a neat hand-drawn version.
But it's hard to fit on a single A4 sheet, sooo... for the first time since around 2004 I installed my old schematic/pcb tools. One of several, but I was most familiar with Protel98, so hoped I'd still remember something of how to use it. Wasn't too painful.

So, good. I'd been meaning to do that for ages. It's a long story, involving some fairly traumatic events back then which kind of turned me off several things, including electronics design.
Collecting old scopes, logic analyzers, and unfinished projects. http://everist.org
 
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