Author Topic: most broken equipment you run into?  (Read 9594 times)

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Offline coppercone2Topic starter

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Re: most broken equipment you run into?
« Reply #25 on: December 11, 2023, 12:05:03 am »
qualified to work in a body shop after only 15 deliveries
 

Offline lugaw

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Re: most broken equipment you run into?
« Reply #26 on: December 11, 2023, 05:32:06 am »
It looks really really bad on the outside but miraculously the inside survived without damage and it is very accurate because of the year 2020 calibration.


I also had a Tektronix AWG615 that looks pristine on the outside but has a shorted 3.3v rail I can't fix. :/
 

Offline RaymondMack

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Re: most broken equipment you run into?
« Reply #27 on: December 11, 2023, 10:19:59 pm »
In my experience, anything mechanical will become faulty at some point. Particularly silver coated switch contacts. I have probably spent more time replacing and/or cleaning damaged/oxidized switches and bad capacitors than bad ICs. I recently repaired 4 different Agilent E36xx series PSUs (approx. 2008-2011 MFD) that had faulty "gold plated" switches made by C&K (on the back side for slave/master operation and remote voltage/current programming). Ended up just putting wire jumpers in place of the switches since they were so damn expensive to replace (replacement switches would have costed more than I paid for the PSUs).

Slide switches are pretty easy to mangle from excessive force and most are not sealed well (if at all), allowing atmospheric gases to easily reach the contacts and induce oxidation. Many, HP/Agilent PSUs use these.
Rocker switches can seize (contacts weld together) in AC mains switching (the contacts generally fail before the rocker action does).
Toggle switches are fairly robust, but are easy to hit and damage accidentally.
Rotary switches are robust mechanically, but oxidize the easiest and are a pain to clean.
Large push button switches are quite fragile (especially locking types). I mostly see the plastic stems break off or the push mechanism seizing from either dust/contaminates or mechanical wear of the track.

Since most analog PSUs (especially from HP/Agilent) have at least one or more of the above switches... I'd vote analog adj. DC PSUs as the most likely to fail TE.
 

Offline coppercone2Topic starter

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Re: most broken equipment you run into?
« Reply #28 on: December 11, 2023, 10:41:19 pm »
and sealed relays don't do too well either.. they often have vent holes. its not a good feature

basically its a vent for whatever the switch makes switching

if you seal it up things get trashed
« Last Edit: December 16, 2023, 05:23:22 pm by coppercone2 »
 

Offline KrudyZ

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Re: most broken equipment you run into?
« Reply #29 on: December 16, 2023, 05:22:11 pm »
I also had a Tektronix AWG615 that looks pristine on the outside but has a shorted 3.3v rail I can't fix. :/

Because you can't find the location of the short or why?
 

Offline ifonlyeverything

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Re: most broken equipment you run into?
« Reply #30 on: December 16, 2023, 06:34:54 pm »
Lately, it's been much of the stuff that I purchase on ebay. Badly packaged by careless sellers

Went through this with SMPS transformer ferrites and AliExpress sellers. Three different sellers, in fact. Careless idiots.
 

Offline DrijSkij

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Re: most broken equipment you run into?
« Reply #31 on: December 18, 2024, 03:42:53 pm »
I dumpster dived a TopWord 6306A from work a month ago. Both Master and Slave didn't work. When I got it home and turned it on there was some brief smoke coming out of the case.
After finding a schematic from this site that was pretty similar, but not exact to this power supply, I found that the first relay on the Master side was blown out. Then to find out the cause of it. It turns out one of the main power rectifiers coming off the big tramsformer was quite nicely shorted, and took out its anger on the poor relay.
So I replaced the relay(it cost about $1) and I found an old rectifier from work. Fixed it nicely.

Then on to the Slave side. This one took some time. After some serious examination, someone took out (desoldered) the two VERY necessary emitter feedback resistors following both of the large pass transistors. I couldn't believe it !  It was so neatly done and hardly noticeable. Initally I was angry and then it eventually became amusing.
 

Offline AndyC_772

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Re: most broken equipment you run into?
« Reply #32 on: December 18, 2024, 04:03:54 pm »
They said they almost all work. Most people get rid of them because they are too old.
I have a plasma TV in my spare room. It *almost* works perfectly, but under some circumstances shows a purple speckle pattern over bright parts of the screen.

Is it usable? Sure, I use it to watch Youtube videos whenever I ride my exercise bike. Most of the time it's perfectly fine. The image is a bit noisy, and of course it gets warm, but that's just normal for the age and technology of the set.

But is it worth *anything*? I doubt it. Couldn't sell it as "fully working" because it isn't. I think I paid something like £25 off Ebay for it, and that was about 4-5 years ago.

So, suppose I want the space, or a better TV. What would you do with it? I'm thinking the tip is a pretty attractive option.


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