Author Topic: When a 2$ AC part becomes a thousand$ repair/replace  (Read 4512 times)

Fastfwd

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When a 2$ AC part becomes a thousand$ repair/replace
« on: September 07, 2016, 06:18:38 AM »
AC stopped working so I call the closest place. Guy comes over shows me the electronic board with a burned diode and tells me they replace the whole board. Calls his supplier and tells me they don't make the part anymore for that 8 years old model so I will have to replace everything and a salesman will contact me; expect 3000-4000$.

Obviously suspect so I call another place with the model number and they tell me the supplier has the part but I still need to pay them to come over and diagnose first.

So now that's first guy 90$(unpaid yet) second guy(120$) future part probably 400$ and I'm guessing another 120$ service fee. For a burned diode??? I don't have the skillset to solder in a new one but surely AC repairmans should.

/rant

Mr. Green

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #1 on: September 07, 2016, 06:38:11 AM »
Did you hear either of them say they'd only replace the diode? Soldering on small boards is not particularly easy. I would think they're replacing the entire board. The board has a part number. You can google it and see if it's inexpensive and perhaps you could do the replacement yourself, if you're comfortable doing that type of thing. The main board on my furnace needs to be replaced this season and I can buy a replacement board online for $150.

Fastfwd

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #2 on: September 07, 2016, 06:50:49 AM »
Yes they are replacing the entire board and it is an expensive part; price to follow but I was told to expect 400$. Surely someone out there ought to have the expertise to solder a diode for less than 400$.

Marvel2017

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #3 on: September 07, 2016, 07:11:10 AM »
It's not that hard to desolder/remove a component and replace. Check youtube, Radio Shack should have everything you need (maybe not the right diode but online for sure) Good luck

I had a $300 board for my windshield wipers burn out a connection on the actual board, I just soldered in a jumper wire to reconnect the components and worked for another 5 years until I sold the car.

GuitarStv

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #4 on: September 07, 2016, 07:42:42 AM »
I've spent a lot of spare time building electronics, and am pretty handy with a soldering iron.  Working on an old amp is great!  You just crack open the case, de-solder a big honking component, then solder a new one in.  They are designed to be maintainable.

Most new electronics are not built in this way.  Often they use incredibly tiny SMT components (much cheaper to buy in large quantity, much cheaper to ship).  At the factory, a robot (or dude in China) places all the components on the board on preset tiny blobs of solder, then they heat the whole board up in an oven and the components melt down into place.  It makes assembly cheap and quick for them.

Unfortunately, this also means stuff is quite tricky to solder for repair . . . first you've got to find a size compatible part (it might not fit if it's a millimeter too large or small), then the heat from hand soldering one of these tiny parts may kill another tiny part, the fine traces on the board will often come up (and render the board inoperable), etc.  It's also quite possible that when the diode burned out, it failed in such a way that some of the other components are shot.  It could be a multi-day job (and a frustrating one, trying to work your probes around the super small areas) to debug each part of the the board.

I don't like it, but that's why the common approach to these problems is to replace the whole thing . . . it makes the most sense based on the way modern electronics are constructed.

CowboyAndIndian

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #5 on: September 07, 2016, 08:25:28 AM »
Yes they are replacing the entire board and it is an expensive part; price to follow but I was told to expect 400$. Surely someone out there ought to have the expertise to solder a diode for less than 400$.

Modern day electronic boards are very complicated compared to about 25 years ago. They use SMD (Surface mount devices) which usually a machine soldered, almost impossible to manually solder. Also, these boards have mutiple layers and track widths are so small it is easy to break or lift off tracks when soldering.

As an ex-electronics engineer, it pains me that the board is not repairable and is just thrown away.

Edit: +1 to GuitarStv's answer. Should have read to the end before replying :-)
« Last Edit: September 07, 2016, 08:27:35 AM by CowboyAndIndian »

RobFIRE

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #6 on: September 08, 2016, 04:32:18 AM »
It is a shame that things like circuit boards on home devices are not designed to be more repairable, but that's how it is at the moment, they are produced in bulk and making them repairable would, at least in the short term, increase the initial production cost. In the longer term, writing now at a time when the USA are about to ratify Paris global emissions treaty, I think it's likely that governments will legislate "maintainability/repairability" and a "right to repair" as a required standard alongside existing safety, energy efficiency, toxicity standards etc. to reduce overall electronic waste. I believe "right to repair" already exists in limited cases in parts of the USA e.g. certain car manufacturers in certain states being required to publish repair manuals?)

So that being the case, currently nobody will resolder a circuit board, sounds like the first guy is an idiot or a salesman in overalls, and the second company are either being cautious (don't want to order a $400 replacement board without investigating, then find customer was wrong so can't sell that board to customer) or are quite happy to bump up the repair cost with an additional call out fee.

If the second repair does go smoothly I'd be asking the second company if they would reduce or waive the second call out fee (they may say yes, no harm in asking politely), and I'd be tempted to report the first company to the relevant government department for deliberately misleading you (Trading Standards in the UK) i.e. if one repair company can get the part why can't another, it would appear they deliberately mislead you to try to increase their sales, which at least in the UK is against the law as companies are required to provide a "reasonable" service. If the government department gets multiple complaints about the same company I'd like to think they would take some action.

projekt

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #7 on: September 08, 2016, 05:21:36 AM »
The big problem is that unless you know a bit about electronics, you can't be sure that the burnt-out diode is the extent of the trouble. When an overvoltage condition or short circuit occurs, the path of destruction is usually along the highest-current path, and it stops when a conducting element turns non-conducting. The diode was probably acting like a fuse. This means that, while the diode is dead, the cause of the overvoltage/short could be elsewhere. You might replace the diode, feel good about it, and then a while later find that doing so allowed some other more expensive part to get toasted. This is the trouble with working blindly on electronics. It really helps to have a schematic if you're going to go ahead and do it.

WRT surface mount soldering, it's definitely doable. I have a soldering station I got new on ebay for around $50 that works great for both surface mount (SMT) and through-hole soldering. There are tutorials on the web for soldering discrete SMT components that are pretty easy to follow.

Relatedly, I have an X-Ray generator that died last year. I called a reputable repair guy and he said it wasn't worth fixing and I should replace it (around $13,000). But he told me that the power supply failed, and that he could replace it but wouldn't stand by the work. I found someone who was selling replacement power supplies (at a high markup) and I bought one for $450. It was an off-the-shelf part I could have bought for $80. But I didn't really pay for the power supply, I paid for his assistance, because he pointed out a bunch of the gotchas on the control board. I then bought a few $2 diodes and fixed the board with the power supply, and it's been working like a charm since. So, sometimes finding a guru can help.

Also, on that job I had a partial schematic.

BlueHouse

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #8 on: September 08, 2016, 06:05:23 AM »
I've spent a lot of spare time building electronics, and am pretty handy with a soldering iron.  Working on an old amp is great!  You just crack open the case, de-solder a big honking component, then solder a new one in.  They are designed to be maintainable.

Most new electronics are not built in this way.  Often they use incredibly tiny SMT components (much cheaper to buy in large quantity, much cheaper to ship).  At the factory, a robot (or dude in China) places all the components on the board on preset tiny blobs of solder, then they heat the whole board up in an oven and the components melt down into place.  It makes assembly cheap and quick for them.

Unfortunately, this also means stuff is quite tricky to solder for repair . . . first you've got to find a size compatible part (it might not fit if it's a millimeter too large or small), then the heat from hand soldering one of these tiny parts may kill another tiny part, the fine traces on the board will often come up (and render the board inoperable), etc.  It's also quite possible that when the diode burned out, it failed in such a way that some of the other components are shot.  It could be a multi-day job (and a frustrating one, trying to work your probes around the super small areas) to debug each part of the the board.

I don't like it, but that's why the common approach to these problems is to replace the whole thing . . . it makes the most sense based on the way modern electronics are constructed.
Thank you for this explanation. The electronics world just became a little more understandable to me.

theglidd

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #9 on: September 08, 2016, 06:49:40 AM »
I had my EMC motor die last winter. HVAC company wanted 1000 bucks to replace the motor.

I ended up doing some research and apparently EMC motors notoriously blow the thermistor on the motor control board.

Bought a soldering iron, a new thermistor, watched a youtube video and had it fixed in an hour for 20 bucks.

acanthurus

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #10 on: September 08, 2016, 04:53:17 PM »
Reworking SMD is not bad unless you have parts without any leads (QFN, etc) or straight up BGA or CSP packages that need reflow.

If it's just a standard SMA/SMB/SMC package diode or something like an SOD-123 two terminal SMT package, that can be done by an amateur who is patient.

The hard part is 1) why did the diode fail, is something else in the vicinity dead too that caused the diode to fail? and 2) figuring out what exactly the diode is (for the non-expert you won't know how to decipher part numbers and manufacturer logos to figure out if it's a zener or a shottky or whatever). An expert can probably look at it and figure out if it's the catch diode in a buck converter or a TVS zener for power spikes based on what's around it.

I designed board level electronics for the oil and gas industry and did my own soldering if something blew up after hours and the techs were gone. I can give you the name of someone who can fix it for cheap if you want to ship the board out and get it back soldered up nicely.

acanthurus

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #11 on: September 08, 2016, 04:55:10 PM »
Actually take a picture and post it here, this would be fun! Let's save some money :)

gimp

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #12 on: September 11, 2016, 02:43:13 AM »
Definitely take a photo... I feel like a good 20% of us are engineers. I'm pretty decent at soldering SMD, as are I'm sure hundreds of readers.

mathjak107

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #13 on: September 11, 2016, 03:58:28 AM »
the diode may have burned because of other parts failing or it may have taken other parts out with it but you can't tell yet as only the diode appears bad visually .

in 40 years of dealing with this stuff i have seen it both ways . with electronics it is rare that the failure of one component does not take several down with it .
« Last Edit: September 11, 2016, 04:00:25 AM by mathjak107 »

Fastfwd

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #14 on: September 12, 2016, 06:04:24 AM »
the diode may have burned because of other parts failing or it may have taken other parts out with it but you can't tell yet as only the diode appears bad visually .

in 40 years of dealing with this stuff i have seen it both ways . with electronics it is rare that the failure of one component does not take several down with it .

--besides it's controlling the device that keeps your house warm in the winter.... depending on where you live it's kind of a big deal....  :)

Montreal. Small 12btu AC unit for the summer and a LOT of electrical heating one unit per room; completely separate systems.

projekt

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #15 on: September 12, 2016, 06:08:27 AM »
12,000BTU is the size of a window unit. Is that all you need? I can't see how that's $3-4k.

Fastfwd

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #16 on: September 12, 2016, 07:19:39 AM »
Picture of the burned part:
https://dl.dropboxusercontent.com/u/4256117/20160912_131552733_iOS.jpg

Yes 12k btus is a little underpowered; it's a separate inside fan outside compressor unit. On the very hottest summer days it has to work pretty much nonstop and even then it only brings down the temperature a little but that's OK I don't want to get used to AC too much and then suffer when I go running outside.

BTDretire

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #17 on: September 12, 2016, 09:06:23 AM »
Picture of the burned part:
https://dl.dropboxusercontent.com/u/4256117/20160912_131552733_iOS.jpg

Yes 12k btus is a little underpowered; it's a separate inside fan outside compressor unit. On the very hottest summer days it has to work pretty much nonstop and even then it only brings down the temperature a little but that's OK I don't want to get used to AC too much and then suffer when I go running outside.
Couple things I question in the picture;
First the big cap, the top looks domed, may just be the way it was manufactured, But I'd be checking it. Second the blue tape on the transformer looks like it has been hot, slightly browned. (could just be the picture) If it is browned, that could mean there is a problem on the load side of the transformer and it was running hot, possibly before the switching transistor gave up.
 Not really a tough repair if you have the test equipment to find what parts are defective. It's nice to run across a single part repair, but with switching power supplies, that is not ususally the case.
Back in the 80s/90s when I did VCR repairs, Panasonic had switching power supplies,
they ended up with a kit of parts to replace if the supply was dead. ISTR it had about 7 parts.
  My best saving repair was on my Ice machine. It has an infrared sensor/reciever
that sensed when the bin was full. It didn't work, company wanted $120 for the part,
I bought an infrared sensor/reciever at Radio Shack for $1.98 and replaced the parts.
Worked perfect.

acanthurus

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #18 on: September 12, 2016, 10:22:17 AM »
Can you read us the capacitance value and rated voltage on that capacitor? You should see a number followed by an "mf" or "uf" and another number followed by "VDC".

Also, on the device labeled Q1 and attached to the tall heatsink, can you see any numbers or letters on the black plastic part of it?

Diode is def gone and the cap does look domed from above, but this looks like a pretty easy part of the circuit to work on. If the copper traces on the back are still good (admittedly the board near that diode looks bad) this might be a pretty easy fix if we can figure out what the right parts to drop in are.

Can you cut the diode out (or just desolder it) and read us all the numbers off it? I see an "08" and can make a guess of that but more would be better.

Also, a part number and manufacturer name from that yellow taped transformer on the bottom right might help. Just to be sure I'm looking at what I think I'm looking at. 
« Last Edit: September 12, 2016, 10:30:09 AM by acanthurus »

Fastfwd

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Re: When a 2$ AC part becomes a thousand$ repair/replace
« Reply #19 on: September 12, 2016, 11:37:19 AM »
I have the new part installed by the experts now. I'm keeping to old one as it seems to be made of 2-3 different boards. With any luck the next that blows up will still be good on the old part.