Refrigerator not working again

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On 9/23/2010 9:36 AM, David wrote:

The majority of HVAC techs have no idea how to do board level repairs. I find cold solder joints all the time and am able to get a system up and running without having to replace an expensive circuit board. The catch is, how much time will it take to repair a one hundred dollar circuit board vs $85.00 per hour. <---- it's a simplified example. Don't yap about how expensive most control boards are. Ask an HVAC tech what wave soldering is and he/she/it smile and wave at you.
TDD
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I used to stuff components for a wave solder. The guy who tended the machine used to say "go with the flow, bro" which we thought was funny.
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"We" ?
Is that you + the voices in your head?
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Every Time You See a Rainbow, God is Having Gay Sex



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HVAC wrote:

Appparently, you are the only one with voices in your head.
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Some of us do, but its not cost effective to do so.

No, control boards are not free, and yes, some of us *DO* know what wave soldering is.
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On 9/24/2010 7:36 AM, Steve wrote:

That would make you the exception. Lack of knowledge in one area doesn't make one stupid or ineffective in their chosen field. Ignorance means you don't know but you can learn, stupid means no way. I'm ignorant about a lot of things so I use what my mother taught me, "If it smells bad, don't eat it." I apply this to everything in my life. 8-)
TDD
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Steve wrote:

Reflow soldering is a lot more common these days. With so much surface mount, wave solder has lost a lot of market share.
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On 9/24/2010 4:18 PM, Michael A. Terrell wrote:

I don't see that much surface mount on the majority of HVAC control boards. I haven't seen the latest supercalafragilistic uber-efficient HVAC system control boards but the simple ones are mostly single or dual layer with components having leads soldered through holes. I don't have customers who can afford that really high end stuff for their homes.
TDD
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even the 13SEER condensers and heat pumps that I install have mother boards in them, as do the gas furnaces I install. Lots of surface mount stuff, double layer boards, optical latching relay instead of a contactor, serial controlled, etc.
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Steve wrote:

I was testing and repairing 16 layer reflowed boards that cost over $8,000 for the components. If the board house was careless handling the blanks you could have over 1000 bad solder joints. I spent a lot of time looking through a stereo microscope, with a hot soldering iron in one hand.
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On 9/25/2010 12:30 AM, Michael A. Terrell wrote:

circuits for an HVAC system need to be closer to an anvil, than to avionics, to meet design lifespan if nothing else. And they need to be field-repairable. If it can't be at component level, there needs to be an industry standard for board interfaces and mounting, so that the unit cost of boards can be low enough to repair at board-swap level. (Yeah, I know, there are always plenty of standards to choose from.)
I know nothing about HVAC beyond 'no worky -> pick up phone'. But I have worked in computers at the field support interface for 20-some years, and have run into similar issues. Engineers in that field violate KISS principle on a regular basis as well, and component level repair vanished years ago.
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aemeijers wrote:

Sigh. It would be great if HVAC electronics were built to Avionics standards. For one thing, Avionics is 100% exempt from lead free solder. For another, equipment design is always at the 'Mission Critical' level. Avionics are built for long life, with little or no maintenance. It is usually there for the life of the aircraft, unless that series undergoes an across the board redesign. Of course, it would double or triple the retail costs of the controller.
One thing I've seen in a lot of failed programmable thermostats is that they use slide switches that are installed before the boards are cleaned. Then the board cleaner washes out all of the contact lubricant.

How do you propose to do that? If you make an interface to handle any possibility, you add a lot of costs. Surface Mount is actually easier to repair, if you know what you are doing and less susceptible to board damage if you know how to solder.
If you are a hack at electronics, then all bets are off.

Strange, because I still repair some motherboards. A lot of failures are bad low ESR electrolytics, or cracked ROHS solder joints. Until I ended up 100% disabled, I repaired 68340 based embedded controllers at the Microdyne factory. I also tested and repaired all of the boards in our dual receiver DSP based RCB-2000 telemetry products.
Contrary to popular belief, having schematics isn't always a help. OTOH, having the datasheets for the ICs is.
A lot of techs have no idea why some things are done. For instance, I see people bitch about 'Those morons put the electrolytics too damn close to the CPU! Why can't the bastards put them on a corner of the motherboard, away from the heat?" Well, they carry a high ripple current, so they are self heating. The CPU us a high current, low voltage device, so the regulator has to be close to the load. Long traces would radiate a lot of EMI. A lot of power would be wasted heating the copper traces, and the inductance would screw up the regulation.
Buy a ESR meter and test the electrolytics on those boards. A little ripple can cause all kinds of problems. 30 years ago I was doing bulk repairs on 'Linear' brand garage door opener controls. Every one of them needed new electrolytics. They were always mounted in hot locations, and powered 24/7. Similar to the environment in HVAC systems.
One thing that makes it hard to repair those boards is that the techs don't use logical troubleshooting methods. They use hunches, or just shotgun a board till it starts working, or they destroy it with sloppy soldering or installing parts wrong.
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On 9/24/2010 9:26 PM, Steve wrote:

Is there a particular brand you install? Me and GB have been installing Goodman and to tell the truth, I haven't bothered examining the darned circuit boards on the newer stuff we install. We have a buddy who's a Standard dealer and he charges a pant-load for his gear and $100/hr. I don't do anywhere near the volume of HVAC work you do so I'd have to defer to your experience. Hell, I was so tired when I got in today, I couldn't stand up for long and had to postpone fixing a leak on a very old Carrier heat pump. I know that sucker has no surface mount devices on its control board, it's older than the girls chase. 8-)
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I install the Rheem "Prestege" -JEZ series almost exclusively for both A/C and heat pump condensers. My entry level systems use a 13SEER condenser, but with the correct coil and air handler/furnace combination, the system is rated 14SEER or better. My "premium" systems are 16+SEER, 2 stage, serial controlled systems. FWIW, I have not installed an R22 system in 5 years, only R410a.
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On 9/25/2010 7:26 AM, Steve wrote:

Me and my homey works fo mostly po folks dat doan has a lots O money. We found a new 3 ton R22 heat pump condensing unit at Johnstone this Spring to replace an old unit for a customer who's air handler and evaporator were in good shape. This Summer, we replaced an old R22 system for a friend with a new R410a system and we darn near toasted to death. It was in the middle of the hottest Summer we've had in a long time with temps in the 100+ range for many days without end. I didn't have to pee for 8 hours, it all came out of thousands of tiny holes in my skin. 8-)
TDD
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Welcome to my world :-)
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On 9/25/2010 9:23 AM, Steve wrote:

I remember many summer days in southern Indiana, working construction, that were like that. We all had to watch each other, and when somebody STOPPED sweating, lead them over to the water cooler and make them take a long break.
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I've not been in Indiana. But, I've seen workers like that.
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aemeijers wrote:

I was out working in the hot Florida sun one day. In an hour I drank three two liter bottles of ice water, and still stopped sweating. It took another bottle of water, and two bottle of soda before I cooled down. Damn, that was scary!
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On Sat, 25 Sep 2010 18:51:44 -0400, Michael A. Terrell wrote:

I'd have probably poured one of the bottles of ice water onto my head, at least until my scalp was cooled to 98F. :-)
Thanks! Rich
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