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printed circuit board repair

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woodbutcher

09-02-2007 06:26:16

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I read a post a few days ago about soldering wires, and the replies from several readers caused me to think about my situation. I have a Fujitsu mini-split heat pump that operates off of printed circuit control boards. To fix its runaway compressor problem last week an AC tech replaced the power control board. That cost me $441.00. After two days of normal operation, it seems to be going back to the original problem. My question to those who have had experience with PCB's is, where can I get the old board repaired? Also, are there any technicians who know how to diagnose the reason for this PCB failure? Most AC repairmen are parts changers, not diagnosticians.
Butch

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tech4

09-03-2007 09:37:42

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 06:26:16

Woodbutcher, sorry I was looking at the 240 volt model that has the phase converter that creates 3 phase power for the compressor. The 120 volt model does not have the phase converter chip but turns on a 12 volt relay for compressor power. I still don�t think you have a problem with that board. That board would normally fail safe and the compressor would not run. I would not be too concerned if the readings on the thermistors did not read the exactly since different ohmmeters with different internal voltages could cause that and most thermistors are also voltage sensitive. If the compressor is cycling then the boards should be ok. If there is a board problem it is more likely the one inside but I don�t think so. No condensation draining is strange with 52 degree air. Either there is something maybe even design that allows the reversing valve to operate on demand to evaporate the condensation from the inside unit or the line is stopped up. Or you happen to have low humidity now. You are referring to the condensate line from the inside unit? Low gas or a gas leak could also cause a problem.

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tech4

09-03-2007 12:45:41

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Re: printed circuit board repair in reply to tech4, 09-03-2007 09:37:42

my guess is that with no condensation that the evaporator coil is freezing and also blocking air flow and causing compressor to run more than normal. I notice that system uses R410A which will run at a higher pressure than R22 your low side should be about 130psi. I would look for leak or low gas.

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woodbutcher

09-03-2007 10:09:36

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Re: printed circuit board repair in reply to tech4, 09-03-2007 09:37:42

Thanks for the info tech4. I would have thought that the condensate line from the inside unit was surely stopped up, but it hasn't overflowed anywhere that I can locate. I've tried my best to clean it. Our humidity is 55% average lately.
Butch

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wavrider

09-03-2007 06:32:45

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 06:26:16

Circuit board repair.

Innovat Corp. 1-800-626-1887, Ask for Derek Holmes, I metthis young man while goiong through Lincoln advanced welder repair school. I am an "old school technician", taught tube theory when I went to school for electronics in the NAVY. Web site is www.innovatcorp.com
This Derek is sharp and Innovat specializes in hard to find or obsolete PCB. As alot of previous posts said it is painstaking and time consuming to repair PCB boards, most repairs require microscope, spent years on one of them doing micro miniature repair for our government. Also it is true not many repair techs. left out there most are pop n swap specialists, and do not do any troubleshooting. There is a cause for your board failure, and it is not the board as you have had it replaced. Believe you are on the right track look looking at the thermistors. You are better of replecing the board if it is available but if it is not then try contacting Innovat and see what they have to say. Good luck

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woodbutcher

09-03-2007 10:13:44

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Re: printed circuit board repair in reply to wavrider, 09-03-2007 06:32:45

Thanks, wavrider. I'll call him tomorrow.
Butch

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woodbutcher

09-03-2007 06:18:14

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 06:26:16

Well, maybe I'm imagining things. I set a thermometer at the outlet. The air temp is 52 degrees when the compressor is running. The system is cycling according to the thermostat setting on the remote. Both lines are cold and wet at the condensing unit. But the reason I noticed this problem is that there is not a drop of condensate being produced. In years past there have been considerable amounts. I thought it was a drain problem. I cleared the lines, but it made no difference.
Butch

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bil b va

09-02-2007 23:46:17

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 06:26:16

is your power source 3 phase ? reason i ask is tech4 statement below about circuit board .

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tech4

09-02-2007 18:17:09

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 06:26:16

Woodbutcher - I have been working on electronics for over 50 years and I learned a long time ago to never say something can't happen in electronics. Looking at the diagram the power control board for the compressor is actually a 3 phase power inverter to drive the compressor. Since the compressor is running I strongly doubt that the power control board is the culprit. I do believe that it is some of the control circuits or components like the thermistors or that the system is low on gas or a blockage. The thermistors can be checked with an ohmmeter but it is difficult to walk you through a step by step test. That board because of its uniques and function is probably the most expensive part in the unit. I am guessing that you have checked to make sure that the inside unit and the outside unit are not blocked for airflow. I find many times it is the simple things that really throws us off. By the way that 3 phase inverter chip would sure make a good converter for folks that need a converter for their saws and drill presses. I might look into that more.

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woodbutcher

09-03-2007 05:07:42

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Re: printed circuit board repair in reply to tech4, 09-02-2007 18:17:09

Well, this is sure some interesting information. As to your question bil b, the unit operates on 110 volts. It has worked well for three years. Like you say tech4, I suspect the problem is caused by something simple. The first local company I called sent a repairman in a nice service truck at 5:00 PM on Friday two weeks ago. When he saw the condensing unit outside he said they don't work on those things. When I told him his boss had assured me that they do work on them, and they can get parts, he agreed to check the outside unit. He checked pressures. They were correct on both lines. Outside coils are clean. He was unwilling to go inside to look at the inside unit (I think because it was quitting time for him.) He offered to make the system work by rearranging the wiring at the compressor. He said that if the thermostat called for the compressor to cut off, though, it would not. There was a possiblity that the coils outside would frost up and the compressor would burn itself up. It was hot that day, and I agreed to his plan, but I called another company Monday morning. The worker they sent spent most of an hour getting the wiring back to the original arrangement. Then he assumed that the circuit board he could see when he took the cover off the inside unit was the only board in the unit. So he went back to the shop and ordered a power control board for the unit. A week later he received a controller assembly PCB for this unit. When he came back to install it he realized that what he meant to order was the power supply PCB. So he left and ordered that. Now that has been replaced by his supervisor, but nobody has done as much diagnosis of the problem as you have, tech4. The resistance for both thermistors is listed on a chart in one of the service booklets. According to my cheap voltmeter, their resistances are about half what the charts say they should be. I took the readings with the thermistors still attached to the circuit board.
The inside coils are partially inaccesible because of the way the unit is mounted. They tend to form a moldy crust during humid weather which I clean from the front of the coils. But I'm not sure how much might be on the backside.
Butch

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MF294-4

09-02-2007 10:06:45

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 06:26:16

we repair our single sided and double sided boards and componets if it doesn't take to many hrs but we have gotten into 4 layer boards and if the problem is the board and not a component, it usually not practical to fix unless a simple wire jumper can solve. Now components and traces are so small and fertlizer is so corrosive, usually and econmically better to change board. Just a sign of the changing times. I'm even obsolite.

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tech4

09-02-2007 09:29:36

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 06:26:16

I do a lot of PC board repair of many different systems. It is usually only cost effective for me and the customer if they have many of the same type boards or they have an expensive piece of equipment down and production is shut down as parts may not be readily available or too costly. Also getting schematics from the manufacturer is difficult. Some manufacturers will not give you the information. I also do repair equipment for friends and family at cost when they have not had much luck with businesses. I am not quite sure what you mean by run away compressor. Do you mean it runs too often or do you mean it is actually over speeding and not controllable? The problem may not even be on the board but a small external thermistor or control that did not get replaced with the new board. I find that most repairmen today are just parts replacers and eventually they will get it. Few are real trouble-shooters.

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tech4

09-02-2007 09:56:17

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Re: printed circuit board repair in reply to tech4, 09-02-2007 09:29:36

I just went to the Fujitsu site and I was surprised that they have their service manuals on there with wiring diagrams and schematics of the boards. But I will tell you that if the board is defective and unless something is real obvious that it would take a lot of time to trace and repair the board and some of the parts may still not be readily available. There are a lot of other external components to the board that may still be defective. As mentioned if the board is defective that it should be in warranty. Another thing to check is to look on the board for a part number and google that part number and see if there is someone else that sells the board cheaper. I just replaced a board in my microwave that was unrepairable and listed for $65 but I found it for $30 postpaid on the internet.

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woodbutcher

09-02-2007 12:04:08

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Re: printed circuit board repair in reply to tech4, 09-02-2007 09:56:17

tech4,
The compressor runs all the time that the breaker is switched on, no matter what the unit is set on.
As you and others mention, the board is under warranty, but I don't plan to replace it until I can be sure what is causing them to fail.
Thanks for all the input on this problem.
Butch

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tech4

09-02-2007 15:57:42

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 12:04:08

Woodbutcher - tell me the model number or the BTU and I will look at the diagram and see if I see something that maybe causing the compressor to run all time. My first thought is that it is not the board unless you have had a power surge or nearby lightning strike. There is a room thermistor and a pipe inlet thermistor that control the compressor. Is it blowing cool air now? Put a thermometer in the outlet and measure the cool air temp in to the room. It should be at about 52 degrees at the outlet.

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woodbutcher

09-02-2007 16:34:09

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Re: printed circuit board repair in reply to tech4, 09-02-2007 15:57:42

tech4,
The model number on the indoor unit is ASU12R1A. It is 12,000 Btu. I have printed the Service Manual and the Service Instruction booklets off the internet. When I offered these to the three techs from two local companies who have made service calls, they were not interested in them. They seemed certain the problem was in the power control board. But the Service Instruction booklet lists a step in troubleshooting that refers to the thermistors you mentioned, and they both attach to a control board that is separate from the power control board.
I will get a thermometer tomorrow and check the temp at the outlet.
Thanks so much for your interest in this.
Butch

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woodbutcher

09-02-2007 16:36:01

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 16:34:09

By the way, in the Fujitsu website, this model is listed under retired models, even though it is only three years old.
Butch

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Fawteen

09-02-2007 06:52:53

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 06:26:16

I did microminiature circuit board repair for a couple of years in the Navy.

It's done under a stereo microscope at somewhere around 70X, it's painstaking and incredibly time consuming. The only boards the Navy repaired that way were boards that were obsolete and completely unavailable from any source. Even in the early 80's when I was doing that sort of work, it was cheaper to buy a new one than to fix an old one. Not unusual to take 40 hours do do a repair, once the problem was located!

Components have gotten smaller in the last 25 years, and the associated circuitry has gotten smaller with it. While repairing internal foil runs is no doubt still technically possible, I can't imagine it being even remotely cost effective if a replacement is available.

As to troubleshooting, I get a little cranky about that. IMHO, very few (if any) "technicians" troubleshoot anymore. They run diagnostics, and the computer tells them what board to swap out, and that's that. Even the military does it, it's just not cost effective to train and equip people to do it the way us antiques did in the days of vacuum tubes and discrete components.

And even if they did, the cost to repair the board would be insane (see above).

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Bob

09-02-2007 06:50:54

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 06:26:16

If the new board is "bad" it should be warranteed.

However, to me, it sounds like there is another problem that was temporarily solved when the "tech" mucked around in the the control box, a bad onnection, perhaps?

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IH2444

09-02-2007 06:49:01

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 06:26:16

Not sure where you could get ti repaired. It would take a good electronics tech with a good set of schematics and such to troubleshoot and fix the board. and most likely a special test jig to troubleshoot and test the board in.
Kinda hard to troubleshoot a board without it connectred to all the proper inputs and outputs.
If it has surface mount chips on it the tool to change one of those chips is a couple of hundred bucks....

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woodbutcher

09-02-2007 07:03:28

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Re: printed circuit board repair in reply to IH2444, 09-02-2007 06:49:01

My thanks to all for the replies. To tell the truth, this is just a glorified window unit without the window. I would have been better off to have bought one for $100.00 at a garage sale and I'd have gotten more years of service that way.
Butch

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bil b va

09-02-2007 12:42:42

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 07:03:28

find you a real hvac mechanic and have it connected the old way with a thermostat and contactor and no control board . wish i was close enough to help you . you could even use a line voltage thermostat to turn the compressor off and on . along with the inside fan or let the inside fan run continiously like a window unit

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woodbutcher

09-02-2007 13:00:26

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Re: printed circuit board repair in reply to bil b va, 09-02-2007 12:42:42

Thanks, I may look into that option.
Butch

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woodbutcher

09-02-2007 13:03:42

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Re: printed circuit board repair in reply to woodbutcher, 09-02-2007 13:00:26

Those items would have to mount outside the space provided for the controls. There might be room in the outside unit, or they could mount on the wall space opposite the inside unit. This might be the way to go. Thanks.
Butch

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