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Furnance Fan Timer Control Board ST9103A1002

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    Furnance Fan Timer Control Board ST9103A1002

    It works for years, then it was having problem with burner turn on and off then on again, fan will not turn on even temperature was reaching to cut off temperature.

    Replacing all Big relays 2 of T9AS5D12-24 and one of G5LE-14 OMRON

    Replacing C6 nichicion 25V 100uf (Red one)

    Replacing those green are lelon 63V47uf, C1 is 25V47uf

    I think C6 is over worked and under capacitance, should be larger but I don't know for sure.
    Attached Files
    Last edited by number22; 12-29-2017, 10:57 PM.

    #2
    Re: Furnance Fan Timer Control Board ST9103A1002

    The first thing I would do is replace all of the caps on the board

    Second thing I would do is look at all of the solder joints these older boards have had a problem with the solder joints if the joint a white in color or are very dull or dark looking or cracked or missing solder resoldered them

    Really look very closely at the terminal joints for bad solder joints if look even a little bit questionable resoldered it use a magnifying glass to look at all of these joints

    What is the part number on “ U1 “ and if this is a LM 555 timer chip I would also recommend that you replace it as well

    What is the part number on the two IC chips that have 4 pins each and they
    are right next to each other ( “ U2A “ and “ U2B “ ) if these are optic sensors I would change them if they are

    Keep in mind that these boards run about $100.00

    I have repaired a few of these before and defrost board as well

    Can you please take a photo of the bottom of the board as well thanks
    Last edited by sam_sam_sam; 12-30-2017, 08:36 PM.
    9 PC LCD Monitor
    6 LCD Flat Screen TV
    30 Desk Top Switching Power Supply
    10 Battery Charger Switching Power Supply for Power Tool
    6 18v Lithium Battery Power Boards for Tool Battery Packs
    1 XBox 360 Switching Power Supply and M Board
    25 Servo Drives 220/460 3 Phase
    6 De-soldering Station Switching Power Supply 1 Power Supply
    1 Dell Mother Board
    15 Computer Power Supply
    1 HP Printer Supply & Control Board * lighting finished it *


    These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

    1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
    2 Hem Saw Computer Stack Board

    All of these had CAPs POOF
    All of the mosfet that are taken out by bad caps

    Comment


      #3
      Re: Furnace Fan Timer Control Board ST9103A1002

      Originally posted by number22 View Post
      I think C6 is over worked and under capacitance, should be larger but I don't know for sure.
      You need to be careful about changing capacitance when it comes to timing circuits this can cause real problems

      Now if it is on the main power supply rail you can put more capacitance up to a point

      What makes you think that this might be the case

      I would only use 35 volt caps on this as a minimum not 25 volts NO
      Last edited by sam_sam_sam; 12-30-2017, 08:19 PM.
      9 PC LCD Monitor
      6 LCD Flat Screen TV
      30 Desk Top Switching Power Supply
      10 Battery Charger Switching Power Supply for Power Tool
      6 18v Lithium Battery Power Boards for Tool Battery Packs
      1 XBox 360 Switching Power Supply and M Board
      25 Servo Drives 220/460 3 Phase
      6 De-soldering Station Switching Power Supply 1 Power Supply
      1 Dell Mother Board
      15 Computer Power Supply
      1 HP Printer Supply & Control Board * lighting finished it *


      These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

      1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
      2 Hem Saw Computer Stack Board

      All of these had CAPs POOF
      All of the mosfet that are taken out by bad caps

      Comment


        #4
        Re: Furnace Fan Timer Control Board ST9103A1002

        Originally posted by number22 View Post
        Replacing those green are lelon 63V47uf
        Use either 63 or 100 volts ones for these unless you know for sure what real running voltage is use a meter on it find out but you might be able to use 50 volts ones instead

        one note on all 47uf caps use 50 volts not 25 volt ones

        Now if they are on the 24 volt power supply rail then yes you can put 50 volts ones in

        I would use the following series “ PK” , “ LXZ “ , or “ FC “

        And for all the other ones I would use the following series “ KY “ , “ KZE “ , “ KYB “ , “ FR “, “FC “ , “ PW “ or any type that has Low ESR valve ( Yes I know that this is not a switching power supply however I would want to make sure that the power supply power is clean )
        Last edited by sam_sam_sam; 12-30-2017, 09:07 PM.
        9 PC LCD Monitor
        6 LCD Flat Screen TV
        30 Desk Top Switching Power Supply
        10 Battery Charger Switching Power Supply for Power Tool
        6 18v Lithium Battery Power Boards for Tool Battery Packs
        1 XBox 360 Switching Power Supply and M Board
        25 Servo Drives 220/460 3 Phase
        6 De-soldering Station Switching Power Supply 1 Power Supply
        1 Dell Mother Board
        15 Computer Power Supply
        1 HP Printer Supply & Control Board * lighting finished it *


        These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

        1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
        2 Hem Saw Computer Stack Board

        All of these had CAPs POOF
        All of the mosfet that are taken out by bad caps

        Comment


          #5
          Re: Furnace Fan Timer Control Board ST9103A1002

          Originally posted by number22 View Post
          It works for years, then it was having problem with burner turn on and off then on again
          It was bouncing on the hi limit.

          Why did you replace the relays w/o checking if they were getting coil voltage first?

          On that note, why are you condemning the board straight away? Check if you've even got power to the circ blower. Does it spin free? If it spins by hand and you've got power to it and there's no rotation, check its run cap.

          Go to your thermostat and change it from "fan auto" to "fan on." This will bypass the control's timer and use another relay & motor winding. Unless its run cap is bad, your circ blower should run. Leave function set on "heat" and set temp accordingly. Change your filter too.

          Gotta get the heat working.
          Last edited by kaboom; 12-30-2017, 08:55 PM.
          "pokemon go... to hell!"

          EOL it...
          Originally posted by shango066
          All style and no substance.
          Originally posted by smashstuff30
          guilty,guilty,guilty,guilty!
          guilty of being cheap-made!

          Comment


            #6
            Re: Furnace Fan Timer Control Board ST9103A1002

            Originally posted by number22 View Post
            It works for years, then it was having problem with burner turn on and off then on again, fan will not turn on even temperature was reaching to cut off temperature.
            Presumably, what you meant to say here was something like:
            "This has been working FINE for many years.

            Then, it started exhibiting a bogus control behavior; the (gas!) burner wouldn't come on when expected. And, once on, it would inexplicably turn off before the thermostat stopped calling for heat (having verified the thermostat's commands when it happened) and turn back on, equally unexpectedly (after how long??).

            Now, the circulating fan (as opposed to the inducer fan -- which does work?) won't come on even after the bruner has come on and heated the heat exchanger to the point where the hi-temperature cutouts INSIDE THE COMBUSTION CHAMBER kick in as a safety measure. I.e., long after the circulating blower should have begun to move the heat from the heat exchanger."
            Does that accurately reflect the symptoms you see? Does it also reflect the checks that you have already performed (e.g., verifying the actions of the thermostat/control system while the furnace is misbehaving)?

            Replacing all Big relays 2 of T9AS5D12-24 and one of G5LE-14 OMRON
            Why? Did you verify that the coil(s) were being energized but the armature(s) weren't, apparently, moving to make/break the contacts as required? How did you verify the armature's actions -- did you probe the connections with the normal loads removed (because those loads are just as "suspect" as anything else)? Are you sure the contacts aren't welded?

            Replacing C6 nichicion 25V 100uf (Red one)

            Replacing those green are lelon 63V47uf, C1 is 25V47uf
            Why? Because somewhere you read that capacitors can be bad? Did you also read that relays can fail? And that fuses can blow? I.e., are you doing these things just because you think they might be the problem? Or, are you basing your repairs on observed facts?

            We had the furnace rapid cycle one day -- igniting, extinguishing, then trying again... until giving up and "resting" before trying again. Pulling off the guards so I could probe the circuit while it was "struggling", I verified that everything was working exactly as it was supposed to! The problem was insufficient gas pressure -- which would cause a weak flame, the sensors in the combustion chamber would NOT heat up quickly enough and the controller would assume the gas wasn't being burned therefore dictating a need to shut it down.

            Turns out, one of the gas supply lines into town had failed so the whole town was unable to meet its gas demands. Calling a plumber/HVAC guy would be a waste (as many people found out!) as there is nothing that could be done until the gas main was repaired.

            I think C6 is over worked and under capacitance, should be larger but I don't know for sure.
            What makes you suspect this? Do you think the folks who designed the board opted to save a few pennies? Have you seen reports (google) of other folks with the same furnace complaining of a similar deficiency in C6?

            Comment


              #7
              Re: Furnance Fan Timer Control Board ST9103A1002

              Wow guys, thanks for commenting on my project.

              U1 is LM2904N. Q1 Q2 are MPS8099. U1A and U2B are optoisolators, Lite-on 814A.

              OMRON G5LE-14 is bad. T9AS5D12-24 are still good, but I already replaced them with new parts.

              Heating Fan and its running cap, Burner Blower Fan and its running cap are all good. This furnace uses oil, so fuel pressure is not issue.

              C6 is positive lead traced LM2904 pin5 and 750Kohm resistor R24, only C6 is rated 25V and 105C, I tested this board with 24VAC to board's X and C connectors at the bottom right corner, and it works before I put it back into furnace; It is just my suspicious that it is under capacitance.

              Comment


                #8
                Re: Furnance Fan Timer Control Board ST9103A1002

                Did you fixed it

                https://cdn.badcaps-static.com/pdfs/...f57090bce4.pdf

                Look at page 3 of this manual

                You might be able to jump together “G” to “Y” or put 24 volts to “G” and “Y” but look on the board and see if you can do either one but you will not be able to do either one with the thermostat hook up
                Last edited by sam_sam_sam; 01-01-2018, 05:43 PM.
                9 PC LCD Monitor
                6 LCD Flat Screen TV
                30 Desk Top Switching Power Supply
                10 Battery Charger Switching Power Supply for Power Tool
                6 18v Lithium Battery Power Boards for Tool Battery Packs
                1 XBox 360 Switching Power Supply and M Board
                25 Servo Drives 220/460 3 Phase
                6 De-soldering Station Switching Power Supply 1 Power Supply
                1 Dell Mother Board
                15 Computer Power Supply
                1 HP Printer Supply & Control Board * lighting finished it *


                These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

                1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
                2 Hem Saw Computer Stack Board

                All of these had CAPs POOF
                All of the mosfet that are taken out by bad caps

                Comment


                  #9
                  Re: Furnance Fan Timer Control Board ST9103A1002

                  Relay K3 has a high failure rate part on these boards.
                  It's unfortunate furnace control boards have nothing to prevent arcing on relay contacts, and so they don't last long. $0.15 in RC snubber parts would make them last.

                  Leave C6 at 100uF. The fan-off time delay already set (DIP switch settings) to run for as short as possible 60sec. ? after call-for-heat ends. The fan-on delay is fixed at 30 sec. on this board.

                  ST9103A installation manual
                  Attached Files
                  Last edited by redwire; 01-01-2018, 05:17 PM.

                  Comment


                    #10
                    Re: Furnace Fan Timer Control Board ST9103A1002

                    The furnace works now.

                    I tested G and Y terminals as FAN on switch, K3 worked.

                    I have set the DIP switch at default 150s.
                    Last edited by number22; 01-01-2018, 07:06 PM.

                    Comment


                      #11
                      Re: Furnance Fan Timer Control Board ST9103A1002

                      That’s good to hear that you got it working again
                      9 PC LCD Monitor
                      6 LCD Flat Screen TV
                      30 Desk Top Switching Power Supply
                      10 Battery Charger Switching Power Supply for Power Tool
                      6 18v Lithium Battery Power Boards for Tool Battery Packs
                      1 XBox 360 Switching Power Supply and M Board
                      25 Servo Drives 220/460 3 Phase
                      6 De-soldering Station Switching Power Supply 1 Power Supply
                      1 Dell Mother Board
                      15 Computer Power Supply
                      1 HP Printer Supply & Control Board * lighting finished it *


                      These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

                      1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
                      2 Hem Saw Computer Stack Board

                      All of these had CAPs POOF
                      All of the mosfet that are taken out by bad caps

                      Comment


                        #12
                        Re: Furnance Fan Timer Control Board ST9103A1002

                        I don't see any mention of how the problem was fixed, or at what point the system started working. Can you give us any information? You replaced the relays in your first post, which would be the first obvious step considering your problem description.

                        This type of relay is used universally in furnaces and in ovens. These relays are NOT high failure rate relays, as evidenced by the fact that they have been running your furnace (and millions of other appliances) reliably for years. A typical failure mode is that the relay pcb solder connections become loose and intermittent, which is consistent with your original problem description. So the real question now is how do you know that the problem is fixed?
                        Is it plugged in?

                        Comment


                          #13
                          Re: Furnace Fan Timer Control Board ST9103A1002

                          sam_sam_sam,
                          I had another board with R1 or R2 burned out, those composite carbon resistors, 100Kohm. and my local store doesn't have this photocoupler 814A but 824H, replaced with it. Another board fixed, didn't bother changing any capacitors on this one.

                          Longbow:
                          For my original post; that board had K3 relay failed. This relay failed so often, it was not even used to drive fan directly, it actually only used for another relay off board, White Rodgers RBM type 184 (lower right corner of picture, the black block with white label).

                          Thanks all for your help.

                          I noticed that new version board, R2 has changed to 1/2W size and value of 46Kohm. (my local HVAC guy had charged me $200 for new board.)
                          Last edited by number22; 01-08-2018, 06:10 PM.

                          Comment


                            #14
                            Re: Furnance Fan Timer Control Board ST9103A1002

                            One relay operating the coil of another relay doesn't sound like an overload situation. Interesting to check the schematic to see what is going on. On the other hand, the coil of heavy duty 120VAC relays reaches into the many Henries of inductance. Turning a coil like that on and off creates inductive back-emf which could make a nice arc on relay #1's contacts. Perhaps the designers did not include correct suppression values to compensate - that would be my guess. Excessive arcing at the contacts. These days they would probably use a triac to do the switching, but even then adequate suppression is needed to prevent triac damage.
                            Is it plugged in?

                            Comment


                              #15
                              Re: Furnance Fan Timer Control Board ST9103A1002

                              I've never seen capacitors/snubbers/MOV's across relay contacts of appliances (dishwashers, stoves), furnace control boards, garage door openers etc.
                              This is why relays fail prematurely.

                              The added cost and added safety risk due to leakage current seem to make manufacturer's not bother putting these penny parts in.

                              Furnace control boards are tested to 100,000 cycles as the part of the safety-endurance test. A older fan timer board such as this does not go through the endurance test, it has no regulatory UL/CSA approvals.

                              Comment

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