Difficulty

Easy

Steps

8

Time Required

                          45 minutes

Sections

1

  • APS and PCB
  • 8 steps

Flags

2

In Progress

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Introduction

What you need

Step 1

              What seems to be the problem?
  • WARNING: This unit can contain high voltages on the order of 6000VDC, pay attention to what you are doing.
  • Disconnect unit power wait 15 minutes for voltage to dissipate and open the top cover.
  • Disconnect the 24VAC power to the high voltage PCB to prevent generating high voltages.

WARNING: This unit can contain high voltages on the order of 6000VDC, pay attention to what you are doing.

Disconnect unit power wait 15 minutes for voltage to dissipate and open the top cover.

Disconnect the 24VAC power to the high voltage PCB to prevent generating high voltages.

1024

Step 2

              Indicator Testing
  • The first was to test the front panel LED indicator to rule out stupidity, but I had a good idea it went well beyond an indicator light as the filter had not been getting dirty.
  • This was a simple test, touch a 9V battery in the correct polarity to the red and black wires coming off the HV board, the indicator should light up brightly, and it did.

The first was to test the front panel LED indicator to rule out stupidity, but I had a good idea it went well beyond an indicator light as the filter had not been getting dirty.

This was a simple test, touch a 9V battery in the correct polarity to the red and black wires coming off the HV board, the indicator should light up brightly, and it did.

Step 3

              Transformer Testing
  • Making sure the yellow and blue wires from the 24VAC transformer are off the HV board, clip on a volt meter and energize the unit with the front panel switch. I should have seen voltage there for about 5 seconds as the air proving switch turned on then off, but got nothing.
  • Turn off the 120VAC power switch.
  • Per the manual, I moved back to the air proving switch, a small board with a PTC thermistor and a triac that energize to provide 120VAC to transformer. With output lead 4 disconnected, connect he volt meter between pin 1 and 4.
  • Energize the unit once again. Still only a few 100mV. Carefully check that there is 120VAC on the incoming posts 2 & 3, yep it’s there.
  • Turn off the 120VAC power once again.

Making sure the yellow and blue wires from the 24VAC transformer are off the HV board, clip on a volt meter and energize the unit with the front panel switch. I should have seen voltage there for about 5 seconds as the air proving switch turned on then off, but got nothing.

Turn off the 120VAC power switch.

Per the manual, I moved back to the air proving switch, a small board with a PTC thermistor and a triac that energize to provide 120VAC to transformer. With output lead 4 disconnected, connect he volt meter between pin 1 and 4.

Energize the unit once again. Still only a few 100mV. Carefully check that there is 120VAC on the incoming posts 2 & 3, yep it’s there.

Turn off the 120VAC power once again.

Step 4

              Debugging
  • At this point, I had three suspects, the transformer, the air proving switch, and after closer inspection, I saw a brown discoloration on one of the high voltage capacitors.
  • I decided to start with the transformer. After removing it from the unit, I checked the secondary and measured about 7 Ohm, reasonable. The primary was open, just to make sure I slowly opened the primary coil and after getting back to the winding, didn’t see anything obvious, but it was still measuring open.
  • On removing the air proving switch, the thermistor checked out at about 1kOhms and responded with a squirt of canned air. All the discretes checked out except for the triac.

At this point, I had three suspects, the transformer, the air proving switch, and after closer inspection, I saw a brown discoloration on one of the high voltage capacitors.

I decided to start with the transformer. After removing it from the unit, I checked the secondary and measured about 7 Ohm, reasonable. The primary was open, just to make sure I slowly opened the primary coil and after getting back to the winding, didn’t see anything obvious, but it was still measuring open.

On removing the air proving switch, the thermistor checked out at about 1kOhms and responded with a squirt of canned air. All the discretes checked out except for the triac.

Step 5

              Reckoning
  • At this point I needed:
  • Air Proving Switch $76.38
  • Transformer $54.30
  • Power Control Board $310.27
  • New unit: $461.99

At this point I needed:

Air Proving Switch $76.38

Transformer $54.30

Power Control Board $310.27

New unit: $461.99

Step 6

              New Parts
  • Looking up the individual parts:
  • Triac TO220AB $1.22
  • 50VA transformer $22.70
  • 2000pF cap, 6kV $0.77 each
  • Total parts plus some spares and a thermistor $38.60
  • Looks like I’m fixing this thing.

Looking up the individual parts:

Triac TO220AB $1.22

50VA transformer $22.70

2000pF cap, 6kV $0.77 each

Total parts plus some spares and a thermistor $38.60

Looks like I’m fixing this thing.

Step 7

              Swap Out Parts
  • Just some careful desoldering with wick and wiggles.
  • All the old parts laid out.

Just some careful desoldering with wick and wiggles.

All the old parts laid out.

Step 8

              Final Testing
  • Reverse the order of testing:
  • Connect the air proving switch and verify voltage at pins 1 & 4.
  • Connect the transformer and verify 24VAC out when energized and the air proving switch is cold.
  • DO NOT USE OR MEASURE THE HIGH VOLTAGE BOARD WITH ANYTHING OTHER THAN NON CONTACT VOLTAGE PROBE.
  • With everything connected, powered up the unit and watched the indicator come on and go off. I turned on the fan to the air unit and the indicator came back on and very carefully bringing the voltage probe near the HV lines, I got some nice chirping.

Reverse the order of testing:

Connect the air proving switch and verify voltage at pins 1 & 4.

Connect the transformer and verify 24VAC out when energized and the air proving switch is cold.

DO NOT USE OR MEASURE THE HIGH VOLTAGE BOARD WITH ANYTHING OTHER THAN NON CONTACT VOLTAGE PROBE.

With everything connected, powered up the unit and watched the indicator come on and go off. I turned on the fan to the air unit and the indicator came back on and very carefully bringing the voltage probe near the HV lines, I got some nice chirping.

To reassemble your device, follow these instructions in reverse order.

Cancel: I did not complete this guide.

Author

                                      with 1 other contributor 


                    Roger Clark

Member since: 12/12/2017

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