Honeywell Power Supply Board for F50A F50E Single Cell

The 208425 not Compatible with the W8600

The 208425G power supply does not provide a connection for the W8600 remote indicator. The 208425G is for a power box without the terminal strip as in photo below on left. If your power box has a terminal strip for the W8600, then this supply does not have the connection for that terminal strip.

If your powerbox has an unused terminal strip because you are not using the W8600, then you can use this power supply and internally not connect the unused terminal strip.

The 208427 series provides a connection for the W8600 but the 208427 is not available for 12½x20, Honeywell only offers the option of replacing the complete powerbox 208422A.

Photo shows power box with and without the terminal strip.

208425 not Air Flow Sensor Compatible

The 208425G does not require an air flow sensor. This power supply runs as soon as 120v is applied. Used in an F50A-E that is wired to the furnace blower or through a sail switch.

This power supply has been configured for use in a power box without the air flow sensor. The animated photo below shows a power box with and without the air flow sensor.

Honeywell has disabled the air flow sensor feature by cutting the jumper J8. Restoring the jumper will allow the use of an air flow sensor. If your F50A-F50E power box has the air flow sensor and it is needed, then you need to replace the complete power box with the 208422A.

Photos of the 208425A in a Power Box

Here is a PDF with high resolution photos of the F50A power box. The photos show the box stripped and then with a new 208425A installed. Also shown is a photo and schematic of the switch with the neon lamp.

Also see the PDF showing the uncommon edge connector and the piggy back connector.

Setting Ionizer Current Jumper J6

The 208425G can be configured for four sizes: 12½x20, 16x25, 20x20, 20x25. A jumper on the power supply board needs to be set based on the overall size of your collector cells. This jumper J6 sets the ionizer current.

SIZE	IONIZER	J6
12 x 20	1.05 mA	1
16 x 25	1.65 mA	2
20 x 20	1.65 mA	2
20 x 25	2.10 mA	3

Power Supply Inspection

First visually inspect the board. Most problems are visible such as a melted transformer winding or a burnt component such as the surge suppressors RV1 RV2.

Check the thin white ceramic resistor R3, the corner wire can break away. This can cause the collector plates to get power but not the ionizer wires.

Continuous cell sparking (for months) can burn out components or wiring. Resonant sparking causes elevated voltage swings that can break down the insulation on the high voltage wires. Check for scorching.

Often the fuse blows when the switching FET Q1 shorts, we believe from line spikes. Check the fuse continuity. A blown fuse typically reads 4.4M ohm because of circuitry in parallel.

The fuse is soldered in and not replaceable. If there is an internal short the fuse blows so to prevent any components from flaring up. Replacing a blown fuse will not fix the problem.

Honeywell does not release the circuit board schematics. Service tech's want to replace the complete board and be confident. Honeywell does not sell the discrete components. We do not do component level repair of the boards.

Replacing the complete board with a new one with a 2 year Honeywell warranty would be the most reliable repair.

Power Supply Bench Test

Here is our procedure to test the 208425G power supply. Warning high voltage shock can cause death.

The 208425G has the air flow sensor disabled, the jumper J8 has been cut. This power supply does not require the air flow sensor to operate. The photo below shows the power supply just needs 120v to power a cell.

Connect 120 vac to terminals P1 and P2. Check the following outputs with respect to chassis ground.

Terminal P3 will output 8.2k vdc
Terminal P2 will be 4.2k vdc
Terminal P5 for the neon lamp outputs 100 vdc

Since high voltage meters are not common, Honeywell provides the neon lamp as reliable voltage indicator. If the high voltage output falls below spec the neon lamp voltage will drop out.

Shorting P3 or P4 to ground has the same effect as the test button. The short will temporarily cause the neon indicator to go out. By tapping P3 to ground you should be able to draw an arc 1/32". Tapping P3 to ground can produce a larger arc near 3/16". These tests are with out the cells connected, the arc will be twice the length with cells connected. See Spark Test pdf.

Evolution of the F50 Power Supply

The F50A was introduced in 1972 and has evolved in to the current F300. The same collector cells that were used in the F50A are still used in the F300. Thus variations of the current F300 power supply are used as the replacements for the prior F50 models.

In 1972 the F50A had an analog power supply as shown bottom-left. Then in 1987 the F50E was released, The F50E was the same as the F50A but with a new electronic power supply that offered two new optional features. The F50E offers an optional remote indicator and an air flow switch.

In 1993 the F50F was introduced with an all new chassis. The F50F now has all the electronics, from a 120v cord to the contacts for the cells built-in to the power box. Now a simple power box swap was a sure fix.

In 1998 the F50F Series 2 was released with a new optional LCD remote indicator that replaced the prior LED indicator. Also the internal power box wiring was improved with molex plug connectors. The connectors simplified manufacturing and power box repairs.

In 2000 the F300 was introduced that was identical to the F50F but the paint color was changed to blue. The F300 now has post filters that will also slide in to the F50F.

240 Volt Power Supply for F50A F50E

Honeywell has discontinued the F50A and F50E 240 volt replacement power supply for the 12½ x 20 models (208425E). The 240 volt complete power box is available.

The 240 volt replacement power box for the 12½ x 20 is the 208422B.

Warranty on Replacement Parts

The Honeywell warranty for F50 Replacement Parts is 2 years. Our customers simply need to ship us the defective part. We test and confirm defective. We then ship back a brand new part at no charge.