Bird Model 43 RF Wattmeter Repair Tips
aka How Do I Fix My Bird Wattmeter?
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If your know a little bit about electronics you can fix your Bird 43 wattmeter should it become intermittent on inoperative. Here are a few tips on what to do if your Bird 43 wattmeter is not working. Don't try these test if you are not at least a little familiar with the electronics. You can damage your meter if you are not careful.
The Bird Model 43 Wattmeters are very robust and rarely fail. There is not a whole lot to them. Most of the electronics are in the elements, not in the wattmeter housing. The wattmeter consists of the transmission line
section, a 30 ua meter movement, and a length of coax connecting the two.
99.9% of the problems I see are with the wattmeter contacts to the elements and the coax on the inside of the wattmeter connected to the transmission line section.
Here are pictures of the locations of the two most common problems,
99% of problems can be found here, the left picture shows the contact finger, the right picture shows the DC connector on the transmission line:
Bird Model 43 Wattmeter Element Repairs and Calibration
- Step one is to isolate the problem. Install a known good element in the Bird wattmeter. Apply some input power to the wattmeter with an RF load connected to the output of the wattmeter. Tap lightly on the element. If the meter reading is intermittent with the tapping the problem is most likely the contact finger in the element socket. Now tap lightly on the Bird wattmeter housing. If this causes intermittent readings then the most likely problem is the coax cable connection to the transmission line section inside the Bird wattmeter. Now read the paragraph below that address the problem.
*Warning - You can damage your wattmeter's meter movement in this step if you are not careful! This test is optional, you can repair/diagnose your watt meter without this test. The meter movements in the Bird Model 43 rarely fail and it is usually obvious when they do (physical damage, etc.).
In the following test you will place your Ohmmeter leads across the 30 ua meter movement in your Bird wattmeter. You will need to remove the back of the wattmeter to access the meter terminals. With my Fluke 189 Digital Ohmmeter I use a 150K resistor in series with my Ohmmeter to get an approximate full scale deflection on the wattmeter's 30 ua meter movement. This resistance value can vary widely with the brand, model, and resistance range selection of your Ohmmeter. Momentarily place the Ohmmeter leads (with the resistor in series) across the brass meter terminals and see if the meter needle deflects. Do this very quickly so that the Ohmmeter voltage does not damage the 30 ua meter movement in the wattmeter. If the wattmeter deflects in this test then the 30 ua meter is 99.9% of the time not the problem.
- If your Bird Model 43 watt meter is intermittent the most likely culprit is the small contact finger in the element socket. The element contact finger can become bent too far out of the element socket and sometimes needs to be pulled out a little bit to make contact with the element. Remove the element and look for the small contact finger on the right side of the socket about halfway down. Pull the contact out until it protrudes slightly into the socket cavity. If you move it out too far the element will not fit into the socket. In this case you can just push the contact back a little bit at a time until only the little bump on the contact finger is protruding into the cavity.
- Check that the contact finger is not displaced vertically and touching the cavity walls. This will create a short circuit and the meter will not work.
- Clean the contact with a light brush with steel wool if it looks discolored or contaminated.
- If the contact finger looks OK then the next most likely problem is the coax DC connector on the transmission line section. Take the rear cover off the wattmeter and check the connector to make sure it is tight. You will need a very thin pliers. If your pliers are too large than it's easiest
to first remove the line section from the housing by unscrewing the two large screws on either side of the element cavity. There's not a lot of room for a pair of pliers when the line section is mounted inside the Model 43. Unscrew the coax connector from the line section and clean the contacts with a light brush with steel wool.
- If the above two checks fail to resolve the problem check the spade lug crimps on the back of the meter. I've found a few Model 43s where the crimp was poor and caused the wattmeter to be intermittent or dead.
- Inspect the contacts on the sides our your elements, they can become contaminated and this will cause a poor connection when the element is in the wattmeter socket. You can lightly brush the contacts with steel wool to keep them clean. Be careful not to remove the gold plating on the elements. A very light brush once or twice is all that is required.
- Check that the glass is not loose above the meter face. If the meter glass is loose you can disassemble the meter from its housing and slide the glass retaining ring back into place. This is not recommended if you are not familiar with delicate meter movements. The meters are magnetic and can become quickly contaminated with metal bits and dust when the movement is removed
from its housing.
- One more warning. If you clean the watt meter glass with a dry cloth it will create a static electric charge on the glass and the meter needle with not deflect correctly. WIPE the meter glass with a damp cloth to remove the charge, or you can wait until the charge dissipates, this can take a day or two.
Pry off the element top with a small screwdriver. I use a small hammer and lightly tap the screwdriver to force it under the element cover. This works with all types of elements. The adhesive used on the metal covers is agressive and it can take considerable force to pry/lift the cover off. The adjuster hole varies with the style elements, some elements do not have an adjuster.
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- The MEK (Methyl Ethyl Keytone) solvent that is used in this procedure can be harmful or dangerous to handle. Read and follow the safe handling and disposal warnings on the MEK container.
- Removing the delicate element cover is the only challenge here. If you have an element with a metal cover you will find that they are very thin and easily damaged/destroyed if you try to pry the cover off. If you place the wattmeter element upside down in about 1/8" of MEK for 24 hours the cover will easily come off. After the 24 hour MEK bath I use an Exacto knife or a single edge razor blade to grab an edge and lift the cover up. Once the cover is off you will see the calibration adjuster.
- Surprise, some elements do not have an adjustment!
- Warning - MEK is toxic and should not be handled with bare hands and the fumes should not be inhaled. Use just enough MEK to immerse the cover of the element. I use a small glass beaker with a cover to minimize the fumes in the area. MEK is available at most hardware stores. Read and follow the warnings on the MEK container for safe handling.
- I've been told that you can remove the wattmeter element covers with a hair dryer or hot air gun. This has not worked well for me. It takes a lot of heat.
- Don't use MEK on the newer Bird elements, it will damage the platic. In general these plastic covers can usually be pried up with a small screwdriver.
A Look Inside The Bird Elements
A Photo Tour of Bird Elements
Calibration and Repair for Bird Wattmeter Elements
Wattmeter Manufacturer Links
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