Test Lights and Bad Grounds

Test Lights and Bad Grounds

Test Light – A probe-type device that lights up, under certain circumstances.  Sold in automotive and other novelty stores, it is used to troubleshoot simple electrical circuits, and other witchcraft.

Test lights are great for troubleshooting tail light circuits on your boat trailer.  They have NO business inside a combi-box.  Telebelt combi-boxes have circuits carrying 24v, 12v, 5v, variable voltage and signal circuits that are read in milliamps.  You can complete circuits, and cause components to fry.  In other words, you can “let the smoke out.”

Basic Rule of Electricity #1 – Smoke makes all electrical things work.  Smoke makes computer chips work. Every time you let the smoke out of a computer chip, it stops working.  Electric motors have to be large to handle all that smoke. A lot of smoke leaks out when they quit working.

Use a multi-meter.  Get one that measures DC voltage, amperage and resistance.  You don’t have to spend hundreds of dollars for a top-of-the-line Fluke meter.  You can get one for less than $10, and it will do what you need.  Keep it in your combi-box.  It will live longer there.

Sooner or later, you might end up calling in with an electrical problem.  You should have a copy of your schematic and a meter.  You are our “eyes and hands” when we troubleshoot over the phone.  We’re not much help if you can’t furnish voltage readings for us.

Bad Grounds

Some of the most difficult calls we get are traced to bad grounds.

I recently had a call from an owner that could not get his TB-105 e-stop to reset.  After going through the steps to figure it out, I determined his e-stop relay was toast.  This was an older TB-105 with a negative Mack battery disconnect.  These were notorious for high resistance at the wire contacts of the Mack switch.  Electrical components that are not properly grounded, can fail.  E-stop relays were particularly sensitive.

I wanted him to check his ground, but he didn’t have a meter.  He did have a test light that lit when he touched the positive and negative terminals of the e-stop relay.  That really doesn’t tell me all I need to know. 

He went and got a $5 meter.  When he connected the meter to the positive and negative e-stop terminals, he read 13.8 volts, since the truck was running.  Then I had him connect the negative lead of the meter to a frame ground and touch the positive lead to the ground side of the e-stop relay.  He read 2.3 volts.  I had him touch the positive lead to the M12 screws (combi-box ground) and he still read 2.3 volts.  In both cases, he should have read zero.

The problem will be traced to the connections on the Mack disconnect switch.  NOTE:  When loosening or tightening nuts on the back side of the switch, use 2 wrenches.  There is a wrench flat at the base of the studs.  Use one wrench on those flats to keep the studs from turning and twisting the wires off internally.

Another way to check the ground is by resistance.  Set your meter to OHMS.  Checking between M12 and a frame ground should read nearly zero ohms.  There is resistance in the wire.  Some meters have a continuity tester in the ohms scale.  They should “beep” when checking this way.

Oh, and meters can check diodes, too.  This way we can help you find the smoked diode in the 25 AMP fan circuit that somebody put a 40 AMP fuse in.      

 

Telebelt Receiver Fuses

The e-stop circuit of Telebelts includes the HBC 735 radio receiver.  Actually, the e-stop circuit supplies power to the radio receiver. 

The images below, A370160 Pg 4 and Pg 5 show the circuit. To view at a larger size, click on each photo individually and they will open in a new window.

The 12V supply (red) goes through the e-stop stations to X81 pin 13.  X-81 is located on the right-hand (hinge side) of the control cabinet.  The power then goes through a fuse in the radio receiver and returns to X81 pin 5, and then through the e-stop stations to 4A17, the e-stop relay. 

 

 

 

This image shows the pin locations on X81.

 

 

 

 

 

 

The image shows the inside of the 735 radio receiver.  There are 4 fuses called out in the image, and their reference numbers correspond to the reference numbers in the image that follows.

 

They are:

42 = Power supply primary – 6.3A

43 = Power supply secondary – 1.0A

44 = Proportional output card – 12.5A

45 = E-Stop card – 4A

 

 

All of these fuses remove by pushing the end cap in slightly and rotating it to the left.  When the cap releases, a spring pushes it out a little.  The fuse will be attached to the cap.  You might need a coin or flat blade screwdriver to remove the cap.

 

RULE #1 – The problem is NOT in the radio system

 

Symptoms of a problem:  

 

E-stop will not reset and there are no LED’s lit on the receiver.

 

FUSE FAILURES IN THE RECEIVER ARE RARE.  Make sure you check all the way through the e-stop circuit (SEE RULE #1).  A blown 4F17 or a bad e-stop button causes the same symptoms.

 

If you have no power at pin X81-13, the problem is NOT in the receiver.  If you have 12V at X81-13 and zero volts at X81-5, check fuses 42 and 43 in the receiver.  Either one of these fuses, when blown, cause these symptoms.

 

Before replacing any fuses and turning power back on, find the short.  Likely places are faulty e-stop buttons or their boxes, or cable shorts between X81 and the radio receiver.  The 90’ cable can be substituted for troubleshooting purposes.

 

E-stop will not reset and there are LED’s lit on the receiver.

 

SEE RULE #1.  There are many possibilities, including:

  • Remote switch problem.  Verify with cable remote
  • See control box schematic:
    • Blown 3F64
    • 4K69 or 3K275 bad or unseated – confirm by flashing 4A17-T33 to 4A17-T-34
    • 4A17 connections bad
    • 4A17 defective
  • Problem with receiver cable from X81 – use 90’ cable to confirm

 

If all else doesn’t correct the problem, check 4A fuse #45 on the e-stop card.  If the receiver cover is off, you will see the “light show,” but attempts to reset will just cause relays on the card to click.

 

E-stop will reset and there are LED’s lit on the receiver.  Only non-proportional functions (toggle switches) work, but moving joysticks only cause the WBV (Boom/Outrigger) selector valve to move.  The actual function levers do not move.

 

RULE #1 might not apply.  This is opposite from when the pilot valve relay is bad, or when you turn on the transmitter but don’t reset.  In that case, the function levers move but the WBV valve does not.   Just to be sure, use the cable remote to confirm the radio problem, then check the 12.5A fuse #44 on the proportional output card.

 

Before replacing any fuses and turning power back on, find the short.  Likely places are faulty cables or plug connectors on MBC valve, or cable shorts between X81 and the radio receiver.  The 90’ cable can be substituted for troubleshooting purposes.