Repairing a craftsman multimeter.

Discussion in 'General Electronics Chat' started by sdowney717, Sep 2, 2012.

  1. sdowney717

    Thread Starter Member

    Jul 18, 2012
    392
    13
    was trying to post this

    repairing small circuit traces on a craftsman multimeter

    I have this nice older digital multimeter which I may have damaged.
    What has stopped working is the k type temperature reading.

    It was working but then I accidently had the probes in the ohm position hole and measured 110 ac volts. There is a fuse I bypassed years ago and that ohm meter position is fused at 650ma listed on the front.

    So I took the meter apart and noticed 2 traces have been obliterated on the back of the board. Just had a small length of copper trace remaining. The traces terminate in little copper traced holes and they look fine. Traces to be repaired are about an inch long.

    These traces are pretty small. What would be the easiest way to attempt a repair?
    I was thinking an extremely tiny insulated wire? Not sure If I have that.
    or
    a small piece of bare copper wire strand pulled from a wire?

    Another issue the beeper sound maker is destroyed?
    It was laying inside the meter in 3 pieces, the wires had broken off. It has a flat disc with a couple solder connections. I snapped it back together but the flat disk rattles around inside the black case?

    shows 2 burned traces.
    [​IMG]

    black speaker, I have no idea If I should try to hook this back up.
    [​IMG]
    ---------------------------------------------
    Editing now, so why is it working in this forum and not in the electronic chat forum?
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    It is not a good idea to have two different threads on one thread, so I have split them for you. Otherwise you will likely get no help at all.

    A large part of the OPs other half can be found here...

    Trying to post but get errors
     
  3. BSomer

    Member

    Dec 28, 2011
    433
    106
    You can fairly easily repair the traces with a small (30AWG, 32AWG) hook up wire. I would use one that is insulated to prevent it from shorting to any exposed pads or vias. Be sure to clean the area real good with isopropyl alcohol and scrap away any of the carbon/burned trace with a sharp x-acto type knife. You should be able to take the wire from via to via and be good.

    Double check the traces on the other side of the board to be sure no damage is there as well.

    As for the piezo buzzer, that one is probably toast. I think you could get another one of similar size and solder that in, if you really want the buzzer that is.

    You mentioned something about bypassing a fuse, this is a bad idea. It is probably the root of the problems you are experiencing now.
     
  4. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    You can put in insulated jumpers if you have convenient solder pads to connect them, but I tend to run a strand of copper wire over the old trace. Personal preference? What the existing damage will allow? Your choice.

    You can try the old piezo noise maker. If it works, fine. If it doesn't, you can get them at Radio Shack.

    PS, put a new fuse in while you're at it or you'll find out how much it costs to be cheap.:D
     
  5. sdowney717

    Thread Starter Member

    Jul 18, 2012
    392
    13
    Thanks for fixing the post, I tried to post several places wondering why it would not post.

    I do have some insulated winding wire that might work. The other thought was using a small lead wire from a 1/8 watt etc... resistor.
    How about gluing the wire down to the board using instant glue?

    The piezo buzzer, do they come in different voltages?
    The meter uses 2 AAA batteries, so what would you use?
     
  6. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    Winding wire...enamel coated? Sure. That will work. Old resistor leads are too stiff. You can glue it in the middle as long as you solder the ends.

    3 volts worth of batteries? How about a 3 volt buzzer?
    You're getting ahead of yourself. Find out if the meter survives surgery before you buy a buzzer.
     
  7. sdowney717

    Thread Starter Member

    Jul 18, 2012
    392
    13
    It has a cracked MOV number is 820k007, the blue disk.
    It must have overheated a lot to do that.
    Is this part available and where?
    I successfully repaired the traces using some old verizon tiny solid copper wire.
    stripped the end and it fit into the tiny holes and then soldered.

    there is a tiny rectangular black transistor next to it. What is the chance that is gone also?

    [​IMG]

    do the mov have no polarity?
     
  8. sdowney717

    Thread Starter Member

    Jul 18, 2012
    392
    13
    I removed the mov and it still does not work on temperature. so I think I will need a new meter.

    I would like to get one that also does capacitor testing and has a clamp meter for amps.

    so want temp, amp clamp meter, capacitor, diode, hertz, transistor, volts, ohms,
    anything missing and anyone got a good model to look at?
     
  9. sdowney717

    Thread Starter Member

    Jul 18, 2012
    392
    13
    It is an 820KD07 varistor
    I took it out of the circuit and it reads 39.5 ohms

    Any thoughts on this item and wonder if it also affects hz reading when removed as I noticed that part of the meter is non functioning.
     
  10. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    Your MOV is bad. Leaving it out to test the meter is OK. It only operates when there is a fault condition.
     
  11. sdowney717

    Thread Starter Member

    Jul 18, 2012
    392
    13
    I followed one of the burned traces and it connects to a small glass diode.
    Diode is exploded.
    Any ideas on a replacement part for this?
    [​IMG]

    [​IMG]
     
  12. sdowney717

    Thread Starter Member

    Jul 18, 2012
    392
    13
    http://www.electronics-tutorials.ws/diode/diode_4.html

    What is the chance the small glass diode is this 1N4148?

    I just replaced the diode with a 1N4148 from Radio Shack and everything except the temp is now working.
    :)
    Temp just not getting any input from the probe.
    :(

    Do you think the varistor being out of the circuit would affect this? I tend to think not. There is a small rectangular surface mount transistor near the varistor and I think it is shorted. measuring across a couple of solder points it is shorted and reverse polarity shows same shorted. Any ideas what it might be? It says Q1 on it?

    I also think I know how this shorted out. I was checking the AC voltage in the boat and had the K style temp probe plugged in. As I leaned against the steering wheel, the metal tip of the probe was touching the metal wheel and I think it caused it to short. It had worked one minute before I did that, and after I finished checking the voltage, it immediately stopped working.

    The k type probe I have is it a simple variable resistor that changes with temperature? If so, it does change slightly the resistance as it gets warm and cold and I tried shorting the probe plug and the meter wont respond. Dont know why it is polarized plug.
    Any ideas? How to test the probe?

    I just found out it is a thermocouple so it will make a voltage?
    http://en.wikipedia.org/wiki/Thermocouple
     
    Last edited: Sep 9, 2012
  13. sdowney717

    Thread Starter Member

    Jul 18, 2012
    392
    13
    I found out that if I short the standard leads, one in common and one in ohms port with the k type probe plugged in, I get readings which vary with temperature but are absurd, such as at RT, minus 235 degrees Fahrenheit.

    If I unplug the k type probe, then the readings go away and meter shows 0L
    So it is doing something with the k type probe connector.

    What is the chance the probe has failed?
    I found a volt chart for k type probes at

    http://www.tempsens.com/thermocouple_pdf/Thermocouple_type_K_table.pdf

    Should my voltmeter be able to sense the small DC voltage from a k type probe?

    It looks like at 100C, it is 100uv?
    Is that 100 millionth of a volt??
    [​IMG]

    here is a better reading table
    http://www.omega.com/temperature/Z/pdf/z204-206.pdf
    so at 1300c it is putting out 54 millivolts?

    If I heat up the thermocouple with a candle, should I be able to see this voltage if checked on the meter?
     
    Last edited: Sep 9, 2012
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