METROTECH 810 locator

Discussion in 'General Electronics Chat' started by inwo, Mar 15, 2014.

  1. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Would anyone have experience or link to circuit information?

    Receiver is dead.

    Powered by 4-9Vs. 2 circuits.

    One 9V circuit with 2-P-9Vs.
    One + & -/9V circuit.

    Lcd is not "on"

    Voltage check shows <3vdc to lcd control chip (low).
    Batteries all checked good.
    Internal battery check= good.

    Accidentally left power switch on overnight. Locator was working the next AM.:eek:

    Display was dim though.

    Sorry for the long story!!!!!!!!!!!!:)

    Battery voltage was only 8.5 each so I put in a new set and it worked perfectly.

    After a few checks/days it is back to low voltage to the lcd and dead.
    New batteries don't bring it back. Still low voltage to lcd.

    I'm confident it's a simple ps problem, but haven't been able to find a likely suspect.

    Heat, cold, and shock have no effect.:(

    Any information out there?
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    If you post good PCB photos (both sides!) the experienced repairers here might be able to offer some simple tests and/or solutions.
     
  3. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,433
    315
    Thanks for taking the time to respond.

    I will stumble thru the circuit eventually.:)

    The layout is such, with 5 boards plugged into a main board, that it would be almost impossible to trouble shoot remotely.

    By the time I get it drawn out, I should be able to solve it.

    Was just hoping on a long shot that someone had inside info.:(

    After 4hrs in. I have a drawn the 5 volt regulator circuit using 1-pnp pass, driven by 2-npn darl. connected.
    Base of darl. is referenced around .6 volts from a voltage divider.

    Top of divider is the +5V output. Bottom of divider is -2.5V from a LM336 (2.5V shunt reg.) between -9V and ground.

    I'm pretty proud of getting this far as earlier I didn't even know what voltages to expect.:p

    All parts and board are plastic coated.:(

    Have the advantage now of circuit working. I can record levels thru the circuit.

    If only I can get it to fail again, I should have a shot.:cool:

    Why it takes 20+ components for a 5V reg. I'll never know. Don't see any current limiting.
    And referencing to -9V?:confused: There are other ways to get the +5 to swing around the .6V BE junction.

    I suspect the shunt reg. as the culprit. It checks low with diode test. Out of circuit. Yet reinstalling it's ok. Subbing 4 signal diode string didn't seem to work. But that was before I understood the circuit.
     
  4. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,433
    315
    Here's what I'm up against..................
     
  5. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,433
    315
    This may help someone else with dead Microtech 810 locator.

    Supply to LCD <2.6V when dead.
    Supply to LCD >5V when working.
    LM336 suspect on middle board.
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Congrats on getting it working. :)

    That's about the worst "regulator" I've ever seen in a commercial device.

    A cheap 7805 would have been a heck of a lot simpler, more reliable, and regulated better.
     
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