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Author Topic: HEATHKIT HM 102 RF POWER METER DEAD  (Read 920 times)
K9EEH
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Posts: 21




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« on: May 06, 2013, 06:27:51 PM »

Picked up a HM 102 at a hamfest...fellow said it worked fine....however when I got home and tried it..The unit
was dead...no meter readings  in all ranges and switch settings.  I have no manual, however downloaded schematic..I am
not to good at troubleshooting so any ideas where to start would be appreciated. Thank you.

Dick
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VA3GUY
Member

Posts: 172




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« Reply #1 on: May 06, 2013, 07:52:42 PM »

My first thought is:  Is there power getting through it?  Maybe there are no connections inside.
For what it's worth.

- Guy
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W6EM
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Posts: 724




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« Reply #2 on: May 06, 2013, 08:30:18 PM »

The HM102 is self powered by sensing RF current.  It has two circuits that develop meter movement energy.  First, look for loose wires from bad solder joints.  Then, check switch contacts to make sure they make/break properly.

Try injecting some current through the meter circuit.  I'm guessing its probably a 100 microamp movement.  Try connecting a 1.5V cell through a 15K resistor to limit the current to see if the meter will deflect.

If it doesn't work on either SWR or power settings, it's probably the meter leads or (I hope not) the meter movement could be bad.

73,

Lee
W6EM
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K8AXW
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Posts: 3666




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« Reply #3 on: May 06, 2013, 08:47:35 PM »

Dick:

I have the HM2102, which is the VHF version of the 102...... as I recall (!)....

Since the unit is pretty old the first thing I would do is clean the switch contacts on S2 and S3, the Sensitivity pot and the pins on the Calibrate jumper.

I would then check the meter movement as Lee points out.  If you still can't get a deflection in either the forward or reverse direction I would then suspect diodes D2 and D3.  They are germanium, not silicone diodes.  Silicone can't be substituted here.

I would then check the continuity of the toroid secondary.  It is pretty fine wire and there is a strong possibility that this winding is either open or connected to the PCB with a cold solder joint.

If all of these steps don't provide joy, then you can always start at page one of the assembly manual and "rebuild" it step by step to see if there is a wiring mistake (even though the guy said it was working OK - Wanna guess how many times I've heard that one?) and at the same time let you examine the solder joints.

Al - K8AXW
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K9EEH
Member

Posts: 21




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« Reply #4 on: May 07, 2013, 07:37:28 AM »

Thanks for the help...Looks like the meter is bad.. I sub a 100ua meter, and everything worked on all power and
swr..

Dick
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