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Old 14th Sep 2017, 4:58 pm   #1
MotorBikeLes
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Default TMK multimeter

My pal who does auto repair stuff has a TMK 500 TU. I checked it over for him a few months ago, but he has just been in bed for 2 weeks, leaving the meter outside. The Ohms range was dead, so I brought it home to check. I stood it overnight on the shelf 18" above my Rayburn -- that will dry out anything -- just in case it was damp.
Flat batteries (2 Xs AA in parallel), so I fitted new, but only slight movement of scale with leads shorted (leads checked, OK). A check with an AA bat suggests DC volts OK, and likewise the 12A DC current range.
Putting my own DVM leads into the com (+R) and VOLTS (-R) shows full battery volts on all resistance and buzzer positions.
A very quick check shows the Ohms pot is OK, full continuity and correct value.
The PCB is marked 500TU-3 and 7512 (date I assume) I have the correct circuit from a recent (closed) TMK500 thread.
Any first suggestions?
Les.
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Old 14th Sep 2017, 6:15 pm   #2
The Philpott
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Default Re: TMK multimeter

Given the choice i prefer prolonged air drying to heat, just in case the heat accelerates corrosion (ever got a pair of scissors wet then dried them out in the sun? They rust almost instantaneously!)

Provided your friend's house isn't too close to the coast i would hope that further drying from all the little crevices will occur over a matter of several days without adverse effects. Other than that i haven't got any specific ideas of the cause.

Anyone..?
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Old 21st Sep 2017, 5:24 pm   #3
MrElectronicman
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Default Re: TMK multimeter

I have a TMK 500, is was my first real meter. Mine has developed a problem with the PCB, which has been worn down by the rotary switch contacts. These contacts are spring loaded and run over the plated copper traces, over the years the plating has worn off and appears to have been embedded in the board material causing shorting between the copper traces.

I have tried cleaning it with some success but the ohms range is still very flaky

The ultimate fix would be to make a new PCB and plate the traces that are used by the switch contacts.
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Old 21st Sep 2017, 10:30 pm   #4
KeithsTV
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Default Re: TMK multimeter

I had problems with my TMK 500 with readings varying on all ranges. Eventually I found it was due to the spring loaded contacts. I took them apart, cleaned and reassembled them resulting in stable readings.

Keith
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