The AM Forum

THE AM BULLETIN BOARD => Technical Forum => Topic started by: wa2tak on March 29, 2023, 03:57:30 PM

Title: OLD Triplett multimeter repair
Post by: wa2tak on March 29, 2023, 03:57:30 PM
I'm trying to get working one of those Chinese mosfet amp kits working.
After weeks of trying...I think I now know what a mosfet is!
Lost a few of the darn SMD's hiding in the carpet.

In the process, I damaged my Triplett 630 APL type 4 ammeter section.
Triplett does not service this old guy.

Thought I'd get some suggestions before I dig into it.

Using 14 vdc + 156 ohm @ 90ma,  the 10 amp meter barely expected
The meter PEGS on 1000ma setting and 100 ma setting.

Using 14 vdc + 2000 ohm @ 7 ma, both 1000 & 100 peg again.
The 10 ma setting WORKS.

Other folks can enjoy current (pun ) circuitry technology ...I'm sticking to my tubes...and point-to-point WIRES.

Title: Re: OLD Triplett multimeter repair
Post by: w7fox on March 29, 2023, 04:45:06 PM
I've taken out at least one meter shunt in each of my VOMs.  Yeah, dumb!  If you can still read the value on the resistor, you can make a new shunt using some thin wire and the copper wire tables.

Title: Re: OLD Triplett multimeter repair
Post by: k4pf on April 01, 2023, 07:23:59 PM


Edibris has the manual for the 630-APL type 4.

If you Google the 'Ayrton shunt', also called a 'universal shunt',
 it will give you hints on how the shunt network was designed.

I have an older Triplett model 630 type 4, about 1980 vintage.
The basic current characteristic on mine is 60uA full scale,
at 300mV drop, when set to the most sensitive shunt position.
The panel meter on mine itself is 50uA full scale, at 250mV drop.

Ed Knobloch

Title: Re: OLD Triplett multimeter repair
Post by: k4pf on April 02, 2023, 04:29:59 PM

Assuming the scales are 1000mA, 100mA, 10mA and 0.1mA
 (like on the Triplett 630APL series 5), the resistors in question are R7 thru R10,
with values 0.25 Ohms, 2.5 Ohms, 25.12 Ohms  and 5K.

The resistor location is illustrated in the manual.  The 630 series 5 manual
is on the edibris BAMA web site, but I was mistaken about series 4
being available there.  Hopefully, Triplett didn't change the part numbers
for the resistors when they went to series 5 from series 4.

I would set the Triplett to say 1000VDC, so the meter isn't loading down
the shunt, or be subject to overcurrent damage while you are troubleshooting.
Then use another Ohmmeter to check the 4 shunt resistors individually.

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands