Problem with multimeter DT9205A

[Automatics]

The problem is when it is on continuity mode on the display shows reading 393 beeper still works but I cant test leds. On 20kΩ/200kΩ display shows 2.40/02.4. The problems appear when accidentally when it was on continuity mode my dad used it in a 220 AC curcuit. I opened it but didn't saw any obvious damages. Any idea how can I fix it or what is wrong with it. Thanks!

 

[PETERDECO]

Welcome to the forum. Something must be toasted inside but not visibly. For less than $10 you can buy a new one.
https://www.ebay.com/itm/3239586558..._ge9LuPldMPl9AzDe5A6FWF3vWHLiWeRoCjisQAvD_BwE

 

[Automatics]

Yeah I know I can buy new one cheap but I was wondering if someone had an idea what could be

 

[Allen Bong]

Here is the schematic of your digital meter meter...

Since you said that your dad connected the probe to AC on the continuity test mode, I'd check all the components connected to point "J" like ptc1 and ptc2, 900K and 100K resistors etc.. IC2b and IC2c (LM324) are probably also gone as well.

 

[Riyadh1959]

Hi every one

The problem is when it is on continuity mode on the display shows reading 180 beeper still works but I cant test leds. On 20kΩ/200kΩ display shows 2.40/02.4 . Any idea how can I fix it or what is wrong with it. Thanks!

 

[73's de Edd]

Riyadh1959 . . . . . . is you also being . . . . . . Automatics . . . . . . .or has he permanently left the arena . . . . .along with Elvis ?

 

[Riyadh1959]

Riyadh1959 . . . . . . is you also being . . . . . . Automatics . . . . . . .or has he permanently left the arena . . . . .along with Elvis ?

I had same problem with referent number?

 

[73's de Edd]

Try the voltmeter functions and see how accurate they are.

 

[Riyadh1959]

Try the voltmeter functions and see how accurate they are.

Try the voltmeter functions and see how accurate they are.

When I test the led food it must be light but it don't ?

 

[73's de Edd]

We know that . . .that's understandable, BECAUSE the diode test function has BLOWN UP ancillary parts within it and 240mv is borderline of being able to light up even the lowest threshold of LED . . . the RED LED.
Come back with the requested functionality and accuracy test of the voltmeter portion of the unit.

 

[Automatics]

Try the voltmeter functions and see how accurate they are.

The AC is ok it shows accurate, the DC is accurate as well. The ohms readings are off whithout anything connected it shows 2.34K and on continuity it shows 399 whitout to be connected to anything but it beeps when it is shorted

 

[73's de Edd]

The problems appear when accidentally when it was on continuity mode my dad used it in a 220 AC curcuit. I opened it but didn't SEE any obvious damages.
I fully suspect, that with the meter being set down on a low ohms test function, such that the rotary switching done by the dial, was setting down near and engaging the R7-R6-R5 divider resistors . . . . that the bottom left corners Q1 . . . 2N9014 . . . . was also ZAPPED with that OVER voltage , so change it out.
If physically having room enough, a conventional short leaded . . . . . those ends bent into L's . . . . . TO-92 cased version could be used .
Or actually, any generic 2N3900-2222-4400 series transistors as subs , as its actually being used in a diode function.

 

[73's de Edd]

Sir Slyman . . . . .Slyman . . . . .
Can you tell us what 2 holes the meter probes were plugged into ?
What position was the meter knob in ?
What voltage or current source was you trying to meter ?

AND THEN . . . . .EVERYTHING BLEW UP !

Then we will know what direction to go.
ALSO is /was that 0.2A chip fuse blown ?

In your repair cleanup, you need to use a typewriter eraser and STRONG solvent and brush to assure all of the carbo-metallic flash deposition at the left end of the 20A copper wire shunt gets cleaned off the PCB.

Initially . . .without having your feedback . . . it looks like 2 of the DC current range current shunts were blown open. . . . .FORTUNATELY . . . .you don't gots what it takes, to blow open R15 current shunt.
According to some . . .OF MANY . . . . DT2905A schematics your 200 ma current range shunt of R17 mounting pads are for a 0.99 ohm resistor and confirm for me . . . . . that the smaller R16 pads are connecting in parallel to R17 so that an optional 27 ohm resistor . . .they say . . . . would trim in that sole 0.99 0hm resistor . . . .on down to a more EXACTING ~ 0.9549839228295821 ohms.
BUT it looks like, to me, that there NEVER was a 27 ohm installed on those R16 pads.
If the next R42, current shunt for the 20 ma current range, is damaged . . . . . . . . 9 ohms is listed for its value.
I would have to see the front of your meter and its switch positions for other DC CURRENT range shunts, if there are others.
BUT I don't think that will be relevant as smaller currents involve HIGHER value current shunt resistor values.Therefore, they wouldn't get damaged.

Considering your access to acquiring those special resistor values and types . . . . . . . . . .this wise old owl . . . . . would use leaded metal film resistors of 1 and 10 ohm values and borrow another meter that will measure DC current .
You then install those new shunt resistors with one end 1/2 folded over full lead length and the other longer lead, then trimmed down, to make them the same length . . . . . to their respective pads.

Then build up a current reference of a 9V transistor type rectangular battery and a 47 om resistor in series with one battery + lead to give yourself an~ 190 ma current reference to test the 200ma DC current range .
Also get a 470 ohm resistor to then later use in the same manner, to test the 20 ma DC current range.

TESTING AND CALIBRATION . . . . .


The meters get interconnected as is shown above, with the series current limiting resistor being changed out in accordance as to whether the 200ma or 20 ma calibration is being set.
The original meter should be exhibiting a bit higher current reading than is being correct, by virtue of a higher stock value resistor having been chosen.
We will now correct for that by taking a 500 ohm variable potentiometer and placing one " flying" hook up wire on its CENTER terminal and another wire on either of the side terminals. Then you connect the two free wire ends to an ohmmeter and rotate the pot to its 500 ohm setting.
Move over to the test hook up now where you will have two meters readings, temporary solder tack the pots flying lead ends across the shunt resistor and very slowly lower the value of the pots parallel resistance s that the serviced meters reading agrees with the "good " referencing meter. When they are matched, shut down and disconnect and read the final adjusted resistance of the pot, that will then be the needed value
of trim resistor that will need to be installed across that ranges current shunt resistor . . . . .you will have to use the closest stock value available and install it across the main shunt resistor for that current range.
Repeat the procedure for the lower current range while using its different current limiting value.
Thaaaaaaaassssit . . . . . . .

Slyman
If you don't spleakee velly good . . .the Englee . . . .you might need some assist in Arabic, from our most honnable and esteemed Pharoan from Egypt . . . .

https://maker.pro/forums/members/pharaon.37549/

73's de Edd . . . . .

WE ARE NOW APPROACHING A TIME WHERE INTELLIGENT PEOPLE ARE BEING
SILENCED, SO THAT STUPID PEOPLE WON'T BE OFFENDED.

.

 

[Delta Prime]

WE ARE NOW APPROACHING A TIME WHERE INTELLIGENT PEOPLE ARE BEING
SILENCED, SO THAT STUPID PEOPLE WON'T BE OFFENDED

So does that mean I can speak?
That was very kind of you to save us a time spot; by the way.