Burnt resistor’s value for MAS830L multimeter

[Jarasmus]

Hello all.

Anybody got a classic cheap multimeter MAS830L? The circuit inside named XT850F.

I’m looking for a burnt SMD resistor’s value, separating Amp inlet.

See attached picture.

Thanks in advance.

 

[Bluejets]

Looks like a shunt ...I'd try the same value as the one above it.

 

[73's de Edd]

It’s weird that its parallel mate didn’t also toast down to the same fate ?
I am also suspicioning it to be a decimal15 ohm unit.
Is that unit auto ranging or do you have to purposefully switch settings to and probably have to swap one meter lead plug in position . . . .when measuring HIGH current ?
Do you remember having measured high current or having forgotten to later switch lead positions back ?.. . . .say if you were then measuring a voltage later ?

 

[Jarasmus]

Looks like a shunt ...I'd try the same value as the one above it.

Yes, it makes sense － same value. No, I didn’t try because I can’t find in my scrap 0.15Ω.. but I did put 0.22Ω (2W) instead －doesn’t work..

 

[Jarasmus]

It’s weird that its parallel mate didn’t also toast down to the same fate ?
I am also suspicioning it to be a decimal15 ohm unit.
Is that unit auto ranging or do you have to purposefully switch settings to and probably have to swap one meter lead plug in position . . . .when measuring HIGH current ?
Do you remember having measured high current or having forgotten to later switch lead positions back ?.. . . .say if you were then measuring a voltage later ?

I’m new to electronics, but programmer in general.

Some moments later I’ve applied same logic － Teo diff value resistors won’t make any sense.

Why then have to be soldered 2SMD x 0.15Ω, but not one 0.15Ω 1W (2W) － still a mystery to me.

Yes, thought the amp-measure (have to swap the positive) I’ve passed to high correct.

I guess I should replace it with 2x 0.15Ω.

But can I install single but simply bigger 0.15Ω, of 2W instead?

 

[bertus]

Hello,

Tou can download a schemaic from here:

Принципиальные схемы мультиметров Mastech - Измерения - Портал радиолюбителей

Принципиальные схемы мультиметров Mastech - Измерения, Принципиальная схема мультиметра Mastech M830B

radio-hobby.org

Bertus

 

[kellys_eye]

Two 0.15ohm resistors in parallel equals 0.075ohms and at 10A will drop 0.75V which just happens to be the amount necessary to forward conduct a transistor junction (to 'switch' something or just indicated an overload situation for example)

 

[Jarasmus]

Two 0.15ohm resistors in parallel equals 0.075ohms and at 10A will drop 0.75V which just happens to be the amount necessary to forward conduct a transistor junction (to 'switch' something or just indicated an overload situation for example

This is super cool explanation. Thanks!

I feel stupid not adding up resistor’s values. Few videos should help to cover this topic quickly.

 

[Jarasmus]

… thanks, but how do I suppose to read this?

 

[Bluejets]

thanks, but how do I suppose to read this?

different model...... you show MAS830L.......link shows M830B...so just use it as a guide, not "as a matter of fact"
Either that or break into the piggy bank and get a new meter....must be all of $30.

 

[Delta Prime]

The circuit inside named XT850F

The reference designators associated with those two particular components in the schematic, are commonly used when different model numbers and or revisions of the board.


Incidentally, if you notice in your photo, the solder pads for an additional component in parallel.
There are actually standards to address this but only for
reliable manufacturers. IEC 60617 (AKA British Standard BS 3939), ANSI standard Y32 (also known as IEEE Std 315), Australian Standard AS 1102.

 

[Delta Prime]

I’m new to electronics, but programmer in general

Isn't hardware fun?

 

[bertus]

Hello,

… thanks, but how do I suppose to read this?

The combined value of R10 should be 0.99 Ohms.

Is the 0.15 connected to the 10 A connections?

Bertus

 

[Jarasmus]

Isn't hardware fun?

For programmers mind it is even more fun! I did never expected I’ll be getting fascinated about it. I’ve always seen it nerdy business.

All started with giving up on shit Chinese controllers and making my own on Arduino and diversión into electronics was right on it doorstep.

Still, I’m very fresh into it, but my beloved Yamaha amplifier is fixed (after 5 year collecting dust), now got few dc-ac inverters to fix (this is how I’ve burnt a multimeters shunt), bit further on a roadmap KiCad learning and kickstart project with open source codes.

And I already feel half-blind with no having oscilloscope…

Wish me luck.

 

[Jarasmus]

~0.075Ω

Supposed 0.15/2 = 0.075
Installed 0.22/3 = 0.0733..

Unfortunately no luck..
I wonder, were there both R 0.15Ω?
Or such slight diff in Ω can output so big error?

See pics attached.

 

[bertus]

Hello,

Again are they on the 10 A connections?
The combination of resistors should be 0.01 Ohms (R11 in the schematic).
The 0.15 Ohms could be a correction on the total.
A possible combination could be 0.011 with 0.11 Ohms.

0.011 and 0.11 are standard values in the E24 range:



The lowest value will burn first when overloaded.

Bertus

 

[Alec_t]

Unfortunately no luck..

If that means you get a reading, but not the value you are expecting, then at least the remainder of the circuit components seem to be working and just the shunt needs adjusting. If it means that you get no reading at all then clearly something else has failed.

 

[Jarasmus]

Hello,

Again are they on the 10 A connections?
The combination of resistors should be 0.01 Ohms (R11 in the schematic).
The 0.15 Ohms could be a correction on the total.
A possible combination could be 0.011 with 0.11 Ohms. The lowest value will burn first when overloaded.

Bertus

Thanks Bertus.

Yes, that’s on 10A outlet.
I’ll try to find combination to make 0.99Ω － this makes more sense actually..

TBA

 

[bertus]

hello,

R11 is the 10 A shunt.
in the schematic it is 0.01 Ohm

bertus

 

[Jarasmus]

hello,

R11 is the 10 A shunt.
in the schematic it is 0.01 Ohm

bertus

‍

This means, that next to original R 0.15 in parallel there was R 0.05 which has burnt.
Referring to schematic.
Right?