5 transistor esr meter

[spdf]

Hello guys,

recently I build 5 transistors esr meter and I found out that on short condition my ammeter value keeps dropping down. After like 5 shorted measurements it shows only half scale ~25 uA. I tried to change R24 with lower value from 300 to 100r (my ammeter is 1900r) but with no luck on general condition.

Any thoughts where I should look? Any help would be appreciated!

[hugo]

Hi,

Have you seen these:

https://youtu.be/3fiUZZlveS0

https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/100

https://www.eevblog.com/forum/projects/jay-diddy-5-transistor-esr-meter/msg933224/#msg933224

Have you checked the DC voltages ?

[spdf]

Ok I measured DC voltages and I have different values on Q5 on collector 1.99V and on base 1.58V

I am powering it up from 12V is that make any difference?

[hugo]

"Ok I measured DC voltages and I have different values on Q5 on collector 1.99V and on base 1.58V" ...

That's your problem, check the values of R18, R19, R21, R22, Q5, what kind of diodes, uammeter do you have, R23 (10k) ?

"I am powering it up from 12V is that make any difference? " ... nope .

[spdf]

I double checked everything and I found these differences from original scheme
R12 33r
R10 3.3r

diodes are D3/D4 1n5711 and D1/D2 1N4002, uammeter is 50uA and 1900 ohm R23 is 10k potentiometer.

Still don't have a clue what is wrong 

And just for the record this is my first project that I have ever made so it's highly possible that I am missing something obvious ;]

[amspire]

Still don't have a clue what is wrong 

The clue is in Hugo's post:

"Ok I measured DC voltages and I have different values on Q5 on collector 1.99V and on base 1.58V" ...

That's your problem, check the values of R18, R19, R21, R22, Q5, what kind of diodes, uammeter do you have, R23 (10k) ?

1.58V on the base is not possible unless something is wrong in the circuit. The R21/R22 voltage divider can only have a maximum voltage of 5V x 10/37 = 1.35V. Base current can lower this, but cannot increase it. It cannot be 1.58V.

So the most like fault is that one or both of R21 or R22 are wrong. For example, R21 is 22K instead of 27K. If that is not the problem, there is something else wrong in that part of the circuit. Faulty connections, strange Q5 problem, something in that Q5 circuit.

Richard

[hugo]

Could you post a picture of your board, high resolution if possible ?

Amspire is right "For example, R21 is 22K instead of 27K."

[spdf]

After a lot of soldering and desoldering I've got damaged my pcb, so a made a new one and everything worked like a charm from the first attempt. It seems there was a problem with a contacts after all.

I would like to thank you guys for your help! Really appreciate that!

[Jay_Diddy_B]

After a lot of soldering and desoldering I've got damaged my pcb, so a made a new one and everything worked like a charm from the first attempt. It seems there was a problem with a contacts after all.

I would like to thank you guys for your help! Really appreciate that!

Hi spdf,

I am glad to hear that it works. Would you like to post a picture of your board and meter in the main thread?

https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/msg171364/#msg171364

Jay_Diddy_B