ESR tester repair.

[vari21]

Hi everyone.
Sorry if im not posting my problem in the right place also about my poor english.
Im trying to repair an ESR tester based on atmega 328, i ve got it from ebay, it comes as a DIY kit. the device has worked succesfully after soldering all it components together.but after a stupid mistake from me (over voltage or backward power plug i dont remember) it stopped working now ,when i push the ON button it wont turn on, i can see the screen lighting up for a half second and after that it stops completely.
i suspected these components atmega328, HT 7550,TL431,and maybe also the s9012 and s9014 but im not electronician skilled i ve already checked all the connections of the board they are OK.
so i need a support from the masters here in order to help me repairing it i ve uploader a picture , and a shematic of the device .thanks in advance.

 

[Nigel Goodwin]

For a start check the voltages on IC2 (HT7550), should be 0V on all pins until you try and turn it ON, then it should be 9V going in and 5V coming out.

 

[vari21]

thanks nigel for quick responce ,i ve desoldered all ht550,tl431 ,s9012,s9014 to test them with my multimeter out of the board because i suspeted them, sorry to not mention this detail ,i broke the ht7550 when i took it out of the board it has legs now.
please nigel what is the right equivalent of it? i could nt find it on the net.

 

[Nigel Goodwin]

Randomly testing components is a VERY poor way to try and repair something, and rarely ends well - the HT7550 and TL341 can't be easily tested on a meter anyway - but are absolutely trivial to test in-circuit, with a voltmeter.

The HT7550 is a small 5V regulator, a 78L05 would do as a replacement, BUT it's pin connections are slightly different, and you'd have to orient it correctly.

 

[unclejed613]

i ve desoldered all ht550,tl431 ,s9012,s9014 to test them with my multimeter out of the board because i suspeted them

in most cases, reversed power supply rails usually damage the first semiconductor they come to, in this case the regulator. if this board were unregulated, then it might be possible for reverse voltage to damage a chip, but it's usually only one of them, because the short circuit clamps the voltage after that.

 

[vari21]

That wht i desoldered all semiconductors to replace them with new fresh parts , i ve ordered a new atmega 328 ,
i ve got another questions if you dont mind i need also to repplace the following transistors just to be sure.
TL431 with ??? i dont have any idea
S9012 with bc548 maybe
,9014 with 2N2222 maybe what do you think ?

 

[Nigel Goodwin]

That wht i desoldered all semiconductors to replace them with new fresh parts , i ve ordered a new atmega 328 ,

Have you ordered one correctly pre-programmed with the required software?, a blank one won't do you any good unless you've got a programmer and the required file to program it with.

As I mentioned earlier, blindly removing, 'testing', and replacing components isn't a good way of repairing things. Simply measuring the 5V output of the regulator IC2 would have eliminated most of the possible affected parts, and 'properly' tested them at the same time.

i ve got another questions if you dont mind i need also to repplace the following transistors just to be sure.
TL431 with ??? i dont have any idea

It's NOT a transistor, it's an IC ( a precision voltage reference), and it's a standard freely available part - either refit the original one, or out a new TL431.

S9012 with bc548 maybe
,9014 with 2N2222 maybe what do you think ?

Just standard little NPN and PNP transistors like BC337 and BC327, or BC547 and BC557 would be fine, as will almost anything really. You just need to be aware of the pin layouts, which may be different.