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IC3 leaking overvoltage?


psxc
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Hello!

 

I have built a working sammichFM and rechecked all soldering points and linkages many many times (first solderings didn't work correclty). The device operates without a problem but there are two things that worry me:

 

a) the output 1/2 has a distorted and very high volume on the other channel, the other one is normal, output 3/4 is normal as well. The volume for the one "faulty" channel is so high that when I play multiple notes, the sound is distorted.

 

I have rechecked and resoldered all the resistors and capacitors in the two "blocks" that lead up to the output 1/2 and checked the IC contact cleanlines with an usb microscope and I can't find any bridges. The soldering points are clean and fused between the legs and the board

 

b) when measuring voltage for the IC3, it is not 5V but 6V!

 

When I first soldered it together long time ago and tested the voltages, i accidentally touched wrong contacts which caused sparking. I think the connection was between the leg connected directly to C5 capacitor and the leg connected to C3 large capacitor plus leg. I can't remember anymore exactly...

 

I have a very simple velleman multimeter. Is there a way to diagnose easily which part is probably damaged and should be replaced? Is 1V overvoltage for the IC's dangerous in the long term (i would assume it is)?

 

My PSU is linear regulated 9V 800mA.

 

Anyone able to give me hint for solving these two problems? Thank you! :rolleyes:

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IC3 is the 78L05 power regulator. If you measure 6V on the output leg (the leg nearest to the power connector) then there is something wrong. I would double check all the components in that area for correct placement (C3, C5, IC3, X1)

 

If everything is placed correct and you say you have seen magic sparkles, then you probably short circuited something. My recommendation is to replace the 78L05.

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  • 2 weeks later...

I did the following checkups:

 

1) replaced IC3 with a new 78L05, and C3, C5, C62, C64, and C65 with new 10, 100 and 2200 uF high quality capacitors which are 50V 105C rated and low ESR

2) used a new regulated psu (9V 700mA)

3) checked the following audio 5V points: C52, C53, C54, C55, R58, R62, IC51, IC52, IC53, IC54, IC3, and the following opl 5V points: IC50, C51, C50, Q50

 

All the audio and opl 5v are showing 5V within +-0,02V, almost all of them are showing 5,00V

 

Still after all these changes the following problems persist:

 

Audio output 1 = completely mute

Audio output 2 = very loud but not distorted anymore

Audio output 3/4 = both work but 3 is *slightly* louder

 

I tested the outputs individually in the ensemble mode.

 

I have not checked the X1.

 

What could i do next to debug this odd problem with my multimeter? Could the unbalanced output problem lie with OPA4348 or perhaps with YAC512? Perhaps the opamp is damaged and it will not amplify one of the outputs? Or the d/a converter? Is there a way to debug either of these chips with only a multimeter? I have spare YAC512's and I'm guessing the opamps are quite easy to get as well.

 

I have also been thinking about updating the firmware (perhaps the mios and fm app are somehow a little messed up from the overvoltage). I have searched the forums through for firmware update and reset instructions as well as the ucapps wiki, but have not unfortunately found any clear indication of how to do this... Also I have browser the Wilba build guide through but there was only information on the first time flashing, not reflashing.

 

I think it would benefit us newbies a lot if someone with write access to the dokuwiki would write a simple beginners guide to updating the firmware (I can do it as well as soon as i know how :smile: ). Also this could be added to the sammichFM wiki page as a new good quality regulated psu: Nordic Power R4W090-070G. It produces very stable output.

 

I would like to know how to reset the sammichFM (there doesn't seem to be a jumper to do this?), and how to set it into receiving mode for updating the fw with mios studio. Whenever i boot sammichFM up and try to send a program, it does not accept it.

 

Thanks for any help on these two issues :rolleyes:

Edited by psxc
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I would love to give more suggestions. However i have to give credit to some people complaining about off-site docu being bad. Wilba's mb6582.org domain seems to be offline. Leaving all the documentation for mb6582, sammichsid and sammichfm unavailable :sad: .

 

Looking at the datasheet for the YAC512 it has a Max supply voltage of 7V. However the OPA4348 has a Max supply voltage of 5.5V. So my main suspect would be the OPA4348. It could very well be that it has been damaged. Replacing it won't be easy as it is a SMD component. If anyone has some other suggestions be my guest.

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