Audio-OPL3 5V check problem

MIDIbox FM
1

Hello,

I just finished both boards on the sammichFM. there seem to be no shorts. the initial tests like testing IC3 ground leg to the other leg marked with orange is 4,98V. I’m using a 9V 800mA psu which the seller said was linear and not switchmode.

But when i put jumpers in the audio and opl3 pins (horizontally) and measure between the orange and blue spots marked in the guide, i get 0,07V instead of 5V. (velleman dvm850bl multimeter set to DC 2v shows 0,07). For example i’ve tested the upper left leg of the opl3 chip against the orange contact points of the IC62 and IC61.

In addition to having audio and opl3 jumpers in i have connected the jm0 and jm1 jumpers to the spaces indicated with white blocks. I don’t have any other jumpers attached (what are the JPB jumpers for, guide says nothing?).

Where should i start debugging? I have checked all the solder spots with a loupe that they look ok.

Can it be that i’ve heated some component too much and it doesn’t not give enough voltage? I’ve tried to avoid giving too much heat to the components. I’m not an expert in soldering but i think i managed to solder the SMD:s pretty well (with no bridges).

The only problem I had was when I was soldering C62 I accidentally picked the 100uF capacitor instead of 10 and had to desolder it and heated the board a bit too much. The thin metallic ring on the backside of the board came partially(?) off when i tried desoldering it with wick. I’ve tested now that the C62 + leg has connection to IC51 leftmost upper leg, and C62 - has connection to ground and the + and - don’t short.

I’ve also checked the resistors (the manual was hard to read because the red stripes looked more like orangish/brownish and it was hard to distinguish them).

Could someone give me a hint in where to debug or what to do next?

Here are pictures for closer inspection on the back:

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post-9632-0-68848300-1326988361.jpeg
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post-9632-0-95511200-1326988392.jpeg
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post-9632-0-81155500-1326988403.jpeg
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and frontside:

post-9632-0-29191200-1326988428.jpeg
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post-9632-0-22671600-1326988438.jpeg
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post-9632-0-92205800-1326988444.jpeg
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post-9632-0-47537600-1326988453.jpeg
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post-9632-0-87190800-1326988666.jpeg
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post-9632-0-45815800-1326988676.jpeg
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post-9632-0-16175300-1326988690.jpeg
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I would be very happy for any help! Also as I’m a beginner i might have forgotten to tell something important or relevant in this post, i’ll be happy to give any extra information needed.

(Ps. How to get rid of the flux? I’ve tried isopropyl alcohol but it just seems to smear the flux all around rather than remove it.)

2

I had a similar problem with my sammichSID. Go back and check /every/ solder joint. It’s a painful process but it helps. In my case, I had a cold solder joint that I couldn’t see with the naked eye. I had to test it by cutting tracks (not so fun). As a result, you could also try to simply reflow solder over some joints.

These issues can be problematic to troubleshoot. If the trace you over-heated (and it’s component) are still functional, it’s probably not that. I don’t think you could have over-heated the SMD chips either as long as you used proper techniques for soldering them (letting them cool sufficiently between soldering, etc.).

3

I went through almost every joint now and they all seem ok so far (i’ve tested by connecting the multimeter to the actual component leg and a spot elsewhere on the pcb to see if the solder has formed a joint).

But the curious thing is:

when i have the audio 5v and opl3 5v jumpers connected, any orange and blue dot connected give 0,066v

but when i have the jumpers removed, the voltage between orange and blue dots is 0,86v

4

Hi psxc,

Giving a look to the pictures it seems to me you have cold soldering and some other are poor of solder tin.

My suggestion is to resolder them and an enrichment of tin.

Bad soldering can give strange things on power too as you say about the 5v

Regards

Antix

5

Hello again. I misunderstood the manual, i thought it said “measure between orange and blue dots” and not orange+ground, blue+ground.

I resoldered the bad solder joints and everything worked right on the first boot, no errors on firmware uploading etc. all audio outputs and everything seems to work properly.

Now i’m happily playing with the sammichFM :slight_smile:

the only thing that worries me is the solder flux that came with the kit. is it “no clean flux” so can i just leave it or should i clean it away? will it corrode the pcbs?