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Odd test tone output


Etaoin
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I built the OPL3 board yesterday and am running into some odd output.

I wanted to post this to see if anyone had this before and whether this was an indication of a dead YMF262.

 

Attached is the output of the test tone program.  First sound it produces when booting MIOS, second comes straight after when starting the test tone program.  It's good funky 80's computer sound, but not the test tone it should produce...

 

 

Notes:

 

I forgot to turn on the ground plane in Eagle and only after drilling did I realize that that also leaves out a couple of traces.  I added those (two I think are missing).  But I don't think the missing ground plane can cause this anyway.  I didn't fancy etching another one.

 

I use UV photo boards so the traces are as crisp as they get.  As I'm getting clean audio, the analog part is probably ok as well.

 

I've "beeped out" the connections to the SMD chips from the pin on the chip to the other end of the trace.  Those should be ok.  I doubt I overheated the chips, although even with over 25 years in DIY and good tools one can never be sure.

 

With the Midibox FM firmware, I do get the startup note, but it is heavily distorted (digital distortion).  That might just be a bad patch though.  Like someone else posted recently, I also have the problem that Midistudio can't write the flash-part of the firmware, so it will probably leave random data as default patch.

 

mbfm_testtone.mp3

Edited by Etaoin
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If you actually don't have a ground plane than it's a surprise anything works at all as all the ground connections would be missing.

 

Essentially to me your post reads: "I might be missing a few traces also the firmware is probably not installed correctly - what could be the problem?". My guess is - you're missing some traces and the firmware isn't installed correctly. How about you fix and validate those two things - in that order?

 

A missing data line between the pic and the opl might cause sonically interesting effects as the parameters never get "fully" or "correctly" set. If the software is broken in random places it may also lead to interesting effects. Really hard to tell what exactly the problem is with so many options :-)

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Obviously it wouldn't work without ground lol   :smile:  but ground on the OPL3 board doesn't need the ground plane.

If you open the board in Eagle without the ground plane, you'll see there is also an almost complete ground trace, which is incorporated in the ground plane.  So for most of the ground connections, the ground plane isn't actually needed for the connection.  That's exactly why I decided I wouldn't etch a new board.  I wouldn't have gone on if all ground connections were missing, obviously...  Where a connection was missing (in two places) I added it.

 

Secondly, the test tone firmware is loading and running fine, and the mp3 is from that one.

 

So no, I'm not missing ground and the firmware is loading fine.

 

 

With the FM firmware (and only with that one) I have exactly the same problem as described here: 

So what I meant was that it can't write the 256 EEPROM bytes.  There are no errors in uploading the firmware itself, which runs fine and responds to midi and patch changes as it should.  As mentioned in that thread, that error would only affect the default patch.

 

 

My question, which started my post, was if this output was typical for a dead YMF?  Because if it is, I can probably stop looking for something else.

Edited by Etaoin
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