Problems with MidiBox FM

MIDIbox FM
1

I am an electronic novice and finally found time to build a MidiBox

Core and FM board and currently have/had the following problems:

Latest Galep 4 eprommer always ors the id-bytes with 0xF0. I fixed this by

initializing the display myself and using device id 0x70 for uploads.

In the Eagle board of the FM from your website there is no connection

from C4/DAC1 VSS to ground.

I built a PSU (powered from a 14V AC transformer) with +12/-12V

outputs and connect a +12V output to the Core power-supply input (and

the FM). With display (Displaytech C162 with backlight) this draws

about 90mA, but the 7805 on the Core (with heatsink) gets very hot

after a while. It seems that the display gets somehow confused (and

damaged) when the 7805 gets hot. There is garbage on the screen. Very

strange..

Finally, most of the time there is no sound coming out of the FM board

when I send notes, using the default patch, although I already heard

an istrument a few times! So it seems to work “basically”.

Maybe someone had similar problems already.

Is it possible that there is a problem multiplexing the display

and the FM over the same port pins?

Could there be a timing problem in the OPL waits (and writes)?

The processor is a PIC18F462, clocked from HS/PLL from a 10 MHz Osc.

I have not connected any digital or anaolg inputs yet.

There is a picture of my boards at

http://www.rainer-keuchel.de/midiboxfm1.jpg

2

Hi Rainer,

I built a PSU (powered from a 14V AC transformer) with +12/-12V

outputs and connect a +12V output to the Core power-supply input (and

the FM). With display (Displaytech C162 with backlight) this draws

about 90mA, but the 7805 on the Core (with heatsink) gets very hot

after a while. It seems that the display gets somehow confused (and

damaged) when the 7805 gets hot. There is garbage on the screen. Very

strange..

the input voltage to the 7805 is too high, the recommented voltage range is between 7V and 10V…

But you are right, it’s strange that the 7805 gets hot with such a low power consumption, could it be that there is a short circuit at one of your boards? What is the total current draw?

Finally, most of the time there is no sound coming out of the FM board

when I send notes, using the default patch, although I already heard

an istrument a few times! So it seems to work “basically”.

Like for the LCD this could be a side effect which is caused by the overheaded 7805.

Is it possible that there is a problem multiplexing the display

and the FM over the same port pins?

Could there be a timing problem in the OPL waits (and writes)?

no

I would suggest to try the circuit with a second power supply which delivers a lower voltage for Core:J1. If this works better, you know where to “debug” (the cheapest solution is the use of a 7809 between the 12V supply and the 7805 input)

Another potential problem that I saw at your pictures is, that you propably forgot to mount R2 of the core module?

Best Regards, Thorsten.

3

Current draw of Core is normally 90mA, although I have seen it go up to 100mA

and pulled the plug.

I will try another power supply and check if R2 is there..

4

Also look at the 3rd post here, http://69.56.171.55/~midibox/forum/index.php?topic=5083.0

I already saw new 7812 that were working bad, so maybe the same thing is happening with your 7805, trying a new one from a different brand(Just to be sure it doesn’t happen an otehr time) would maybe solve the problem if nothing else works.