hi, i recently built a core module which does nothing on start up, the voltage seems to be right in all places, the pic was preburned with mios v1.9c, but when i turn the power on all that happens is the backlight switches on, i get nothing over midi and no characters on screen.
i’m a newbie when it comes to this stuff, so i’m not really sure what to do, i did notice that apart from the lcd backlight turning on, IC3 (7805?) and the back of the lcd gets very hot
The regulator shouldn’t get hot with just the LCD and core.. If you remove the LCD just for now, then you can narrow the problem down to something wrong with the core or PSU. What are you powering it with?
so are there no components that i could replace to solve it,or should i just start again and build another one?
also after buying a new multimeter rather tahn using the one i was (which is quite probably older than me), it seems that the voltage is actually around about 1.7 where it should be 5v…
Sounds to me like your 7805 is broken. solder it out and check the incoming voltage. Should be between 7V and 10V. (In the case your using a 9V psu its surely 9V). then solder a new 7805 in your core and measure for shorts. no shorts ==> test again
yeah it was as the pictures are, and i have just tried switching it round to the opposite of the pictures, with exactly the same results, (1.6v where there’s meant to be 5v…)
Should be enough, but with a backlighted lcd 9V is the better choice I think.
when the PSU can deliver 7.5V, there´s no reason to use 9V. You´d just get even more heat on the regulator.
But you should measure the current that is drawn from the PSU. If your LCD gets hot, I suppose the backlight just draws so much current that the PSU can´t keep up the 7.5 V. There are LCDs where the backlight can draw more than 500mA when adjusted to max. Either the backlight is turned fully up or you´ve got a soldering error around the backlight pot. Is the backlight extremely bright? can you adjust the brightness? You could disconnect just the backlight and find out if the core boots up without it.
BTW, broken caps are extremely rare. The chances that exchanging caps or resistors brings any good are perhaps 1%. First again double and tripple check for shorts on the whole module.
well i changed a capacitor (c5 2200uF) for a new one and removed the lcd, now there is slightly under 5v (4.6v) where there should be 5, and when powered the module sends out several hundred 1 or 2 byte sysex messages (they seem to all be 00 0F or 00 0F 00), with the occasional clock, stop and active sense message over midi according to midi monitor…
4.6V is still too low - this Midi nonsense shows that the PIC is continuously resetting itself. I suppose the regulator still gets hot (even without display)? Again: please measure the current, i.e. disconnect one side of the supply wire coming from the PSU and put your multimeter inbetween in mA mode. another test: Disconnect core, pull out the PIC and the optocoupler, then measure the resistance between Vdd and Vss (e.g. PIC socket pin 31 and 32 or between the legs of the 2200uF capacitor). You´ve most definitely got a short somewhere. Use a magnifying glass and carefully inspect all solder joints.
If you´ve got a decent digital camera, perhaps it would be an idea to post hi-res closeup pics of bottom and top of your board.
the regulator does not get hot anymore, and after adding solder to some joints i got 4.7 and after changing the psu voltage to ‘6v’ (it sends out 9.6v at this, it sent out 7.5v before when set to an even lower voltage, i think the potentiometer on it must be misaligned) i now get 4.99v across vs/vd, on power i get 8 sysex bytes: F0 00 00 7E 40 00 01 F7 …which is a good startup unless i’m mistaken, so now should i try reconnecting the lcd?
I bought a 7.5V 1000mA wall adapter for the MIDIBOX, what´s supposed to be more than OK.
It measures 9.5V when not connected to the MIDIBOX, but 6.5V when connected.
It makes MIDIBOX run when no LCD connected, but when I connect the LCD nothing shows up in the LCD, and I have no SysEx commands sent.
When I measure Voltages in the Core module I see that once the LCD is connected the voltage drops below 4.6V. So, I suppose this Wall adapter does not deliver what it says it does..
I´m using the MIDIBOX with another WA without problem.
Again: please measure the current, i.e. disconnect one side of the supply wire coming from the PSU and put your multimeter inbetween in mA mode.
The current measured is 260 mA. That´s a shitty PSU, isn´t it?. It was supposed to deliver 1A!!! All other things taken into account, could this be your case?
The current measured is 260 mA. That´s a shitty PSU, isn´t it?. It was supposed to deliver 1A!!! All other things taken into account, could this be your case?
That’s ok. Your powersupply can deliver max. 1A . The 260mA is the amount of current your Midibox “soaks” out of the powersupply. If you soak 1A your PSU will deliver 1A.
Go for it