Hello people

Anything at least distantly related to MegaDrum

Re: Hello people

Postby Aaron » Sat Nov 17, 2007 12:15 pm

does this device have a pre-out (bypasses the amplifier) if so try it.

it could be something like a faulty amplifier ic.

but i wouldnt expect an amp ic to lockup the unit, but its possible .
Aaron
 
Posts: 34
Joined: Tue Oct 30, 2007 1:48 am
Location: Melbourne, Australia

Re: Hello people

Postby baguette » Sat Nov 17, 2007 12:43 pm

i listened the audio again and it reminds me a lot to something i experienced with burned audio cds: after several years they ACBed the same way! so actually i think it is more likely a problem in the digital data path (some kind of "data loss")
It could be however a voltage problem - check the D-A converter! seems to be the IC with the white alesis sticker besides voltage regulation. see below what component it actually is!
baguette
 
Posts: 19
Joined: Thu Nov 01, 2007 11:22 am

Re: Hello people

Postby Goldie » Sat Nov 17, 2007 2:46 pm

I measured voltage regulators as you told me, directly on pins with steady hand :D . They are named 7805 (left one) and 7905 (right one).

Pin 1 (red) and 2 (black) on 7805 = 24,5v
Pin 2 (black) and 3 (red) on 7805 = 10,3

Pin 1 (black) and 2 (red) on 7905 = 0.00v
Pin 2 (black) and 3 (red) on 7905 = 0.00v

Pin 1 (red) and 2 (black) on 7905 = 28,8v
Pin 2 (black) and 3 (red) on 7905 = 17,6v

Those colors are pins on my multimeter. Black is connected to COM, red is connected to V. Multimeter is switched to 200v ACV.
Goldie
 
Posts: 60
Joined: Mon Nov 12, 2007 5:04 pm

Re: Hello people

Postby Goldie » Sat Nov 17, 2007 7:12 pm

Ok here is the news.

Working configuration - only pcb with headphones and volume connected

It worked 4-5 hours out of box - no problem at all. As soon i put it all together it crashed after 5 minutes. I measured and only thing that changed is:

Pin 1 (red) and 2 (black) on 7805 = 22,2v - 2,3v drop

Ok, i'm optimistic now :shock: I'll try now to see if anything gets hot, which i doubt.
Goldie
 
Posts: 60
Joined: Mon Nov 12, 2007 5:04 pm

Re: Hello people

Postby Goldie » Sat Nov 17, 2007 7:26 pm

Voltage regulator 7905 gets hot, 7805 doesn't.
Goldie
 
Posts: 60
Joined: Mon Nov 12, 2007 5:04 pm

Re: Hello people

Postby baguette » Sat Nov 17, 2007 8:35 pm

you must set the voltmeter to DC if you measure at the voltage regulators. They output direct current ( as opposed to AC (alternate current) which changes polarity at 50 hz)

I think the power supply unit (which you plug in the outlet) outputs AC and the two diodes on the board make it to dc, the one to positive dc and the other to negative dc. This means that everything after the diodes must be measured in DC. I think the voltages you measured don't mean a thing, sorry.

By the way it is normal that voltage regulators get hot. It might also be normal that the positive gets hotter than the negative because the positive supplies analog and digital part of the circuit while the negative supplies only the analogue part (amplifier).

Measure DC again and post the results.

By the way, could it be that ther is a sort of mechanical shortcut once it is in the box? it seems strange that it overheats that fast inside, and not at all outside. Maybe it leaks current when assembled which will make go some component down.
baguette
 
Posts: 19
Joined: Thu Nov 01, 2007 11:22 am

Re: Hello people

Postby Goldie » Sat Nov 17, 2007 8:42 pm

You my hero baquette 8-)

10,16v 5,00v
-13,30v -5,02v

Does this make any sense?

I've checked pcb is not touching case, i'll check some more for shortcuts.
Goldie
 
Posts: 60
Joined: Mon Nov 12, 2007 5:04 pm

Re: Hello people

Postby Aaron » Sun Nov 18, 2007 1:34 pm

what are the outputs specified on the adapter?
Aaron
 
Posts: 34
Joined: Tue Oct 30, 2007 1:48 am
Location: Melbourne, Australia

Re: Hello people

Postby Goldie » Sun Nov 18, 2007 1:48 pm

Hi drummers.

Citat from Alesis homepage: "Both of these are AC transformers with an output of 10 volts AC, 7.5 VA current capacity."

Mine is 9V - 7VA but i assume its same model as one above. They only have 3 models P2, P3, P4 models. Mine should be P3.

http://www.alesis.com/support/faqs/general_power.html
Goldie
 
Posts: 60
Joined: Mon Nov 12, 2007 5:04 pm

Re: Hello people

Postby baguette » Sun Nov 18, 2007 10:12 pm

Goldie wrote:You my hero baquette 8-)

10,16v 5,00v
-13,30v -5,02v

Does this make any sense?

I've checked pcb is not touching case, i'll check some more for shortcuts.


these are good values, at least the output values: The voltage regulators are specified for +5 and -5 volts output and they seem to do their job.
Do they do the same when the board is ACBing? i mean in the very same moment, i.e. run it in the box until it crashes and then measure immediately.

However, it might also be possible for instance that the output voltage is fluctuating lets say between 4 and 5 volts in a "high" frequency, i.e. 50 Hz (60 in the states i think), producing digital headache. In this case you don't now how the voltmeter reacts, if it measures the mean value over the time (which would be 4.5 volt) or something else - by the way this it what happens for the input voltages. They are somewhat "wavy" and the regulators shall stabilize the waves, at a lower voltage level. Therefore, it is not perfectly clear what your measurements mean at this side.

Try to have a look at the A/D converter, what is below the sticker? if you can make out a standard component we can maybe have a look at it.

Concerning the power supply - if you have one that gives 9v ac but should be 10v, it is possible that it is causing trouble. In particular it could cause wavieness of the regulated voltage (5V). In this case it is not obvious why it should make a difference between in-box and off-box but you never know...
It is even very likely that 9V AC are not enough to produce stable +5V and -5V : together they are 10V :) The exact calculation is a bit different but you must also take into account that there must be 1.4 volt dropout between input and output of a voltage regulator to work properly.

If you have another AC supply handy, you could try it. Even if the output is more than 10V, the reguators are designed to handle up to 30V input voltage (but will produce more heat - it's a weird game ;) ).
baguette
 
Posts: 19
Joined: Thu Nov 01, 2007 11:22 am

PreviousNext

Return to Off topic

Who is online

Users browsing this forum: Google [Bot] and 7 guests