oops

[PKV]

I have a DOD 512 effects unit. It has the usual 9V DC jack. Unfortunately, the adapter I was using allows you to change the polarity of the input voltage, and I had it set incorrectly. How far gone do we think the unit is? Its indicator LED's flash when power is applied, but there's no signal at all...any ideas?

[fixr1984]

Check for a bad diode. Hopefully there was a reverse polarity
diode and It saved the rest of the circuit.....

[petemoore]

  I read up on the reviews at HC, I get the idea this is a digital unit.
  If your'e not used to debugging, there is probably a diode near or directly attached where the power supply comes in, a reverse polarity protection diode.
  I know of 3 ways these can be wired.
  one is right across the V+/- rails.
  another is 'across the rails' but with the + side having a small resistor [like ~100ohm] between V+ and the rest of the board / diode.
  the third is series in the V+ line.
  Perhaps, Ive never seen it but seems possible, that the LED circuit comes before the protection diode and therefore still works when the diode goes.
  or...the diode went and the LED withstood the reverse voltage.
  Once you start into chip/polarized component debugging...for digital, I'm off the wagon.

[PKV]

yeah, it's a digital unit. I located the diodes right where you said they'd be, and they seem to be fine - I have a tiny micronta DMM that has a diode check option; there seems to be life there. Would it make any sense to plug the thing in (observing proper polarity of course) and checking for voltage around the board? if it turns into replacing the IC's I'm not sure it will end up being worth it, and I currently have no idea how to test those things otherwise.

thanks for the replies

[O]

Did you check the diodes while in the circuit? You have to unsolder one end and THEN test them.

[PKV]

Did you check the diodes while in the circuit? You have to unsolder one end and THEN test them.

thanks O, and no I did not know that. I feel like I'm getting closer to using the thing for parts. Even if I can check the diodes properly, there's no guarantee I'll be able to effect any repairs...do the diodes need power to be tested?

[PKV]

Please also bear in mind I have little to no experience in circuit construction/theory, though I understand many of the concepts

[petemoore]

  I remember getting beep one way, not the other on diode used as Reverse Polarity Protector [between V+/-], that means good diode. [?
  Not sure what kind of chips/what kind of voltages to look for where...you could follow from the PS rails and see if you can find Gnd and V+ on the chip, then check the voltages there anyway.
  I don't know what chips or whether they're proprietary or if data sheets are avialable for them, data sheet might be a good thing to have if you were to persue this anyway...
  Yeap, even if sockets would fit where the chips are...and you could find the chips...*might not be ttoo badd...
 
 

[PKV]

the datasheets sound like a good idea, thanks - at the very least I'll learn more...