GFS Brownie overdrive pedal

[Gunn_Slinger]

Hi guys. Have an old gfs brownie pedal. Not used for a few years.
Plugged it in and smelled burning. Took it apart. Found a burnt part..
( resister or diode...cant tell. Posting pics. Can anyone tell what part it is
and what to replace it with? Thanks.
ps the 9v supply was bad.

[eschertron]

A clean-looking board, to be sure! If you suspect that the PS caused the component to fail, look to see where that is in relation to the power jack. It looks like a diode to me, and I'd think it was there as a reverse-voltage-protection scheme. Closer inspection might reveal its likely function, and from that, its likely design specification. Maybe.

[Gunn_Slinger]

Thanks. In the pic that shows the top of the board, you can see on the top right the part that is burned up. Can't make out any writing so don't know what it is. I'm going to take it out but doubt I can get any info on it. It comes off the power input jack.

[alexradium]

that is a protection diode,in parallel with the main supply,its burnt because a reverse polarity or AC supply was applied to the pedal.
Usually its a 1N400x diode,cathode to positive voltage and anode to ground.
That's a bad way to protect a circuit,in fact its easy that after the diode went south,the IC gets fried too,and the filter caps can be damaged.

[eschertron]

It's nice that the IC is socketed.

[g1]

Are you 100% sure it was the right power supply?
If not, it could be a protection diode that fried, then in turn fried the supply.

[Gunn_Slinger]

I smelled it burn, yanked the AC adapter. When I took it apart that was the only part that looked damaged. I'll put a new one in if I know what it is and fire it up with my one spot.
Alex thinks its a 1N400x diode,cathode to positive voltage and anode to ground. If so, I will get one and see what happens. I watched a utybe vid on how to test the chips, but it has to be powered .

[eschertron]

IIRC the diode works in 'protection mode' to dump (short out) a reverse voltage condition to prevent those reverse voltages from reaching sensitive components. If the 1A (or thereabouts) current limit of the diode is exceeded, it burns and no longer acts to protect the circuit. So if we are sure that the right voltage and polarity are applied to the circuit - say by using a 9VDC cell on the handy connector - we don't need that diode. It only 'works' when it is trying to save the device. You may find that the unit is OK, or at least find out what else is suspect, before sourcing repair parts.

[Helmholtz]

that is a protection diode,in parallel with the main supply,its burnt because a reverse polarity or AC supply was applied to the pedal.
Usually its a 1N400x diode,cathode to positive voltage and anode to ground.
That's a bad way to protect a circuit,in fact its easy that after the diode went south,the IC gets fried too,and the filter caps can be damaged.

In the vast majority of cases the protection diode junction fuses and leaves the diode in short-circuit fault. This condition protects the rest of the circuit but may damage the power-supply.

[Gunn_Slinger]

Not sure, but I won't be using that power supply again. I have a good one spot. Was just to lazy to pull it out of its storage box.

[Gunn_Slinger]

So, what does everyone think....am I safe replacing it with the one Alex suggested?
The 1N400x diode,cathode to positive voltage and anode to ground ?
And, where would be the best place to find that part?
Thanks guys
Clay
ps
I looked at these diodes . What voltage ( 50v, 100v, 400v )
would be right?
Thanks

[Enzo]

Some shunting diodes are common and wired reverse bias in case wrong polarity power is applied. But other shunting diodes are zeners, say a 10v zener where a 9v supply is expected, like that. Seems to me Boss does that.

[alexradium]

So, what does everyone think....am I safe replacing it with the one Alex suggested?
The 1N400x diode,cathode to positive voltage and anode to ground ?
And, where would be the best place to find that part?
Thanks guys
Clay
ps
I looked at these diodes . What voltage ( 50v, 100v, 400v )
would be right?
Thanks

any 1N4007 will do,but the circuit works the same with or without it,you have to check out if everything works,but i bet that ic is damaged.
Boss pedals had a little resistor in series before the diode,when the diode went short,the high current burned the resistor,opening the circuit so it was finally safe.
Today we have only gurus that know how to sell garbage at premium price.

[alexradium]

this is a Rat clone with a clipping switch.

[eschertron]

this is a Rat clone with a clipping switch.

Too bad we can't see the printing on that diode
But a diode to be sure. As was said, if it (successfully?) protected the rest of the circuit, removing it will not hurt the box's intended function. You should be able to test whether it is open or short. If, as Helmholtz suggests, it failed short then it would have protected the box at the expense of the power adapter. Remove the burnt diode and try it.