HELP, I KILLED MY PEDAL!!!

[Jon MY]

Hi
i built a ts808 clone from the ggg site and it worked fine until i stupidly plugged into a positive ground adapter and now it doesn't work 
Anyways what do i need to replace to get it working again.

Thanks Much Jon

[Meanderthal]

 Start with d5, c12, and c7, see if that does it...

[Jon MY]

Thanks but there is no d5 on the layout
and i did add a diode for d3 in the same direction as d1 if that matters

i really don't know much about electronics so thanks for the help

[Meanderthal]

 Aw, jeeze, I was looking at the schematic...

http://www.generalguitargadgets.com/pdf/ggg_its8_sc.pdf

The protection diode isn't on the layout... oops. Try c7 first anyway, then the chip ,then q1, then q2, in that order. Or replace the cap first, then check and post your voltages as per the "What to do when it dosen't work" thread.

[ubersam]

Pop in a new opamp. I reverse powered a TS circuit once and the only thing that got killed was the opamp. Granted, the circuit wasn't reverse powered too long.

[MikeH]

And do yourself a favor, and add a protection diode when you get it working again.

[R.G.]

A good thing to do is to set your mind to expecting to replace every polarized part on the board. That way you won't be piecemealing the parts orders and you're more likely to get a working device back.

And do put some kind of protection into the next version. It helps a lot in preventing instant death for pedals.

[Izzy]

@ R.G Keen
If we put some silicon diode between +9 V and ground in opposite direction that should help to prevent such problems, right?

[darron]

@ R.G Keen
If we put some silicon diode between +9 V and ground in opposite direction that should help to prevent such problems, right?

that acts like a fuse right and becomes the first thing to fry? the other way might be to use a schottky diode running in series with the power input. that stops all problems but drops the voltage a tiny bit, thus changing the tone i suppose. i'd be really interested in reading a thread on this to learn more...

congratulations on building a ts808 clone as your first project Jon!

[Cliff Schecht]

The diode shouldn't fry if you don't keep the power on too long, but even if it does, it's a much easier part to replace than the electrolytics, opamps and trannies.

[gez]

Headroom isn't really an issue as the signal is being pretty much clamped in the TS, so better to use a series diode, not one across the rails...unless you use that polyswitch idea Paul linked to once. 

[ubersam]

The diode shouldn't fry if you don't keep the power on too long, but even if it does, it's a much easier part to replace than the electrolytics, opamps and trannies.

Just paraphrasing what someone else told me: the reveresed diode accross the dc supply input works by shunting the incoming current to "ground", until the diode burns out, and when it does, there will no longer be any protection. The diode in series with the dc input seems like a better approach.  I just built the BSIAB2 and used a 1N914 (or was is a 1N4148?) because I did not have a schottky. The voltage drop was under half a volt, around 300-350mV. Not a big deal for me since my power supply puts out about 9.5V. A schottky diode supposedly drops the least amount of voltage, making it a better choice for the task.

[Processaurus]

I've used these schottky diodes for series polarity protection in the pedals I've made since steve started carrying them.  If I remember right they drop about .3v

[Rafa]

Try c7 first anyway

I thought caps where difficult to burn
Cheers
Rafa

[Cliff Schecht]

Try c7 first anyway

I thought caps where difficult to burn
Cheers
Rafa

Electrolytics (C7 is a 47uF one) will pop if you wire them backwards.

[R.G.]

There is a fair amount of discussion of polarity protection circuits at GEO (http://www.geofex.com).
The simple ones are not too good, the good ones are not all that simple. Shunt reverse biased diodes are easy and cheap, but they can burn out under prolonged reversals. Series diodes work perfectly, but subtract a diode drop from the power supply voltage all the time.

The MOSFET polarity protector is an "active diode" formed from a MOSFET, and provides the protection of a series diode, but only drops 10mV to 50mV from the power supply. But it costs you $0.50 for a MOSFET and a resistor instead of $0.05 for a diode.

There are other schemes as well.

Probably the most used is the shunt reverse biased diode.

[darron]

thanks R.G. (:

[Jon MY]

Hi
I want to thank everyone for their suggestions and help.
as of now it is still not working but i did replace c7 as was suggested and will measure the voltages.

my question for now is what components should i check?
GGG has a list of what the voltages should be for the ic, q1, and q2 but what else should i check?

Anyways
Thanks Much
Jon

[Meanderthal]

Check/ replace the other electrolytics too.

[Jon MY]

Check/ replace the other electrolytics too.

well i have been checking for continuity and the other electrolytics (c7 c12) are responding.
also i am not getting any response in continuity for c8 and maybe c10

jon