Boss GE-7 will not pass signal

[Ampzone]

New to the forum.  Having a problem with a GE-7 not passing sound, the light does not come on.  The unit was plugged into a 5v AC power supply that outputted only AC.  This may have killed the pedals power supply.  Any ideas on a fix or solution?
Picture of the board I have.

[PRR]

Where power comes to the board, there is a diode and a cap. Replace these. Look in that area for burns.

[R.G.]

Paul is correct. The first thing that AC power into a pedal usually burns out is the shunt polarity protection diode. From there, it depends on how long it was left plugged in and how susceptible that particular circuit is.

If left on long enough, it will generally kill every single susceptible component on the PCB. Worse yet, can well 'semi-kill' many parts. The actual repair is dependent on what your use is. If you make your living with the pedal on stage, you need to do a much more thorough and preemptive repair than if you use it for fun and can stand a series of repairs as successive things (maybe) fail.

There are two variations of the GE7 (at least). A quick look did not turn up a schemo that matches what I think your pedal is. I suspect yours is the newer version.

Look at D2 and the cap beside it first. It's likely that D2 is shorted. Replace that and the big cap next to it. Then apply the right power supply voltage and test for the full power supply voltage between pins 4 and 8 on all three 8-pin DIP packages.

[PRR]

> There are two variations of the GE7 (at least).

Yeah, his pic didn't match the schem I found, so I started with the generic guess.

[Ampzone]

Paul is correct. The first thing that AC power into a pedal usually burns out is the shunt polarity protection diode. From there, it depends on how long it was left plugged in and how susceptible that particular circuit is.

If left on long enough, it will generally kill every single susceptible component on the PCB. Worse yet, can well 'semi-kill' many parts. The actual repair is dependent on what your use is. If you make your living with the pedal on stage, you need to do a much more thorough and preemptive repair than if you use it for fun and can stand a series of repairs as successive things (maybe) fail.

There are two variations of the GE7 (at least). A quick look did not turn up a schemo that matches what I think your pedal is. I suspect yours is the newer version.

Look at D2 and the cap beside it first. It's likely that D2 is shorted. Replace that and the big cap next to it. Then apply the right power supply voltage and test for the full power supply voltage between pins 4 and 8 on all three 8-pin DIP packages.

Hi R.G - Thanks for weighing in.  I have been out with holdiay travel. Now ready to tackle this.  I replaced the diode and cap.  I did not however have the exact part# diode so I used a 1n005 and a 50v 50uf cap.   Still no power.  The 5v AC power was left in for appx 1-2min tops.

[R.G.]

I replaced the diode and cap.  I did not however have the exact part# diode so I used a 1n005 and a 50v 50uf cap.   Still no power.

1N4005 would be fine, as would a 50V cap. So other things are dead.

The 5v AC power was left in for appx 1-2min tops.

Sadly, 1-2 minutes is enough to kill things.

Next two tasks:
- ideally, search and find the schematic for your particular vintage of GE7.

- put 9V on the power inlet and start measuring DC voltages from signal ground to
> the protection diode on the PCB
> pins 4 and 8 of the dual opamps, if that's what they are. OK, before this, read the part number off the DIP packages and make sure they are duals.

If you find the schemo, you can do a better job.

If all else fails, make up a list of all the semiconductors and electro caps and replace them all.

[Ampzone]

Next two tasks:
- ideally, search and find the schematic for your particular vintage of GE7.

- put 9V on the power inlet and start measuring DC voltages from signal ground to
> the protection diode on the PCB
> pins 4 and 8 of the dual opamps, if that's what they are. OK, before this, read the part number off the DIP packages and make sure they are duals.

If you find the schemo, you can do a better job.

If all else fails, make up a list of all the semiconductors and electro caps and replace them all.

Thanks for the info.  Just to make sure the op-amps are the 8pin (the 3 JRC).  I see 4 transistors and three more electro caps I can replace. There are two long black rectangular parts (right side of board in pic) I am not sure if they need replacing.
There is a zener diode D2 and C13 Cap as well? Should those be replaced. Can a 1n005 be used in place of this zener diode D2?
Thanks

[bluebunny]

FYI, I found a mention of "022D JRC 4037" on another audio forum.  Allegedly, they're TL072s, but under a JRC moniker (and apparently the 4037 part is a date code).

[Mike Burgundy]

Blue:
http://www.ti.com/product/tl022
Ampzone: The other monolythic IC's (yes, they are IC's) might be a pain to replace. You may have to make a replacement board to fit in a different package, these may be hard to find.
Zeners are usually well, used for a specific trait they have which will not work with a regular diode (they actlike a diode, conducting one way and not the other, right up to a threshold voltage. Beyond that, they conduct in reverse bias. This lets you clamp a voltage exactly to a zeners threshold - overvoltage spike protection is one use). That said, I don't think passive semiconductors will have been killed.
Edit: Sheesh, what am I saying. The polarity diode will have been killed, and I fear the zener (if that wasn't already part of the protection stuff) may also have died. It's not the voltage that gets you, its the current. I must be only part awake. sorry.

[Ampzone]

Blue:
http://www.ti.com/product/tl022
Ampzone: The other monolythic IC's (yes, they are IC's) might be a pain to replace. You may have to make a replacement board to fit in a different package, these may be hard to find.
Zeners are usually well, used for a specific trait they have which will not work with a regular diode (they actlike a diode, conducting one way and not the other, right up to a threshold voltage. Beyond that, they conduct in reverse bias. This lets you clamp a voltage exactly to a zeners threshold - overvoltage spike protection is one use). That said, I don't think passive semiconductors will have been killed.
Edit: Sheesh, what am I saying. The polarity diode will have been killed, and I fear the zener (if that wasn't already part of the protection stuff) may also have died. It's not the voltage that gets you, its the current. I must be only part awake. sorry.

Hi Mike - Ok so I tested the old polarity diode which I replaced with a new 1n004 without checking it first (stupid). Anyways it reads 270k in one direction and 1.457m and rising in the other direction. I think it may ok.  Using a Fluke 177 meter on the uf setting each electrolytic reads appx the correct uf value. So I am guessing they caps are ok.  So I am not sure what to look for now. 

[bluebunny]

Blue:
http://www.ti.com/product/tl022

Yes, that would make a whole lot more sense!    

[Mike Burgundy]

The electrolytics *will* have sustained damage. They might be ok for now, but they will fail earlier, suffer from leakage and/or increased hum. That's what RG meant with "semi-kill".
RG already gave you the next move - check voltages around the circuit (black lead to ground):
battery+
+ side of protection diode
IC pins etc. For regular duals (which TL022 are) you should be looking at (approximately)
pin1 4.5V
pin2 4.5V
pin3 4.5V
pin4 0V(ground)
pin5 4.5V
pin6 4.5V
pin7 4.5V
pin8 9V

For trannies, it depends on type and application in the circuit. Run through the debug sticky. If you don't know the pinout, check a datasheet.

@blue - it's sometimes annoying how manufatcurers seem to make up parts of the productnumbers. On the other hand, I just said something infinitely stupid in this thread, so don't sweat it ;P

[Ampzone]

The electrolytics *will* have sustained damage. They might be ok for now, but they will fail earlier, suffer from leakage and/or increased hum. That's what RG meant with "semi-kill".
RG already gave you the next move - check voltages around the circuit (black lead to ground):
battery+
+ side of protection diode
IC pins etc. For regular duals (which TL022 are) you should be looking at (approximately)
pin1 4.5V
pin2 4.5V
pin3 4.5V
pin4 0V(ground)
pin5 4.5V
pin6 4.5V
pin7 4.5V
pin8 9V

For trannies, it depends on type and application in the circuit. Run through the debug sticky. If you don't know the pinout, check a datasheet.

@blue - it's sometimes annoying how manufatcurers seem to make up parts of the productnumbers. On the other hand, I just said something infinitely stupid in this thread, so don't sweat it ;P

Thanks Mike - I get no voltage on the IC pins going from pedal chassis to any pin..  No cables are plugged in.

[R.G.]

If the unit uses input jack switching for power, not having a cord plugged into the input (probably) or output (maybe) jack will not turn on power to the unit, so there will be no voltages.

Need to find or trace a schematic.

[Ampzone]

If the unit uses input jack switching for power, not having a cord plugged into the input (probably) or output (maybe) jack will not turn on power to the unit, so there will be no voltages.

Need to find or trace a schematic.

found it:)
http://music-electronics-forum.com/attachments/14434d1310037533-ge-7-equalizer-vintage.pdf

[Ampzone]

If the unit uses input jack switching for power, not having a cord plugged into the input (probably) or output (maybe) jack will not turn on power to the unit, so there will be no voltages.

Need to find or trace a schematic.

I noted earlier the protection Diode at D2 may not have been bad...if this is case could parts downstream still get cooked but D2 lived?  I replaced the D2 diode without checking it assuming it was dead, but out of circuit the readings I get are 270k in one direction and 1.457m and rising in the other direction.