Boss ge 7 won't turn on

[Jun1001]

I bought a boss ge-7 secondhand, but it doesn't power on. So I contacted the seller and bought it at a very low price because it doesn't power on.
The pcb looks very clean, so I wonder where it would be if there was a problem





After reading that there may be a problem with the capacitor and diode in the middle of the right side of the picture on the back, I remove it and measured it with a multimeter, but since my multimeter is a very cheap product, there was no problem with the measurement result, so I put it back on

This article is written in a translator, so I'm sorry if there's anything weird

[GibsonGM]

This may help, at least to understand how the switching works. Schematics for the GE-7 (same as most other Boss pedals) can also be found on the internet.  You are going to have to read some voltages for us to be able to help.

http://www.geofex.com/Article_Folders/bosstech.pdf

[ElectricDruid]

Welcome Jun!

How are you powering the pedal? With a power supply, or with a battery? Could you take a photo that shows all the power wiring please? On the photo, we can only see wires going off the side.

You could also try putting your multimeter (set to voltage) on pins 8 and 4 of those '022 8-pin chips. I'm guessing those are TL022 low current op-amps, so you should see 9V across those supply pins. If the board has no power, you won't get any voltage there.

[Jun1001]

Welcome Jun!

How are you powering the pedal? With a power supply, or with a battery? Could you take a photo that shows all the power wiring please? On the photo, we can only see wires going off the side.

You could also try putting your multimeter (set to voltage) on pins 8 and 4 of those '022 8-pin chips. I'm guessing those are TL022 low current op-amps, so you should see 9V across those supply pins. If the board has no power, you won't get any voltage there.

I'm using a new 9V battery. Then can I connect the battery and measure it with a multimeter on 8 and 4 pins of 022? Or do I have to press the power button after connecting and measure it?

[ElectricDruid]

I'm using a new 9V battery. Then can I connect the battery and measure it with a multimeter on 8 and 4 pins of 022? Or do I have to press the power button after connecting and measure it?

Power button?! Does the GE-7 have a power button now?

You might have to plug a guitar lead into the input, to power it up. Is that what you meant?

HTH

[Jun1001]

I'm using a new 9V battery. Then can I connect the battery and measure it with a multimeter on 8 and 4 pins of 022? Or do I have to press the power button after connecting and measure it?

Power button?! Does the GE-7 have a power button now?

You might have to plug a guitar lead into the input, to power it up. Is that what you meant?

HTH

yes. Thank you for answering and sorry for my wrong knowledge.
I'm not sure if I did it right, but after connecting the battery, input and output, I measured pin 4 and pin 8 of three 022, but the measured value keeps coming up as zero.

[R.G.]

This pedal uses a single reverse-biased diode for polarity protection. In the Boss schematic, this is D5. It is possible that this diode is short-circuited. Check D5 and see if this has happened in your pedal.

Reverse biased diodes are good for reverse protection in some cases, but connecting a high current or AC (not DC) power supply to the pedal can burn out the protection diode, making it shorted. When this happens, it will act unpowered with all power supplies, even batteries.

[Jun1001]

This pedal uses a single reverse-biased diode for polarity protection. In the Boss schematic, this is D5. It is possible that this diode is short-circuited. Check D5 and see if this has happened in your pedal.

Reverse biased diodes are good for reverse protection in some cases, but connecting a high current or AC (not DC) power supply to the pedal can burn out the protection diode, making it shorted. When this happens, it will act unpowered with all power supplies, even batteries.

Do you know where D5 is in the pcb? I keep looking but I can only see D1 to D4 and D6.

[antonis]

The only power diode on your PCB is the one next to electro cap (100μF according to Boss schematic) which, IMHO, looks fine..



But you can easily test it via a DMM in diode test mode..

[Jun1001]

The only power diode on your PCB is the one next to electro cap (100μF according to Boss schematic) which, IMHO, looks fine..



But you can easily test it via a DMM in diode test mode..

The first thing I did when I first saw this pcb was to check that diode and the capacitor next to it. The diode was fine, I couldn't check the capacitor properly, but it looked fine

[GibsonGM]

Gotta track from where power enters the board to where it stops. 

Got power at D5?

Is the battery snap or adapter (or both) broken?

If power at D5/cap, then where does the power trace break before the opamps?  Did someone get in there and create a short on the 9V trace?   Power off with jack plugged into input, what is the resistance reading across the battery snap (or D5 to ground)?   

All these basic questions have to be answered to get a sense of what might be going on.

[antonis]

Schematics with reverse polarity protection diode  marked as D5 correspond to the following PCBs..



OP's PCB is another kettle of fish..

[GibsonGM]

It was what I found - should be close enough to find voltages!   

[antonis]

Let's take it from the very first clueless beginning..

Is, by any chance, your IN plug stereo..??
(if yes, there is no connection between jack's sleeve and ring, hence no continuity for battery negative pole..)

Does Diode's cathode (the edge with stripe) make contact with battery (+)..??
(continuity test..)

Is there power (9V) on Diode's cathode (DMM's black lead on any convenient ground)..??

[GibsonGM]

Take it farther back. Make sure the battery is fresh!

[duck_arse]

Take it farther back. Make sure the battery is fresh!

..... and doesn't get hot while on test. if hot, then 0V, short somewhere. also, welcome. not you, Gibson, Jun1001.

[Jun1001]

 Suddenly this gray wire cutted and I don't know where it was connected     

[GibsonGM]

Do you mean that it was moved so much it broke from somewhere? 

Look on each potentiometer and jack to see if there are strands still there. 

It may help to see if that wire has continuity with ground. If not, what is the resistance to pin 1 and pin 7 of that opamp?

[Kevin Mitchell]

Suddenly this gray wire cutted and I don't know where it was connected     

Ground to the input jack according to the schematic.

Old solid-core wires fatigue and break easily. More often than not these old wires are responsible for the trouble.
The previous owner could have been experiencing sporadic loss of signal and would "fix" it by wiggling the jack. That would surely fail completely after so long.

I'd bet that wire is why the pedal isn't turning on. By design the stereo input jack is used as a normally-open switch for the battery ground to the circuit so that it may not be turned on without a jack inserted into the input. With this wire broken the circuit is not getting it's ground reference.

[Jun1001]

Suddenly this gray wire cutted and I don't know where it was connected     

Ground to the input jack according to the schematic.

Old solid-core wires fatigue and break easily. More often than not these old wires are responsible for the trouble.
The previous owner could have been experiencing sporadic loss of signal and would "fix" it by wiggling the jack. That would surely fail completely after so long.

I'd bet that wire is why the pedal isn't turning on. By design the stereo input jack is used as a normally-open switch for the battery ground to the circuit so that it may not be turned on without a jack inserted into the input. With this wire broken the circuit is not getting it's ground reference.

Thank you. I found a broken mark on the input jack and it looks like the wire on the input jack is correct