Looking for Boss GE-6 EQ Pedal Schematic

[DrGonz78]

I was wondering if anyone has a copy of this schematic to pass along? I am at a point where signal is passing through the pedal, but signal is not effected when activated. All voltages on the chips are good. Actually I found a shorted zener diode (D1) on the board. On the zener it has B311 printed on it, but I don't find any datasheet to relate the part. I know these sometimes have BZX as the prefix or something. Just cannot figure out what the rating is for the zener diode and a schematic might help big time, thanks.

[Jazz P Bass]

Boss GE-7 Schematic

I have attached the GE-7 schematic.

As far as I know, the difference is the GE-7 added an overall level control & one more EQ band.

Check the gates of the switching fet's (Q4 & 5) to see if the flip-flop circuit is working.

I do not see any zener diodes.

[DrGonz78]

Thanks Jazz! Yeah it's just tough trying to figure out what part I have here in this one. I guess the schemes should be very close. D4 on that scheme looks to be a zener diode. I will do more troubleshooting later.

[Jazz P Bass]

[QUOTE=DrGonz78;331840] D4 on that scheme looks to be a zener diode.QUOTE]
Missed that.

The circuit is labeled 'Check'.

According to the GE-7 manual, that is the On/Off indicator LED.
If the battery is low, the LED will be very dim or will not illuminate at all, when the unit is On.

[Jazz P Bass]

The Boss DD-3 uses a 5.1V 500mw zener in the check circuit.

The part# is RD5.1EB-3.

[DrGonz78]

Well searching trying to make sense out of the B311 turned out backwards. 11B3 is 11volt graded at B3 rating or something of that sort. So I don't think a 12volt 500mw would be a bad choice of replacement and installed it with no further troubles. I saw another zener diode on the board that reads 51B3 so there is that zener in the check circuit. I traced out the board in relation to the schematic of the GE-7 and D1 on mine is really D5 on the GE-7 scheme that you attached. Furthermore I am attaching a "Vintage" version of the GE7 and on that one my D1 relates to D2. I did not have any symptoms of a dimly lit check led. I can just look at the part of the 11B3 and know it's a zener diode. Searching for 11B3 shows up as a zener diode, yet on the "vintage" GE7 that D2 can be a vanilla type IN4004 or something similar. Is there really any harm putting a zener in place of a standard diode? The voltages to the power pin on the chips are fine. I bet the diode was shorted when someone did not use an older ACA type power supply and reversed polarity through the circuit.

So to explain first, my Q1-Q5 are actually the complete opposite as on the schematic Jazz posted but it seems right by function. When looking at voltages for my Q5 then refer to Q1 on the schematic. Same goes all the way through... On my board Q1-Q2 are K30A-y transistors and Q3-Q5 are C945 transistors. REFER TO SCHEMATIC THAT JAZZ POSTED EARLIER...

Q1 D = 6v G = 205mv S = 6v >>> Q5 on GE-7 scheme
Q2 D = 6v G = 90mv S = 5.7v >>> Q4 ' '
Q3 E = 553mv C = 550mv B = 1.14v >>> Q3 ' '
Q4 E = 527mv C = 553mv B = 1.1v >>> Q2 ' '
Q5 E = 3.2mv C = 5.62v B = 360mv >>> Q1 ' '

The Q3 & Q4 are the flip flops and are really Q2 & Q3 on the schematic that Jazz posted earlier in the thread. I am attaching the other "Vintage" version of the GE-7 schematic, but it has been modded a bit. It is missing Q1 and I could not locate it at all on the vintage schematic. Sorry this is so confusing, but hopefully it will help. I am suspecting that the one or both of the RC3403ADB Quad IC's are bad. Thanks again for the help.

[Jazz P Bass]

Does the Indicator LED illuminate when the on/off switch is depressed?
It does not appear that the flip-flop circuit is flip-flopping.


Suspecting a bad IC should be followed up with testing the IC.

You should see a signal at both fet drains. ( dry & wet)
The flip-flop circuit then selects which signal passes to the output jack.

Walk the signal through.
Start at the input & check each output pin of the IC's, looking for signal.
Heck, a bad level pot would kill the wet signal.

[DrGonz78]

Yes the pedal light responds when click on and off. I tested Q3 & Q4 better and think they are working.
With pedal off
Q3 E = 540mv C= 540mv B = 1.12v
Q4 E= 197mv B = 590mv When I touch probe to Collector pin turns on the pedal
With pedal on
Q3 E = 520mv B = 198mv Touching probe to collector pin turn off the pedal
Q4 E = 520mv C = 540mv B = 1.12v

So I think that is good right? I don't think I noticed that touching the collector pins caused the unit to on or off. So my measurements on my prior post were incorrect.

Also I scoped the pedal looking for signal
When unit turned on or off I have signal on every pin of IC1 or IC2 except 4 and 11. There is signal at both of the drains for Q1 and Q2 FETS. I cleaned the slider pots to make sure they were not mucking up my wet signal and I have signal going through the pins that lead into the where the slide pots are located. Still the pedal does not react to frequency of equalization and still passes signal on or off. It sounds better now that I cleaned it up, but still not functioning as it should.

I am not really sure what Q5 is doing (realize that Q5 is really Q1 on the schematic we are following) and that part confuses me most. I scope the output jack pin and there is my test signal. However, at the base and emitter on my Q5 no signal, which seems odd to me. I had a few BC546 transistors and swapped out all the C945(Q3-Q5), observing the difference in pin layouts. Pedal was exactly the same and nothing changed. I tested each transistor while they were out and they all seem fine, so I put them back in. I am a bit stumped at this point and give up for tonight.

Edit: One last thing... I just measured the resistance across D1 and either way I measure it settles down to about 40k(jumps around a bit). That is in circuit but seems strange I measure the other zener diode 5.1B3 and it is OL one & 20m the other way. Will have to think about replacing that diode tomorrow. Also here is another GE-7 schematic that has parts list too. It says 10E2 for D5 which would be D1 on the GE-6.

[Jazz P Bass]

O/k, you have signal on the drain of each switching fet.
I would now look at the source pin.
Are the fet's switching on & off?
You should have a signal on one & not the other & then it should toggle.

The EQ part is a simply an active tone control.
Each frequency is an rc network.

[DrGonz78]

So when the unit is off I have signal at the source on Q1 and no signal at the source for Q2. With pedal turned on I have signal at both source pins. That would be that Q2 is not turning off then right?

Edit: So my flip flops are still not working or something related to that part of the circuit?

[Jazz P Bass]

So Q1 is Q5 on the schematic.
Q2 is Q4.

When the unit is off, Q1 should pass signal.
Q2 should block it.

When the unit is on, Q1 should be blocked & it is not.

I think the flip flop is working because the On led is working.

So Q1 is bad or it's gate voltage is.

[DrGonz78]

Yup doing some research on a stomp box website I found someone trying to fix a GE-6 type EQ pedal. Somewhat similar situation and I have dug into testing voltages. For example, measuring at R20 on the schematic we are looking at we should see 4.5v at that 33k resistor and I measure 6.2v. Pulling up one side of R20 we should be seeing 0v across C18, but that is not the case. With R20 in circuit I measure 8.5v across C18 and then pulling up R20 measuring across C18 I measure 5.2v, when it should be close to 0v. So somthing is pulling up the voltage and in the thread that I reading about this is was a bad IC1. I have posted on that other site to do more tests to check the IC. I will let you know how it turns out Jazz and always appreciate your help troubleshooting. Thanks!

[DrGonz78]

Well it's all fixed and working fine now! Turned out that the two rc3403ADB dual quad op amps were bad. I pulled out the first IC1 and then I started to see about 5.2v where I was seeing 8.7 before on the pins. The pedal was functional at that point but the IC2 voltages were out of bounds still, with a pop when switching on/off. Switched out the other IC2 and bingo we have a winner. All the 4.5v type voltages are intact and I learned something new about repairing effect pedals. BTW a TL074 chip is a good replacement but I did not want to wait to have them shipped. So I ran over to Fry's and bit the bullet to use NTE859, which did the job. Thanks for the help again and glad that little pesky pedal is complete.