Tl072 Voltage Problem

guidoilieff · July 17, 2015, 12:01:40 AM

I have a problem with Craig Anderton tremolo

http://www.generalguitargadgets.com/pdf/ggg_catrem_lo.pdf
http://www.generalguitargadgets.com/pdf/ggg_catrem_sc.pdf

The voltage in the tl072 on pins 1,2,5 and 6 is 1v and starts to drop slowly to 0 when I unplug it. Ic gets hot in seconds. I alredy switched ics.
If I measure without the tl072 its 0,50 volts

Here are the normal values:

Pin 1 0.01v
Pin 2 0.01v
Pin 3 0v
Pin 4 -9.1v
Pin 5 0v
Pin 6 0v
Pin 7 0v
Pin 8 9.3v

everything else is fine.

PRR · July 17, 2015, 12:12:50 AM

What is on the supply pins, 4 and 8, without and with the chip?

Hot TL072 really suggests reversed voltage.

guidoilieff · July 17, 2015, 12:30:08 AM

Quote from: PRR on July 17, 2015, 12:12:50 AM
What is on the supply pins, 4 and 8, without and with the chip?

Hot TL072 really suggests reversed voltage.

pin 4 -9v
pin 8 9v

guidoilieff · July 17, 2015, 01:33:13 AM

Also, whats that S on the pcb? I wired it but have no idea what i does.

MaxPower · July 17, 2015, 01:56:27 AM

Since 5 is connected to ground, how do you measure 1 volt there?

Question for the experts here: Shouldn't all the readings around the Tl072 be 0 DC volts (other than the power supply inputs)?

guidoilieff · July 17, 2015, 04:07:56 AM

Quote from: MaxPower on July 17, 2015, 01:56:27 AM
Since 5 is connected to ground, how do you measure 1 volt there?

Question for the experts here: Shouldn't all the readings around the Tl072 be 0 DC volts (other than the power supply inputs)?

I hook the black lead of the dmm to ground and stick the red probe to pin 5.
Triple checked or more.

Cozybuilder · July 17, 2015, 08:53:01 AM

Quote from: guidoilieff on July 17, 2015, 01:33:13 AM
Also, whats that S on the pcb? I wired it but have no idea what i does.

When a plug is inserted into the input jack, this connects ground to the 6K8 resistor (R15) at the base of the transistor (Q1), pulling it low, thus turning it on. This then feeds +9V to the Max1044 (IC3), providing power to the circuit. Its a clever way of using the ground to feed +9V to the circuit.

If you could post clear detailed photos of your build, perhaps one of us can spot something.

guidoilieff · July 17, 2015, 04:58:21 PM

Quote from: Cozybuilder on July 17, 2015, 08:53:01 AM
Quote from: guidoilieff on July 17, 2015, 01:33:13 AM
Also, whats that S on the pcb? I wired it but have no idea what i does.

When a plug is inserted into the input jack, this connects ground to the 6K8 resistor (R15) at the base of the transistor (Q1), pulling it low, thus turning it on. This then feeds +9V to the Max1044 (IC3), providing power to the circuit. Its a clever way of using the ground to feed +9V to the circuit.

If you could post clear detailed photos of your build, perhaps one of us can spot something.

guidoilieff · July 17, 2015, 05:04:07 PM

the LED blinks, changes rate and the switch works ok. Rewired everything and still the same.

Cozybuilder · July 17, 2015, 05:56:38 PM

I don't see any obvious miswiring, the R's that are readable are marked correctly (except R15, you have 8K2, not 6K8), the electros are oriented correct, can't read any of the cap values. It looks like you made sure the positive rail is not contacting the two traces between the cap (C6). What I do see is a lot of solder spatters and what looks like rosin flux. Try cleaning this off first- some folks here like alcohol for that (I prefer a little kerosene then alcohol). Paul hinted that there may be voltage reversal- I don't see where, but hopefully someone else can spot something.

guidoilieff · July 17, 2015, 08:34:44 PM

Quote from: Cozybuilder on July 17, 2015, 05:56:38 PM
I don't see any obvious miswiring, the R's that are readable are marked correctly (except R15, you have 8K2, not 6K8), the electros are oriented correct, can't read any of the cap values. It looks like you made sure the positive rail is not contacting the two traces between the cap (C6). What I do see is a lot of solder spatters and what looks like rosin flux. Try cleaning this off first- some folks here like alcohol for that (I prefer a little kerosene then alcohol). Paul hinted that there may be voltage reversal- I don't see where, but hopefully someone else can spot something.

I dont think either that 2k of difference would make a short. Caps are good. Already checked for shorts in places that look suspicious. Flux isnt conductive, or is it?

Cozybuilder · July 18, 2015, 03:15:43 PM

I agree that the <2K difference on the pulldown resistor won't make a difference. My concern is that there may be a small solder splatter held in place by the flux that could be shorting a couple of traces (it doesn't take much). Its an easy thing to eliminate that possibility.

mcknib · July 18, 2015, 07:15:22 PM

Don't know if I'm missing something here never built the circuit but on the GGG modified schem Q1's a 3906 PNP and in the layout diagram it's a 3904 NPN.

Surely that would have some bearing on the circuit working correctly if you used the wrong type?

slacker · July 19, 2015, 06:55:28 AM

Good spot, it should be a PNP, using an NPN won't turn the power off. The layout has another mistake, there's no connection from the board ground to signal ground, there should be a wire from G on the board to one of the jack sleeves or the negative on the DC jack. From the photos It looks like guidoilieff has added the connection though.

guidoilieff · July 19, 2015, 04:01:06 PM

I have no idea which transistor is the right one, but I don't think thats whats making the tl072 overheat either.

mcknib · July 19, 2015, 09:07:25 PM

Do you have a broken trace between pin 4 and C8 the very bottom track just below where you've scraped the solder off at C6 it's hard to see.

guidoilieff · July 20, 2015, 01:08:00 AM

Quote from: mcknib on July 19, 2015, 09:07:25 PM
Do you have a broken trace between pin 4 and C8 the very bottom track just below where you've scraped the solder off at C6 it's hard to see.

Tested with the dmm. The track is fine. There is a design error where C6 is, ground was touching the positive track. What you're seeing is the shadow of C6 pin.

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

mcknib · July 20, 2015, 09:53:23 AM

Just for info I'm far from an expert but from Cozybuilder's explanation on what the 'S' pad is for, we know Q1's a PNP I e-mailed JD over at GGG and he confirms it should be a 2N3906 PNP and he'll sort it on the layout.

Another observation C6 100uF looks to be the same size as the 10uF's and C8 10uF looks to be bigger it could of course just be the voltage ratings but thought I'd mention it just in case.

guidoilieff · July 20, 2015, 12:30:30 PM

Quote from: mcknib on July 20, 2015, 09:53:23 AM
Just for info I'm far from an expert but from Cozybuilder's explanation on what the 'S' pad is for, we know Q1's a PNP I e-mailed JD over at GGG and he confirms it should be a 2N3906 PNP and he'll sort it on the layout.

Another observation C6 100uF looks to be the same size as the 10uF's and C8 10uF looks to be bigger it could of course just be the voltage ratings but thought I'd mention it just in case.

oh... I read HE'LL SHORT IT... like a short circuit

caps are fine, thanks

News:

Tl072 Voltage Problem