RAT trouble

weston5952 · January 15, 2005, 08:59:06 PM

I finsihed assembling a Rodent last weekend according to the layouts at GGG. I didn't work correctly and after much frustration took the advice of a member of this forum to take a few days off and come back to it. Well I'm back and I have triple checked my wiring and and everything seems to look good but it still does not work. To review this is what it does do when I hook everything up. When in bypass mode, the signal comes through nice and clean. The volume pot will turn the LED on and off (i find that really weird). When I switch the effect on, the LED comes on (it no longer responds to the volume pot) but no signal gets through. Last weekend I checked the traces with the audible continuity test on my multimeter and I didn't find anything that look suspicious. I am new to all of this circuit stuff so any sugestions are greatly appreciated. I will post some pics just incase anyone might be a ble to spot something that would be a problem. Please note that I did omit the 9v battery from the circuit and therefore used a mono jack for the input. Thanks for all of your time and help towards helping me to get this thing to work in advance.

The Rodent Layout

sir_modulus · January 15, 2005, 11:21:40 PM

Aight. This is where you Gutsify the pedal. Take off the fancy LED work, and just wire the input to the inpt jack, and the output to the output jack. No switch, no LED. Now I can see from just looking that one of those tracse looks cracked. Check for continuity between the traces before anything else. The trace that loooks cracked will be above the word "traces" in the last sentance.

Hope that helps,

Nish

weston5952 · January 16, 2005, 01:11:19 AM

I'll try to "gutsify" the pedal and I will recheck the traces. Thanks for the help.

Peter Snowberg · January 16, 2005, 01:57:37 AM

Try running your iron along all the traces on your board and coat them all with solder so that you don't see any copper at all. That should take care of any cracked traces and it will make the board last a long time too.

NaBo · January 16, 2005, 01:17:35 PM

like i always do myself, and suggested in your last thread

I'd like to help you with your wiring, but its kind of hard to follow since its all the same colour... you must have something connected incorrectly. check those traces, run over them with solder, then check your wiring again (check GGG tech pages to make sure you're reading components right).

then, if you still dont have it up and running, snap a pic of the component side of your board that shows the orientation of electrolytics, transistors, diodes, and your LM308. then, if its not too much trouble, label where each wire is connected to. I'm making a rodent this week and i'll be happy to check it all against mine if you make it easier on me

weston5952 · January 16, 2005, 02:45:12 PM

Thanks so much for all of your help. I went over all of my traces with solder and checked my wiring again and it still does not work. NaBo, here is a pic of the component side of the PCB and a pic that shows where all of the wires go to.

Fret Wire · January 16, 2005, 02:56:32 PM

Take your IC pin voltages and post them.

weston5952 · January 16, 2005, 03:26:40 PM

how do i measure IC pin volatages, Fret Wire?

Fret Wire · January 16, 2005, 03:46:40 PM

Take your DMM, and set to 0-20v. Clip or place the black lead on one of your grounds, and touch the red lead to each pin (leg) of the IC (LM308). Looking at your pic, you see the IC has a semi-circular cutout at one end. Consider that the top. To the left of the cutout is pin 1, to the right is pin 8.

The order down the left side:
1
2
3
4

The order down the right is:
8
7
6
5

Also, make sure the battery is in, the switch is one and a patch cord into the input jack to power up. Post voltages like this: 8.73, 4.42, etc.

Here's a data sheet of a similar IC (NTE 938M), the pin numbers are near the bottom of the page.
http://www.nteinc.com/specs/900to999/pdf/nte938.pdf

markusw · January 16, 2005, 04:36:14 PM

Did you check for shorts? Once I had 2 pins of an opamp shorted. I chould barely see it because it was about as thick as a hair.

Markus

petemoore · January 16, 2005, 04:47:25 PM

GOod one is to clip DMM black lead to ground at Batt. clip, set to beep mode, see that ground is made where indicated for the cct, also see that ground is not getting into V+, saves on batteries and other stuff...I do that alot, especially if I power up in effect mode, and hear no 'clik'...I pull the battery immediately and see that no - is getting into + at the PS before powering up again.
I doubt that's it but I do it alot, have caught shorts there and found debug info that way too.
Clip to + batt clip and check that V+ is about the same as the batttery with circuit loading it [or the same...some Cct's use a small series PS V+ resistor].

petemoore · January 16, 2005, 04:49:13 PM

Quote from: petemooreGOod one is to clip DMM black lead to ground at Batt. clip, set to beep mode, see that ground is made where indicated for the cct, also see that ground is not getting into V+, saves on batteries and other stuff...I do that alot, especially if I power up in effect mode, and hear no 'clik'...I pull the battery immediately and see that no - is getting into + at the PS before powering up again.
I doubt that's it but I do it alot, have caught shorts there and found debug info that way too.
Clip to + batt clip and check that V+ is about the same as the batttery with circuit loading it [or the same...some Cct's use a small series PS to V+ resistor].

Testing the cct out of the Sw, Signal and PS jacks, and box...divides and eliminates alot of the process of elimination IME.

weston5952 · January 16, 2005, 05:30:09 PM

Here are the IC pin voltages:

1. 9
2. 9
3. 10
4. 10
5. 8
6. 10
7. 7.5
8. 7.5

My multimeter is analog so these are as accurate as I can get.

Fret Wire · January 16, 2005, 05:58:21 PM

If you look at the data sheet, pin 7 should be roughly supply (battery) voltage. Pin 6 should be half of that. Pins 2 & 3 should also be about half supply voltage. Pin 4 should be zero. Pin 5 is not connected. I can't help you with voltage on pins 1, 8, & 5,... I've never built a rat before, so maybe someone who has can check all your voltages.

But it is evident that you do have a component, soldering, or wiring problem. Did you check all your traces with a good magnifying glass to make sure no pads are bridged (touching).

http://www.generalguitargadgets.com/diagrams/rodentpl.gif

weston5952 · January 16, 2005, 06:12:02 PM

I can't see any bridged pads but I will go over it with a magnifying glass and let you know if I find anything.

I just realized that I measured the wrong pads on the board for the IC. I did it again and here is what I got.

1. 7.5v
2. 10v
3. 7.5v
4. 0v
5. 8v
6. 10v
7. 10v
8. 9v

Fret Wire · January 16, 2005, 06:34:37 PM

Check the polarity of C6 & C11, they look backwards. The stripe down the side is neg.

Torchy · January 16, 2005, 06:39:51 PM

crp

Torchy · January 16, 2005, 06:53:58 PM

crp

Fret Wire · January 16, 2005, 07:06:38 PM

Good call Torchy, the board is inverted. I was just looking at the two caps at the front of the chip, then I noticed the reversed electros. I didn't pay attention to the resistors to the sides. I missed that R1, 4, 5, are on the wrong side. :oops:
http://www.generalguitargadgets.com/diagrams/rodentpl.gif

As they say...back to the etching board.

Torchy · January 16, 2005, 07:18:10 PM

crp

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RAT trouble