RAT trouble

weston5952 · January 16, 2005, 08:19:37 PM

darn. is there an easy way to make it work or will the opamp not fit in correctly since it is backwards. Thanks for noticing that. I guess I could etch another board if I have to. darn, darn darn!!!! At least that is probably what is wrong...

sir_modulus · January 16, 2005, 10:40:37 PM

Wow and I thought I was dumb!

Lol, just kidding! Don't worry, stupid mistakes are the easiest to make. I remeber when I blew up a tube amp's $400 output transformer, because I (indirectly) wired the AC line....to ground :oops:

You won't believe how common it is to etch a board backwards...I've also etched an Electric mistress backwards.... cardinal waste of board....

Try it again, and hope for the best!

Nish

aaronkessman · January 16, 2005, 11:21:55 PM

couldnt you just install the opamp on the underside of the board? it might be a little difficult, but it'd save you from having to do a whole new board.

alternatively, couldnt you bend the pins backwards?

NaBo · January 17, 2005, 12:27:52 AM

lol... aww man, i feel dumber for not noticing it sooner.

If im not completely mistaken, you *could* desolder and reverse all your electrolytics and diodes, and use wires to flip the op-amp, and twist the transistor, but my guess is you'd probably just end up with a headache, a mess of criss-crossed wires, and more than likely another non-functional circuit-- not fun!

you should probably just desolder, re-etch, re-drill, and repopulate

the plus side is, you've learned a lot, and all your off-board wiring is mostly done

weston5952 · January 17, 2005, 03:02:18 AM

would it be possible like aaron said to install the opamp on the other side of the board? And just flip any polarized components that are backwards, which leads to the question could any of the components been damged while it was wired incorrectly? If I can't just flip stuuf around I guess I etch another board. Thanks so much for all of you help!

petemoore · January 17, 2005, 03:10:05 AM

Now i'm 'reversed too'
Someone typed about bending [carefully] the OA leads all the way back to where they're sticking up, and that 're-reversed' it for him. You may be able to do that...I don't know, see what you think.
I've bent leads back all the way like that N/P [carefully of course] I just got turned around...I'm sure you can figure if that could straighten your wiring out.

Peter Snowberg · January 17, 2005, 04:25:24 AM

Good call Torchy. :idea:

I've done it too.

:oops:

Here is your easiest fix....

(1) Check all electrolytics and flip any that need flipping.
(2) Check diode D3. Make sure the band is toward the center of the board and the connection to Q1. I can't tell as it's covered in the picture.
(3) Remount (replace if you have extras) Q1 and Q2, keep them on the front, but spin them 180 degrees when you re-install so that the flat side is opposite of where it is now.
(4) Remove the IC from the socket and bend the pins so that they point UP instead of DOWN.

Reinstert chip with it's bottom now facing you.

Fire it up and check for operation.

NaBo · January 17, 2005, 05:19:53 AM

LOL this is hilarious! i actually just checked my rat PCB, drawn and etched months ago (i guess before i knew/cared much about pinouts and such), and guess what... mine's backwards too!!! :x!!!

I think it's because there's no scale on the PCB layout for that project... it was too easy to forget whether i flipped it or not before i printed it and drew it! :oops:

Sooo, since we're in the same boat now, and i have no copper clad or etchant right now, and no access to a dremel, and really want to make a rat... heh... I'm cooking up a layout for the "Backwards-PCB-Rodent (with extra mojo)" right now. i'll post it when im done!

NaBo · January 17, 2005, 05:45:18 AM

Done! Didn't see that Peter already described the changes... but either way, this is useful

It's a big pic, but i don't wanna just link to it after all that work making it look nice!

Hope it helps!

sir_modulus · January 17, 2005, 08:14:03 AM

Awsome! Now it's this kindof wishful thinking that makes this forum worthwhile!

Cheers,

Nish

Peter Snowberg · January 17, 2005, 12:41:58 PM

NaBo, that's HOT!

Very, very, very cool!

weston5952 · January 17, 2005, 03:22:00 PM

cool NaBo. That is funny that I am not the only one that etched the board backwards. I guess I will try to fix my board according to your layout. Thanks for putting that together and for all of you guys' help in figuring out my stupid mistake.

weston5952 · January 17, 2005, 04:11:43 PM

okay, D3 was fine, I rotated the transistors 180, and bent the pins on the opamp and reinserted it upside down but is still does not work, no sound comes out however the volume pot did stop controling the LED. At least I am making some progress. I guess I should check the transistors and opamp to make sure I did not damage them. Maybe even the diodes too. How can I check these with my multimeter to see if they are still working? Thanks again!!!

Peter Snowberg · January 17, 2005, 06:01:23 PM

What you need now is an audio probe.

Check the FAQ section for construction (1 cap and a cable or jack+cable).

Use the schematic and follow the sound from the input jack. See how far it makes it. I wouldn't be surprised if the transistors and/or IC died. What voltages do you see on the IC now?

weston5952 · January 17, 2005, 06:17:05 PM

my ic voltages in pin order 1-8 are:

5
2
0
0
0
9
10
0

peter, what faq page has the probe on it? i dont see it on the diy or geo faq.

Peter Snowberg · January 17, 2005, 06:49:24 PM

5 ==== compensation
2 - input
0 + input
0 V-
0 ====
9 out
10 V+
0 ==== compensation

Quote from: weston5952peter, what faq page has the probe on it? i dont see it on the diy or geo faq.

Sorry, it's the FAQ forum :oops:

Here is the thread: http://diystompboxes.com/sboxforum/viewtopic.php?t=18264

The DC voltage on pins 2 and 6 should be the same. Check for solder bridges or hairs of unetched copper around pin 6, C7, R6, and C13. You might want to use a razor blade to scratch the surface between the traces to be sure.

It may also be that the transistors and/or the IC are fried.

weston5952 · January 17, 2005, 10:16:28 PM

i did not see and solder bridges or unetched copper. As far as the audio probe, I just threw together a quick one but don't really know what I am listining for or even if I amusing it correctly. I am grounding the sleeve and touching the lead probe on different parts of the circuit. I just hear little clicks out of the amp most of the time. Thanks for you patience in helping me figure this out!

Peter Snowberg · January 17, 2005, 11:28:21 PM

Quote from: weston5952i did not see and solder bridges or unetched copper. As far as the audio probe, I just threw together a quick one but don't really know what I am listining for or even if I amusing it correctly. I am grounding the sleeve and touching the lead probe on different parts of the circuit. I just hear little clicks out of the amp most of the time. Thanks for you patience in helping me figure this out!

You're welcome.... that's why we're all here!

When using the audio probe, you're just looking to hear the signal from your guitar. Strum the strings and touch the probe to the effect input. You should hear the guitar. Now go into the circuit a ways and check for a signal at pin 3 of IC1. If you hear guitar at pin 3 which is the input but you don't hear anything at pin 6 which is the output, you have a fried LM308.

The places I would test would be....
(1) the input jack
(2) pin 3 of IC1
(3) pin 6 of IC1
(4) the filter pot
(5) the junction of R9, C9, and Q1
(6) the + side of C10 followed by the minus side

Knowing how far the signal gets will make finding the next problem fairly simple.

You'll get it going!

NaBo · January 19, 2005, 03:50:56 PM

oh boy... lol...

i just soldered MY backwards rat up today, "proto-wired" it with gator clips, and i'm getting no distortion whatsoever! :\

signal traced right through to the end without much change. I neglected to use the volume pot, but that shouldnt affect it.

It's taken apart cuz im about to make an ugly face and need the clips, but i'll have to hook it up again sometime soon and check the voltages.

sheesh. i coulda just left the clips on my big muff and been playing that all morning instead of messing with this thing!!! ah well, im sure we'll get the dumb thing working right sooner or later. better be worth it!

NaBo · January 26, 2005, 04:39:26 PM

THERE WE GO! i got mine working!!! know what it was? i soldered both ends of C5 to ground :oops:

also, i found a little error in JD's layout... the drive pot works backwards and misses out on all the sweet slightly-dirty sounds you can get from this thing. joining lug 3 to lug 2 (the schematic shows this way) instead of lug 1 fixes that.

give us an update, weston! if its still not working, i have a working backwards-PCB-rat-extra-mojo-version to compare to now :wink:

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RAT trouble