Jordan J-700 Distortion

[c.wright]

OK, i checked the I/O resistance: Output to ground: .6 ohm, Input to ground: 13.5K
Cap at C102 checks out OK
Used audio probe at pin 3 and 1 - no signal passes through either of those.

Switch checks out OK, and have even jumpered/bypassed completely, to no avail.
Also, have resoldered all wiring to/from board, and re-melted all solder points.
Pulled the 50K pot completely out of the circuit, it checks OK.

Can I throw that 6458 chip into something else to confirm it's good?
Like, I have a tubescreamer with a socket, can i drop it in there, since it's a dual opamp too?

With the circuit engaged, the only places I get anything with the audio probe is on the output tip connector, and on the middle lug of the 50K... which acts weirdly in that I can hear the signal if the pot is at the 12oclock position, but it fades if I roll it full on or off.

I'm sorry if I've missed a request for data here, I've tried to go through all the posts and fill any requests.
Just hassle me again if I've left something out.


Thank you again for all your help!!

[Ice-9]

You really should have a signal at pin 3. When i suggest using a probe i assume you are using it this way -: guitar plugged into the input of the effect and then the probe connected to the amp. If you get no signal from pin 3 or any of the directly connected circuit at this point then i would use the probe and follow my schematic from the input to the junctions of   

c106 -c107 if signal there probe at
c106 - r108   if there is a signal there then probe
juntion r108 - r106 -  pin3

[c.wright]

When i suggest using a probe i assume you are using it this way -: guitar plugged into the input of the effect and then the probe connected to the amp.

Sorry, I keep saying I'm using an audio probe, but in reality it's a 70's Micronta Signal Injector... the sweet grey one with the battery in the handle that keeps falling apart in your hands as you use it and the red light that lights up to let you know its working...

So, i have the guitar, cable, pedal, cable, amp setup, and then I'm just poking the Injector everywhere trying to hear the high pitched 'beep'.
And, with the effect engaged, the only place i hear the beeeeep is on the middle lug of that 50K pot...

[Sir H C]

OK, i checked the I/O resistance: Output to ground: .6 ohm, Input to ground: 13.5K
Cap at C102 checks out OK
Used audio probe at pin 3 and 1 - no signal passes through either of those.

Switch checks out OK, and have even jumpered/bypassed completely, to no avail.
Also, have resoldered all wiring to/from board, and re-melted all solder points.
Pulled the 50K pot completely out of the circuit, it checks OK.

Can I throw that 6458 chip into something else to confirm it's good?
Like, I have a tubescreamer with a socket, can i drop it in there, since it's a dual opamp too?

With the circuit engaged, the only places I get anything with the audio probe is on the output tip connector, and on the middle lug of the 50K... which acts weirdly in that I can hear the signal if the pot is at the 12oclock position, but it fades if I roll it full on or off.

I'm sorry if I've missed a request for data here, I've tried to go through all the posts and fill any requests.
Just hassle me again if I've left something out.


Thank you again for all your help!!

Output is shorted if you measure .6 ohms.

[c.wright]

Output is shorted if you measure .6 ohms.

Ah, but I just noticed if I turn that 50K to the middle, I actually get about 13K on the output resistance....
I'm getting more confused.

[oskar]

13k with pot in the middle sounds normal. 0k output to ground means the volume pot was all the way down when
you measured it.

[SG6505]

I really suggest that you build the audio probe that aron describes. That way you can hear whats going on and describe to us what you hear wich will be helpful for us. I did a search on the Micronta, didn't find much but I got the impression it's a logic probe, +-5V digital signals? Correct me if I'm wrong.

Did you click the switch when you measured input/output to GND? Does it change/short if you do? Please try that with full volume.

Please build Arons probe and probe the points suggested earlier with the probe connected to the amp and sweep the pots at each point and desribe what you hear to us. 

Yes, you can test the 6458 in your tubescreamer.

Check in soon with your results

[c.wright]

13k with pot in the middle sounds normal. 0k output to ground means the volume pot was all the way down when
you measured it.

Yes, this is true, but if you refer to my earlier post, you'll see I'm talking about also only getting signal with the probe in the mid position - ONLY the middle, not full ON, or OFF. If you max the knob it rolls off again - working almost like a 'pan' pot or something.

I really suggest that you build the audio probe that aron describes. That way you can hear whats going on and describe to us what you hear wich will be helpful for us. I did a search on the Micronta, didn't find much but I got the impression it's a logic probe, +-5V digital signals? Correct me if I'm wrong.

Yeah, you're wrong. It just makes a long beep/buzz/beeeeeeeeee noise, that you can (only) hear in the circuit when you get the probe close enough or touch it to a component or trace. As for hearing what is going on and describing it to you, there is nothing to hear, as I've said, except for the sound of the probe on that middle lug of 50K...


grrrr. sorry if I'm coming off testy (testes?) - been up all night poking around on it, and getting frustrated.
Ready to take a shotgun approach and just start pulling components and replacing with new verified parts until the effect works - and then work my way backwards again until it stops. That would nail it down...

Shoot, it's only like 20 parts, if that! Probably coulda started that on tuesday and been long done by now.

[SG6505]

No problem, I sertainly know that debuggingforeighthourstraight frustration. The reason I asked about hearing what is going on is that when you say you got signal when the pot is in mid position and fade when you go up and down I suspect  oscillation in the circuit. Is the probe picking up the actual signal or is it only indicating signal/no signal with a self generated beep?

I am sorry about nagging you but I have read your posts and I think you have to describe symptoms a little further.

When you plug it into an amp, is it dead silent or humming? Dead silence indicates short, humming open circuit.

Does it pass signal when bypassed?

When you wrote "no signal on the amp cords tip" did you mean amp cords tip or guitar/signal generator cords tip?

Again, sorry for nagging but I am really curious to hear the result of the following operation:

Sacrifise a guitar cord, cut/desolder the plug in one end  and connect the screen to GND and the plug the other end into a guitar amp. Then inject signal to input thru a guitar cord connected to input jack. Then take the signal wire from the cable you connected to the amp and probe:

Signal lug on input jack.

Both legs on the component side of c107

same for c106 and R108

If you get no signal here try desolder the yellow cable from P12 to the switch and probe again.

This should rule out/indicate problems on the input side of the op-amp. I know it's a pita but debugging is all about being systematic.

I am going away for the weekend in a couple of hours and I dont know if I am going to be able to check in on your progress until sunday but good luck and keep us updated.

[oskar]

1  4.8
2  4.8
3  4.25
4  0
5  0                <---      should be grounded?
6  9.1              <---     should be low, 0 or ~1v...
7  9.1              <---     should be low, 0 or ~1v...
8  9.6

Pin 5 looks grounded, 0V but is it?
Pin 6 and 7 should buffer pin 5 voltage...

Could pin 7 be shorted to V+?

and here are some pin voltages: (1-8, counterclockwise around chip, right?)
-- circuit w/o IC, AND circuit with 6458 installed--
1  .025ish and drops
2  .025ish and drops
3  4.2
4  0
5  0
6  0
7  0                <---
8  9.6             <---

Well,  apparently not!?

Oscillations, post above, that would be if the distortion pot is shot. Then there would be homoungus gain and no filtering.
try a cap between pin 2 and 3.

[Sir H C]

1  4.8
2  4.8
3  4.25
4  0
5  0                <---      should be grounded?
6  9.1              <---     should be low, 0 or ~1v...
7  9.1              <---     should be low, 0 or ~1v...
8  9.6

Pin 5 looks grounded, 0V but is it?
Pin 6 and 7 should buffer pin 5 voltage...

Could pin 7 be shorted to V+?

and here are some pin voltages: (1-8, counterclockwise around chip, right?)
-- circuit w/o IC, AND circuit with 6458 installed--
1  .025ish and drops
2  .025ish and drops
3  4.2
4  0
5  0
6  0
7  0                <---
8  9.6             <---

Well,  apparently not!?

Oscillations, post above, that would be if the distortion pot is shot. Then there would be homoungus gain and no filtering.
try a cap between pin 2 and 3.

If you look, it seems they are not using the second op-amp in the chip, it is just one input to ground other to the output.  If you look at the PCB, pin 5 and 4 are connected together.

[oskar]

Sorry, I was perhaps unclear.
When you only use one of the two amps in a dual, the unused is allways stabilised. Otherwise it could oscillate and consume energy.
pin 5 to ground. pin6 and 7 together. It's a buffer with noninverting input to ground and should be giving us a low output.

But pin 7 is high. Weird?
I could be all wrong, I'm too tired right now         bye for now!



oskar

[aron]

Again, here is the order of debugging.
Plug your guitar or injector into the input of the pedal.
Verify good voltages on the chip.
Next, assuming the schematic posted is pretty correct, build an audio probe, either strum or start the injector.
Place the audio probe at pin 3 of the op amp. If you don't hear anything, your problem is either C106 or R108.
Assuming everything is good, place the audio probe at pin 1, you should hear the signal. It should get louder if you turn the gain up.
Assuming that's good, then proceed to listen to the output chain C102, R101, etc... until the output.

This shouldn't take too long.

[c.wright]

SUCCESS!

Well, after taking the 'shotgun' approach, and replacing all the caps, I was still having no luck...
So, I re-read your last post, Aron:

Again, here is the order of debugging.

...

And all of a sudden it hit me, my #@$%# signal injector isn't doing any good if something is shorted before the output...
so run a jumper from the output and start probing with that!!!
...I know, 'duh'... you've been trying to tell me that all along - but my head wasn't clear enough and I missed the obvious...

If I might quote from: http://www.diystompboxes.com/smfforum/index.php?topic=29816.0
'Gather the things you'll need: #7 A calm, open mind. I don't like to admit this in open company, but one of the deepest episodes of rage I ever felt was when I had been flogging this one poor circuit board to death and even though all the hookup wires and parts were in the right place, nothing worked for hours. The madder I got, the LESS capable I was of noticing the real problem. You gotta clear your head first.'


SO - what was it, you're dying to know?!

6458 op-amp, dead. Subbed with 4558.
Once I did this, I probed as per Aron's instructions, and discovered I was indeed getting signal off pin 3.
Chased that toward the output end of things, and it all crapped out at junction of R101, D101, D102.
Replaced R101, nothing, pulled clipping diodes D101,102 -
VOILA.
D102 was the other guilty party.

Now, a couple questions remain for me - and they might seem inconsequential, but if anyone can give me a theory or an answer, I would greatly appreciate it.
-I've been working from Mick Taylor's hand-drawn schematic, and the Anubics Distortion+ schematic.
-The Distortion + schematic shows a 2K2 BEFORE the LED.
-The actual J700 unit has NOTHING before the LED, but a resistor after.
-It seemed whenever I swapped from the 6458 to the 4558, the LED would blow.

I did pull R102 (the resistor after the LED) and measure, but now I can't remember if the value jived with the markings.
Regardless, I threw a 2K2 inline BEFORE the LED, and that stopped things from blowing.

So, my questions:
Why would swapping the IC (power disconnected, mind you) cause the LED to keep blowing?
Was/is R102 cooked?
why R102 AFTER the LED? Was this a mistake in the engineering? Or will it limit current even whether it is before or after the LED in the circuit?
I'm sorry if this is rudimentary, my electrical theory is pretty much non-existant, and I'm not afraid to admit that i'm just a model-builder here.

All that aside:
Thank you Aron, for getting me back down to earth (no pun intended)!!

I AM STOKED, not just because I got an actually unremarkable pedal working for a customer, but because I LEARNED a WHOLE bunch of stuff in the process.
I have a dead LITTLE BIG MUFF on my bench that has been there for, um, FIVE YEARS, and I am ready to take a whole new crack it it now that I have this new experience under my belt.

And thank-you everyone else for your effort - I hope everyone has a great Christmas or whatever holiday you're observing!


oh yeh... how's it sound???

...pretty much like a distortion + !! 

[aron]

COOL! Glad you got it working and you probably learned so much in the process than if you had just fixed it immediately!

Sounds like a diode shorted out or something. Interesting.

>-The actual J700 unit has NOTHING before the LED, but a resistor after.

Should be ok, series components  - order doesn't matter (I know, I'm still amazed by it. It doesn't make sense intuitively)

> Regardless, I threw a 2K2 inline BEFORE the LED, and that stopped things from blowing.

Maybe the old resistor was too low a value or maybe the LED was changed?

> Why would swapping the IC (power disconnected, mind you) cause the LED to keep blowing?

I have no idea. I'm glad you got it working! I had similar debugging sessions with a ROSS distortion+ clone as well. IC blown, I forget what else, but it was not totally obvious.

Aron

[oskar]

    Great!

Why would swapping the IC (power disconnected, mind you) cause the LED to keep blowing?

Well, maybe soldering caused some of the problems. But physically pulling out an IC from the socket and putting a new one in?
Don't think it could have killed the LED.
Are you using one of these?

Was/is R102 cooked?

Did you measure the resistance?
A resistor can fail shorting out/ lower resistance.

[8mileshigh]

Congrats of getting the circuit working, I really enjoy these debugging threads.  How much are you going to charge for the repair ? You probably invested $1000.00 worth of your time   

Chris

[Ice-9]

Well done, and i bet you felt good at the end to have won the challenge.

[c.wright]

Congrats of getting the circuit working, I really enjoy these debugging threads.  How much are you going to charge for the repair ? You probably invested $1000.00 worth of your time  

Nah, even at what I consider an EXTREME business rate of $25/hr I think I had a total of 10 hours in that - maybe 12... but I had decided before i even started working on it that I wouldn't charge more than $100 total for the effort.

...and actually, the guy is on a budget, so I'm only charging him $75!

It works out in my book, because I got to learn something from the experience, AND I got my hands on a fairly obscure (if mundane) pedal, which I got to document and tweak on. So - everybody wins!
...and yeah, Aron, I DID learn WAY more than if i'd fixed it real quick!

Well done, and i bet you felt good at the end to have won the challenge.

Capital "F" -YEAH it felt good!

Are you using one of these?

Gimme a break. 



Merry Christmas Everybody!

[oskar]

Are you using one of these?

Gimme a break. 

oops sorry!...