FX90 Analog Delay Troubleshooting and Repair help please

[guitjr]

1) It depends on how much stubborn you are...
2) No
2b) Who did suspect it?
3) No
4) Yes, but you should, at least, know what unit you're reading...

1) I am stubborn and patient (often at the expense of being sensible and practical)

2b) I think that was you.

4) I think this related to when I said

Pins 2 and 4 of MN3101 both read 22.88 (don't know what units).

which meant that when I engaged these two pins with the meter in "Measure Frequency and Duty Cycle" mode I got a reading of 22.88. I suspect this is not a frequency? and I don't know what a "duty cycle" is, unitwise.

But you didn't say HOW sound changes, does it become noise? Or it detunes? Or both?

I will do this again and try to provide a better description of what happens.

that cap under t3 looks bad... i think its the 10uf from btween 22k and 22k (off of the ne570 pin12)...   i know, it might be nothing...
as a last ditch, try plugging it in normally and poke around with feedback all the way up, move caps wiggle resistors turn knobs back and forth fast...  see if you can get it to do anything, buzz click and remember where and what did it... electro caps can go bad, could replace em all...   

I'll do this with a single string tone and report back...

Part of this is about getting something working that was working fine just months ago.
Part of this is about learning how to debug an electronic circuit.

Thanks

[Fender3D]

1) I am stubborn and patient (often at the expense of being sensible and practical)

Ok then it should not be a concern if you have to redo your checks, but step by step this time.
I just saw, in your previous post you have no signal @ 570's pin2 and 3... check if it's not a faulty trimmer...

So apply signal and probe each circuit block, I mean:
signal to input, amp probe at TL's pin 7,
then, signal at 27k/27k/0.018u node amp probe at 570's pin 11 and so on

When you get to BBD, check WHAT signal (amp probe) you have @ pins 3-4.
It may (should) be delayed... check it out. Fingering 3101 should detune it...

Then report

PS
I didn't suspect MN3101.. (everybody knows the butler did it!   )
I just suggested to check if there was a clock signal at its pins.
If 22.88 are KHz then it is the clock signal, if 22.88 is duty cycle you always have clock but BBD won't work.
Duty cycle should be ~50%

edit:
probing might not work with guitar signal.
Find yourself a signal generator (oscillator, iPod...)

[guitjr]

I know for you guys this all is a piece of cake.

Not so for me. It's involving a bit of a learning curve. So excuse me if the questions I'm going to ask are stupid.

I discovered:

1)   Turning the board over (and over, and over, and over...) repeatedly results in breaking the connections between the chassis components-to-board wires (in, out, ground, led, seitch, etc.) I'm going to replace the (3-4") wires with longer (7-10") ones. Will replacing these wires compromise the situation at all? (I understand that I will be shortening them when the repair is complete.)
2)   I've tried to draw a picture of the schematic by taking a photograph and actually drawing lines from component to component. Bad idea (really complicated) Is this the approach I should take?
3)   I discovered that it's a lot easier backlighting the printed circuit and tracing the lines by looking through the board. (duh!) However there's a bit of lag involved in my eyes getting used to looking into a light to trace the connections and using reflected light to read the resistors. Is this the best way to follow a circuit board (or are all of you capable of turning the board around and immediately understanding what's going where)
4)   Back to my resistor color code chart: I'm noticing that the 27K resistors I'm supposed to be checking (clearly visible in one of the earlier graphics I posted on this thread) are Red-Red-Orange (22K) Is this something you would expect? Are the resistor values specified in the schematic approximate or exact? (Note: There was a time this unit worked as advertised.)

Instrument questions: (I'm a bit timid using my DMM because of the following questions... I'm surprised I've never found them addressed but attribute the fact to my questions being sooooo basic.)
5)   If I set my DMM to any setting (V~,V-, resistance, etc.) and poke my DMM leads anywhere on this circuit will I know that I can't ruin the instrument?  Is there anywhere I can't poke this meter or any setting I can't set on this meter for this powered circuit?
6)   In order to check the resistance of in-circuit resistors (leads across the resistor(s) in question) must I disconnect the battery completely or can I do so with the battery in?

Some preliminary results (using a sine wave generator from my droid):
7)   Low volume signal present on TL022 pin 6
/8)   High volume signal present on TL022 pin 7
9)   High volume signal at two pins on TR1

p.s. I'm not giving up! But this would be a lot easier if I could find that butler!!

[Fender3D]

No pun inteded, but I really think you need some basic before...

http://www.dummies.com/how-to/content/basic-electronic-components-and-what-they-do.html

http://www.dummies.com/how-to/content/how-to-measure-voltage-on-an-electronic-circuit.html

Just 2 starting points, buying the book on the right, should be next step.

Then you should start with a simpler circuit, easier to understand and eventually clone.

If you really need and don't hate your delay pedal, you'd better look for a proper service center.

[duck_arse]

all that fender said ^, 100%. however, your persistence suggests the answers above won't soothe your furrowed brow, so.

from my point of view, for you, playing guitar is a piece of cake. it's all relative. no stupid questions, just stupid answers. them, for me, are a piece of cake.

some board tracers will take a digital camera shot of each side, and magic them-up in the computer softwares, gimp, photshop, somethings like that. others slog it out with squared paper, pencil and dmm. yet others fossick about and find what has come before them.

if you can solder the wires back on, having them break is a pain, but not really a problem. I believe modern speak terms them "issues". longer wires are fine if they help. they can stay longer if they help, don't cause any noise or re-assembly problems.

if the board was working with 22k fitted, don't worry about them. the difference in value won't make much difference to how the circuit works in 90% of situations. it may be the factory ran outta 27k that day, things like that happen often.

the dmm will not damage a circuit, powered or not, unless you drop (or throw) said dmm onto said circuit. if you try to measure resistance when the circuit is powered, you will get wrong readings, and may very well damage the dmm. measuring current incorrectly may damage the dmm, and will stop the circuit working, but won't damage the circuit. using ac range to measure dc will result in no reading, dc range measuring ac will give bad readings. you won't damage the circuit, or the meter.

you don't want to be shorting pins together with clumsy meter probing, this CAN lead to disaster. but only sometimes. to be sure a resistor is a resistance, you will need to lift one leg from the circuit. when they are parallel w/ other components, they will measure LESS than their banded value (but never more). when they are across capacitors, the reading will take some time to settle, as the cap discharges.

I can't help you with what signals should be where in one of these circuits, sorry. I'm not sure which butler you seek.

[Fender3D]

...if the board was working with 22k fitted, don't worry about them. the difference in value won't make much difference to how the circuit works in 90% of situations. it may be the factory ran outta 27k that day, things like that happen often...

True, but schematic shows 2 22K resistors on the right near 570, on board they are exactly where he's checking...
There are other 27K on board and schematic, just elsewhere...

[duck_arse]

also true, but he doesn't trust the schem as matching his board, or he wouldn't be tracing it all out ....

[guitjr]

OK...I'm not t...h...a...t bad.

I got into electronics (Amateur Radio – General Class) in the early 60s; took apart (and part-catalogued) more televisions than I care to think about; constructed a few cw (continuous wave/aka morse code) transmitters, a number of Heathkit projects (VTVM...); had a B&K scope (which I guess I could've used now); etc. It was about TTL/RTL time that I had to move away from this hobby to pursue college interests... And I'll never forget that it wasn't a smart idea to curiously use a pair of pliers to bridge the gap between the poles of the telegraph key I'd hooked up to a code oscillator (I assumed that since this wasn't in a chassis, and only generated a small tone) that it would be safe)...but I did experience flying backwards into a wall 6 feet away!

The digital camera shot/reverse idea is (conceptually) brilliant (I'm good enough at Photoshop to do that). I'll give it a try (I feel renewed...and will plug on my signal tracing once I've got the matching photos in order-I could've sworn the 22K resistors are where three of the 27K should be...but I'll check again.)

And the comments regarding DMM or circuit damage are exactly what I am looking to know. As well as the relative resistance readings. Enough that I'm posting another thread to get more information about these troubleshooting issues.