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Almost newbie needs to troubleshoot electric guitar effect

Discussion in 'Electronic Basics' started by goldenhound, Sep 13, 2008.

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  1. goldenhound

    goldenhound Guest

    I've built some kits, and can use a soldering iron, but know almost
    nothing about trying to troubleshoot a battery-powered electric guitar
    effect. Its an Electro Harmonix Electric Mistress Flanger, and it
    consists of about two dozen components. I can find where the power
    source connects to the board. I hit the first IC and I don't get a
    signal, but am I doing it right? How do I test it?

    I built a signal probe. I plug a CD player into the "guitar in", and
    touch the probe to the PCB trace (which connects to an audio
    amplifier), and the music comes out of the amp if I'm following the
    trace correctly. Will that help me find the bad component?

    1. I should be able to trace power, no?

    2. How do you follow a trace on a PCB when it hits an IC or cap or
    resistor? Do you have to disconnect it or ?

    Whats a good reference for troubleshooting PCB boards and circuits?
    Either on the web or in a book?

    TIA mucho,
    Rob
     
  2. it might... I guess better than nothing.
    you have to know what the ic does. It has inputs and outputs... to follow a
    passive component you just "go through" the component. (same thing sorta
    happens inside the ic but its extremely complex and you don't know the
    "connections" so you have to know the macro function)

    First look for the obivous. Any burned components or burnt smell? Any broken
    wires or traces or loose components?

    Look at what is happen? No power? No sound? Distorted sound, etc...

    Look at the input, output and power stages. This are the ons likely to go
    first. Components such as resistors and capacitors rarely go back so they
    can be ignored at first(although if they do go bad and it's not obvious it
    can be very frustrating figure it out). Digital logic also rarely goes bad.

    Thing's like diodes, transistors, regulators, op amps, etc.. are the first
    bet.

    The main thing is to test power.. because it is the easiest and obviously if
    it's not getting power your not going to get anywhere and this is really the
    place that gets screwed the most(people trying to power it with different
    voltage than it's rated for).

    In fact I'd test the power pin of all the IC's starting with the power stage
    and at the same time test the diodes(which you can try to do in circuit but
    doesn't always work but might lead to a quick answer).

    What you'll probably find is that either the power stage or discrete
    transistors are bad but it could be something as simple as the input or
    output comming loose or a connection breaking do to wear.
     
  3. tempus fugit

    tempus fugit Guest

    You say you hit the 1st IC and yhou dont get a signal. You need to know what
    that IC is and what pins to test to see if your audio should be travelling
    down that path. DId you get the schematic that was linked in an earlier
    reply? Also, what's wrong with the flanger? Knowing what the symptoms are
    can help us to point you in the right direction. It's hard to suggest a plan
    of action for testing when we dont know what the problem is.
     
  4. It really would help to see the schematic, especially since all kinds
    of things get misnamed.

    Since by definition a flanger, if this really is a flanger, the
    audio is split into two paths, one going through a delay line
    and the other going directly to the output, where it's combined
    with the output of the delay line.

    Hence, if there's no audio at the output, then it's likely something
    really simple. Either an early buffer stage, or a stage at the output
    that combines the two signal paths. Otherwise, there would be audio
    at the output, just no flanging effect if there was something wrong
    with the delay line.

    Which of course reinforces the need for understanding before
    troubleshooting. If you can look at a schematic and see "oh, that's
    just buffering the input and that resistor brings some of its signal
    to the output, then it's less daunting than seeing this big expensive
    IC and assuming that must be where the problem lies.

    Michael
     
  5. Jamie

    Jamie Guest

    As some one else here had provided a schematic (nice of them :)), I
    took the liberty to examine it.

    The device, being nothing more than what I call a reverb unit more or
    less, could be a little beyond your current technical skill level to
    properly debug the problem with out future possible damage using the
    methods you have out lined.
    In case you didn't get the link to the schematic provided by another
    poster here.
    http://www.diystompboxes.com/pedals/EHmistress_deluxe.jpg

    List of things I would check for.

    #1.

    Pin's 12 and 14 of the SAD 1024A chip need to have a square wave or
    near to it pulse train signal to get the serial chip moving is data down
    the registers. Not sure with the present equipment you have at hand how
    you're going to determine this ? ;/ Maybe if you had a logic probe it
    could help using the pulse LED option to determine if its running.

    And the rest of the idea's you can ask for if you think #1 isn't
    beyond your skill set.

    P.S.
    If you plan on doing this kind of work, you really should think
    about investing in a multimeter with Freqenency,Capacitance, Resistance,
    voltage, amps etc...
    You don't need a high end unit for what you're doing.

    http://webpages.charter.net/jamie_5"
     
  6. That's assuming the schematic the original poster is using is the same.
    We don't yet know that, it's possible he has a schematic that is labelled
    as the device, when it's not. Or, there may be multiple schematics of
    the same commercial device, but which come from different sources
    so they are not all quite alike. Ie, if a bunch of people traced out
    the circuit, and the put it on the web, there's no guarantee that they
    all match since someone might have made an error in the tracing.
    Well no. It would be called a reverb if it was that. It's all in how
    you combine that delay with the original signal, so the waveform actually
    changes. You are talking about a small delay, so the delayed signal
    summed with the original will cause a new waveform. Note that the
    sound effect requires the delay to be varied continuously.

    I'm not sure we've really heard from the original poster about
    what isn't happening. I don't recall it being clear from the original
    anything beyond "it's not working", which is ambiguous since it could
    mean the whole thing is dead, or it could mean he doesn't get the
    flanging effect.

    The whooshing sound he's expecting to hear won't be there unless
    whatever varies the element that controls the delay is functioning.
    Like I said, because of that mixing at the output, there should be
    an output signal whether the delay is working or not.

    SO if there's no sound at the output at all, he either doesn't
    have power to the devices, or something is wrong with the input
    buffers (assuming the schematic he is following is about what
    many websearch hits show).

    If he has output sound, but none of the effect he's expecting, then
    it's the delay that needs attention, be it whatever the making
    the delay (the sad1024 if it's the common schematic), the clocking
    of that delay IC, and maybe whatever is varying that clocking of
    that delay IC.

    Since the delay is so small, he won't be able to tell if it's working
    by waiting to hear a sound at the input come out a tad later. He'll
    only be able to tell if there's a different sound at the output.

    So if there's sound at the output, he ought to disconnect the delay
    from that output, put in a temporary switch or something so it's easy
    to compare, and then see if switching out the delay causes a change
    in the sound. That's not definitive, but if he hears something,
    that helps to narrow down where the problem lies. If there's no
    change, then likely there's no delay in effect, the reason to be
    determined.

    Figure out the frequency of the clock to the delay line (once
    again assuming it is that schematic in circulation) and if it's in
    audio range, one can carefully attach an audio amplifier through
    a coupling capacitor to the clock and see if they hear something.

    Michael
     
  7. Guest

    Very nice of them, indeed! Thank you Christofire!!

    Unfortunately, the schematic referenced on DIYSTOMPBOXES was the
    *Deluxe* EH Electric Mistress. Mine is just the Electric Mistress, 2
    - 9v version circa 1979. I bought it brand new, but it sat for a long
    time and when I pulled it out to try it, I get no sound out of it.

    To be more precise, I plug guitar into input, and plug output to amp.
    With the footswitch off, I get a clean signal, footswitch on (FX
    engaged), I get nothing - no sound at all. Originally, opening up the
    FX I found what looked like the positve power wire from the batteries
    had broken off from the PCB. I looked at it with a mag glass and
    found where I thought it should go and resoldered it. Didn't help.
    Maybe its in the wrong place?

    I scoured the net and found a couple of the schematics (that *used* to
    be on DIYSTOMPBOXES.com, but have since disappeared), but I guess I
    can't attach them to my posts, right? Can I upload them to someone
    who is hosting so I can have a real link to show what I mean?

    I'd also like to show the front / back of my PCB to show what I've
    done, which may not be correct. I don't know how to relate a
    schematic to the actual circuit which is probably essential, right?

    Maybe these schematics aren't right? I'm not finding the components
    on the PCB where I think they should be according to the schematic.

    Do I understand (thanks to Jon Slaughter) that this whole problem
    might be due to a bad diode, or transistor? I'm going to have to
    round up data sheets on the IC's involved and see if I'm getting power
    out of them.

    I have purchased two $35+ multimeters (probably chinese) that claim to
    be able to test transistors and capacitors, but I'll have to remove
    them to test. Is this where I should start? Testing each of the
    components values? Or is there a way to test them in-circuit? Or
    should I pull the diodes and test them first?

    Thanks to you all for weighing in on this. Maybe this effect *will*
    work again someday!

    Rob
     
  8. goldenhound

    goldenhound Guest

    Very nice of them, indeed! Thank you Christofire!!

    Unfortunately, the schematic referenced on DIYSTOMPBOXES was the
    *Deluxe* EH Electric Mistress. Mine is just the Electric Mistress, 2
    - 9v version circa 1979. I bought it brand new, but it sat for a long
    time and when I pulled it out to try it, I get no sound out of it.
    To be more precise, I plug guitar into input, and plug output to amp.
    With the footswitch off, I get a clean signal, footswitch on (FX
    engaged), I get nothing - no sound at all. Originally, opening up the
    FX I found what looked like the positve power wire from the batteries
    had broken off from the PCB. I looked at it with a mag glass and
    found where I thought it should go and resoldered it. Didn't help.
    Maybe its in the wrong place?
    I scoured the net and found a couple of the schematics (that *used* to
    be on DIYSTOMPBOXES.com, but have since disappeared), but I guess I
    can't attach them to my posts, right? Can I upload them to someone
    who is hosting so I can have a real link to show what I mean?

    I'd also like to show the front / back of my PCB to show what I've
    done, which may not be correct. I don't know how to relate a
    schematic to the actual circuit which is probably essential, right?

    Maybe these schematics aren't right? I'm not finding the components
    on the PCB where I think they should be according to the schematic.

    Do I understand (thanks to Jon Slaughter) that this whole problem
    might be due to a bad diode, or transistor? I'm going to have to
    round up data sheets on the IC's involved and see if I'm getting power
    out of them.

    I have purchased two $35+ multimeters (probably chinese) that claim to
    be able to test transistors and capacitors, but I'll have to remove
    them to test. Is this where I should start? Testing each of the
    components values? Or is there a way to test them in-circuit? Or
    should I pull the diodes and test them first?

    Thanks to you all for weighing in on this. Maybe this effect *will*
    work again someday!

    Rob
     
  9. JeffM

    JeffM Guest

    If they're on the 'Net, they have addresses. Right?
    Just cut & paste the URL into your post.
    Right. Thise groups have "binary" or "binaries" in their names.
    http://www.google.com/search?q=Image-Hosting&num=100

    "No-crap Image Hosting"
    http://www.google.com/search?q=cach...-*-*-*-*-*-*-*+bayimg+free+censorship&strip=1
     
  10. goldenhound

    goldenhound Guest

    Good idea Chris, about posting the jpgs there. I'll do that. Yes,
    I've been using Google for my searching.
     
  11. goldenhound

    goldenhound Guest

    They *used* to be on DIYSTOMPBOXES.com. They have dead links on that
    site now. However, I downloaded them sometime ago when the links were
    still good.

    Thanks much for the urls to post the photos. I checked with my ISP
    and they have a picture share area. I might give that a try, but if
    it doesn't work, I'll go with one of the sites you provided. I don't
    use a newsreader so I can't really upload schematics / photos to
    alt.binaries.schematic.electronic, though it would serve the community
    better. Once I get setup to do that I will because I'm sure there are
    others looking for that schematic.
     
  12. JeffM

    JeffM Guest

    No sweat.
    My cnet link talks about how *most* hosts are bitches
    about what's proper for their sites and what's not.
    That article is about the host that's NOT a bitch.
    http://bayimg.com
    If you START with the most-permissive host, you've got it nailed in
    one.
    Why use a host that's accepting of *some* content and not of other?
    Actually, if you check postings to these groups over the last several
    weeks
    as well as the News for Nerds sites,
    you'll see that the political posturing the NY Attorney General
    pressured[1] NY ISPs into blocking all of the alt.* Big 8 hierarchy
    on the pretence of stopping kiddie porn,
    so some folks who *are* using a newsreader got screwed recently.
    (Many of those chickenshit ISPs also made it a nation-wide policy
    and/or dropped ALL of their Usenet access[2].)
    I don't agree. (See my previous point for starters.)
    The persistence of stuff on most NNTP binaries servers
    is also pretty short.
    The Pirate Bay's image hosting service
    has everybody beat in that regard as well.

    Considering Bayimg and BitTorrent,
    I don't see the point of binaries groups any more.
    a.b.s.e just seems to be a place
    for folks to needlessly cross-post text-only posts
    (further reducing the persistence of images there).
    ..
    ..
    [1] It appears they were eager for an excuse to close Port 119...
    [2] ...and take their NNTP servers offline.
    The "I" in ISP has less meaning every day;
    most of those would be happy to be Port-80-only.
     
  13. goldenhound

    goldenhound Guest


    Michael,

    Using some sites that JeffM has suggested, I was able to get on one
    that was relatively painless. Please feel free to take a look at
    Stellan's schematic of the EH Electric Mistress (2x9V battery
    version). I'm not sure of the accuracy of the schematic. I still
    have to shoot the component side of the flanger and then I'll post
    both the solder side and component side (if that's a help).

    As you had mentioned, I'm getting no audio on the output side when the
    flanger's engaged. If you can tell me what components are involved in
    the buffering stage, and the output stage that would be a big help. I
    can try troubleshooting those portions.

    Stellan's EH Electric Mistress schematic
    http://img233.imageshack.us/img233/3200/ehelectricmistressschemxu1.gif

    Thanks in advance,
    Rob
     
  14. My guess is that the oscillator isn't oscillating. That will prevent
    the sad1024 from working.

    Do you have any test equipment at all? An AC voltmeter will tell you
    if it is oscillating. Measure the AC voltage between pin 10 and 11. If
    it is 0, then you have no oscillation. Comnpare the voltage of the
    various output pins of the comparator (LM339) to ground (pin 10 on the
    4013).

    If there isn't any oscillation on the comparator, then that is the
    problem. Check the circuit around the comparator for cold solder
    joints, etc.

    If there IS oscillation, see if it is on pin 10 and 14 of the sad1024.
    If it is, you sad1024 is bad, or not connected to the input for some
    reason. See if the signal is getting through to the SAD. The analog
    signal enters at pin 15.

    Regards,
    Bob Monsen
     
  15. goldenhound

    goldenhound Guest

    Thanks Bob - I'll check it out. But as Michael Black mentioned in his
    post - if the SAD 1024 was bad, wouldn't I get some kind of audio thru
    the output instead of none at all? The signal would be clean, with no
    FX but it would be something, right?
     
  16. JeffM

    JeffM Guest

    As these things are called stomp boxes,
    *broken stuff* would be my suspicion.
    Yup.
    He didn't have the print to look at then.
    As Monsen said, it has to get thru the 4558/4558 stages first
    to get to the 13k.
    If one or both of those opamps are shot, you get zilch.
    ..
    ..
    ....and you sure do blockquote a lot more than is necessary.
     
  17. Actually, he is right. I misread the schematic... the point of a
    flanger is to add the 'current' signal to a delayed signal. So, even
    if the delay chip is hosed, he should hear the input, without flanging
    effect, if the SAD is dead or if the oscillator isn't oscillating.

    So, it is probably the input stage that is AFU. The OP should check
    the input to the SAD, and work backwards towards the input to the box
    to see where the signal is failing.

    The OP could also check whether there is signal on the output of the
    opamp (the 4558 in the schematic). That is pin 1 or 7 of the 4558 if
    you are using one of those. The power pins are 4 and 8. 4 should be at
    ground, and 8 should be at Vcc, whatever that is, probably 9V.

    Regards,
    Bob Monsen
     
  18. goldenhound

    goldenhound Guest

    Hi Bob,
    This is a dumb question but looking at the data sheet and the
    schematic for the SAD 1024, does pin 2 (IN A) feed one set of 512
    buckets, and pin 15 (IN B) feed the other set? If so, should I get
    signal on either of those two pins?
    AFU=I think I know what that means?
    OP=?
    When you say signal, does that imply using an oscilliscope (which I
    don't have), or are you talking
    about actually "hearing" a guitar through that pin with some device
    (like an audio probe)?
    Yes. The 4558 is on the board. I'll check those as well - I'm hoping
    tonight. So I should have something to report tomorrow.

    JeffM said:
    OK - I see that. The leg with the 13k ohm resistor is the bypass,
    correct? That makes sense now.
    ..
    ..
    "...and you sure do blockquote a lot more than is necessary. "

    Probably a carryover from my job. I have a habit of trying to be as
    verbose as possible.

    Thanks again gentlemen for mapping my next moves.
    Rob
     
  19. First, I misinterpreted the original post, especially since this
    is the basics newsgroup. I read it as meaning you'd found a schematic
    and built it, which throws in wiring errors and untested parts into
    the mix.

    Since it's actually a commercial unit, and was working but suddenly
    not, it's actually easier.
    But then the chances are good that you didn't connect the wire to
    the right place. For it to be the right place and yet it still
    not working seems too odd a coincident.

    And this is where I stalled. Any of us could see immediately upon
    looking at the unit whether it was reconnected in the right place or
    not, could easily check that voltage is reaching the ICs, and then
    quickly isolate what part of the circuit isn't working.

    Translating that into steps that you can follow becomes harder.
    The schematic helps, since then we can see what's there. But I'm
    also concerned that even if you can point to the schematic you found,
    that there is still a small variable that the schematic may not
    be correct; either because someone drew the schematic from
    the circuit board and introduced error(s), or because there
    were small variations through the production of the unit that may
    not match your unit.

    The schematic that seems to be all over the place shows the input
    signal going through two stages of op-amps. If the unit gets
    no power, those op-amps won't work, and you'll hear nothing. Since
    you hear nothing at all, either one of those stages have gone
    bad, or they aren't getting power. It's far easier to expect
    them to not have power, especially since you had a broken wire,
    than to look for something more complicated.

    You get a voltmeter, measure the pin on the op-amp where power
    goes, and see if it's getting voltage. Easy, except maybe
    the schematic I found doesn't match your unit and then we have
    to describe how to find pin 1 so you can count pins properly,
    and maybe describe how to find that IC.

    If there's no voltage there, then that reinforces the notion
    that you reconnected the wire to the wrong place. Then it
    requires finding the exact schematic, and then seeing where one
    should connect the wire.

    And then there may be worry that when you reconnected it to
    the wrong place, it's done damage. ONe hopes not, but that's
    always there.

    Michael
     
  20. goldenhound

    goldenhound Guest

    .. Any of us could see immediately upon
    I hope to be able to post the front / back of the PCB tonight:
    Here's what I have which I believe is representative - Feel free to
    take a look:

    Stellan's EH Electric Mistress schematic
    http://img233.imageshack.us/img233/3200/ehelectricmistressschemxu1.gif
     
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