Almost newbie needs to troubleshoot electric guitar effect

[JeffM]

goldenhound wrote:

http://bayimg.com/CAKkKaaBm
(solderside of EH Electric Mistress 1979)
http://bayimg.com/gakkmaabM
(inverted component side of EH Electric Mistress 1979)

1) Try to work with a maximum line length of ~72 characters on Usenet.

2) Rather than linking to the *page*, just link to the *image*.
http://bayimg.com/image/cakkkaabm.jpg
http://bayimg.com/image/gakkmaabm.jpg
(If you can cut & paste the URL into a blank page/tab
and it still works, then deep linking is allowed.)

Nothing is obviously weird on the component side.
Putting a bit more light on it before snapping it would have been
good.

3) How anyone expects to inspect a board when it's covered in rosin,
I don't know (though looking at the cheezy technique on the schematic
--as mentioned by Black,
I shouldn't be surprised by the poor workmanship).

An acid brush with bristles trimmed to ~3/16"
and some alcohol and elbow grease does the trick.
http://www.google.com/images?q=Disposable-acid-brush

 

[goldenhound]

On Sep 18, 10:17 pm, JeffM <jef...@email.com> wrote:

goldenhound wrote:
http://bayimg.com/CAKkKaaBm
(solderside of EH Electric Mistress 1979)
http://bayimg.com/gakkmaabM
(inverted component side of EH Electric Mistress 1979)

1) Try to work with a maximum line length of ~72 characters on Usenet.

Will do.

2) Rather than linking to the *page*, just link to the *image*.http://bayimg.com/image/cakkkaabm.jpghttp://bayimg.com/image/gakkmaabm.jpg

Good information.

Nothing is obviously weird on the component side.
Putting a bit more light on it before snapping it would have been
good.

Actually, I reduced the exposure because it was too bright.

3) How anyone expects to inspect a board when it's covered in rosin,
I don't know (though looking at the cheezy technique on the schematic
--as mentioned by Black,
I shouldn't be surprised by the poor workmanship).

This is Electro Harmonix, circa 1979, NYC. All about sweat-shop
production. The cheapest, noisiest fx on the market at the time.
Very budget, but had some pretty brilliant hippie designers. And
you're complaining about a little rosin on the PCB? )

An acid brush with bristles trimmed to ~3/16"
and some alcohol and elbow grease does the trick.http://www.google.com/images?q=Disposable-acid-brush

Thanks for that.

Anyway, I found that pin 5 of the 4558 received guitar signal. But no
signal on output of any of the pins.

Checking with VOM set to DCV - I've been using the black wire off the
battery to the guitar in jack as the ground and checking all the pins,
with the fx turned on (fx is turned on by inserting a guitar cord),
and the stomp switch engaged. I get no voltage anywhere. If I probe
direct to the battery ground and touch components, everything shows
like 17+ volts DC. I know this is a dumb question, what am I doing
wrong?

 

[Jasen Betts]

On 2008-09-21, goldenhound <goldenhound104@gmail.com> wrote:

Anyway, I found that pin 5 of the 4558 received guitar signal. But no
signal on output of any of the pins.

Checking with VOM set to DCV - I've been using the black wire off the
battery to the guitar in jack as the ground and checking all the pins,
with the fx turned on (fx is turned on by inserting a guitar cord),
and the stomp switch engaged. I get no voltage anywhere. If I probe
direct to the battery ground and touch components, everything shows
like 17+ volts DC. I know this is a dumb question, what am I doing
wrong?

check all of the cables inside the box, especially the one for battery
negative.

check the switch-action of the guitar jack that it actually works.

because from your desctiption above it seems that atleast one of them
are not doing their job.

Bye.
Jasen

 

[Peter Bennett]

On Sun, 21 Sep 2008 13:30:50 -0700 (PDT), goldenhound
<goldenhound104@gmail.com> wrote:

Anyway, I found that pin 5 of the 4558 received guitar signal. But no
signal on output of any of the pins.

Checking with VOM set to DCV - I've been using the black wire off the
battery to the guitar in jack as the ground and checking all the pins,
with the fx turned on (fx is turned on by inserting a guitar cord),
and the stomp switch engaged. I get no voltage anywhere. If I probe
direct to the battery ground and touch components, everything shows
like 17+ volts DC. I know this is a dumb question, what am I doing
wrong?

If I'm reading this correctly, it sounds like the wire between the
battery ground terminal and the board is broken somewhere - likely in
the battery connector.



--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

 

[JeffM]

goldenhound blockquoted (badly):

2) Rather than linking to the *page*, just link to the *image*.http://bayimg.com/image/cakkkaabm.jpghttp://bayimg.com/image/gakkmaabm.jpg

If you are going to use Google to post,

recognize that, by default, it does a lousy job (long links,
whitespace, etc).
There IS a trick.
http://groups.google.com/group/sci.electronics.design/browse_frm/thread/bad6531ce8b26df3?q=as-well-as-other-things+THE-TRICK+Google.blockquotes.them+long-links+get.butchered
http://groups.google.com/group/sci.electronics.design/msg/e9c664619f01d764?q=*-*-4-ways+monospaced-*+To.read.ASCII.prints.from.Google+zzz+Before+%26fwc-*+Show.original+Fixed.text+Notepad+Proportional-*

sweat-shop production
[...]And you're complaining about a little rosin on the PCB? )

Silly me. Actually, I was commenting on the prep work

by the repair depot in Portland that's handling this job. ;-)

Anyway, I found that pin 5 of the 4558 received guitar signal.
But no signal on output of any of the pins.

Again, with the crap job they did on the schematic,

http://img233.imageshack.us/img233/3200/ehelectricmistressschemxu1.gif

the pinout of the circuit isn't clear.
http://web.archive.org/web/19981203015201/http://www.xs4all.nl/~ganswijk/chipdir/giicm/MC1558.txt

I'll ASSuME we're talking about
|
|8
5 | \
----|+ \ 7 3 | \
| >---------|+ \ 1
----| / | >----
6 | / ----| /
|4 2 | /
|
Do confirm or correct. How to view ASCII art:
http://groups.google.com/group/sci.electronics.design/msg/e9c664619f01d764?q=*-*-4-ways+monospaced-*+To.read.ASCII.prints.from.Google+zzz+Before+%26fwc-*+Show.original+Fixed.text+Notepad+Proportional-*

Checking with VOM set to DCV -
I've been using the black wire off the battery to the guitar in jack

Ever wonder why they didn't call those things "jills"?

as the ground and checking all the pins,
with the fx turned on (fx is turned on by inserting a guitar cord),
and the stomp switch engaged[,]

Unless the switch uses more than 2 terminals,

it is mostly meaningless.

I get no voltage anywhere.

http://www.google.com/search?q=define:continuity

Something is "open".
That jack has more than 2 elements
and it sounds like the juice isn't passing from one to the next.
http://www.google.com/images?q=burnishing-tool+%2Bcontacts
The *wb4hfn* item is good.
You may also be able to knock off the crud
by just inserting a rough piece of paper between the contacts,
engaging the contacts, and dragging the paper thru.
Well-used paper money is one such material.

A clip lead can temporarily jumper a defective set of contacts.

If I probe

The word you seek is "reference".

direct to the battery ground and touch components,
everything shows like 17+ volts DC.

....because there is a complete circuit (of sorts) then.

 

[goldenhound]

On Sep 21, 4:37 pm, JeffM <jef...@email.com> wrote:

Silly me.  Actually, I was commenting on the prep work
by the repair depot in Portland that's handling this job.  ;-)

Ahem...guilty as charged!

Do confirm or correct.  How to view ASCII art:http://groups.google.com/group/sci.electronics.design/msg/e9c664619f0...

Thanks for the info on viewing ASCII art.
Looking at your schematic of the pinout of the 4558, what you've
expressed looks right.

Ever wonder why they didn't call those things "jills"?

Not until you brought it up - but yeah. And the 1/4" phone plug -
call it "Jack"? I don't know.

That jack has more than 2 elements
and it sounds like the juice isn't passing from one to the next.

Hmm. I'd love to try that right now, but I'll have wait until I get
home.
The input jack has a stereo plug that, when a guitar plug is inserted,
juice
then flows into the circuit. I did check it, but didn't try to clean
it.

A clip lead can temporarily jumper a defective set of contacts.

I'll try that as well. Thanks for all the tips and suggestions, Jeff.

Rob

 

[goldenhound]

On Sep 21, 4:31 pm, Jasen Betts <ja...@xnet.co.nz> wrote:

On 2008-09-21, goldenhound <goldenhound...@gmail.com> wrote:


check the switch-action of the guitar jack that it actually works.

Sounds reasonable. I'm going to check them tonight.

Thanks,
Rob

 

[Michael Black]

On Tue, 23 Sep 2008, goldenhound wrote:

On Sep 21, 4:37 pm, JeffM <jef...@email.com> wrote:
Something is "open".
That jack has more than 2 elements

You may also be able to knock off the crud
by just inserting a rough piece of paper between the contacts,

During checking last night, (which didn't yield much - the stomp
switch actually is working), a wire broke.
This is the yellow wire (18v) from the wall wart jack that connects to
a pad on the PCB (see the solderside photo link.), which in turn
passes thru the 741 opamp, and then passes to an electrolytic 10uF
cap.

Once I re-soldered the wire, I was checking the 10uF electrolytic cap
that is fed from that yellow wire,
and found voltage on one side, but not the other. Unsoldering it and
checking continuity I found it open.

But, capacitors aren't just used for coupling signals (and blocking

DC), they are also used to bypass and filter. When they are bypassing
and filtering, one side in the circuit is usually going to ground,
so not finding voltage on the other side means nothing.

And capacitors will not show continuity between terminals, at least
not after a brief time (the length of time dependent on the value
of capacitance, the more there is the more delay).

If this is the 10uF capacitor connected to the arm of the 100k "trim"
pot, then all it's doing is keeping noise off that point, and one
side is indeed grounded. That capacitor not working or not being
there will not cause the unit to fail, at best there will be noise.

The trick to troubleshooting is to find the general area, and then
narrow down the fault. Just going through components will take
forever, and is open to misinterpretation since in circuit
they may appear different from when they are outside the circuit.
You don't want to have to desolder and resolder every component
finding this problem.

So you look at the collector of that 2N5037 connected to that 741.
If there's the right voltage, the schematic says 12volts, then that
section cannot be the fault. If there's no voltage there, then
something before that point is not right.

If the proper voltage is there, you need to look elsewhere, looking at
the unit as multiple stages and seeing where the DC voltage disappears
or where the audio signal disappears.

Michael

 

[goldenhound]

On Sep 21, 4:37 pm, JeffM <jef...@email.com> wrote:

Something is "open".
That jack has more than 2 elements

You may also be able to knock off the crud
by just inserting a rough piece of paper between the contacts,

During checking last night, (which didn't yield much - the stomp
switch actually is working), a wire broke.
This is the yellow wire (18v) from the wall wart jack that connects to
a pad on the PCB (see the solderside photo link.), which in turn
passes thru the 741 opamp, and then passes to an electrolytic 10uF
cap.

Once I re-soldered the wire, I was checking the 10uF electrolytic cap
that is fed from that yellow wire,
and found voltage on one side, but not the other. Unsoldering it and
checking continuity I found it open.

I said to myself, "Self, this isn't helping things". Tonight I'll
pickup a new 10uF electrolytic and try it out. I won't be able to do
it tonight (band practice), but will work on it Wednesday.

 

[JeffM]

goldenhound wrote:

and found voltage on one side,

You're thinking too much in black-and-white terms.

It's possible to have no DC voltage present on something
and have it still significant AC-wise.

but not the other.

....usually called "Ground" or "Return" or "Zero-volt reference".

Unsoldering it and checking continuity I found it open.

aka "normal".

Look at the symbol for a cap.
The plates are seperated by an INSULATOR.
When you first hook a (discharged) cap to an (analog) ohmeter,
you should see a small "kick".
When you then reverse the leads,
the needle should move in the other direction
--perhaps pinned against zero for a while.
Capacitors should NOT give a *constant* reading.

If you have valid supply voltages on the parts,
it's time to start doing an AC test on the circuit.
Put a signal in and see how far it gets.
An oscope is ideal; an amplifier with input leads and a speaker is
good;
an ac voltmeter works too.

 

[goldenhound]

On Sep 23, 12:44 pm, JeffM <jef...@email.com> wrote:

goldenhound wrote:
An oscope is ideal; an amplifier with input leads and a speaker is
good;

Soldered the 10uf ecap back into place.
I then hooked up an mp3 player into the input and started checking it
with an audio probe.
It seemed I was getting audio everywhere.

I hooked my guitar up and found that
when the input was not making contact with the box, I'd get no
signal. I would also
get no signal if I bolted it down to the case. But if I made contact
with the case, and
held the input jack in my hand, and strummed my guitar, I'd get audio
to the amp. No
flanging, but audio nonetheless. So, now I get clean (unengaged
switch) bypassed signal,
and a slightly lower audio with the footswitch engaged? But no
flanging?